Sexual Size Dimorphism Depends Drastically on Environment: The Case Study in Ground Beetles

The issue of sexual size dimorphism (SSD) variation is relevant due to the identification of mechanisms by which animals adapt to changing environmental conditions. Using the database of the ground beetle Carabus granulatus, compiled from measurements of more than 8000 individuals, we estimated the nature of size variation in beetles captured in different parts of their range, including most of Russia and Europe. ANOVA showed that the sizes of both females and males vary statistically significantly across regions, although not always to the same extent. Therefore, SSD values were assessed not only for each sample by region as a whole, but also for each of the six studied traits (for C. granulatus as a whole), as well as the variability of SSD values for each trait in each of the 13 studied populations. SSD was the highest in the southern regions of the species' range (Bulgaria, Italy) and decreased monotonically northward. The highest SSD values were recorded for elytra length and pronotum width (0.08-0.09), while for the others, they were significantly lower (0.05). Methodological and ideological issues in assessing and applying SSD data in animal populations are discussed.