''Akodon caenosus'' is a

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 genus ''

Akodon ''Akodon'' is a genus consisting of South American grass mice. They mostly occur south of the Amazon Basin and along the Andes north to Venezuela, but are absent from much of the basin itself, the far south of the continent, and the lowlands west ...

'' found in northwestern

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 ...

and south-central

Bolivia , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

. Since its description in 1918, it has been alternatively classified as a separate species or a subspecies of '' Akodon lutescens'' (formerly ''Akodon puer''). The species ''Akodon aliquantulus'', described from some very small Argentine specimens in 1999, is now recognized as a

synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

of ''A. caenosus''. ''Akodon caenosus'' is very small, averaging in weight, and variable in coloration, but generally brown. The underparts are sharply different in color from the upperparts. The skull has a short rostrum (front part), broad

interorbital region The interorbital region of the skull is located between the eyes, anterior to the braincase. The form of the interorbital region may exhibit significant variation between taxonomic groups. In oryzomyine rodents, for example, the width, form, an ...

(between the eyes), and 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 ...

. 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 34

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

s. ''A. caenosus'' mostly occurs in

Yungas The Yungas (Aymara ''yunka'' warm or temperate Andes or earth, Quechua ''yunka'' warm area on the slopes of the Andes) is a bioregion of a narrow band of forest along the eastern slope of the Andes Mountains from Peru and Bolivia, and extends into ...

vegetation and breeds mainly during the winter. It shares its range with many other

sigmodontine 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 species c ...

rodents, including three other species of ''Akodon''.

Taxonomy

E. Budin collected the first specimen of the species on August 21, 1917, in

Jujuy Province Jujuy is a province of Argentina, located in the extreme northwest of the country, at the borders with Chile and Bolivia. The only neighboring Argentine province is Salta to the east and south. Geography There are three main areas in Jujuy: * ...

, northwestern Argentina, and the next year

Oldfield Thomas Michael Rogers Oldfield Thomas (21 February 1858 – 16 June 1929) was a British zoologist. Career Thomas worked at the Natural History Museum on mammals, describing about 2,000 new species and subspecies for the first time. He was appoin ...

used the animal as the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

of a new

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 '' Akodon puer'', a Bolivian species. He described the new subspecies ''Akodon puer cænosus'' as darker and duller in color than the Bolivian form, but otherwise identical. In 1920, Thomas recognized additional differences between the two after examining more specimens and classified the Argentine form as a separate species, ''Akodon cænosus''. Most subsequent authors followed this arrangement, but since the 1980s some have placed the form (now spelled ''caenosus'') in ''A. puer'' again.Jayat et al., 2010, p. 25 In 1990, Philip Myers and others reviewed the ''

Akodon boliviensis ''Akodon boliviensis'', also known as the Bolivian grass mouse or Bolivian akodont,Musser and Carleton, 2005, p. 1093 is a species of rodent in the family Cricetidae. It is found in the Andes from southeastern Peru through Bolivia into north ...

'' group, which includes ''A. puer'' and ''A. caenosus'', and again considered ''caenosus'' as a subspecies of ''puer''.Myers et al., 1990, p. 66 They retained ''caenosus'' as a separate subspecific name for the Argentine populations of ''puer'' because of its small size, dark fur,Myers et al., 1990, p. 73 and distinctive

.Myers et al., 1990, p. 74 Myers and colleagues had included the name ''lutescens'' J.A. Allen, 1901, as a subspecies of ''Akodon puer'' Thomas, 1902, and in 1997 Sydney Anderson noted that the older name ''lutescens'' should instead be used for the species because of the

Principle of Priority 270px, '' valid name. Priority is a fundamental principle of modern botanical nomenclature and zoological nomenclature. Essentially, it is the principle of recognising the first valid application of a name to a plant or animal. There are two asp ...

; therefore, he utilized the combination ''Akodon lutescens caenosus'' for the Argentine subspecies. Through the 1990s and 2000s, authors continued to differ on the classification of ''caenosus'' as either a full species or a subspecies or ''puer'' (=''lutescens''). Two small ''Akodon'' collected in 1993 in

Tucumán Province Tucumán () is the most densely populated, and the second-smallest by land area, of the provinces of Argentina. Located in the northwest of the country, the province has the capital of San Miguel de Tucumán, often shortened to Tucumán. Neigh ...

, northwestern Argentina, were given the name ''Akodon diminutus'' in 1994, but that name is a ''

nomen nudum In taxonomy, a ''nomen nudum'' ('naked name'; plural ''nomina nuda'') is a designation which looks exactly like a scientific name of an organism, and may have originally been intended to be one, but it has not been published with an adequate descr ...

'' and therefore not available for use under the

International Code of Zoological Nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the ...

. In 1999, Mónica Díaz and others described these animals more fully as a new species, ''Akodon aliquantulus'', which they considered closely related to ''A. puer caenosus''.Díaz et al., 1999, p. 786 The specific name means "how little" or "how few" in Latin and refers to the small size of the species and the small sample Díaz and colleagues could use.Díaz et al., 1999, p. 794 In 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, ...

'',

Guy Musser Guy Graham Musser (August 10, 1936 – October 2019) was an American zoologist. His main research was in the field of the rodent subfamily Murinae, in which he has described many new species. Musser was born in Salt Lake City, Utah. He attended ...

and

Michael Carleton Michael may refer to: People * Michael (given name), a given name * Michael (surname), including a list of people with the surname Michael Given name "Michael" * Michael (archangel), ''first'' of God's archangels in the Jewish, Christian an ...

termed the differentiation between ''A. aliquantulus'' and ''A. lutescens'' (=''puer'') "unimpressive" and recommended further taxonomic research.

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 proposed for ''A. aliquantulus'' include "Diminutive Akodont" and "Tucumán Grass Mouse". In 2010, Pablo Jayat and colleagues reviewed the members of the ''Akodon boliviensis'' group in Argentina. On the basis of

sequences In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is called t ...

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,Jayat et al., 2010, p. 5 they found ''A. caenosus'' to be closest to ''A. lutescens'' and '' A. subfuscus'', forming 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, ...

that was the sister group to a clade of the remaining species in the ''A. boliviensis'' group—''A. boliviensis'', '' A. spegazzinii'', '' A. sylvanus'', and '' A. polopi''. They classified ''A. caenosus'' as a species separate from ''A. lutescens'' because the two forms did not form a single clade (''A. caenosus'' was instead closer to ''A. subfuscus''), and because the difference between the cytochrome ''b'' sequences of ''A. lutescens'' and ''A. caenosus'' was relatively high at 3.5%. ''A. aliquantulus'' was reduced to a

of ''A. caenosus'', because they found no substantial

morphometric 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 ...

al differentiation between the two and could not replicate the characters Díaz and colleagues had noted as diagnostic for ''A. aliquantulus''.

Description

''Akodon caenosus'' is the smallest of the Argentine members of the ''A. boliviensis'' group–indeed, among the smallest of all species of ''Akodon''.Díaz et al., 1999, p. 795 The upperparts are uniformly colored, but their tone is variable: generally ochraceous brown, but approaching yellow, red, or olivaceous in some individuals. Reddish tones occur mostly in lactating females. High-altitude animals are generally lighter, but there is also conspicuous variation within populations.Jayat et al., 2010, p. 24 The ears are similar to the upperparts, but some individuals have the sides more rich and clear in color. The underparts are clearly different in color, varying from light gray to yellowish or reddish. There are yellowish rings around the eyes,Jayat et al., 2010, p. 18 which are more highly developed in high-altitude populations. There are white to yellowish hairs on the fore- and hindfeet. The tail is variably covered with hair and is dark brown above and white to buffy below. In the skull, the rostrum (front part) is short, the

(between the eyes) is broad and hourglass-shaped, and the

is small. 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 ...

, is narrow, with poorly developed zygomatic notches at their front, but there is considerable variation in the features of the plate. 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 ...

) extend back to between the first molars. The mesopterygoid fossa, the openings behind the bony palate, is very narrow. 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 ...

(lower jaw), the masseteric ridges, which anchor some of the chewing muscles, extend to near the front margin of the first molar. 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 ...

, raising in the back part of the mandibular bone that accommodates the root 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 poorly developed. The upper incisors are orthodont (with the chewing edge in the horizontal plane) to slightly opisthodont (with the chewing edge inclined backward). The

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 ...

show some accessory crests and other features, such as the anteroloph on the first upper molar and the

mesoloph 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 ...

on the first and second upper molar. In twelve adult Argentine ''A. caenosus'', total length is , averaging ; tail length is , averaging ; hindfoot length is , averaging ; ear length is , averaging ; and weight is , averaging . The

includes 34

s with 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 40 major arms (2n = 34, FN = 40). The

autosome An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosome, allosomal (sex chromosome) pairs, which may have different structures. The DNA in au ...

s includes three large and one very small pairs of metacentrics, with two long arms, and twelve small to medium-sized

acrocentric The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers a ...

pairs, which have a long and a very short arm. The

X chromosome The X chromosome is one of the two sex-determining chromosomes (allosomes) in many organisms, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and XO sex-d ...

is medium-sized and subtelocentric, with a long and a short arm, and the

Y chromosome The Y chromosome is one of two sex chromosomes (allosomes) in therian mammals, including humans, and many other animals. The other is the X chromosome. Y is normally the sex-determining chromosome in many species, since it is the presence or abse ...

is very small and is acrocentric in Jujuy specimens, but metacentric in those from Tucumán. The karyotype is separated from that of ''A. lutescens'' by three

Robertsonian translocation Robertsonian translocation (ROB) is a chromosomal abnormality wherein a certain type of a chromosome becomes attached to another. It is the most common form of chromosomal translocation in humans, affecting 1 out of every 1,000 babies born. It doe ...

s. Members of the ''Akodon boliviensis'' group, including ''A. caenosus'', are generally similar and difficult to separate, but they differ in relative cranial measurements and some other characters. ''A. spegazzinii'' is larger than ''A. caenosus''; ''A. sylvanus'' is darker and has less contrast between the upper- and underparts and less well-developed eye-rings; ''A. polopi'' has a squared interorbital region and more well-developed ridges on its skull; and ''A. boliviensis'' is paler and has more densely furred ears.

Distribution and ecology

''Akodon caenosus'' is found from northwestern Argentina into south-central Bolivia. In Bolivia, it occurs in

Tarija Tarija or San Bernardo de la Frontera de Tarixa is a city in southern Bolivia. Founded in 1574, Tarija is the largest city and capital and municipality within the Tarija Department, with an airport (Capitán Oriel Lea Plaza Airport, (TJA)) offe ...

and

Chuquisaca Department Chuquisaca () ( ay, Chuqisaka; qu, Chuqichaka) is a department of Bolivia located in the center south. It borders on the departments of Cochabamba, Tarija, Potosí, and Santa Cruz. The departmental capital is Sucre, which is also the consti ...

s.Anderson, 1997, p. 422 Its Argentine distribution extends from far northern

Salta Salta () is the capital and largest city in the Argentine province of the same name. With a population of 618,375 according to the 2010 census, it is also the 7th most-populous city in Argentina. The city serves as the cultural and economic ce ...

to southern Catamarca at altitudes ranging from . It is mostly found in

, but also in the highest levels of the Chaco and the lowest of the Andean mountain grasslands. It occurs together with ''A. boliviensis'', ''A. sylvanus'', '' A. simulator'', and species of ''

Oxymycterus ''Oxymycterus'' is a genus of rat-like rodents commonly known as hocicudos. They are endemic to South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively sma ...

'', ''

Calomys Vesper mice are rodents belonging to a genus ''Calomys''. They are widely distributed in South America. Some species are notable as the vectors of Argentinian hemorrhagic fever and Bolivian hemorrhagic fever. The genus was originally named ''He ...

'', ''

Phyllotis ''Phyllotis'' is a genus of rodent in the family Cricetidae. These mice are commonly confused with '' Auliscomys, Graomys'' and '' Loxodontomys.'' ''.'' In order to tell these genera apart, one must look at the tail. Species in the genus ''Ph ...

'', ''

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 ...

'', ''

Necromys ''Necromys'' is a genus of South American sigmodontine rodents allied to ''Akodon''. This genus has also been known as ''Cabreramys'' or more recently ''Bolomys'', and the northern grass mouse (''N. urichi'') has recently been transferred from ' ...

'', '' Andinomys'', ''

Graomys ''Graomys'' is a genus of rodent in the family Cricetidae. It contains the following species: * Central leaf-eared mouse (''Graomys chacoensis'') * Pale leaf-eared mouse The pale leaf-eared mouse (''Graomys domorum'') is a species of rodent i ...

'', and ''

Abrothrix ''Abrothrix'' is a genus of rodent in the tribe Abrotrichini of family Cricetidae. It contains the following living species:Teta et al., 2017 *''Abrothrix andina'' *''Abrothrix hershkovitzi'' *''Abrothrix hirta'' *''Abrothrix illutea'' *''Abrothri ...

''. Breeding occurs throughout the year, but mostly from November to January, during the summer.

Molt In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...

ing occurs mostly during the winter and autumn. The oestrid fly ''

Cuterebra apicalis ''Cuterebra'', or rodent bots, is a genus of bot flies that attack rodents and similar animals. Etymology The genus name ''Cuterebra'' is a blend of the Latin words ''cutis'' : skin and ''terebra'' : borer with apparent shortening of expected '' ...

'' and the flea '' Hectopsylla gracilis'' have been recorded from ''A. caenosus''. The mites '' Androlaelaps fahrenholzi'', '' Androlaelaps rotundus'', and ''

Eulaelaps stabularis ''Eulaelaps'' is a genus of mites in the family Haemogamasidae. Species * '' Eulaelaps arboricola'' Uchikawa, 1978 * '' Eulaelaps dremomydis'' Gu & Wang, 1984 * '' Eulaelaps feideri'' (Fain, 1962) * '' Eulaelaps heptacanthus'' Yang & Gu, 1985 * ...

'' have been found on ''A. aliquantulus''.Lareschi et al., 2003, p. 60

Conservation status

The

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

currently assesses ''A. aliquantulus'' as "

Data Deficient A data deficient (DD) species is one which has been categorized by the International Union for Conservation of Nature (IUCN) as offering insufficient information for a proper assessment of conservation status to be made. This does not necessaril ...

" because so little is known about it, but notes that ranching and fire may threaten it.Pardinas and Jayat, 2008 ''Akodon lutescens'', including ''A. caenosus'', is assessed as "

Least Concern A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...

" because of its wide distribution, large population, and ability to persist in disturbed habitats. However, habitat loss may threaten Yungas populations.Dunnum et al., 2008

Footnotes

References

Literature cited

*Anderson, S. 1997
Mammals of Bolivia, taxonomy, and distribution
Bulletin of the American Museum of Natural History 231:1–652. *Díaz, M.M., Barquez, R.M., Braun, J.K. and Mares, M.A. 1999
A new species of ''Akodon'' (Muridae: Sigmodontinae) from northwestern Argentina
(subscription required). Journal of Mammalogy 80(3):786–798. *Duff, A. and Lawson, A. 2004. Mammals of the World: A checklist. New Haven: A & C Black, 312 pp. *Dunnum, J., Vargas, J., Bernal, N., Zeballos, H., Vivar, E., Patterson, B., Jayat, J. and D'Elia, G. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.2.
www.iucnredlist.org
. Downloaded on April 3, 2010. *International Commission on Zoological Nomenclature. 1999
International Code of Zoological Nomenclature
Fourth edition. London: The International Trust for Zoological Nomenclature. *Jayat, J.P., Ortiz, P.E., Salazar-Bravo, J., Pardiñas, U.F.J. and D'Elía, G. 2010

( ttp://www.mapress.com/zootaxa/2010/f/z02409p061f.pdf abstract. Zootaxa 2409:1–61. *Lareschi, M., Autino, A.G., Díaz, M.M., and Barquez, R.M. 2003
New host and locality records for mites and fleas associated with wild rodents from northwestern Argentina
Revista de la Sociedad Entomológica de Argentina 62(3–4):60–64. *Lareschi, M., Sanchez, J.P., Ezquiaga, M.C., Autino, A.G., Díaz, M.M. and Barquez, R.M. 2010
Fleas associated with mammals from northwestern Argentina, with new distributional reports
(subscription required). Comparative Parasitology 77(2):207–213. *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. *Myers, P., Patton, J.L. and Smith, M.F. 1990
A review of the ''boliviensis'' group of ''Akodon'' (Muridae: Sigmodontinae) with emphasis on Perú and Bolivia
Miscellaneous Publications of the Museum of Zoology, University of Michigan 177:1–89. *Pardinas, U. and Jayat, J.P. 2008. . In IUCN. IUCN Red List of Threatened Species. Version 2009.2.
www.iucnredlist.org
. Downloaded on April 3, 2010. *Pinto, C.M. and Claps, G.L. 2005. First record of ''Cuterebra almeidai'' (Guimaraes and Carrera) from Argentina, new host records for ''Cuterebra apicalis'' Guerin-Meneville, and list of ''Cuterebra'' (Diptera: Oestridae) in the collection of the Instituto-Fundacion Miguel Lillo, Tucuman, Argentina. Proceedings of the Entomological Society of Washington 107(3):572–575. *Thomas, O. 1918
On small mammals from Salta and Jujuy collected by Mr. E. Budin
Annals and Magazine of Natural History (9)1:186–193. *Thomas, O. 1920
A further collection of mammals from Jujuy
Annals and Magazine of Natural History (9)5:188–196. {{Good article Akodon Mammals of Argentina Mammals described in 1918 Taxa named by Oldfield Thomas