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 wa sps that attacks all of the different groups of Lepidoptera. We explore her e the phylogenetic signal in three gene (mitochondrial COI and 16S, and nuc lear 28S) fragments as an assessment of their utility in resolving generic relationships within this species-rich insect group. These genes were chose n because their level of sequence divergence is thought to be appropriate f or this study and because they have resolved relationships among other brac onid wasps at similar taxonomic levels. True phylogenetic signal, as oppose d to random signal or noise, was detected in the 16S and 28S data sets. Phy logenetic 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 con centrated on a few well-supported clades. Some rapidly evolving sites may b e too saturated to be phylogenetically useful. Nonetheless, the sequence da ta (nearly 2300 nucleotides) used here appear to exhibit the appropriate le vel of variation, theoretically, to resolve the relationships studied. More over, the clades that are well. supported by the data are usually supported by more than one data set and represent different levels of sequence diver gence. We suggest that the lack of phylogenetic signal observed is an indic ation of the presence of many short internal branches on the phylogeny bein g estimated, which in turn might be the result of a rapid diversification o f the taxa examined. Relative specialization of diet, which is typically as sociated with parasitic behavior, is believed to result in high radiation r ates, which may have been especially high in microgastrine wasps because of the great diversity of their lepidopteran hosts. This hypothesis of a rapi d diversification caused by an abundance of host species remains speculativ e and more data will. be needed to test it further. (C) 1999 Academic Press .