The mitochondrial genomes of ladybird beetles and implications for evolution and phylogeny

Ladybirds formed the most familiar beetle group, namely the family Coccinellidae, whose internal relationships remain unclear. In particular, the subfamily relationships could not be well resolved in previous studies based on the conventional nuclear and/or mitochondrial gene fragments. In this study, we used next-generation sequencing to obtain new mitochondrial genomes (mitogenomes) from 13 species representing four coccinellid subfamilies (i.e., Coccinellinae, Epilachninae, Coccidulinae and Chilocorinae). Together with 24 existing mitogenome sequences of Cucujoidea, we conducted phylogenetic analyses to investigate the deep phylogenetic relationships in Coccinellidae, under maximum likelihood and Bayesian inference criteria. The analyses from nucleotide datasets resulted in a largely identical tree topology, where Epilachninae and Coccinellinae were monophyletic groups. The Scymninae and Coccidulinae were recovered as non-monophyletic. Amino acids differed from nucleotides in that the Epilachninae was retrieved as paraphyletic, with respect to Epilachna admirabilis. Ancestral state reconstruction suggested that the plant eating ladybird beetles arose within an aphidophagous/coccidophagous clade. In addition, three independent shifts toward coccidophagy and one shift toward mycophagy occurred in Coccinellidae.