Oryzomys Palustris
   HOME

TheInfoList



OR:

The marsh rice rat (''Oryzomys palustris'') is a
semiaquatic In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semiaquatic animals include: * Verte ...
North American
rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...
in the family
Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At almost 608 species, it is the second-largest family of mammals, and has m ...
. It usually occurs in
wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...
habitats, such as
swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...
s and
salt marsh A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated ...
es. It is found mostly in the eastern and southern United States, from
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
and
Kansas Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the ...
south to
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...
and northeasternmost
Tamaulipas Tamaulipas (), officially the Free and Sovereign State of Tamaulipas ( es, Estado Libre y Soberano de Tamaulipas), is a state in the northeast region of Mexico; one of the 31 states which, along with Mexico City, comprise the 32 Federal Entiti ...
, Mexico; its range previously extended further west and north, where it may have been a
commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...
in corn-cultivating communities. Weighing about , the marsh rice rat is a medium-sized rodent that resembles the common
black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white have o ...
and
brown rat The brown rat (''Rattus norvegicus''), also known as the common rat, street rat, sewer rat, wharf rat, Hanover rat, Norway rat, Norwegian rat and Parisian rat, is a widespread species of common rat. One of the largest muroids, it is a brown o ...
. The upperparts are generally gray-brown, but are reddish in many Florida populations. The feet show several specializations for life in the water. The skull is large and flattened, and is short at the front.
John Bachman John Bachman (February 4, 1790 – February 24, 1874) was an American Lutheran minister, social activist and naturalist who collaborated with John James Audubon to produce ''Viviparous Quadrupeds of North America'' and whose writings, particul ...
discovered the marsh rice rat in 1816, and it was formally described in 1837. Several
subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
have been described since the 1890s, mainly from Florida, but disagreement exists over their validity. The
Florida Keys The Florida Keys are a coral cay archipelago located off the southern coast of Florida, forming the southernmost part of the continental United States. They begin at the southeastern coast of the Florida peninsula, about south of Miami, and e ...
population is sometimes classified as a different species, the silver rice rat (''Oryzomys argentatus''). Data from the
mitochondrial A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is use ...
cytochrome ''b'' gene indicate a deep divergence between populations east of Mississippi and those further west, which suggests that the western populations may be recognized as a separate species, ''Oryzomys texensis''. The species is part of the genus ''
Oryzomys ''Oryzomys'' is a genus of semiaquatic rodents in the tribe Oryzomyini living in southern North America and far northern South America. It includes eight species, two of which—the marsh rice rat (''O. palustris'') of the United States and ...
'', which also includes several others occurring further south in Mexico, Central America, and northwestern South America, some of which have previously been regarded as subspecies of the marsh rice rat. One, ''
Oryzomys couesi ''Oryzomys couesi'', also known as Coues's rice rat, is a semiaquatic rodent in the family Cricetidae occurring from southernmost Texas through Mexico and Central America into northwestern Colombia. It is usually found in wet habitats, such as m ...
'', occurs with the marsh rice rat in Tamaulipas and southern
Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
. The marsh rice rat is active during the night, makes nests of sedge and grass, and occasionally builds runways. Its diverse diet includes plants, fungi, and a variety of animals. Population densities are usually below 10 per ha (four per acre) and home ranges vary from 0.23 to 0.37 ha (0.57 to 0.91 acres), depending on sex and geography. Litters of generally three to five young are born after a pregnancy around 25 days, mainly during the summer. Newborns are helpless at birth, but are weaned after a few weeks. Several animals prey on the marsh rice rat, including the barn owl, and it usually lives for less than a year in the wild. It is infected by many different parasites and harbors a
hantavirus ''Orthohantavirus'' is a genus of single-stranded, enveloped, negative-sense RNA viruses in the family ''Hantaviridae'' within the order ''Bunyavirales''. Members of this genus may be called orthohantaviruses or simply hantaviruses. Orthohantav ...
that also infects humans. The species is not of conservation concern, but some populations are threatened.


Taxonomy

The marsh rice rat is classified as one of eight species in the genus ''
Oryzomys ''Oryzomys'' is a genus of semiaquatic rodents in the tribe Oryzomyini living in southern North America and far northern South America. It includes eight species, two of which—the marsh rice rat (''O. palustris'') of the United States and ...
'', which is distributed from the eastern
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
(marsh rice rat) into northwestern
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
('' O. gorgasi'').Carleton and Arroyo-Cabrales, 2009, p. 106 ''Oryzomys'' previously included many other species, which were reclassified in various studies culminating in contributions by Marcelo Weksler and coworkers in 2006 that removed more than 40 species from the genus. All are placed in the tribe
Oryzomyini Oryzomyini is a tribe of rodents in the subfamily Sigmodontinae of the family Cricetidae. It includes about 120 species in about thirty genera,Weksler et al., 2006, table 1 distributed from the eastern United States to the southernmost parts of ...
("rice rats"), a diverse assemblage of over 100 species, and on higher taxonomic levels in the subfamily
Sigmodontinae The rodent subfamily Sigmodontinae includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the specie ...
of the family
Cricetidae The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At almost 608 species, it is the second-largest family of mammals, and has m ...
, along with hundreds of other species of mainly small rodents, most of which occur in South and Central America. In the United States, the marsh rice rat is the only oryzomyine rodent except for ''
Oryzomys couesi ''Oryzomys couesi'', also known as Coues's rice rat, is a semiaquatic rodent in the family Cricetidae occurring from southernmost Texas through Mexico and Central America into northwestern Colombia. It is usually found in wet habitats, such as m ...
'' in a small area of southern Texas; the only other sigmodontines present are several species of
cotton rat A cotton rat is any member of the rodent genus ''Sigmodon''. Their name derives from their damaging effects on cotton as well as other plantation crops, such as sugarcane, corn, peanut and rice. Cotton rats have small ears and dark coats, and a ...
s (''Sigmodon'') in the southern half of the country.


Early history

The marsh rice rat was discovered in 1816 in
South Carolina )''Animis opibusque parati'' ( for, , Latin, Prepared in mind and resources, links=no) , anthem = " Carolina";" South Carolina On My Mind" , Former = Province of South Carolina , seat = Columbia , LargestCity = Charleston , LargestMetro = ...
by
John Bachman John Bachman (February 4, 1790 – February 24, 1874) was an American Lutheran minister, social activist and naturalist who collaborated with John James Audubon to produce ''Viviparous Quadrupeds of North America'' and whose writings, particul ...
.Chapman, 1893, p. 43 Bachman intended to describe the species as ''Arvicola oryzivora'', but sent a specimen to
Richard Harlan Richard Harlan (September 19, 1796 – September 30, 1843) was an American paleontologist, anatomist, and physician. He was the first American to devote significant time and attention to vertebrate paleontology and was one of the most importan ...
and Charles Pickering at the
Academy of Natural Sciences The Academy of Natural Sciences of Drexel University, formerly the Academy of Natural Sciences of Philadelphia, is the oldest natural science research institution and museum in the Americas. It was founded in 1812, by many of the leading natura ...
in Philadelphia to confirm its identity.Audubon and Bachman, 1854, p. 216 Another specimen, from
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
, was found in the academy's collection, and Harlan took it upon himself, against Pickering's wishes, to describe the new species as ''Mus palustris'', proclaiming it one of the few true rats of the United States. The specific name ''palustris'' is Latin for "marshy" and refers to the usual habitat of the species.Merritt, 1987, p. 173; Schwartz and Schwartz, 2001, p. 192 In 1854, in ''The quadrupeds of North America'', Bachman redescribed it as ''Arvicola oryzivora'', considering it more closely related to the
vole Voles are small rodents that are relatives of lemmings and hamsters, but with a stouter body; a longer, hairy tail; a slightly rounder head; smaller eyes and ears; and differently formed molars (high-crowned with angular cusps instead of low-c ...
s then placed in the genus '' Arvicola'', and also recorded it from
Georgia Georgia most commonly refers to: * Georgia (country), a country in the Caucasus region of Eurasia * Georgia (U.S. state), a state in the Southeast United States Georgia may also refer to: Places Historical states and entities * Related to the ...
and
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...
. Three years later,
Spencer Fullerton Baird Spencer Fullerton Baird (; February 3, 1823 – August 19, 1887) was an American naturalist, ornithologist, ichthyologist, Herpetology, herpetologist, and museum curator. Baird was the first curator to be named at the Smithsonian Institution. He ...
argued that the referral of the species to ''Arvicola'' was erroneous and introduced a new generic name for the marsh rice rat, ''Oryzomys''.Baird, 1857, pp. 458, 482, 484; Goldman, 1918, p. 9 The name combines the Greek ''oryza'' "rice" and ''mys'' "mouse" and refers to the rat's habit of eating rice. At the time, ''Oryzomys'' was recognized either as a full genus or as a
subgenus In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed between t ...
of the now-defunct genus '' Hesperomys'', but since the 1890s, it has been universally recognized as a genus distinct from ''Hesperomys'', with the marsh rice rat (''Oryzomys palustris'') as its
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...
.


Species boundaries and subspecies

In the 1890s, several
subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
of the marsh rice rat were described from the United States: ''O. p. natator'' from Florida in 1893, ''O. p. texensis'' from Texas in 1894, and ''O. p. coloratus'' from elsewhere in Florida in 1898.
Clinton Hart Merriam Clinton Hart Merriam (December 5, 1855 – March 19, 1942) was an American zoologist, mammalogist, ornithologist, entomologist, ecologist, ethnographer, geographer, naturalist and physician. He was commonly known as the 'father of mammalogy', a ...
recognized ''O. p. natator'' as a separate species in 1901 and described a subspecies of it, ''O. p. floridanus'', but considered ''O. p. texensis'' to be nearly identical to
nominate Nomination is part of the process of selecting a candidate for either election to a public office, or the bestowing of an honor or award. A collection of nominees narrowed from the full list of candidates is a short list. Political office In the ...
''O. p. palustris''. In his 1918 revision of North American ''Oryzomys'',
Edward Alphonso Goldman Edward Alphonso Goldman (July 7, 1873 – September 2, 1946) was an American zoologist and botanist. He worked extensively in Mexico with Edward William Nelson and described and revised many groups of mammals. He was born Edward Alphonso Goltman i ...
again recognized all these as a single species, ''Oryzomys palustris''. He distinguished four subspecies, which he said formed a "closely intergrading series"—''O. p. palustris'' from New Jersey to southeastern Mississippi and eastern Missouri; ''O. p. natator'' in central Florida; ''O. p. coloratus'' (including ''O. natator floridanus'' Merriam) in southern Florida; and ''O. p. texensis'' from western Mississippi and southeastern Kansas to eastern Texas. Two additional subspecies were described by William J. Hamilton in 1955 from southern Florida: ''O. p. planirostris'' from Pine Island and two miles (3 km) north of
Fort Myers Fort Myers (or Ft. Myers) is a city in southwestern Florida and the county seat and commercial center of Lee County, Florida, United States. The Census Bureau's Population Estimates Program calculated that the city's population was 92,245 in 20 ...
and ''O. p. sanibeli'' from
Sanibel Island Sanibel is an island and city in Lee County, Florida, United States. The population was 6,382 at the 2020 census. It is part of the Cape Coral-Fort Myers, Florida Metropolitan Statistical Area. The island, also known as Sanibel Island, constitut ...
. Also in 1955, Claude W. Hibbard described a new species of ''Oryzomys'', ''O. fossilis'', from
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
deposits in
Kansas Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the ...
, on the basis of small differences in characters of the tooth with living marsh rice rats. In 1965, Walter Dalquest demoted this species, later also found in Texas, to a subspecies, because it does not differ more from living marsh rice rats than the latter differ from each other.Dalquest, 1965, p. 70 Merriam and Goldman had recognized that a number of Central American species, including ''Oryzomys couesi'' and numerous forms with more limited distributions, are related to the marsh rice rat. ''O. couesi'' ranges north to southernmost Texas, where its distribution meets that of the marsh rice rat. In 1960, Raymond Hall argued that specimens from the contact zone were intermediate between the local forms of ''O. couesi'' and the marsh rice rat, and accordingly included the former in the marsh rice rat. While reporting on the ecology of Texan ''O. couesi'' in 1979, Benson and Gehlbach noted that populations of ''O. couesi'' and the marsh rice rat there were in fact distinct, with the latter being smaller and less brown and more gray in color; their
karyotype A karyotype is the general appearance of the complete set of metaphase chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is disce ...
s were also distinct. Since then, the two have generally been retained as distinct species, as supported by further research; a 1994 study even found the two to occur at some of the same places (in
sympatry In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sh ...
) in southern Texas and nearby
Tamaulipas Tamaulipas (), officially the Free and Sovereign State of Tamaulipas ( es, Estado Libre y Soberano de Tamaulipas), is a state in the northeast region of Mexico; one of the 31 states which, along with Mexico City, comprise the 32 Federal Entiti ...
, Mexico. In 1973, rice rats were discovered at Cudjoe Key in the
Florida Keys The Florida Keys are a coral cay archipelago located off the southern coast of Florida, forming the southernmost part of the continental United States. They begin at the southeastern coast of the Florida peninsula, about south of Miami, and e ...
, and in 1978 Spitzer and Lazell described this population as a new species, ''Oryzomys argentatus''.Spitzer and Lazell, 1978, p. 787 The status of this form—either a distinct speciesGoodyear, 1991, p. 423 or not even subspecifically distinct from ''O. palustris natator''Humphrey and Setzer, 1989, p. 557—has remained controversial since; the 2005 third edition of ''
Mammal Species of the World ''Mammal Species of the World: A Taxonomic and Geographic Reference'' is a standard reference work in mammalogy giving descriptions and bibliographic data for the known species of mammals. It is now in its third edition, published in late 2005, ...
'' does not recognize ''O. argentatus'' as a separate species, but acknowledges a need for further research.Musser and Carleton, 2005, p. 1153 A 2005 study using
microsatellite A microsatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from one to six or more base pairs) are repeated, typically 5–50 times. Microsatellites occur at thousands of locations within an organism's genome. ...
DNA found that Florida Keys rice rats exhibit low genetic variation and are significantly different from
Everglades The Everglades is a natural region of tropical climate, tropical wetlands in the southern portion of the U.S. state of Florida, comprising the southern half of a large drainage basin within the Neotropical realm. The system begins near Orland ...
rice rats; the study concluded in favor of classifying the Keys rice rat as a "distinct vertebrate population".Wang et al., 2005, p. 575 This population probably diverged from mainland rice rats about 2000 years ago.Wang et al., 2005, p. 581 Among the described subspecies, a 1989
morphometrical Morphometrics (from Greek μορϕή ''morphe'', "shape, form", and -μετρία ''metria'', "measurement") or morphometry refers to the quantitative analysis of ''form'', a concept that encompasses size and shape. Morphometric analyses are co ...
study by Humphrey and Setzer separated only two—''O. p. natator'' from much of Florida (including ''O. p. coloratus'', ''O. p. planirostris'', ''O. p. sanibeli'', and ''O. p. floridanus'', as well as ''O. p. argentatus'') and ''O. p. palustris'' from the rest of the range (including ''O. p. texensis''). However, Whitaker and Hamilton in their 1998 book on the ''Mammals of the Eastern United States'' recognized ''O. p. planirostris'' and ''O. p. sanibeli'' as separate subspecies, but merged all others into ''O. p. palustris'', and placed ''O. argentatus'' as a separate species; their classification was based on their emphasis of overwater gaps as agents of biological diversification and a critique of shortcomings in Humphrey and Setzer's study, not on a reanalysis of the data. In 2010, Delton Hanson and colleagues published a study of the relationships among populations of ''Oryzomys'' on the basis of data from three genes—the
mitochondrial A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is use ...
gene cytochrome ''b'' (''Cytb'') and two
nuclear Nuclear may refer to: Physics Relating to the nucleus of the atom: * Nuclear engineering *Nuclear physics *Nuclear power *Nuclear reactor *Nuclear weapon *Nuclear medicine *Radiation therapy *Nuclear warfare Mathematics *Nuclear space *Nuclear ...
markers,
exon An exon is any part of a gene that will form a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. The term ''exon'' refers to both the DNA sequence within a gene and to the corresponding sequen ...
1 of the interphotoreceptor retinoid-binding protein gene (''Rbp3'') and
intron An intron is any nucleotide sequence within a gene that is not expressed or operative in the final RNA product. The word ''intron'' is derived from the term ''intragenic region'', i.e. a region inside a gene."The notion of the cistron .e., gene. ...
2 of
alcohol dehydrogenase Alcohol dehydrogenases (ADH) () are a group of dehydrogenase enzymes that occur in many organisms and facilitate the interconversion between alcohols and aldehydes or ketones with the reduction of nicotinamide adenine dinucleotide (NAD+) to N ...
gene 1 (''Adh1-I2'').Hanson et al., 2010, p. 337 The ''Cytb'' data placed all marsh rice rats studied sister to a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
containing various populations of ''O. couesi''; the mean genetic distance between the two groups was 11.30%. The marsh rice rats fell into two main groups, differing on average by 6.05%, one containing animals from Mississippi, southwestern Tennessee, and further west, and the other including specimens from Alabama and further east. Within the eastern group, variation was only about 0.65%, though examples of the putative subspecies ''O. p. palustris'', ''O. p. coloratus'', ''O. p. sanibeli'', and ''O. p. planirostris'' were all included. Data from both of the slower-evolving nuclear markers ''Rbp3'' and ''Adh1-I2'' also placed examples of ''Oryzomys'' in two main clades, but did not recover the western and eastern groups of the marsh rice rat as separate clades. In addition, ''Adh1-I2'' placed a Costa Rican population within the marsh rice rat clade and some other southern ''Oryzomys'' specimens closer to the marsh rice rat than to the ''O. couesi'' group. The combined data supported the western and eastern clades within the marsh rice rat and placed the Costa Rican population marginally closer to the marsh rice rat than to ''O. couesi''. Using the genetic species concept, the authors suggested that the western populations of the marsh rice rat be recognized as a separate species, ''Oryzomys texensis''. They recommended further research in the Mississippi–Alabama–Tennessee region, where the ranges of the two meet.Hanson et al., 2010, p. 342


Common names

Many
common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contrast ...
s have been proposed for the marsh rice rat. Early describers used "rice meadow-mouse" and "rice-field mouse"Baird, 1857, p. 482 and in the early 1900s, name such as "rice rat", "marsh mouse", and "swamp rice rat" came into use. Some of the subspecies received their own common names, such as "Florida marsh mouse",Stone and Cram, 1903, p. 130 "swimming rice rat", and "Central Florida rice rat" for ''O. p. natator'';Goldman, 1918, p. 25 "Bangs' marsh mouse", "Cape Sable rice rat",Eliot, 1905, p. 181 and "Everglades rice rat" for ''O. p. coloratus'';Goldman, 1918, p. 26 and "Texas rice rat" for ''O. p. texensis''.Goldman, 1918, p. 27 The species is now usually known as the "marsh rice rat", although "marsh oryzomys" has also been in recent use. The Florida Keys form (''O. p. argentatus'') is known as the "silver rice rat".


Description

The marsh rice rat is a medium-sized rodent that looks much like the common
black Black is a color which results from the absence or complete absorption of visible light. It is an achromatic color, without hue, like white and grey. It is often used symbolically or figuratively to represent darkness. Black and white have o ...
and
brown rat The brown rat (''Rattus norvegicus''), also known as the common rat, street rat, sewer rat, wharf rat, Hanover rat, Norway rat, Norwegian rat and Parisian rat, is a widespread species of common rat. One of the largest muroids, it is a brown o ...
s, but has greater differences in color between the upper- and underparts. The fur is thick and short. The upperparts are generally gray to grayish brown, with the head a bit lighter, and are sharply delimited from the underparts, which are off-white, as are the feet. It has small
cheek pouch Cheek pouches are pockets on both sides of the head of some mammals between the jaw and the cheek. They can be found on mammals including the platypus, some rodents, and most monkeys, as well as the marsupial koala. The cheek pouches of chipmunks ...
es. The ears are about the same color as the upperparts, but a patch of light hairs is in front of them. The tail is dark brown above and may be paler below. The
guard hair Guard hair or overhair is the outer layer of hair of most mammals, which overlay the fur. Guard hairs are long and coarse and protect the rest of the pelage (fur) from abrasion and frequently from moisture. They are visible on the surface of the fu ...
s are long and have unpigmented, silvery tips. When rice rats swim, air is trapped in the fur, which increases buoyancy and reduces heat loss. As in most other oryzomyines, females have eight
mammae A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in primat ...
.Carleton and Musser, 1989, p. 23 The fore feet have four and the hind feet five digits. On the fore feet, the
ungual tuft In mammals, ungual tufts are tufts of hairs at the base of claws of the forefeet and hindfeet. Their presence has been used as a character in cladistic studies of the Cricetidae, a large family of rodents.Weksler, 2006, p. 19 Rice rats Membe ...
s (tufts of hair on the digits) are absent.Weksler, 2006, p. 23 The hind feet are broad and have a short fifth digit. Many of the
pads Pads (also called leg guards) are a type of protective equipment used in a number of sports and serve to protect the legs from the impact of a hard ball, puck, or other object of play travelling at high speed which could otherwise cause injuries t ...
are reduced, as are the ungual tufts, but small interdigital webs are present. The Florida Keys form, ''P. o. argentatus'', has even more reduced ungual tufts. Many of these traits are common adaptations to life in the water in oryzomyines. Some geographic variation in fur color occurs; western populations (''P. o. texensis'') are lighter than those from the east (
nominate Nomination is part of the process of selecting a candidate for either election to a public office, or the bestowing of an honor or award. A collection of nominees narrowed from the full list of candidates is a short list. Political office In the ...
''P. o. palustris''), and Florida populations are generally more tawny or reddish than either, with those from southern Florida (''P. o. coloratus'') being brighter than those from the center of the state (''P. o. natator''). The Florida Keys form (''P. o. argentatus'') is silvery,Kays and Wilson, 2000, p. 108 and the two other Florida forms—''P. o. planirostris'' and ''P. o. sanibeli''—lack the reddish tones of mainland Florida populations and are instead grayish, resembling ''P. o. planirostris'', or brownish (''P. o. sanibeli'').Humphrey and Setzer, 1989, p. 558 In 1989, Humphrey and Setzer reviewed variation in color among Florida populations. They found ''P. o. argentatus'' to be substantially lighter and ''P. o. planirostris'' and ''P. o. sanibeli'' to be somewhat darker than mainland populations, and ''P. o. argentatus'' to have a less yellow fur, but found no significant differences in redness. Substantial variation within populations also was found. Total length is , tail length , hind foot length , and body mass , with males slightly larger than females. The largest individuals occur in Florida and along the
Gulf Coast The Gulf Coast of the United States, also known as the Gulf South, is the coastline along the Southern United States where they meet the Gulf of Mexico. The coastal states that have a shoreline on the Gulf of Mexico are Texas, Louisiana, Mississ ...
east of the Mississippi River delta.Goldman, 1918, p. 22 The
stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...
has the characteristic pattern of sigmodontines (
unilocular A locule (plural locules) or loculus (plural loculi) (meaning "little place" in Latin) is a small cavity or compartment within an organ or part of an organism (animal, plant, or fungus). In angiosperms (flowering plants), the term ''locule'' usu ...
-hemiglandular); it is not split in two chambers by an incisura angularis and the front part (
antrum ''This is a disambiguation page for the biological term. For the 2018 horror movie, see Antrum (film)'' In biology, antrum is a general term for a cavity or chamber, which may have specific meaning in reference to certain organs or sites in the bod ...
) is covered by a
glandular epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...
. The
gall bladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, although ...
is absent, a
synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...
(shared-derived character) of Oryzomyini. The
karyotype A karyotype is the general appearance of the complete set of metaphase chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is disce ...
includes 56 chromosomes and a
fundamental number A karyotype is the general appearance of the complete set of metaphase chromosomes in the cells of a species or in an individual organism, mainly including their sizes, numbers, and shapes. Karyotyping is the process by which a karyotype is disce ...
of 60 chromosomal arms (2n = 56, FN = 60). The form of the
sex chromosome A sex chromosome (also referred to as an allosome, heterotypical chromosome, gonosome, heterochromosome, or idiochromosome) is a chromosome that differs from an ordinary autosome in form, size, and behavior. The human sex chromosomes, a typical ...
s has been used to distinguish the marsh rice rat from ''Oryzomys couesi'', but may be too variable among ''Oryzomys'' species to be useful in differentiating them.Hershkovitz, 1987, p. 154
X chromosome inactivation X-inactivation (also called Lyonization, after English geneticist Mary Lyon) is a process by which one of the copies of the X chromosome is inactivated in therian female mammals. The inactive X chromosome is silenced by being packaged into a ...
occurs in the marsh rice rat, though the animal lacks LINE-1
retrotransposons Retrotransposons (also called Class I transposable elements or transposons via RNA intermediates) are a type of genetic component that copy and paste themselves into different genomic locations (transposon) by converting RNA back into DNA through ...
, which have been suggested as components of the inactivation process. Mutants with fused or additional molars and with light fur have been recorded in laboratory colonies;Wolfe, 1982, p. 4 the abnormal molars are apparently the result of a single
autosomal recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...
mutation. At about 50%,
hematocrit The hematocrit () (Ht or HCT), also known by several other names, is the volume percentage (vol%) of red blood cells (RBCs) in blood, measured as part of a blood test. The measurement depends on the number and size of red blood cells. It is norm ...
(the proportion of red blood cells in the blood) is high in the marsh rice rat compared to other rodents; this may be an adaptation that enables the rice rat to increase oxygen capacity while swimming under water.


Male reproductive anatomy

The
glans penis In male human anatomy, the glans penis, commonly referred to as the glans, is the bulbous structure at the distal end of the human penis that is the human male's most sensitive erogenous zone and their primary anatomical source of sexual p ...
is long and robust,Hooper and Musser, 1964, p. 13 averaging long and broad, and the baculum (penis bone) is long. As is characteristic of the Sigmodontinae, the marsh rice rat has a complex penis, with the distal (far) end of the baculum ending in three digits. The central digit is notably larger than those at the sides. The outer surface of the penis is mostly covered by small spines, but a broad band of nonspinous tissue is seen. The papilla (nipple-like projection) on the dorsal (upper) side of the penis is covered with small spines, a character the marsh rice rat shares only with ''
Oligoryzomys ''Oligoryzomys'' is a genus of rodents in the tribe Oryzomyini of family Cricetidae. Many species are known as pygmy rice rats or colilargos.Musser and Carleton, 2005 The genus is found from Mexico to Tierra del Fuego and includes approximately 1 ...
'' and ''Oryzomys couesi'' among oryzomyines examined. On the
urethral process The urethra (from Greek οὐρήθρα – ''ourḗthrā'') is a tube that connects the urinary bladder to the urinary meatus for the removal of urine from the body of both females and males. In human females and other primates, the urethra con ...
, located in the crater at the end of the penis, a fleshy process (the subapical lobule) is present; it is absent in all other oryzomyines with studied penes except ''O. couesi'' and ''
Holochilus brasiliensis ''Holochilus brasiliensis'', also known as the Brazilian marsh ratMusser, G.G. and Carleton, M.D. 2005. Superfamily Muroidea. Pp. 894–1531 in Wilson, D.E. and Reeder, D.M. (eds.)Mammal Species of the World: a taxonomic and geographic refer ...
''. The baculum is deeper than it is wide. Some features of the accessory glands in the male genital region vary among oryzomyines. In the marsh rice rat, a single pair of
preputial gland Preputial glands are exocrine glands that are located in the folds of skin front of the genitals of some mammals. They occur in several species, including mice, ferrets, rhinoceroses, and even-toed ungulates and produce pheromones. The glands pla ...
s is present at the penis. As is usual for sigmodontines, two pairs of
ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...
prostate The prostate is both an Male accessory gland, accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found only in some mammals. It differs between species anatomically, ...
glands and a single pair of
anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
and
dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...
prostate glands exist. Part of the end of the vesicular gland is irregularly folded, not smooth as in most oryzomyines.


Skull

The marsh rice rat has a large, flattened skullWolfe, 1982, p. 1 with a short and broad rostrum. The nasal and
premaxillary The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...
bones extend back beyond the point where the lacrimal,
frontal Front may refer to: Arts, entertainment, and media Films * ''The Front'' (1943 film), a 1943 Soviet drama film * ''The Front'', 1976 film Music * The Front (band), an American rock band signed to Columbia Records and active in the 1980s and e ...
, and
maxillary bone The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The tw ...
s meet. In ''P. o. planirostris'', the rostrum is flatter than in mainland Florida forms, in which it is more convex, and the nasals are said to be relatively longer in ''P. o. argentatus''.Spitzer and Lazell, 1978, p. 788 The
zygomatic plate In rodent anatomy, the zygomatic plate is a bony plate derived from the flattened front part of the zygomatic arch (cheekbone). At the back, it connects to the front (maxillary) root of the zygomatic arch, and at the top it is connected to the ...
, the flattened front part of the
zygomatic arch In anatomy, the zygomatic arch, or cheek bone, is a part of the skull formed by the zygomatic process of the temporal bone (a bone extending forward from the side of the skull, over the opening of the ear) and the temporal process of the zygomati ...
(cheekbone), is broad and develops a notch at its front end. The arches themselves are robust and contain small but distinct
jugal bone The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anato ...
s. The
sphenopalatine foramen The sphenopalatine foramen is a Foramina of the skull, foramen in the skull that connects the nasal cavity with the pterygopalatine fossa. Structure The processes of the superior border of the palatine bone are separated by the ''sphenopalatine no ...
, an opening in the side of the skull above the molars, is large; it is much smaller in ''O. couesi''. The narrowest part of the region between the eyes is towards the front and the edges are lined by prominent shelves. The marsh rice rat has a narrow
braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...
lined by prominent ridges and a narrow
interparietal bone An interparietal bone (os interparietale or Inca bone or ''os inca var.'') is a dermal bone situated between the parietal and supraoccipital. It is homologous to the postparietal bones of other animals. In humans, it corresponds to the upper p ...
. According to Goldman, Florida animals (''P. o. coloratus'' and ''P. o. natator'') generally have the largest and broadest skulls, and the western specimen (''P. o. texensis'') has a somewhat smaller and narrower skull than those from the east outside Florida (''P. o. palustris''). In ''P. o. argentatus'', the skull is also relatively narrow. The
incisive foramina In the human mouth, the incisive foramen (also known as: "''anterior palatine foramen''", or "''nasopalatine foramen''") is the opening of the incisive canals on the hard palate immediately behind the incisor teeth. It gives passage to blood vesse ...
, openings in the front part of the
palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sepa ...
, reach backward between the molars. The palate is long, extending substantially beyond the third molars. The back part, near the third molars, is usually perforated by prominent
posterolateral palatal pits In anatomy, posterolateral palatal pits are gaps at the sides of the back of the bony palate, near the last molars.Weksler, 2006, p. 34 Posterolateral palatal pits are present, in various degrees of development, in several members of the roden ...
, which are recessed into fossae (depressions). The mesopterygoid fossa, the gap behind the end of the palate, is perforated by sphenopalatine vacuities, which are set far to the front. The condition of the
arteries An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...
in the head is highly
derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...
. The subsquamosal fenestra, an opening in the back part of the skull determined by the shape of the
squamosal bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral c ...
, is present. The squamosal lacks a suspensory process that contacts the
tegmen tympani The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external auditor ...
, the roof of the
tympanic cavity The tympanic cavity is a small cavity surrounding the bones of the middle ear. Within it sit the ossicles, three small bones that transmit vibrations used in the detection of sound. Structure On its lateral surface, it abuts the external auditory ...
, a defining character of oryzomyines. Some openings occur in the
mastoid bone The mastoid part of the temporal bone is the posterior (back) part of the temporal bone, one of the bones of the skull. Its rough surface gives attachment to various muscles (via tendons) and it has openings for blood vessels. From its borders, ...
. In the
mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
, the
mental foramen The mental foramen is one of two foramina (openings) located on the anterior surface of the mandible. It is part of the mandibular canal. It transmits the terminal branches of the inferior alveolar nerve and the mental vessels. Structure The m ...
, an opening just before the first molar, opens sidewards, not upwards as in a few other oryzomyines. The upper and lower masseteric ridges, which anchor some of the chewing muscles, join at a point below the first molar and do not extend forward beyond that point.Weksler, 2006, p. 42 The
capsular process In rodents, the capsular process or projection is a bony capsule that contains the root of the lower incisor. It is visible on the labial (outer) side of the mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest ...
, a raising of the bone of the back of the mandible that houses the back end of the
incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, whe ...
, is present, but not as large as in ''O. couesi''.


Teeth

The
dental formula Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolo ...
is (one upper and one lower incisor and three upper and three lower
molars The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
),Whitaker and Hamilton, 1998, p. 279 as usual in muroid rodents. The upper incisors are well developed and strongly opisthodont, with the chewing edge located behind the vertical plane of the teeth.Carleton and Musser, 1989, p. 37 The molars are
bunodont The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
, with the cusps higher than the connecting crests, and
brachydont The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...
, low-crowned, as in most other oryzomyines. Many accessory crests, including the mesoloph on the upper molars and the mesolophid on the lower molars, are present, another trait the marsh rice rat shares with most but not all other oryzomyines. The flexi and flexids (valleys between the cusps and crests) at the labial (outer) side of the molars are closed by cingula (ridges). The upper molars have two longitudinal rows of cusps, not three as in the black and brown rats. The first and second upper molars are oval in form and the flexi do not extend to the midline of the molars.Weksler, 2006, p. 44 The anterocone, the front cusp of the upper first molar, is not divided in two by an indentation at its front ( anteromedian flexus), but does display a hollow in the middle, the anteromedian fossette, which divides it into separate cuspules at the labial and lingual (inner) sides of the molar. A crest, the anteroloph, is present behind the labial cuspule, but in older animals, the cusps and the crest are united into a single structure by wear. In the third upper molar, the cusps at the back are reduced and scarcely distinguishable. As in most oryzomyines, the upper molars all have one root on the inner (lingual) side and two on the outer (labial) side; in addition, the first upper molar usually has another small labial root. The first lower molar is rounded at the front end and the labial and lingual conules of the anteroconid, the frontmost cusp, are barely distinct. The second lower molar is elongated and has a crest, the anterolophid, before the two cusps that form the front edge of the molar in some other oryzomyines, the
protoconid Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn i ...
and
metaconid Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn ...
. A distinct ridge ( anterolabial cingulum) is at the outer front (anterolabial) edge of the molar, before the protoconid. The lower third molar is about as long as the second and also has an anterolophid, albeit a less well-defined one. The first lower molar has large roots at the front and back of the tooth and usually one or two smaller ones in between, at the labial and lingual side. The second and third lowers molars have either two roots, one labial and one lingual, or only one at the front, and another large root at the back.


Postcranial skeleton

As usual in oryzomyines, 12 ribs are present. The first rib articulates with both the last
cervical In anatomy, cervical is an adjective that has two meanings: # of or pertaining to any neck. # of or pertaining to the female cervix: i.e., the ''neck'' of the uterus. *Commonly used medical phrases involving the neck are **cervical collar **cerv ...
(neck) and first
thoracic The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
(chest) vertebrae, a synapomorphy of the Sigmodontinae. The anapophyses, processes at the back of vertebrae, are absent from the fifth
lumbar In tetrapod anatomy, lumbar is an adjective that means ''of or pertaining to the abdominal segment of the torso, between the diaphragm and the sacrum.'' The lumbar region is sometimes referred to as the lower spine, or as an area of the back i ...
. Between the second and third
caudal vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e, hemal arches (small bones) are present with a spinous back border. The
entepicondylar foramen The entepicondylar foramen is an opening in the distal (far) end of the humerus (upper arm bone) present in some mammals. It is often present in primitive placentals, such as the enigmatic Madagascan ''Plesiorycteropus''. In most Neotominae and al ...
is absent, as in all members of the Sigmodontinae; if present, as in some other rodents, this foramen perforates the distal end of the
humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...
.


Physiology

In poor conditions, the weight of the
adrenal gland The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex which ...
may increase up to 200%,Wolfe, 1982, p. 2 and rice rats are unable to conserve water well when
dehydrated In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
,Stalling and Haynes, 1982, p. 301 and in water contaminated with oil, they swim less and their mortality increases. The median amount of radiation needed to kill a marsh rice rat is 5.25  Gy and the lethal dose of
potassium cyanide Potassium cyanide is a compound with the formula KCN. This colorless crystalline salt, similar in appearance to sugar, is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications includ ...
is 7.20 mg/kg; both values are relatively low for cricetid rodents. In one study, wild rice rats in radioactively contaminated areas did not show signs of disease. Exposure to more daylight and higher food availability cause increased development of the
gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...
s in both adult and juvenile rice rats. When the
pineal gland The pineal gland, conarium, or epiphysis cerebri, is a small endocrine gland in the brain of most vertebrates. The pineal gland produces melatonin, a serotonin-derived hormone which modulates sleep, sleep patterns in both circadian rhythm, circ ...
is removed or
melatonin Melatonin is a natural product found in plants and animals. It is primarily known in animals as a hormone released by the pineal gland in the brain at night, and has long been associated with control of the sleep–wake cycle. In vertebrates ...
is administered in male rice rats, the testes are reduced and tend to regress into the body.


Distribution and habitat

The marsh rice rat currently occurs in much of the eastern and southern United States, northeast to southern New Jersey, and south to southeastern Texas and far northeastern
Tamaulipas Tamaulipas (), officially the Free and Sovereign State of Tamaulipas ( es, Estado Libre y Soberano de Tamaulipas), is a state in the northeast region of Mexico; one of the 31 states which, along with Mexico City, comprise the 32 Federal Entiti ...
, Mexico. The northernmost records in the interior United States are in eastern
Oklahoma Oklahoma (; Choctaw language, Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a U.S. state, state in the South Central United States, South Central region of the United States, bordered by Texas on the south and west, Kansas on the nor ...
, southeastern
Kansas Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the ...
, southern
Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it is bordered by eight states (tied for the most with Tennessee ...
and
Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolita ...
, and the southern half of
Kentucky Kentucky ( , ), officially the Commonwealth of Kentucky, is a state in the Southeastern region of the United States and one of the states of the Upper South. It borders Illinois, Indiana, and Ohio to the north; West Virginia and Virginia to ...
, but the species is absent in much of the
Appalachia Appalachia () is a cultural region in the Eastern United States that stretches from the Southern Tier of New York State to northern Alabama and Georgia. While the Appalachian Mountains stretch from Belle Isle in Newfoundland and Labrador, Ca ...
ns. Fossils of the marsh rice rat are known from
Rancholabrean The Rancholabrean North American Land Mammal Age on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from less than 240,000 years to 11,000 years BP, a p ...
(late Pleistocene, less than 300,000 years ago) deposits in Florida and Georgia and remains referred to the extinct subspecies ''O. p. fossilis'' are from the
Wisconsinan The Wisconsin Glacial Episode, also called the Wisconsin glaciation, was the most recent glacial period of the North American ice sheet complex. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cor ...
and
Sangamonian The Sangamonian Stage (or Sangamon interglacial) is the term used in North America to designate the last interglacial period. In its most common usage, it is used for the period of time between 75,000 and 125,000 BP.Willman, H.B., and J.C. Frye, 1 ...
of Texas and
Illinoian The Illinoian Stage is the name used by Quaternary geologists in North America to designate the period c.191,000 to c.130,000 years ago, during the middle Pleistocene, when sediments comprising the Illinoian Glacial Lobe were deposited. It precedes ...
and Sangamonian of Kansas. In the Florida Keys, rice rats occur on most of the Lower Keys, but are absent from the Upper Keys, which are of a different geological origin and were probably never connected to the mainland. The western and eastern ''Cytb'' clades within the marsh rice rat may represent expansions from different
glacial refugia A glacial refugium (''plural refugia'') is a geographic region which made possible the survival of flora and fauna in times of ice ages and allowed for post-glacial re-colonization. Different types of glacial refugia can be distinguished, namely nu ...
which the species was restricted to during a
glacial period A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
. Cave and archeological remains indicate that the range of the marsh rice rat has extended substantially further north and west earlier in the
Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...
, into central Texas, eastern
Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the southwe ...
, southwestern
Iowa Iowa () is a state in the Midwestern region of the United States, bordered by the Mississippi River to the east and the Missouri River and Big Sioux River to the west. It is bordered by six states: Wisconsin to the northeast, Illinois to the ...
, central Illinois, southern
Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th s ...
, southern
Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...
,
West Virginia West Virginia is a state in the Appalachian, Mid-Atlantic and Southeastern regions of the United States.The Census Bureau and the Association of American Geographers classify West Virginia as part of the Southern United States while the Bur ...
, and southwestern
Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
. Most northern archeological sites date from about 1000 CE and are associated with
corn Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. Th ...
cultivation, but in some older cave sites the rice rat is found with the extinct giant armadillo ''
Dasypus bellus ''Dasypus bellus'', the beautiful armadillo, is an extinct armadillo species endemic to North America and South America from the Pleistocene, living from 1.8 mya—11,000 years ago, existing for approximately . Slightly larger than its living r ...
'', suggesting warm climatic conditions. Perhaps a warm period during the
Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...
enabled the rice rat to disperse northward and when the climate cooled,
relict A relict is a surviving remnant of a natural phenomenon. Biology A relict (or relic) is an organism that at an earlier time was abundant in a large area but now occurs at only one or a few small areas. Geology and geomorphology In geology, a r ...
populations were able to survive in the north as
commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...
s in corn-cultivating Native American communities. Some subfossil animals are slightly larger than living marsh rice rats, possibly because environmental constraints were relaxed in commensal populations. In Tamaulipas and southern Texas, the ranges of the marsh rice rat and the related ''Oryzomys couesi'' meet;Schmidt and Engstrom, 1994, p. 914 in parts of Kenedy, Willacy and Cameron counties, Texas, and in far northeastern Tamaulipas, the two are
sympatric In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sh ...
(occur in the same places).Schmidt and Engstrom, 1994, p. 916 In experimental conditions, they fail to interbreed and genetic analysis yields no evidence of
gene flow In population genetics, gene flow (also known as gene migration or geneflow and allele flow) is the transfer of genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent a ...
or hybridization in the wild.Schmidt and Engstrom, 1994, p. 920 Compared to ''O. couesi'', the marsh rice rat shows less genetic variability within but more between populations in the contact zone, probably because the species is restricted to isolated populations near the coast. The marsh rice rat occurs in several habitats, ranging from coastal salt marshes to mountain streams and clearings. It is
semiaquatic In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semiaquatic animals include: * Verte ...
, spending much time in the water, and usually occurs in wetland habitats. It prefers areas where the ground is covered with grasses and sedges, which protect it from predators. In southern Illinois, marsh rice rats are more likely to occur in wetlands with more herbaceous cover, visual obstruction, and nearby grasslands. The species also occurs in drier uplands, which serve as sinks for young, dispersing animals and as refuges during high tide.Kruchek, 2004, p. 569 Rice rats are adept overwater dispersers; studies on islands off
Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...
's
Delmarva Peninsula The Delmarva Peninsula, or simply Delmarva, is a large peninsula and proposed state on the East Coast of the United States, occupied by the vast majority of the state of Delaware and parts of the Eastern Shore regions of Maryland and Virginia ...
show that they readily cross 300-m (1000 ft) channels between islands.


Behavior and ecology

Marsh rice rats are active during the night, so are rarely seen, although they may be among the most common small mammals in part of their range. They build nests of sedge and grass, about large, which are placed under debris, near shrubs, in short burrows, or high in aquatic vegetation. They may also use old nests of
marsh wren The marsh wren (''Cistothorus palustris'') is a small North American songbird of the wren family. It is sometimes called the long-billed marsh wren to distinguish it from the sedge wren, also known as the short-billed marsh wren. Taxonomy The ma ...
s (''Cistothorus palustris''),
red-winged blackbird The red-winged blackbird (''Agelaius phoeniceus'') is a passerine bird of the family Icteridae found in most of North America and much of Central America. It breeds from Alaska and Newfoundland south to Florida, the Gulf of Mexico, Mexico, and ...
s (''Agelaius phoeniceus''),
muskrat The muskrat (''Ondatra zibethicus'') is a medium-sized semiaquatic rodent native to North America and an introduced species in parts of Europe, Asia, and South America. The muskrat is found in wetlands over a wide range of climates and habitat ...
s (''Ondatra zibethicus'') or round-tailed muskrats (''Neofiber alleni''). Marsh rice rats sometimes make large runways or dig burrows. They are accomplished and willing swimmers, easily swimming more than under water, and often seek safety in the water when alarmed. Rice rats in the Florida Keys occasionally climb in vegetation, but never higher than . Marsh rice rats are very clean and extensively groom themselves, perhaps to keep their fur water-repellent. They are aggressive towards conspecifics and emit high-pitched squeaks while fighting. In dense vegetation, their perceptual range (the distance from which an animal can detect a patch of suitable habitat) is less than . When released outside of their natural wetland habitat, marsh rice rats generally move either upwind or downwind (anemotaxis), perhaps to move in a straight line, which is an efficient strategy to find suitable habitat. Many animals prey on marsh rice rats. The barn owl (''Tyto alba'') is among the most important; one study found that 97.5% of vertebrate remains in barn owl Owl pellet, pellets were marsh rice rats. Other predators include birds such as marsh hawks (''Circus cyaneus''), and barred owls (''Strix varia''); snakes such as cottonmouths (''Agkistrodon piscivorus''); American alligator, alligators (''Alligator mississippiensis''); and carnivorans like raccoons (''Procyon lotor''), red foxes (''Vulpes vulpes''), American mink (''Neogale vison''), weasels (''Mustela'' and ''Neogale'' sp.), and striped skunks (''Mephitis mephitis''). Many parasites have been recorded on the marsh rice rat, including various Acari, ticks and mites, Louse, lice, and fleas among external parasites and many nematodes and digeneans, a pentastomid, and several coccidians among internal parasites (see ''Parasites of the marsh rice rat''). Periodontitis, a bacterial disease affecting the jaws, is particularly virulent in marsh rice rats; the animal has been proposed as a model for research on the disease in humans. The identity of the bacterial agent remains unknown. Vitamin E, fluoride, and iodide protect against bone loss associated with this disease in the rice rat and a high-sucrose diet increases the severity of periodontitis. A case of kyphosis has been observed in a North Carolina marsh rice rat.


Population dynamics

The population density of the marsh rice rat usually does not reach 10 per ha (4 per acre).Whitaker and Hamilton, 1998, p. 281 The weather may influence population dynamics; in the
Everglades The Everglades is a natural region of tropical climate, tropical wetlands in the southern portion of the U.S. state of Florida, comprising the southern half of a large drainage basin within the Neotropical realm. The system begins near Orland ...
, densities may exceed 200 per ha (80 per acre) when flooding concentrates populations on small islands,Bloch and Rose, 2005, p. 302 In the Florida Keys, population density is less than 1 per ha (0.4 per acre). On Breton Island (Louisiana), Breton Island, Louisiana, perhaps an atypical habitat, home ranges in males average about and in females about . A study in Florida found male home ranges to average and female . Population size is usually largest during the summer and declines during winter, although populations in Texas and Louisiana may be more seasonally stable. Animals also often lose weight during winter. Population size varies dramatically from year to year in southern Texas.Schmidt and Engstrom, 1994, p. 917 In coastal Mississippi, storms probably do not cause the population to decline substantially, and in Texas, inundation of its habitat did not significantly influence population density. However, in Mississippi, flooding did cause a marked decline in rice rat abundance. In the northern part of its range, the species often occurs with the meadow vole (''Microtus pennsylvanicus''), but no evidence shows they compete with each other. In the south, the hispid cotton rat (''Sigmodon hispidus'') and the rice rat regularly occur together; water levels are known to influence relative abundance of these two species in Florida.Wolfe, 1982, p. 3 The cotton rat is mainly active during the day, which may help niche differentiation, differentiate its niche from that of the rice rat.


Diet

The marsh rice rat takes both vegetable and animal food, and is more carnivorous than most small rodents are; dominant food items vary seasonally. Plants eaten include species of ''Spartina'', ''Salicornia'', ''Tripsacum'', and ''Elymus (plant), Elymus'', among others; it mainly eats seeds and succulent parts. It prefers ''Spartina alterniflora'' that has been fertilized with nitrogen and mainly eats the inner tissue of the stem, perhaps because nitrogen-fertilized plants contain much less dimethylsulfoniopropionate in their inner tissues.Otto et al., 2004, p. 1922 The marsh rice rat was a major pest on rice plantations, feeding on the rice when it was newly planted. It also eats the fungus ''Endogone'' at times. Animals that are important to the marsh rice rat's diet include insects, fiddler crabs, and snails, but the species is known to eat many other animals, including fish, clams, and juvenile ''Graptemys'' and ''Chrysemys'' turtles. They scavenge on carcasses of muskrats, deermouse, deermice, and sparrows, and may be the most important predator on eggs and young of the marsh wren.Whitaker and Hamilton, 1998, p. 280; Wolfe, 1982, p. 3 Rice rats also eat eggs and young of the seaside sparrow (''Ammodramus maritimus'')Post, 1981, p. 35 and are aggressive towards the sparrow, apparently leading it to avoid nesting in ''Juncus'' in a seaside salt marsh in Florida. On islands in North Carolina, rice rats consume eggs of Forster's tern (''Sterna forsteri''). They have been observed preying on alligator eggs in Georgia. Laboratory studies have found that rice rats assimilation (biology), assimilate 88% to 95% of the energy in their food. They lose weight when fed on ''Spartina'', fiddler crabs, or sunflower seeds alone, but a diet consisting of several of those items or of mealworms is adequate to maintain weight. In an experiment, marsh rice rats did not show hoarding behavior, but wild rice rats have been observed carrying food to a nest. Even when they live in uplands, they mostly eat water plants and animals, although they consume some upland plants.


Reproduction and lifecycle

Breeding occurs mostly during the summer. Some studies report that breeding ceases entirely during the winter, but winter breeding occurs as far north as Virginia, primarily because photoperiod influences their circadian rhythm which determines breeding. In both Texas and Virginia, variation in reproductive activity in females is less than in males. In the south of its range, animals may breed less when the summer is at its warmest. The duration of the estrous cycle ranges from 6 to 9 days, with an average of 7.72 days. Estrus occurs again after a litter is born. Copulation (zoology), Copulatory behavior in the marsh rice rat is similar to that in laboratory brown rats. Before mating starts, "the male pursues the running female from behind."Dewsbury, 1970, p. 268 The male then repeatedly mounts and dismounts the female; not all mounts result in an ejaculation. Penetrations only last for about 250 ms, but during mating, the penetrations and the intervals between them become longer.Dewsbury, 1970, p. 269 Even when a male is satiated after mating, it is able to copulate again when a new female is introduced (the Coolidge effect).Dewsbury, 1970, p. 271 Partly because of resistance by the female, the frequency of ejaculation during mating is rather low in marsh rice rats as compared to laboratory rats, hamsters, and deermice.Dewsbury, 1970, p. 274 After a gestation of about 25 days, three to five young are usually born, although litter sizes vary from one to seven. Females may have up to six litters a year. Newborns weigh 3 to 4 g (about 0.10 to 0.15 oz) and are blind and almost naked. About as many males as females are born. The external ears (pinnae) soon unfold and on the first day, claws are visible and the young emit high-pitched squeaks. On the second day, they are able to crawl, and during the third to fifth days, the whiskers and eyelids develop. On the two subsequent days, the mammae and incisors become visible and the animals become more active. Between the eighth and 11th days, the eyes open, the fur develops, and the young begin to take solid food. Weaning occurs on the 11th to 20th day, according to different studies. Considerable variation is reported in body masses at different ages, perhaps because of geographic variation. Sexual activity commences when the animals are about 50 to 60 days old. In the wild, rice rats usually live for less than a year; one study suggested that the average lifespan is only seven months.Negus et al., 1961, p. 103


Human interactions

The marsh rice rat is generally of little importance to humans, which is perhaps why it is not as well studied as some other North American rodents. In 1931, Arthur Svihla noted that virtually no information had been published on the habits and life history of the marsh rice rat since the 1854 publication of Audubon and Bachman's description. Writing on Everglades mammals, Thomas E. Lodge notes that although the name "rat" may associate it unpleasantly with the introduced black and brown rats, its appearance is more endearing, even cute. J.S. Steward proposed the marsh rice rat as a model organism in 1951 to study certain infections to which other rodents used at the time are not susceptible. The marsh rice rat is quite susceptible to periodontitis and has been used as a model system for the study of that disease. The marsh rice rat is the primary host of the Bayou virus (BAYV), the second-most common agent of
hantavirus ''Orthohantavirus'' is a genus of single-stranded, enveloped, negative-sense RNA viruses in the family ''Hantaviridae'' within the order ''Bunyavirales''. Members of this genus may be called orthohantaviruses or simply hantaviruses. Orthohantav ...
infections in the United States. About 16% of animals are infected and the virus is most prevalent in old, heavy males. The virus may be transmitted among rice rats through bites inflicted during fights. It is also present in rice rat saliva and urine, and human infections may occur because of contact with these excreta. Two related hantaviruses, Catacama virus and Playa de Oro virus, are known from ''Oryzomys couesi'' in Honduras and western Mexico, respectively. An arenavirus normally associated with woodrats (''Neotoma'') has also been found in Florida marsh rice rats. Antibodies against ''Borrelia burgdorferi'', the bacterium that causes Lyme disease in the United States, have been found in marsh rice rats in Virginia, Maryland, North Carolina, and Tennessee. Another pathogenic bacterium, ''Bartonella'', is known from Georgia marsh rice rats. The 2016 IUCN Red List assesses the conservation status of the marsh rice rat as "Least Concern", because it is a common, widespread, and stable species without major threats that occurs in several protected areas. The Florida Keys form is rare and in decline and is threatened by competition with the black rat, predation by domestic cats, habitat loss, and loss of genetic variation; it is considered endangered. At the northern edge of its distribution, the marsh rice rat is listed as threatened in Illinois, and whether it persists in Pennsylvania is unclear; it probably formerly occurred in tidal marshes on the Delaware River. In Illinois, its population may have regenerated because wetlands have been developed to protect waterfowl and shorebirds and because suitable wetlands often develop in abandoned coal-mining operations. A 2001 study projected that climate change would reduce the range of the marsh rice rat in Texas, where it is now common, but may become threatened by habitat loss in the future. A study at the Paducah Gaseous Diffusion Plant found that rice rats accumulate more polychlorinated biphenyls, but less heavy metal than white-footed mouse, white-footed mice (''Peromyscus leucopus'').Smith et al., 2002, p. 261


References


Literature cited

*Abuzeineh, A.A., Owen, R.D., McIntyre, N.E., Dick, C.W., Strauss, R.E. and Holsomback, T. 2007
Response of marsh rice rat (''Oryzomys palustris'') to inundation of habitat
(subscription required). ''The Southwestern Naturalist'' 52(1):75–78. *Allen, J.A. 1894
On the mammals of Aransas County, Texas, with descriptions of new forms of ''Lepus'' and ''Oryzomys''
''Bulletin of the American Museum of Natural History'' 6:165–198. *Audubon, J.J. and Bachman, J. 1854
The quadrupeds of North America. Vol. III
New York: V. G. Audubon, 348 pp. *Baird, S.F. 1857
Mammals: General report upon the zoology of the several Pacific railroad routes
Reports of explorations and surveys to ascertain the most practicable and economical route for a railroad from the Mississippi River to the Pacific Ocean (Senate executive document 78, Washington, D.C.) 8(1):1–757. *Bangs, O. 1898
The land mammals of peninsular Florida and the coast region of Georgia
''Proceedings of the Boston Society of Natural History'' 28:157–235. *Beiraghi, S., Rosen, S., Wright, K., Spuller, R. and Beck, F.M. 1988
Effect of stannous fluoride and iodine on root caries and bone loss in rats
''Ohio Journal of Science'' 88(3):99–100. *Benson, D.E. and Gehlbach, F.R. 1979
Ecological and taxonomic notes on the rice rat (''Oryzomys couesi'') in Texas
(subscription required). ''Journal of Mammalogy'' 60(1):225–228. *Bloch, C.P. and Rose, R.K. 2005
Population dynamics of ''Oryzomys palustris'' and ''Microtus pennsylvanicus'' in Virginia tidal marshes
(subscription required). ''Northeastern Naturalist'' 12(3):295–306. *Brunjes, J.H., IV and Webster, W.D. 2003. Marsh rice rat, ''Oryzomys palustris'', predation on Forster's tern, ''Sterna forsteri'', eggs in coastal North Carolina. ''Canadian Field-Naturalist'' 117(4):654–657. *Cameron, G.N. and Scheel, D
Getting warmer: Effect of global climate change on distribution of rodents in Texas
(subscription required). ''Journal of Mammalogy'' 82(3):652–680. *Cantrell, M.A., Carstens, B.C. and Wichman, H.A. 2009
X chromosome inactivation and ''Xist'' evolution in a rodent lacking LINE-1 activity
''PLoS ONE'' 4(7):e6252; 1–9. *Carleton, M.D. and Arroyo-Cabrales, J. 2009
Review of the ''Oryzomys couesi'' complex (Rodentia: Cricetidae: Sigmodontinae) in Western Mexico
''Bulletin of the American Museum of Natural History'' 331:94–127. *Carleton, M.D. and Musser, G.G. 1984. Muroid rodents. Pp. 289–379 in Anderson. S. and Jones, J.K., Jr. (eds.). Orders and families of Recent mammals of the world. John Wiley and Sons, New York, 686 pp. *Carleton, M.D. and Musser, G.G. 1989
Systematic studies of oryzomyine rodents (Muridae, Sigmodontinae): a synopsis of ''Microryzomys''
''Bulletin of the American Museum of Natural History'' 191:1–83. * *Chamberlain, M.J. and Leopold, B.D. 2003
Effects of a flood on relative abundance and diversity of small mammals in a regenerating bottomland hardwood forest
(subscription required). ''The Southwestern Naturalist'' 48(2):306–309. *Chapman, F.M. 1893
Description of a new subspecies of ''Oryzomys'' from the Gulf States
''Bulletin of the American Museum of Natural History'' 5:43–46. *Childs, H.E., Jr. and Cosgrove, G.E. 1966
A study of pathological conditions in wild rodents in radioactive areas
(subscription required). ''American Midland Naturalist'' 76(2):309–324. *Chu, Y.-K., Owen, R.D., Sánchez-Hernández, C., Romero-Almarez, M. de L. and Jonsson, C.B. 2008
Genetic characterization and phylogeny of a hantavirus from Western Mexico
(subscription required). ''Virus Research'' 131:180–188. *Cohen, M.E. and Meyer, D.M. 1993
Effect of dietary vitamin E supplement and rotational stress on alveolar bone loss in rice rats
(subscription required). ''Archives of Oral Biology'' 38(7):601–606. *Dalquest, W.W. 1962
The Good Creek Formation, Pleistocene of Texas, and its fauna
(subscription required). ''Journal of Paleontology'' 36(3):568–582. *Dalquest, W.W. 1965
New Pleistocene formation and local fauna from Hardeman County, Texas
(subscription required). ''Journal of Paleontology'' 39(1):63–79. *Dewsbury, D.A. 1970
Copulatory behaviour of rice rats (''Oryzomys palustris'')
(subscription required). ''Animal Behaviour'' 18:266–275. *Durden, L.A. and Kollars, T.M., Jr. 1997. The fleas (Siphonaptera) of Tennessee. ''Journal of Vector Ecology'' 22(1):13–22. *Edmonds, K.E., Jr., Riggs, L. and Stetson, M.H. 2003
Food availability and photoperiod affect reproductive development and maintenance in the marsh rice rat (''Oryzomys palustris'')
(subscription required). ''Physiology & Behavior'' 78:41–49. *Eliot, D.G. 1905
A checklist of mammals of the North American continent, the West Indies and the neighboring seas
''Field Columbian Museum Zoological Series'' 6:1–761. *Esher, R.J., Wolfe, J.L. and Layne, J.N. 1978
Swimming behavior of rice rats (''Oryzomys palustris'') and cotton rats (''Sigmodon hispidus'')
(subscription required). ''Journal of Mammalogy'' 59(3):551–558. *Eubanks, B.W., Hellgren, E.C., Nawrot, J.R. and Bluett, R.D. 2011
Habitat associations of the marsh rice rat (''Oryzomys palustris'') in freshwater wetlands of southern Illinois
(subscription required). ''Journal of Mammalogy'' 92(3):552–560. *Forys, E.A. and Dueser, R.D. 1993
Inter-island movements of rice rats (''Oryzomys palustris'')
(subscription required). ''American Midland Naturalist'' 130(2):408–412. *Goldman, E.A. 1918
The rice rats of North America
''North American Fauna'' 43:1–100. *Goodyear, N.C. 1987
Distribution and habitat of the silver rice rat, ''Oryzomys argentatus''
(subscription required). ''Journal of Mammalogy'' 68(3):692–695. *Goodyear, N.C. 1991
Taxonomic status of the silver rice rat, ''Oryzomys argentatus''
(subscription required). ''Journal of Mammalogy'' 72(4):723–730. *Goodyear, N.C. 1992
Spatial overlap and dietary selection of native rice rats and exotic black rats
(subscription required). ''Journal of Mammalogy'' 73(1):186–200. *Hall, E.R. 1960
''Oryzomys couesi'' only subspecifically different from the marsh rice rat, ''Oryzomys palustris''
(subscription required). ''The Southwestern Naturalist'' 5(3):171–173. *Hamilton, W.J., Jr. 1955. Two new rice rats (Genus ''Oryzomys'') from Florida. ''Proceedings of the Biological Society of Washington'' 68:83–86. *Hanson, J.D., Indorf, J.L., Swier, V.J. and Bradley, R.D. 2010
Molecular divergence within the ''Oryzomys palustris'' complex: evidence for multiple species
(subscription required). ''Journal of Mammalogy'' 91(2):336–347. *Harlan, R. 1837
Description of a new species of Quadruped, of the order Rodentia, inhabiting the United States
''The American Journal of Science'' 31(2):385–386. *Hershkovitz, P.M. 1987
First South American record of Coues' marsh rice rat, ''Oryzomys couesi''
(subscription required). ''Journal of Mammalogy'' 68(1):152–154. *Hibbard, C.W. 1955
The Jinglebob interglacial (Sangamon?) fauna from Kansas and its climatic significance
''Contributions from the Museum of Paleontology, University of Michigan'' 12:179–228. *Hofmann, J.E., Gardner, J.E. and Moris, M.J. 1990. Distribution, abundance, and habitat of the marsh rice rat (''Oryzomys palustris'') in southern Illinois. ''Transactions of the Illinois State Academy of Science'' 83(3–4):162–180. *Hooper, E.T. and Musser, G.G. 1964
The glans penis in Neotropical cricetines (Family Muridae) with comments on classification of muroid rodents
''Miscellaneous Publications of the University of Michigan Museum of Zoology'' 123:1–57. *Humphrey, S.R. and Setzer, H.W. 1989
Geographic variation and taxonomic revision of rice rats (''Oryzomys palustris'' and ''O. argentatus'') of the United States
(subscription required). ''Journal of Mammalogy'' 70(3):557–570. *Hunt, R.H. and Ogden, J.J. 1991
Selected aspects of the nesting ecology of American alligators in the Okefenokee Swamp
(subscription required). ''Journal of Herpetology'' 25(4):448–453. *Kays, R.W. and Wilson, D.E. 2000
Mammals of North America
Princeton and Oxford: Princeton University Press, 240 pp. *Kollars, T.M., Jr., Ourth, D.D., Lockey, T.D. and Markowski, D. 1996. IgG antibodies to ''Borrelia burgdorferi'' in rodents in Tennessee. ''Journal of Spirochetal and Tick-Borne Diseases'' 3(3–4):130–134. *Kosoy, M.Y., Elliott, L.H., Ksiazek, T.G., Fulhorst, C.F., Rollin, P.E., Childs, J.E., Mills, J.N., Maupin, G.O. and Peters, C.J. 1996
Prevalence of antibodies to arenaviruses in rodents from the southern and western United States: evidence for an arenavirus associated with the genus ''Neotoma''
(subscription required). ''American Journal of Tropical Medicine and Hygiene'' 54(6):570–576. *Kosoy, M.Y., Regnery, R.L., Tzianabos, T., Marston, E.L., Jones, D.C., Green, D., Maupin, G.O., Olson, J.G. and Childs, J.E. 1997
Distribution, diversity, and host specificity of ''Bartonella'' in rodents from the southeastern United States
''American Journal of Tropical Medicine and Hygiene'' 57(5):578–588. *Kruchek, B.L. 2004
Use of tidal marsh and upland habitats by the marsh rice rat (''Oryzomys palustris'')
(subscription required). ''Journal of Mammalogy'' 85(3):569–575. *Leopard, E.P. 1979
Periodontitis. Animal model: periodontitis in the rice rat (''Oryzomys palustris'')
''American Journal of Pathology'' 96(2):643–646. *Lodge, T.E. 2005. The Everglades handbook: understanding the ecosystem. 2nd edition. CRC Press, 302 pp. *Loxterman, J.L., Moncrief, N.D., Dueser, R.D., Carlson, C.R. and Pagels, J.F. 1998
Dispersal abilities and genetic population structure of insular and mainland ''Oryzomys palustris'' and ''Peromyscus leucopus''
(subscription required). ''Journal of Mammalogy'' 79(1):66–77. *McIntyre, N.E., Chu, Y.-K., Owen, R.D., Abuzeineh, A., de la Sancha, N., Dick, C.W., Holsomback, T. Nisbett, R.A. and Jonsson, C. 2005
A longitudinal study of Bayou virus, hosts, and habitat
''American Journal of Tropical Medicine and Hygiene'' 73:1043–1049. *Merriam, C.H. 1901
Synopsis of the rice rats (genus ''Oryzomys'') of the United States and Mexico
''Proceedings of the Washington Academy of Sciences'' 3:273–295. *Merritt, J.F. 1987. ''Guide to the mammals of Pennsylvania''. University of Pittsburgh Press, 408 pp. *Milazzo, M.L., Cajimat, M.N., Hanson, J.D., Bradley, R.D., Quintana, M., Sherman, C., Velásquez, R.T. and Fulhorst, C.F. 2006
Catacamas virus, a hantaviral species naturally associated with ''Oryzomys couesi'' (Coues' oryzomys) in Honduras
''American Journal of Tropical Medicine and Hygiene'' 75(5):1003–1010. *Miller, G.S., Jr. and Kellogg, R. 1955
List of North American Recent mammals
''United States National Museum Bulletin'' 205:i–xii+1–954. *Musser, G.G. and Carleton, M.D. 2005
Superfamily Muroidea
Pp. 894–1531 in Wilson, D.E. and Reeder, D.M. (eds.)
''Mammal Species of the World: a taxonomic and geographic reference''. 3rd ed
Baltimore: The Johns Hopkins University Press, 2 vols., 2142 pp. *Negus, N.C., Gould, E. and Chipman, R.K. 1961
Ecology of the rice rat, ''Oryzomys palustris'' (Harlan), on Breton Island, Gulf of Mexico, with a critique of the critical stress theory
''Tulane Studies in Zoology'' 8(4):93–123. *Nesmith, C.C. and Cox, J. 1985. Red-winged blackbird nest usurpation by rice rats in Florida and Mexico. ''Florida Field Naturalist'' 13(2):35–36. *O'Farrell, T.P. and Dilley, J.V. 1975
A comparison of radiation response, cyanide toxicity and sulfur transferase activity in native North American rodents
(subscription required). ''Comparative Biochemistry and Biophysiology'' 50B:443–447. *Oliver, J.H., Magnarelli, L.A., Hutcheson, H.J. and Anderson, J.F. 1999
Ticks and antibodies to ''Borrelia burgdorferi'' from mammals at Cape Hatteras, NC and Assateague Island, MD and VA
(abstract only). ''Journal of Medical Entomology'' 36(5):578–587. *Otte, M.L., Wilson, G., Morris, J.T. and Moran, B.M. 2004
Dimethylsulphoniopropionate (DMSP) and related compounds in higher plants
(subscription required). ''Journal of Experimental Botany'' 55(404):1919–1925. *Oz, H.S. and Puleo, D.A. 2011
Animal models for periodontal disease
''Journal of Biomedicine and Biotechnology'' 2011:754857. *Post, W. 1981
The influence of rice rats ''Oryzomys palustris'' on the habitat use of the seaside sparrow ''Ammospiza maritima''
(subscription required). ''Behavioral Ecology and Sociobiology'' 9(1):35–40. *Reid, F.A. 2006. ''A Field Guide to Mammals of North America'', 4th ed. Boston: Houghton Mifflin Co. *Richards, R.L. 1980. Rice rat (''Oryzomys'' cf. ''palustris'') remains from southern Indiana caves. ''Proceedings of the Indiana Academy of Sciences'' 89:425–431. *Rose, R.K. and McGurk, S.W. 2006. Year-round diet of the marsh rice rat, ''Oryzomys palustris'', in Virginia tidal marshes. ''Virginia Journal of Science'' 57(3):115–121. *Schmidly, D.J. and Davis, W.B. 2004. ''The mammals of Texas''. 2nd edition. University of Texas Press, 501 pp. *Schmidt, C.A. and Engstrom, M.D. 1994
Genic variation and systematics of rice rats (''Oryzomys palustris'' species group) in southern Texas and northeastern Tamaulipas, Mexico
(subscription required). ''Journal of Mammalogy'' 75(4):914–928. *Schooley, R.L. and Branch, L.C. 2005
Limited perceptual range and anemotaxis in marsh rice rats ''Oryzomys palustris''
(subscription required). ''Acta Theriologica'' 50(1):59–66. *Schwartz, C.W. and Schwartz, E.R. 2001. ''The wild mammals of Missouri''. University of Missouri Press, 368 pp. *Shklair, I.L. and Ralls, S.A. 1988. Periodontopathic micro-organisms in the rice rat (''Oryzomys palustris''). ''Microbios'' 55:25–31. (abstract only) *Smith, P.N., Cobb, G.P., Harper, F.M., Adair, B.M. and McMurry, S.T. 2002
Comparison of white-footed mice and rice rats as biomonitors of polychlorinated biphenyl and metal contamination
(subscription required). ''Environmental Pollution'' 119(2):261–268. *Sofaer, J.A. and Shaw, J.H. 1971
The genetics and development of fused and supernumerary molars in the rice rat
''Journal of Embryology and Experimental Morphology'' 26(1):99–109. *Spitzer, N.C. and Lazell, J.D., Jr. 1978
A new rice rat (genus ''Oryzomys'') from Florida's Lower Keys
(subscription required). ''Journal of Mammalogy'' 59(4):787–792. *Steward, J.S. 1951
The swamp rice rat (''Oryzomys palustris natator'') as a possible laboratory animal for special purposes
(subscription required). ''The Journal of Hygiene'' 49(4):427–429. *Stone, W. and Cram, W.E. 1903
''American animals: a popular guide to the mammals of North America north of Mexico, with intimate biographies of the more familiar species''
Doubleday, Page & Company, 316 pp. *Svihla, A. 1931
Life history of the Texas rice rat (''Oryzomys palustris texensis'')
(subscription required). ''Journal of Mammalogy'' 12(3):238–242. *Voss, R.S. and Linzey, A.V. 1981
Comparative gross morphology of male accessory glands among Neotropical Muridae (Mammalia: Rodentia) with comments on systematic implications
''Miscellaneous Publications of the University of Michigan Museum of Zoology'' 159:1–41. *Wang, Y., Williams, D.A. and Gaines, M.S. 2005
Evidence for a recent genetic bottleneck in the endangered Florida Keys silver rice rat (''Oryzomys argentatus'') revealed by microsatellite DNA analyses
(subscription required). ''Conservation Genetics'' 6:575–585. *Webster, W.D. 1987
Kyphosis in the marsh rice rat (''Oryzomys palustris'')
''Journal of Wildlife Diseases'' 23(1):171–172. *Weksler, M. 2006
Phylogenetic relationships of oryzomyine rodents (Muroidea: Sigmodontinae): separate and combined analyses of morphological and molecular data
''Bulletin of the American Museum of Natural History'' 296:1–149. *Weksler, M., Percequillo, A.R. and Voss, R.S. 2006
Ten new genera of oryzomyine rodents (Cricetidae: Sigmodontinae)
''American Museum Novitates'' 3537:1–29. *Whitaker, J.O. and Hamilton, W.J. 1998
''Mammals of the Eastern United States''
Cornell University Press, 583 pp. *Winkler, A.J. 1990
Small mammals from a Holocene sequence in central Texas and their paleoenvironmental implications
(subscription required). ''The Southwestern Naturalist'' 35(2):199–205. *Wolfe, J.L. 1982
Oryzomys palustris
''Mammalian Species'' 176:1–5. *Wolfe, J.L. and Esher, R.J. 1981
Effects of crude oil on swimming behavior and survival in the rice rat
(subscription required). ''Environmental Research'' 26:486–489. {{Featured article Mammals of the United States Oryzomys Mammals of Mexico Mammals described in 1837 Taxonomy articles created by Polbot Taxa named by Richard Harlan