Molecular evolution of the wingless gene and its implications for the phylogenetic placement of the butterfly family Riodinidae (Lepidoptera: papilionoidea).

The sequence evolution of the nuclear gene wingless was investigated among 34 representatives of three lepidopteran families (Riodinidae, Lycaenidae, and Nymphalidae) and four outgroups, and its utility for inferring phylogenetic relationships among these taxa was assessed. Parsimony analysis yielded a well-resolved topology supporting the monophyly of the Riodinidae and Lycaenidae, respectively, and indicating that these two groups are sister lineages, with strong nodal support based on bootstrap and decay indices. Although wingless provides robust support for relationships within and between the riodinids and the lycaenids, it is less informative about nymphalid relationships. Wingless does not consistently recover nymphalid monophyly or traditional subfamilial relationships within the nymphalids, and nodal support for all but the most recent branches in this family is low. Much of the phylogenetic information in this data set is derived from first- and second-position substitutions. However, third positions, despite showing uncorrected pairwise divergences up to 78%, also contain consistent signal at deep nodes within the family Riodinidae and at the node defining the sister relationship between the riodinids and lycaenids. Several hypotheses about how third-position signal has been retained in deep nodes are discussed. These include among-site rate variation, identified as a significant factor by maximum likelihood analyses, and nucleotide bias, a prominent feature of third positions in this data set. Understanding the mechanisms which underlie third-position signal is a first step in applying appropriate models to accommodate the specific evolutionary processes involved in each lineage.