[Seasonal changes in the brain and skull sizes of small mammals]

A comparative study of seasonal-age dynamics of brain size in six small mammal species, Clethrionomys glareolus, C. rutilus, Microtus oeconomus, M. gregalis (Rodentia); Sorex araneus, S. minutis (Insectivora) has been carried out. The analysis of seasonal changes in brain weight confirms the existence of autumn-winter regression of brain weight, which takes place at the organism level. The regression is less pronounced in voles than in shrews. The decrease in brain weight both in voles and in shrews is accompanied by the decrease in height (capacity) of brain capsule of cranium. In spring the brain weight increase and reaches its maximal specific values in wintered voles in summer. In wintered shrews the brain weight never reaches the value, inherent in young animals before winter regression. The analysis of the data obtained and published data on variability of craniometric features allowed to conclude that seasonal changes in brain size, accompanied by the changes in capacity of cranium capsule might be considered as a general pattern for a large group of palearctic and nonarctic species of small mammals.