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Phodopus
''Phodopus'', a genus of rodents in the hamster subfamily Cricetinae—a division of the larger family Cricetidae—is a lineage of small hamsters native to central Asia that display unusual adaptations to extreme temperatures. They are the only known hamsters that live in groups and, in some cases, rely on significant contributions by males to the raising of offspring. They are nocturnal and active throughout the year; they do not hibernate. Species of ''Phodopus'', together with members of the genera ''Cricetulus'', ''Allocricetulus'' and ''Tscherskia'' are called "dwarf hamsters" because of their small size (roughly ) relative to other hamsters.〔
Like other hamsters, members of ''Phodopus'' have a round body shape, short tails and cheek pouches in which they can store food. They all live in dry conditions with extreme temperatures. They inhabit the forests, steppes and semi-deserts of Mongolia, Siberia, China and Kazakhstan. Fossils of ''Phodopus'' have been found in Pleistocene and Pliocene deposits in Europe and Asia.
''Phodopus'' species are commonly sold as pets.〔 They are also used as laboratory organisms for a variety of studies, especially involving seasonal endocrine variation. Some species are considered to be agricultural pests.
All three species are widespread and probably abundant, and are assessed as Least Concern (LC) by the IUCN Red List.〔〔〔 However, their ecology and population dynamics are not well understood. Historical records indicate they were once common in places where they no longer occur.〔 Consequently, they are listed in the Kazakhstan Government Regulation of Approval of Rare and Endangered Animal and Plant Species Index (2006).〔
==Systematics==
''Phodopus'' is one of seven genera within the subfamily Cricetinae, a group of rodents distributed throughout Eurasia. It contains hamsters distinguished from other hamsters by small size, short tails and fur covered feet.〔 Fossils assignable to the genus occur in the Pleistocene in Europe and in the Late Pliocene of Kazakhstan,[〕 despite the fact that molecular data suggest the lineage is no younger than 8.5 million years.]
G.S. Miller first described the genus ''Phodopus'' in 1910, designating ''Cricetulus bedfordiae'' as its type species.〔 (''C. bedfordiae'' is the species now called ''P. roborovskii''.)〔 The genus name derives from ancient Greek ''phodos'' (φωδος, genitive of ''phos'' φως "blister") and ''pous'' (πους "foot") and refers to the large pad on the sole of each foot.〔
Morphology has proved inadequate in providing characters for phylogenetic analyses of the subfamily Cricetinae, but the group appears to be monophyletic based on molecular analyses. The genus ''Phodopus'' is one of three well-supported lineages in Cricetinae, the other two being the genus ''Mesocricetus'' and the Cricetus-related group (''Cricetus'', ''Tscherskia'', ''Allocricetulus'', and ''Cricetulus''). Analysis of chromosomes supports these three lineages. ''Phodopus'' is sister to all other Cricetinae (meaning that it is the first lineage to diverge in the clade). Using several molecular dating techniques, researchers have determined that the ''Phodopus'' lineage may have originated 8.5 to 12.2 million years ago (mya). Other genetic dating analyses suggest a somewhat earlier origination of 13.5–14.1 mya. Fossils assignable to the genus are unknown before about 2.5 million years ago, but failure to identify the remains accurately may contribute to the apparent lack of older fossils.
As shown in the cladogram, ''Phodopus roborovskii'' is sister to ''Phodopus campbelli'' + ''Phodopus sungorus''. The validity of ''P. campbelli'' as a species has been controversial. Some biologists consider it to be a subspecies of ''P. sungorus''. Neumann et al.〔 determined that, at least for cytochrome b, ''P. campbelli'' and ''P. sungorus'' do not display the level of genetic divergence characteristic of sister rodent species. Both taxa have 2n=28 chromosomes. However, evidence from hybridization with ''P. sungorus'' has suggested to some researchers that they are in fact separate species.
''P. roborovskii'', on the other hand, has levels of genetic divergence from the other two taxa in the genus characteristic of genera among small mammals. ''P. roborovskii'' is also distinct from the other species morphologically (in its smaller body size and pelage, for example) and ecologically (preferring sandy, arid habitats). ''P. roborovskii'' has 2n=34 chromosomes. For these reasons, Neumann et al.〔 suggest removing ''P. sungorus'' and ''P. campbelli'' to the genus ''Cricetiscus''.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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