Phylogenetic signal in the COI, 16S, and 28S genes for inferring relationships among genera of Microgastrinae (Hymenoptera; Braconidae): evidence of a high diversification rate in this group of parasitoids.

The subfamily Microgastrinae is a highly diversified group of parasitoid wasps that attacks all of the different groups of Lepidoptera. We explore here the phylogenetic signal in three gene (mitochondrial COI and 16S, and nuclear 28S) fragments as an assessment of their utility in resolving generic relationships within this species-rich insect group. These genes were chosen because their level of sequence divergence is thought to be appropriate for this study and because they have resolved relationships among other braconid wasps at similar taxonomic levels. True phylogenetic signal, as opposed to random signal or noise, was detected in the 16S and 28S data sets. Phylogenetic analyses conducted on each microgastrine data set, however, have all resulted in poorly resolved trees, with most clades being supported by low bootstrap values. The phylogenetic signal, if present, is therefore concentrated on a few well-supported clades. Some rapidly evolving sites may be too saturated to be phylogenetically useful. Nonetheless, the sequence data (nearly 2300 nucleotides) used here appear to exhibit the appropriate level of variation, theoretically, to resolve the relationships studied. Moreover, the clades that are well supported by the data are usually supported by more than one data set and represent different levels of sequence divergence. We suggest that the lack of phylogenetic signal observed is an indication of the presence of many short internal branches on the phylogeny being estimated, which in turn might be the result of a rapid diversification of the taxa examined. Relative specialization of diet, which is typically associated with parasitic behavior, is believed to result in high radiation rates, which may have been especially high in microgastrine wasps because of the great diversity of their lepidopteran hosts. This hypothesis of a rapid diversification caused by an abundance of host species remains speculative and more data will be needed to test it further.