Latitudinal trends in body length distributions of European darkling beetles (Tenebrionidae)

The largest species of many invertebrate taxa occur in tropical regions. Nevertheless systematic studies on temperature and latitudinal trends in body size distributions of specific taxa have given inconclusive results and did not unequivocally corroborate existing models of body size evolution. We studied regional body size distributions of tenebrionid beetles across Europe to infer climate dependent trends that could be linked to the postglacial colonization of Europe. Even after correction for sample size effects and phylogenetic relatedness we found an increase in average and maximum body length towards southern Europe. Body size distributions were right skewed and skewness and the width of the distribution decreased significantly with temperature, indicating a more homogeneous species composition with respect to body size at lower latitudes. Our study supports the view that maximum size of heterothermic arthropods is limited by ambient temperature, which triggers the rate of metabolism. Our results contradict models that predict an increase in body size at higher latitudes.