Heat over heritability: Increasing body size in response to global warming is not stabilized by genetic effects in Bechstein's bats

How well populations can cope with global warming will often depend on the evolutionary potential and plasticity of their temperature-sensitive, fitness-relevant traits. In Bechstein's bats (Myotis bechsteinii), body size has increased over the last decades in response to warmer summers. If this trend continues it may threaten populations as larger females exhibit higher mortality. To assess the evolutionary potential of body size, we applied a Bayesian 'animal model' to estimate additive genetic variance, heritability and evolvability of body size, based on a 25-year pedigree of 332 wild females. Both heritability and additive genetic variance were reduced in hot summers compared to average and cold summers, while evolvability of body size was generally low. This suggests that the observed increase in body size was mostly driven by phenotypic plasticity. Thus, if warm summers continue to become more frequent, body size likely increases further and the resulting fitness loss could threaten populations.

Automated summary

The ability of populations to cope with global warming depends on the evolutionary potential and plasticity of their temperature-sensitive traits. In Bechstein's bats, body size has increased due to warmer summers, but this may have negative impacts on the survival of larger females. The study finds that the increase in body size is mainly driven by phenotypic plasticity rather than genetic factors, suggesting a potential threat to population fitness if warm summers become more frequent.