Body size and body conditions of two dung beetles species (Coleoptera: Scarabaeidae) related to environmental temperatures

Abstract

Temperature affects the body size of animals, which is an important trait in natural and sexual selection. Insects do not have complex mechanisms of temperature control, thus temperature changes affect their life aspects, from enzymatic reactions to behavior. The amount of fat stored by insects is also influenced by temperature and constitutes a tissue with biosynthetic and metabolic activity, acting as an energy reservoir. We assessed the effect of environmental temperature due to elevation and seasonal temperature variations on body size and condition of two dung beetles species: Canthon rutilans cyanescens and Dichotomius sericeus (Coleoptera: Scarabaeinae). Both species are abundant in southern Brazilian forests, but they differ in habits: the first is a diurnal roller whereas the later is a nocturnal tunneler. Summer months and sites with lower elevations and higher temperatures presented larger C. rutilans cyanescens. A linear relationship exists between body size and soil temperatures, whereas the temperature positively influences the body length. Furthermore, C. rutilans cyanescens from cooler sites had more body fat. Individuals of D. sericeus were also larger in summer months, however, we did not find differences in the proportion of fat or a relation between body size and temperature. Thus, the body size of dung beetle species varies in relation to temporal factors, as both species are larger in summer. More interesting was to observe that the species with a diurnal habit, even though smaller in colder places, has a higher proportion of fat, which indicates an evolutionary response to environmental pressure.