Body size of Italian greater horseshoe bats (Rhinolophus ferrumequinum) increased over one century and a half: a response to climate change?

Variation in body size is thought as one of the main responses to climate change, yet studies exploring the existence of this pattern are limited by the scarcity of long temporal datasets. Bats are promising candidates for the occurrence of climate-driven changes in body size because their life cycle is highly sensitive to ambient temperature. Although a reduction in body size would adaptively imply more efficient heat dissipation under a climate change scenario, dehydration caused by heatwaves would in fact be limited by a larger body size, so either responses may be predicted. An increasing body size over time might also be the consequence of a longer growth season secured by a warmer climate. On such bases, we tested the hypothesis that body size varied in the bat Rhinolophus ferrumequinum from Italian populations between 1869 and 2005 by examining forearm length (FAL) in 78 spatially independent specimens, and found that FAL increased over that period. We also ruled out that body size varied over space in relation to latitude (as predicted by Bergmann’s rule) or insularity, besides confirming the occurrence of sexual dimorphism (females being larger than males). This study illustrates a rare example of an increasing body size trend in a mammal species measured over ca. a century and a half, potentially unveiling a response to environmental variation.