Cognitive skills of common shrews (Sorex araneus) vary with seasonal changes in skull size and brain mass

In a rare phenomenon, shrews and few other species cope with seasonal environments by reducing and regrowing brain size, potentially at the cost of changes in cognitive abilities. Here, we confirm an extensive, seasonal shrinkage (21.4%) and regrowth (17.0%) of brain mass in winter and spring, respectively, in common shrew (Sorex araneus L.) in Southern Germany. In a spatial learning task experiment individuals with reduced winter brain size covered larger distances to find food, compared to the relatively large brained summer juveniles and regrown spring adults. By reducing their brain mass, these shrews may reduce their energetic demands, but at the cost of cognitive performance, implying a complex trade-off for coping with seasonally fluctuating resources. These results are relevant for our understanding of evolution and the dynamics of mammalian nervous systems in response to environmental changes.publishe