Increased gene sampling yields robust support for higher-level clades within Bombycoidea (Lepidoptera)

This study has as its primary aim the robust resolution of higher-level relationships within the lepidopteran superfamily Bombycoidea. Our study builds on an earlier analysis of five genes (similar to 6.6 kbp) sequenced for 50 taxa from Bombycoidea and its sister group Lasiocampidae, plus representatives of other macrolepidoteran superfamilies. The earlier study failed to yield strong support for the monophyly of and basal splits within Bombycoidea, among others. Therefore, in an effort to increase support specifically for higher-level nodes, we generated 11.7 kbp of additional data from 20 genes for 24 of 50 bombycoid and lasiocampid taxa. The data from the genes are all derived from protein-coding nuclear genes previously used to resolve other lepidopteran relationships. With these additional data, all but a few higher-level nodes are strongly supported. Given our decision to minimize project costs by augmenting genes for only 24 of the 50 taxa, we explored whether the resulting pattern of missing data in the combined-gene matrix introduced a nonphylogenetic bias, a possibility reported by others. This was achieved by comparing node support values (i.e. nonparametric bootstrap values) based on likelihood and parsimony analyses of three datasets that differ in their number of taxa and level of missing data: 50 taxa/5 genes (dataset A), 50 taxa/25 genes (dataset B) and 24 taxa/25 genes (dataset C). Whereas datasets B and C provided similar results for common nodes, both frequently yielded higher node support relative to dataset A, arguing that: (i) more data yield increased node support and (ii) partial gene augmentation does not introduce an obvious nonphylogenetic bias. A comparison of single-gene bootstrap analyses identified four nodes for which one or two of the 25 genes provided modest to strong support for a grouping not recovered by the combined-gene result. As a summary proposal, two of these four groupings (one each within Bombycoidea and Lasiocampidae) were deemed sufficiently problematic to regard them as unresolved trichotomies. Since the alternative groupings were always highly localized on the tree, we did not judge a combined-gene analysis to present a problem outside those regions. Based on our robustly resolved results, we have revised the classification of Bombycoidea: the family Bombycidae is restricted to its nominate subfamily, and its tribe Epiini is elevated to subfamily rank (Epiinae stat.rev.), whereas the bombycid subfamily Phiditiinae is reinstated as a separate family (Phiditiidae stat.rev.). The bombycid subfamilies Oberthueriinae Kuznetzov & Stekolnikov, 1985, syn.nov. and Prismostictinae Forbes, 1955, syn.nov., and the family Mirinidae Kozlov, 1985, syn.nov. are established as subjective junior synonyms of Endromidae Boisduval, 1828. The family Anthelidae (Lasiocampoidea) is reincluded in the superfamily Bombycoidea.