Sexual size dimorphism in Ground Beetles and its modeling in latitude gradient

Abstract

Large-scale systematic patterns of variation lie in the heart of organismic biology and have interested biologists ever since the beginning. These are most obvious in terms of body size, probably the single most important quantitative trait of an individual. In this relation Ground Beetles are poorly studied, though they are regarded to be sensitive to environmental changes and are accepted bioindicators. Beetles were sampled in 8 provinces of Russia, situated at different latitudes. We measured elytra length in six paleartic eurytopic species of carabids. We used mixed linear models to infer the mean latitude effect on size and sexual dimorphism of females and males. Regression coefficients in both sexes were negative and differed in different species. In C. cancellatus, C.hortensis, P. niger modulus of regression coefficients were larger in females, then, in that species females were more variable than males. In C. granulates and P. melanarius modulus of regression coefficients were larger in males, then, in those species males were more variable in latitude gradient. It is noteworthy that species, sharing the same ecological niches, had different strategies in realizing sex – specific body size variation in latitude gradient. E. g., C. granulatus - C. cancellatus, P. niger - P. melanarius. In general body size decreased in latitude gradient both in females and males. Shifts were steeper in Carabus species, than in Pterostichus.  Despite SSD occurred in some analyzed latitudes and mainly at the margins of area, modeling results did not confirm opinion that SSD systematically changes in latitude gradient.