An examination of ecological rules on phenotypic variation in Coccinella septempunctata (Coleoptera: Coccinellidae) - a comparison between environmental factors and elytra spot size variation

Introduced species often encounter environments that are similar to those in the native range. Whether they evolve similar phenotypes in these environments may depend on both genetic and environmental factors. Coccinella septempunctata is an invasive species that was introduced as a biological control agent from Eurasia to North America to manage agricultural pest insects. Elytra spot size was examined because it was known to vary in the native range and it was likely important for the physiology of the species. We examined whether spot size variation in C. septempunctata of native and introduced populations followed the ecological patterns called Gloger’s rule and thermal melanism hypothesis. We also compared a correlation between environmental factors (e.g., temperature and precipitation) and the spot size variation between native and introduced ranges. A total of 1,457 individuals of C. septempunctata were collected from 63 locations from native and introduced ranges. Our results showed a positive correlation between precipitation and spot size in both native and introduced ranges, which suggests that spot size variation follows Gloger’s rule. There was no correlation between temperature and spot size overall; however, there was a negative correlation between spot size and temperature in the introduced range, but not in the native range. Thus, introduced populations also followed thermal melanism hypothesis. We will discuss potential underlying mechanisms of environmental and genetic factors on spot size variation between native and introduced ranges.