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

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 pro- foundly 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 diversi- fication rate of different clades using phylogenetic trees based on a representative taxon sampling and six genes. We also investi- gated 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 [Current Zoology 60 （5）： 561-570, 2014 ]