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''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''. ''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 (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.〔Thomas, 1918, pp. 189–190〕 In 1920, Thomas recognized additional differences between the two after examining more specimens and classified the Argentine form as a separate species, ''Akodon cænosus''.〔Thomas, 1920, p. 193〕 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'' 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 karyotype.〔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; 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, 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.〔Díaz et al., 1999, p. 795; Jayat et al., 2010, p. 23〕 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'', Guy Musser and Michael Carleton termed the differentiation between ''A. aliquantulus'' and ''A. lutescens'' (=''puer'') "unimpressive" and recommended further taxonomic research.〔Musser and Carleton, 2005, p. 1093〕 Common names proposed for ''A. aliquantulus'' include "Diminutive Akodont"〔Musser and Carleton, 2005, p. 1092〕 and "Tucumán Grass Mouse".〔Duff and Lawson, 2004, p. 59〕 }} |2= }} }} }} 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,〔Jayat et al., 2010, p. 5〕 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''.〔Jayat et al., 2010, fig. 1, p. 9〕 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%.〔Jayat et al., 2010, p. 43, fig. 1〕 ''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''.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Akodon caenosus」の詳細全文を読む スポンサード リンク
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