Trends of specialisation in rodents: the hamsters, subfamily Cricetinae (Cricetidae, Rodentia, Mammalia)

Abstract

An ecomorphological analysis was applied to hamsters, Cricetinae. This subfamily includes seven genera and 18 species which inhabit forest-steppes, steppes, and semi-deserts of Palaearctic Eurasia. The main goals of this study were: (1) to reveal the morphological peculiarities of hamsters and the ecological meaning of these peculiarities, (2) to estimate the levels of specialisation in different hamster species, (3) to reveal the ecomorphological diversity of Cricetinae, and (4) to reconstruct the course of adaptive evolution in hamsters. Hamsters possess a specific combination of ecomorphological traits: a relatively broad head, moderately developed external sense organs, cheek pouches, short hind feet, and a short tail. These and other morphological traits are predominantly associated with nocturnal activity, non-bounding locomotion, relatively good digging ability, poor climbing ability, aggressiveness, granivory with a tendency to herbivory, and hoarding behaviour. The least specialised hamster is Tscherskia triton, and the most specialised is Mesocricetus raddei. Four ecomorphs were distinguished: (1) rat-like hamsters (Cansumys (?), Tscherskia), (2) ‘smaller hamsters’ (Allocricetulus curtatus, most Cricetulus, Phodopus), (3) ‘larger hamsters’ (Allocricetulus eversmanni, Cricetus, Mesocricetus), and (4) Tibetan hamsters (Cricetulus alticola, C. kamensis). It is assumed that the adaptive evolution of hamsters started from a mouse-like ancestor and passed three grades of adaptive evolution: (1) rat-like hamsters, (2) typical hamsters, represented by ‘smaller’ and ‘larger’ ecomorphs, which differ in size and skull morphology, and (3) Tibetan hamsters, which show reverse evolution from a ‘smaller hamsters’ construction to a more mouse-like construction.

Keywords:

• Cricetinae
• hamsters
• specialization
• ecomorphology
• adaptive evolution