Mitochondrial DNA phylogeny and the evolution of host-plant use in palearctic Chrysolina (Coleoptera, Chrysomelidae) leaf beetles

The genus Chrysolina consists of specialized phytophagous leaf-beetles (Coleoptera, Chrysomelidae) with feed on several plant families. Then is no explicit phylogenetic hypothesis available for this genus, which includes 65 subgenera and more than 400 species with a wide distribution. We obtained 839-bp sequence data from the 16S rDNA and cytochrome oxidase subunit I(COI) mitochondrial genes. Thirty Chrysolina taxa representing eight host-plant affiliations, two species of the closely related genus Oreina, and two outgroups were sampled. These data sets were used separately and combined to obtain the mitochondrial cladogram of the group using maximum-parsimony and maximum-likelihood criteria. The results were compared to current proposals for Chrysolina systematics that are based on morphological, ecological, and karyological data. The trees obtained were in the most part congruent with the proposed ancestral association of Chrysolina to Lamiaceae based on chromosome number in several lineages. A minimum of five host-plant switches from the ancestral state inferred at the family level and two at the subclass level suggests the absence of parallel evolution of beetles and their host plants, Another switch leading to oligophagy at the family level was deduced to have occurred in the lineage of the subgenus Chrysolina s.str.