Parallel Molecular Evolution of Cardenolide Resistance Across Insect Orders

Abstract

As our knowledge of genetics and evolution expands, it appears that sometimes the path that evolution will take can be predictable. There exist evolutionary constraints, like negative pleiotropic effects, that push adaptations into certain patterns. This study expands upon a survey of adaptations that allow certain insects to consume toxic plant compounds, called cardenolides. In 2012, Zhen et al. characterized parallel molecular evolution in insects that consume cardenolides, primarily at two amino acid sites. Glu111 and Asn122 were consistently subject to substitution across the insect orders Hemiptera, Coleoptera, and Lepidoptera. This study widens the breadth of the survey by including four more orders: Diptera, Orthoptera, Mantodea, and Hymenoptera. By broadening the study across these divergent lineages, we investigate if the previously observed evolutionary patterns continue into taxa that come from different environments and genetic backgrounds. We find that evolution appears to be quite predictable across all seven of these orders, as identical amino acid substitutions frequently occur in the same positions.