Seasonal Body Size Plasticity and the Generality of Dehnel's Phenomenon in Sorex Shrews

AbstractDehnel's phenomenon describes a seasonal and reversible winter decrease in body size, which is a trait that predicts total energy demand. However, the phenomenon remains less well studied than common energy-saving or energy-seeking strategies of mammals. Here, we explore the generality of Dehnel's phenomenon in Sorex shrews on three continents. First, we use new field sampling to document seasonal phenotypic change in masked shrews (Sorex cinereus) in North America at the lowest latitude yet investigated for this species (35.7°). This includes the first documentation of appendicular skeleton remodification in Sorex. Summer-to-winter decreases in S. cinereus body mass, braincase height, and femur length were 13%, 11.5%, and 8.7%, respectively, with subsequent increases of each in second-year individuals. Second, we compile a comprehensive dataset of studies relevant to Dehnel's phenomenon to test whether seasonal plasticity in Sorex globally is related to climate, demonstrating that body and braincase plasticity are functions of cold season temperatures. Meta-analytical models for both of these traits generalized by (a) applying at both inter- and intraspecific scales and (b) predicting the seasonal change newly observed for S. cinereus. Our results support body size plasticity as an environmentally responsive innovation in these very small homeothermic mammals.