Steep converse Bergmann's cline in a carrion beetle: between‐ and within‐population variation in body size along an elevational gradient

Abstract

AbstractBody size is an integrative trait with substantial fitness consequences in animals. Geographical clines in body size have fascinated biologists because of their potential to provide insight into the mechanisms governing local adaptation and phenotypic plasticity. In this complex study, we focused on variation in body size of Silpha carinata (Coleoptera: Silphidae) along elevation gradients in Central Europe. Altitudinal clines were investigated separately for males and females as sex‐specific responses to environmental conditions are documented for a variety of insect species. To identify potential underlying mechanisms responsible for observed patterns, a common garden experiment and investigation of within‐population variation in body size were performed. Body size of S. carinata recorded in nature sharply decreased with increasing altitude in both genders, whereas sexual size dimorphism did not change with altitude. The degree of within‐population variation in body size recorded in nature did not change with altitude. Under standardized laboratory conditions, higher altitude females produced smaller eggs than those from lower altitude. This size difference persisted to the very end of the larval period. Unfortunately, only few offspring survived till adulthood in the laboratory and thus precise analysis of offspring adult sizes was unfeasible, but between‐population differences in body size seems to persist to adulthood. The observed converse Bergmann's cline in S. carinata fits well with what has been predicted for large, carnivorous, univoltine insect species. Until now, investigation of within‐population variation in body size is rare in insects, and future complementary studies focused on this issue are highly needed as within‐population variation could explain body size patterns observed at between‐population level.