The strength of temperature-mediated selection on body size in a wild insect population

Abstract

Body size is a crucial element of an organism's ecology and evolution, and is known to be influenced by natural selection. Here, we estimated the strength of temperature-mediated selection on body size in a wild population of the striped ground cricket, Allonemobius socius. We found that extremely high, but naturally occurring temperatures, selected for larger body sizes, as expected. The strength of this selection pressure was strong, with the univariate selection gradients being β = 0.591 ± 0.237; βσ = 0.281 ± 0.112; and βμ = 3.95 ± 1.58 (± sx̄). These results suggest that periodically occurring temperature extremes can influence the evolution of body size in wild populations of A. socius and other orthopterans. Furthermore, these selection pressures may contribute to the often observed size cline known as the Converse of Bergmann's rule, and become more prevalent in the future as temperatures increase due to global warming.