Molecular evolution and radiation of dung beetles in Madagascar

Madagascar is the world's fourth largest island and has a wide range of climates and ecosystems. Environmental diversity combined with long history of isolation (160 Myr) has generated a high level of endemism at different taxonomic levels, making Madagascar one of the hotspots of global biodiversity. Dung beetles, represented by the two tribes of Canthonini and Helictopleurini, exemplify a large insect taxon. Helictopleurini are completely endemic to Madagascar while Canthonini are endemic at generic level. Using data from mitochondrial and nuclear genes, phylogenetic relationships were investigated in a sample of 44 species. The phylogeny for Canthonini consists of several distinct clades, possibly reflecting multiple colonization of Madagascar. The phylogeny does not support the current taxonomy for all genera. The phylogeny for Helictopleurini lacks statistical support at supra-specific level, and genetic divergence among the Helictopleurini species is comparable with that among species within genera in Canthonini. These results suggest that Helictopleurini has undergone rapid speciation and most likely more recently than Canthonini, consistent with the estimated radiation time based on mtDNA mutation rates in insects and with knowledge about the systematics and geographic distribution of dung beetles worldwide. A detailed analysis of sequence composition identified common patterns in Malagasy dung beetles and other insects.