Abstract:

The extent shape of organisms (body size and the allometry of specific parts) is not only the base for taxonomy, but also the key functional traits for understanding the interaction between organisms and environmental conditions. The geographical variance of body size, allometry, and the underlying mechanisms are fundamental for insect biogeography, but have not been fully documented. In this paper, we compiled data on body size (body length and body width), aspect ratio (body length/body width), and distribution of ladybirds in 28 provinces in China. Meanwhile, we obtained environmental variables representing temperature and precipitation from freely available data. To explore the spatial variance and environmental correlates of body size and aspect ratio in different species groups with various trophic positions, correlation and regression analyses were performed separately on herbivorous and predaceous ladybirds. Our results show that there is evident latitudinal gradient for body size of ladybirds, i.e., body length or width increases with increasing latitude. This is consistent with Bergmann’s rule. Temperature-related variables are the main drivers of geographic variance of body size, because ladybirds usually overwinter as adults, and those with larger body size have more fat and therefore are more resistant to starvation in winter. Herbivorous ladybirds are always larger than predaceous ladybirds in terms of body length and width along the latitudinal gradients. This is due to discrepancies in food and nitrogen concentrations, with predaceous ladybirds having higher nitrogen concentrations than herbivorous ladybirds. Aspect ratio increases significantly with latitude for predaceous ladybirds, but not for herbivorous ladybirds. This may be explained by the high spatial dispersion of prey for predaceous ladybirds, which are further influenced by their own host plants. The most important environmental variables controlling geographic variance in aspect ratio of predaceous ladybirds are precipitation-related, but not temperature-related variables. This is because decreasing precipitation will lead to increasing patchiness of vegetation and subsequently prey for predaceous ladybirds. Increasing aspect ratio and accordingly flying ability is an adaptive response under these conditions. We concluded that, at the provincial scale in China, temperature-related and precipitation-related variables are the main determinant factors for body size and aspect ratio of herbivorous and predaceous ladybirds, respectively; and their magnitude of effects on body shape depends on the trophic positions.

Key words: ladybirds, body size, environmental factor, body length, body width, aspect ratio