Akodon caenosus

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Akodon caenosus
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Cricetidae
Subfamily: Sigmodontinae
Genus: Akodon
Species:
A. caenosus
Binomial name
Akodon caenosus
Thomas, 1918
Akodon caenosus distribution.svg
Distribution in Argentina and Bolivia. [2]
Synonyms [3]
  • Akodon puer cænosusThomas, 1918 [4] [fn 1]
  • Akodon caenosus: Thomas, 1920 [6]
  • Akodon diminutusBarquez, Díaz, and Goytia, 1994 [fn 2]
  • Akodon lutescens caenosus: Anderson, 1997 [7]
  • Akodon aliquantulusDíaz, Barquez, Braun, and Mares, 1999 [8]

Akodon caenosus is a rodent in the genus Akodon found in northwestern Argentina and south-central Bolivia. 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 of A. caenosus.

Contents

Akodon caenosus is very small, averaging 19.3 g (0.68 oz) 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 (between the eyes), and narrow braincase. The karyotype includes 34 chromosomes. A. caenosus mostly occurs in Yungas vegetation and breeds mainly during the winter. It shares its range with many other sigmodontine rodents, including three other species of Akodon.

Taxonomy

E. Budin collected the first specimen of the species on August 21, 1917, in Jujuy Province, northwestern Argentina, and the next year Oldfield Thomas used the animal as the holotype of a new subspecies 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. [9] In 1920, Thomas recognized additional differences between the two after examining more specimens and classified the Argentine form as a separate species, Akodon cænosus. [10] Most subsequent authors followed this arrangement, but since the 1980s some have placed the form (now spelled caenosus) in A. puer again. [11] In 1990, Philip Myers and others reviewed the Akodon boliviensis group, which includes A. puer and A. caenosus, and again considered caenosus as a subspecies of puer. [12] They retained caenosus as a separate subspecific name for the Argentine populations of puer because of its small size, dark fur, [13] and distinctive karyotype. [14] 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; therefore, he utilized the combination Akodon lutescens caenosus for the Argentine subspecies. [7] 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). [11]

Two small Akodon collected in 1993 in Tucumán Province, northwestern Argentina, were given the name Akodon diminutus in 1994, but that name is a nomen nudum and therefore not available for use under the International Code of Zoological Nomenclature. [15] 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. [16] 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. [17] In the 2005 third edition of Mammal Species of the World , Guy Musser and Michael Carleton termed the differentiation between A. aliquantulus and A. lutescens (=puer) "unimpressive" and recommended further taxonomic research. [18] Common names proposed for A. aliquantulus include "Diminutive Akodont" [19] and "Tucumán Grass Mouse". [20]

Akodon boliviensis group
Relationships within the Akodon boliviensis species group according to analysis of cytochrome b data. [21]

In 2010, Pablo Jayat and colleagues reviewed the members of the Akodon boliviensis group in Argentina. On the basis of sequences from the mitochondrial cytochrome b gene, [22] they found A. caenosus to be closest to A. lutescens and A. subfuscus , forming a clade 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 . [23] 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%. [24] A. aliquantulus was reduced to a synonym of A. caenosus, because they found no substantial morphometrical differentiation between the two and could not replicate the characters Díaz and colleagues had noted as diagnostic for A. aliquantulus. [11]

Description

Akodon caenosus is the smallest of the Argentine members of the A. boliviensis group [3] –indeed, among the smallest of all species of Akodon. [25] The upperparts are uniformly colored, but their tone is variable: generally ochraceous brown, but approaching yellow, red, or olivaceous in some individuals. [3] Reddish tones occur mostly in lactating females. High-altitude animals are generally lighter, but there is also conspicuous variation within populations. [26] 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. [3] There are yellowish rings around the eyes, [27] which are more highly developed in high-altitude populations. [3] There are white to yellowish hairs on the fore- and hindfeet. [28] The tail is variably covered with hair and is dark brown above and white to buffy below. [26]

In the skull, the rostrum (front part) is short, the interorbital region (between the eyes) is broad and hourglass-shaped, and the braincase is small. The zygomatic plate, the flattened front part of the zygomatic arch, is narrow, with poorly developed zygomatic notches at their front, but there is considerable variation in the features of the plate. The incisive foramina (openings in the front part of the palate) extend back to between the first molars. The mesopterygoid fossa, the openings behind the bony palate, is very narrow. In the mandible (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, raising in the back part of the mandibular bone that accommodates the root of the incisor, 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 show some accessory crests and other features, such as the anteroloph on the first upper molar and the mesoloph on the first and second upper molar. [26]

In twelve adult Argentine A. caenosus, total length is 124 to 169 mm (4.9 to 6.7 in), averaging 151 mm (5.9 in); tail length is 46 to 75 mm (1.8 to 3.0 in), averaging 62 mm (2.4 in); hindfoot length is 20 to 26 mm (0.79 to 1.02 in), averaging 21 mm (0.83 in); ear length is 12 to 15 mm (0.47 to 0.59 in), averaging 13 mm (0.51 in); and weight is 10.5 to 27.5 g (0.37 to 0.97 oz), averaging 19.3 g (0.68 oz). [29] The karyotype includes 34 chromosomes with a fundamental number of 40 major arms (2n = 34, FN = 40). [26] The autosomes includes three large and one very small pairs of metacentrics, with two long arms, and twelve small to medium-sized acrocentric pairs, which have a long and a very short arm. The X chromosome is medium-sized and subtelocentric, with a long and a short arm, and the Y chromosome 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 translocations. [14]

Members of the Akodon boliviensis group, including A. caenosus, are generally similar and difficult to separate, [27] but they differ in relative cranial measurements and some other characters. [30] A. spegazzinii is larger than A. caenosus; [26] A. sylvanus is darker and has less contrast between the upper- and underparts and less well-developed eye-rings; [11] A. polopi has a squared interorbital region and more well-developed ridges on its skull; [31] and A. boliviensis is paler and has more densely furred ears. [32]

Distribution and ecology

Akodon caenosus is found from northwestern Argentina into south-central Bolivia. [33] In Bolivia, it occurs in Tarija and Chuquisaca Departments. [34] Its Argentine distribution extends from far northern Salta to southern Catamarca at altitudes ranging from 400 to 3,100 m (1,300 to 10,200 ft). It is mostly found in Yungas, 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 , Calomys , Phyllotis , Oligoryzomys , Necromys , Andinomys , Graomys , and Abrothrix . Breeding occurs throughout the year, but mostly from November to January, during the summer. Molting occurs mostly during the winter and autumn. [11] The oestrid fly Cuterebra apicalis [35] and the flea Hectopsylla gracilis have been recorded from A. caenosus. [36] The mites Androlaelaps fahrenholzi , Androlaelaps rotundus , and Eulaelaps stabularis have been found on A. aliquantulus. [37]

Footnotes

  1. ↑ Article 32.5.2 of the International Code of Zoological Nomenclature mandates that specific names first published with a ligature such as æ are to be corrected. [5]
  2. ↑ Nomen nudum (naked name, not fulfilling the requirements of the International Code of Zoological Nomenclature). [3]

Related Research Articles

Philip Myers's akodont is a recently described species of grass mouse from Misiones Province, Argentina. Like other grass mice, A. philipmyersi is a small, non-descript, greyish-brown mouse with prominent ears. The species was recognized as distinct from other grass mice on the basis of unique features of karyology, genetic sequence, cranial measurements, and general morphology.

<i>Akodon</i> Genus of rodents

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 of the Andes. Akodon is one of the most species-rich genera of Neotropical rodents. Species of Akodon are known to inhabit a variety of habitats from tropical and tropical moist forests to altiplano and desert. Fossils are known from the late Pliocene onwards.

<i>Necromys</i> Genus of rodents

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 has recently been transferred from Akodon.

<span class="mw-page-title-main">Pygmy fruit bat</span> Species of bat

The pygmy fruit bat, also known as the grey fruit bat, is a species of megabat.

Oligoryzomys chacoensis, also known as the Chacoan colilargo or Chacoan pygmy rice rat, is a rodent species from South America. It is found in the Gran Chaco region of southeastern Bolivia, southwestern Brazil, Paraguay, and northeastern Argentina. Its karyotype has 2n = 58 and FNa = 74.

<i>Oligoryzomys flavescens</i> Species of rodent

Oligoryzomys flavescens, also known as the flavescent colilargo or yellow pygmy rice rat is a species of rodent in the genus Oligoryzomys of family Cricetidae. It is found in southern South America, occurring in southern Brazil, Paraguay, Uruguay, and northeastern Argentina. Its karyotype has 2n = 64-66 and FNa = 66–70.

<i>Lundomys</i> A semiaquatic rat species from southeastern South America.

Lundomys molitor, also known as Lund's amphibious rat or the greater marsh rat, is a semiaquatic rat species from southeastern South America.

<i>Pseudoryzomys</i> Genus of rodent from South America with one species

Pseudoryzomys simplex, also known as the Brazilian false rice rat or false oryzomys, is a species of rodent in the family Cricetidae from south-central South America. It is found in lowland palm savanna and thorn scrub habitats. It is a medium-sized species, weighing about 50 grams (1.8 oz), with gray–brown fur, long and narrow hindfeet, and a tail that is about as long as the head and body. The IUCN has assessed its conservation status as being of least concern, although almost nothing is known about its diet or reproduction.

<i>Akodon albiventer</i> Species of rodent

Akodon albiventer, also known as the white-bellied grass mouse or white-bellied akodont, is a species of rodent in the family Cricetidae. It is found in the Andean highlands from southeastern Peru to southwestern Bolivia, northwestern Argentina, and far northeastern Chile at elevations from 2400 m to over 5000 m.

Akodon boliviensis, also known as the Bolivian grass mouse or Bolivian akodont, is a species of rodent in the family Cricetidae. It is found in the Andes from southeastern Peru through Bolivia into northwestern Argentina.

Akodon budini, also known as Budin's akodont or Budin's grass mouse, is a species of rodent in the family Cricetidae. It is found in the Andes of northwestern Argentina and adjacent Bolivia. The species is named after Emilio Budin, an Argentine specimen collector who worked with Oldfield Thomas.

<i>Akodon spegazzinii</i> Species of rodent found in Argentina

Akodon spegazzinii, also known as Spegazzini's akodont or Spegazzini's grass mouse, is a rodent in the genus Akodon found in northwestern Argentina. It occurs in grassland and forest at 400 to 3,500 m above sea level. After the species was first named in 1897, several other names were given to various populations now included in A. spegazzinii. They are now all recognized as part of a single, widespread and variable species. Akodon spegazzinii is related to Akodon boliviensis and other members of the A. boliviensis species group. It reproduces year-round. Because it is widely distributed and common, Akodon spegazzinii is listed as "least concern" on the IUCN Red List.

<i>Akodon sylvanus</i> Species of rodent

Akodon sylvanus, also known as the forest grass mouse or woodland akodont, is a species of rodent in the family Cricetidae. It is found only in a small part of northwestern Argentina.

Oligoryzomys destructor, also known as Tschudi's colilargo or the destructive pygmy rice rat, is a species of rodent in the genus Oligoryzomys of family Cricetidae. It is found along the eastern Andes from southern Colombia, through Ecuador, Peru, and Bolivia into northern Argentina. Its karyotype has 2n = 60 and FNa = 76.

The southern climbing mouse is a species of rodent in the family Cricetidae. It is found in Argentina and Bolivia in forested valleys and on slopes on the eastern side of the Andes Mountains.

<span class="mw-page-title-main">Plains viscacha rat</span> Species of rodent

The plains viscacha rat, plains vizcacha rat, red viscacha rat, or red vizcacha rat is a species of rodent in the family Octodontidae native to Argentina. It is one of three species in the genus Tympanoctomys.

Reigomys primigenus is an extinct oryzomyine rodent known from Pleistocene deposits in Tarija Department, southeastern Bolivia. It is known from a number of isolated jaws and molars which show that its molars were almost identical to those of the living Lundomys. On the other hand, the animal possesses a number of derived traits of the palate which document a closer relationship to living Holochilus, the genus of South American marsh rats, and for this reason it was placed in the genus Holochilus when it was first described in 1996. The subsequent discoveries of Noronhomys and Carletonomys, which may be more closely related to extant Holochilus than H. primigenus is, have cast its placement in Holochilus into doubt, and it was ultimately made the type species of a separate genus, Reigomys.

<span class="mw-page-title-main">Abrotrichini</span> Tribe of rodents

Abrotrichini, also known as the Andean clade or southern Andean clade, is a tribe of rodents in the subfamily Sigmodontinae. It includes about fifteen species in four genera, distributed in South America from southern Peru to southernmost South America, including the Patagonian steppes. The earliest known fossils are from the Pliocene of Argentina.

<i>Cryptonanus</i> Genus of marsupials

Cryptonanus is a genus of opossums from South America. It includes five species found from Bolivia to Uruguay and eastern Brazil, one of which is now extinct. Although the first species were discovered in 1931, the genus was not recognized as distinct from Gracilinanus until 2005. It includes small opossums with generally grayish, sometimes reddish, fur that are mainly distinguished from other opossums by characters of the skull.

Akodon polopi is a species of rodent in the family Cricetidae. It is found in Argentina.

References

  1. ↑ Jayat, J.; Pardinas, U. (2019). "Akodon caenosus". IUCN Red List of Threatened Species . 2019: e.T114956458A22380244. doi: 10.2305/IUCN.UK.2019-1.RLTS.T114956458A22380244.en .
  2. ↑ Anderson, 1997, p. 422; Jayat et al., 2010, p. 25
  3. 1 2 3 4 5 6 Jayat et al., 2010, p. 23
  4. ↑ Thomas, 1918, p. 189
  5. ↑ International Commission on Zoological Nomenclature, 1999, Art. 32.5.2
  6. ↑ Thomas, 1920, p. 192
  7. 1 2 Anderson, 1997, p. 421
  8. ↑ Díaz et al., 1999, p. 788
  9. ↑ Thomas, 1918, pp. 189–190
  10. ↑ Thomas, 1920, p. 193
  11. 1 2 3 4 5 Jayat et al., 2010, p. 25
  12. ↑ Myers et al., 1990, p. 66
  13. ↑ Myers et al., 1990, p. 73
  14. 1 2 Myers et al., 1990, p. 74
  15. ↑ Díaz et al., 1999, p. 795; Jayat et al., 2010, p. 23
  16. ↑ Díaz et al., 1999, p. 786
  17. ↑ Díaz et al., 1999, p. 794
  18. ↑ Musser and Carleton, 2005, p. 1093
  19. ↑ Musser and Carleton, 2005, p. 1092
  20. ↑ Duff and Lawson, 2004, p. 59
  21. ↑ Jayat et al., 2010, fig. 1
  22. ↑ Jayat et al., 2010, p. 5
  23. ↑ Jayat et al., 2010, fig. 1, p. 9
  24. ↑ Jayat et al., 2010, p. 43, fig. 1
  25. ↑ Díaz et al., 1999, p. 795
  26. 1 2 3 4 5 Jayat et al., 2010, p. 24
  27. 1 2 Jayat et al., 2010, p. 18
  28. ↑ Jayat et al., 2010, pp. 23–24
  29. ↑ Jayat et al., 2010, table 1
  30. ↑ Jayat et al., 2010, pp. 24, 25, 41
  31. ↑ Jayat et al., 2010, p. 41
  32. ↑ Jayat et al., 2010, p. 21
  33. ↑ Jayat et al., 2010, p. 25; Anderson, 1997, p. 422
  34. ↑ Anderson, 1997, p. 422
  35. ↑ Pinto and Claps, 2005, p. 572
  36. ↑ Lareschi et al., 2010, p. 212
  37. ↑ Lareschi et al., 2003, p. 60

Literature cited

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