Habitat-dependent diversification and parallel molecular evolution: Water scavenger beetles as a case study

Abstract

Abstract Habitat shift is a key innovation that has contributed to the extreme diversification of insects. Most groups are well-adapted to more or less specific environments and shifts usually only happen between similar habitats. To colonize a profoundly different habitat type does not only present ecological opportunities but also great challenges. We used Hydrophiloidea (water scavenger beetles) as a system to study transitions between terrestrial and aquatic environments. We estimated the diversification rate of different clades using phylogenetic trees based on a representative taxon sampling and six genes. We also investigated possible evolutionary changes in candidate genes following habitat shifts. Our results suggest that the diversification rate is relatively slow (0.039?0.050 sp/My) in the aquatic lineage, whereas it is distinctly increased in the secondarily terrestrial clade (0.055?0.075 sp/My). Our results also show that aquatic species have a G (Glycine) or S (Serine) amino acid at a given site of COI, while terrestrial species share an A (Alanine) amino acid with terrestrial outgroups. This indicates that habitat factors may create selection pressure on the evolution of functional genes and cause homoplasy in molecular evolution.