''Euryoryzomys russatus'', also known as the russet oryzomys, russet rice rat, or big-headed rice rat, is a species of

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 is a member of the genus ''

Euryoryzomys ''Euryoryzomys'' is a genus of rodents in the tribe Oryzomyini of family Cricetidae. It includes six species, which are distributed in South America. Until 2006, its members were included in the genus ''Oryzomys'', but they are not closely related ...

'', which was split off from ''

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 ...

'' in 2006. It was first described by

Johann Andreas Wagner Johann Andreas Wagner (21 March 1797 – 17 December 1861) was a German palaeontologist, zoologist and archaeologist who wrote several important works on palaeontology. Career Wagner was a professor at the University of Munich, and curator ...

in 1848. It is found in southern

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

, eastern

Paraguay Paraguay (; ), officially the Republic of Paraguay ( es, República del Paraguay, links=no; gn, Tavakuairetã Paraguái, links=si), is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to th ...

and northeastern

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

. It is considered a large species in its genus, with a reddish-brown coat, long tail length, and large skull. It is a terrestrial rodent, spending its time foraging for seeds, fruits, and insects. It is listed by the IUCN as least concern, although studies have shown it to be influenced by anthropogenic disturbances. Predators consist of small members of the order Carnivora.

Etymology

The prefix eury- comes from the Greek word 'eurys'' meaning "wide" or "broad". The specific epithet ''russatus'' comes from the Latin word 'russatus', meaning "clothed in red".

Taxonomy

''Euryoryzomys russatus'' (Wagner, 1848) is the currently accepted name for the russet rice rat. It is a member of the order Rodentia and family Cricetidae with the genus ''Euryoryzomys'' comprising six valid species.

Distribution and habitat

''Euryoryzomys russatus'' is found in continental Brazil and outlying islands. This species is also found in Bolivia, Argentina, and Paraguay. It is found along altitudinal gradients consisting of lowland and mountainous (

montane Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial f ...

) areas. It is found in the

Atlantic Forest The Atlantic Forest ( pt, Mata Atlântica) is a South American forest that extends along the Atlantic coast of Brazil from Rio Grande do Norte state in the northeast to Rio Grande do Sul state in the south and inland as far as Paraguay and th ...

as well as some areas of the

Amazon rainforest The Amazon rainforest, Amazon jungle or ; es, Selva amazónica, , or usually ; french: Forêt amazonienne; nl, Amazoneregenwoud. In English, the names are sometimes capitalized further, as Amazon Rainforest, Amazon Forest, or Amazon Jungle. ...

. Specific locations where ''E. russatus'' has been collected include: Desterro Environmental Conservation Unit central

Santa Catarina Island Santa Catarina Island ( pt, Ilha de Santa Catarina) is an island in the Brazilian state of Santa Catarina, located off the southern coast. It is home to the state capital, Florianópolis. Location Santa Catarina Island is approximately 54 km ...

, Brazil (live specimens); Alem Paraiba,

Minas Gerais Minas Gerais () is a state in Southeastern Brazil. It ranks as the second most populous, the third by gross domestic product (GDP), and the fourth largest by area in the country. The state's capital and largest city, Belo Horizonte (literally ...

, Brazil (museum specimens);

Guaricana National Park The Guaricana National Park ( pt, Parque Nacional Guaricana) is a national park in the state of Paraná, Brazil. It protects a mountainous area holding a remnant of Atlantic Forest. Location The Guaricana National Park covers parts of the munici ...

, Paraná, Brazil (museum specimens);

Ilha do Cardoso Ilha do Cardoso (''Cardoso Island'') is an island belonging to the city of Cananéia, São Paulo, Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and ...

São Paulo São Paulo (, ; Portuguese for 'Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the GaWC a ...

, Brazil (museum specimens); Parana, Southern Brazil (genetic identification from scat of predatory felines); Picinguaba, São Paulo, Brazil (live specimens);

Rio de Janeiro Rio de Janeiro ( , , ; literally 'River of January'), or simply Rio, is the capital of the state of the same name, Brazil's third-most populous state, and the second-most populous city in Brazil, after São Paulo. Listed by the GaWC as a b ...

, Brazil (live specimens);Costa, M.A.R., Maldonado Jr, A., Bóia, M.N., Lucio, C.S. & Simões, R.O. 2014. a new species of Hassalstrongylus (Nematoda: Heligmonelidae) from Euryoryzomys russatus (Rodentia: Sigmodontinae) in the Atlantic forest, Brazil. Neotropical Helminthology, vol. 8, n°2, jul-dec, pp. 235-242. Morro Grande Forest Reserve, São Paulo, Brazil (live specimens). This species is considered a forest specialist, dwelling only in habitats that have extensive forest canopy cover.Püttker, T. A. A. Bueno, C. Santos de Barros, S. Sommer, R. Pardini. 2013. Habitat specialization interacts with habitat amount to determine dispersal success of rodents in fragmented landscapes, ''Journal of Mammalogy'', Volume 94, Issue 3, 11:714–726, https://doi.org/10.1644/12-MAMM-A-119.1 Abundance and immigration rates have been shown to increase as forest coverage increases.

Life history

Morphology

The genus ''Euryoryzomys'' is described as having

pelage Fur is a thick growth of hair that covers the skin of mammals. It consists of a combination of oily #Guard hair, guard hair on top and thick #Down hair, underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as ...

that varies from yellow in color to a red-brown dorsally, while having a lighter ventral color.Weksler, M.; Percequillo, A. R.; Voss, R. S. (2006-10-19). "Ten new genera of oryzomyine rodents (Cricetidae: Sigmodontinae)" (PDF). ''American Museum Novitates''.

American Museum of Natural History The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...

. 3537: 1–29. The ears are typically medium to large. Vibrissae (whiskers) do not extend past the ears. Most species possess a jugal (with the exception of '' E. lamia''). ''Euryoryzomys russatus'' is described as having a large skull and relatively large body length; with a body length range of . Weights have been recorded in some studies, and averaged .Naxara, L., Pinotti, B., & Pardini, R. (2009). Seasonal Microhabitat Selection by Terrestrial Rodents in an Old-Growth Atlantic Forest. ''Journal of Mammalogy'', ''90''(2), 404–415. Retrieved from http://www.jstor.org/stable/30224486 The tail averages between in length. Pelage of the rice rat is a reddish-brown on the dorsal portion of the body and white on the ventral portion. The pinnae and tail are both grey in color. The fore and hindlimbs are a pale pink, along with the nose. The facial vibrissae are black in color. Parietals in ''E. russatus'' possess no lateral expansions.

Ecology

''Euryoryzomys russatus'' is a nocturnal, terrestrial rodent that moves primarily over leaf litter found on the forest floor.Ricardo S. Bovendorp, Jessica A. Laskowski and Alexandre R. Percequillo 2016. A first view of the unseen: nests of an endangered Atlantic Forest rat species. Mammalia (Short Note): 1-4. DOI 10.1515/mammalia-2015-0178 A seasonal microhabitat selection study found variation in microhabitat choice in warm-wet and cool-dry seasons. ''Euryoryzomys russatus'' was shown to have greater abundance in areas with woody debris, low leaf litter height, and high arthropod biomass during the warm-wet season and during the cool-dry season the greatest abundance was seen in areas with high leaf litter humidity. It is an opportunistic eater, consuming seeds, fruit, and insects when possible.Powers AM, Mercer DR, Watts DM, Guzman H, Fulhorst CF, Popov VL and Tesh RB (1999) Isolation and genetic characterization of a hantavirus (Bunyaviridae: Hantavirus) from a rodent, ''Oligoryzomys microtis'' (Muridae), collected in northeastern Peru Am J Trop Med Hyg 61:92–98Bergallo, H. & Magnusson, W. (2004). Factors affecting the use of space by two rodent species in Brazilian Atlantic forest. Mammalia. 68. 121-132. 10.1515/mamm.2004.013. A study of seed predation in the Brazilian Atlantic forest found ''E. russatus'' to be an efficient seed predator, eating a majority of seeds offered (with an exception to those with a mass greater than that of the observed individuals). A study of the population dynamics of a population of ''E. russatus'' on Santa Catarina Island in southern Brazil showed them to have nearly equal sex ratios. Populations of ''E. russatus'' have been shown to have a monogamous mating system.Antunes, P., Campos, M., Oliveira-Santos, L., & Graipel, M. (2009). Population dynamics of Euryoryzomys russatus and Oligoryzomys nigripes (Rodentia, Cricetidae) in an Atlantic forest area, Santa Catarina Island, Southern Brazil. ''Biothemes, 22'' (2), 143-151. doi: https://doi.org/10.5007/2175-7925.2009v22n2p143 Females show reproductive activity throughout the year, and correlate with availability of food resources. The nests of ''E. russatus'' are cup-shaped, and built with fibers from bamboo and other grasses from the family

Poaceae Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns an ...

. Offspring are born

altricial In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the mome ...

, lacking hair, and with eyes and ears closed. A study tracking individuals of ''E. russatus'' calculated the average number of offspring per pregnancy (from survey of pregnant females and nestlings) to be 3.6, with three to six nestlings being typical.

Genetics

Genetic analyses have grouped different populations of ''E. russatus'' into three clades using mitochondrial and nuclear gene regions, however no subspecies have been identified. A study focused on the genetic structuring of populations in the Atlantic Rain Forest of southern Brazil found no genetic structuring throughout the species distribution. Through karyotyping of ''E. russatus'' individuals from Parque Estadual da Serra do Mar (Santa Virginia, Brazil) it was found that they possess a chromosome number of 2n=80. This number is shared with '' E. emmonsae'' and '' E. nitidus''.

Conservation

''Euryoryzomys russatus'' is listed as a species of least concern by the IUCN as of September 2016. However, studies have shown this species to be susceptible to anthropogenic disturbances such as habitat degradation or destruction.

Predators

Studies have found the ''E. russatus'' to be a prey item of several neotropical feline species including

jaguarundi The jaguarundi (''Herpailurus yagouaroundi'') is a wild cat native to the Americas. Its range extends from central Argentina in the south to northern Mexico, through Central and South America east of the Andes. The jaguarundi is a medium-sized ...

(''Puma yagouaroundi''),

oncilla The oncilla (''Leopardus tigrinus''), also known as the northern tiger cat, little spotted cat, and tigrillo, is a small spotted cat ranging from Central America to central Brazil. It is listed as Vulnerable on the IUCN Red List, and the popul ...

(''Leopardus tigrinus'') and

ocelot The ocelot (''Leopardus pardalis'') is a medium-sized spotted wild cat that reaches at the shoulders and weighs between on average. It was first described by Carl Linnaeus in 1758. Two subspecies are recognized. It is native to the southwes ...

(''Leopardus pardalis'').

Domestic cats The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of t ...

(''Felis silvestris catus)'' have also been shown to prey on ''E. russatus''.

Parasites

Research into the gastrointestinal parasites of ''E. russatus'' found eight different

endoparasites Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

in island and continental populations. A new species of

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

, ''Hassalstrongylus luquei'', was found in the small intestine of ''E. russatus''. A single individual was found to possess antibodies from a systemic fungal infection with ''

Paracoccidioides brasiliensis ''Paracoccidioides brasiliensis'' is a dimorphic fungus and one of the two species that cause paracoccidioidomycosis (the other being ''Paracoccidioides lutzii).'' The fungus has been affiliated with the family Ajellomycetaceae (division Ascomyco ...

''. A study on ''Rickettsia rickettsii'', Brazilian Spotted-fever has shown ''E. russatus'' to be a host for the tick species ''Amblyomma ovale'', which is a known vector for the zoonotic disease.

References

{{Taxonbar, from=Q1761424 Euryoryzomys Rodents of South America Mammals of Argentina Mammals of Brazil Mammals of Paraguay Mammals described in 1848 Taxa named by Johann Andreas Wagner