Phylogeny of pteromalid parasitic wasps (Hymenoptera: Pteromalidae): initial evidence from four protein-coding nuclear genes.

Chalcidoidea (approximately 22,000 described species) is the most ecologically diverse superfamily of parasitic Hymenoptera and plays a major role in the biological control of insect pests. However, phylogenetic relationships both within and between chalcidoid families have been poorly understood, particularly for the large family Pteromalidae and relatives. Forty-two taxa, broadly representing Chalcidoidea but concentrated in the 'pteromalid lineage,' were sequenced for 4620 bp of protein-coding sequence from four nuclear genes for which we present new primers. These are: CAD (1719 bp) DDC (708 bp), enolase (1149 bp), and PEPCK (1044 bp). The combined data set was analyzed using parsimony, maximum likelihood, and Bayesian methods. Statistical significance of the apparent non-monophyly of some taxonomic groups on our trees was evaluated using the approximately unbiased test of Shimodaira [Shimodaira, H. 2002. An approximately unbiased test of phylogenetic tree selection. Syst. Biol. 51(3), 492-508]. In accord with previous studies, we find moderate to strong support for monophyly of Chalcidoidea, a sister-group relationship of Mymaridae to the remainder of Chalcidoidea, and a relatively basal placement of Encarsia (Aphelinidae) within the latter. The 'pteromalid lineage' of families is generally recovered as monophyletic, but the hypothesis of monophyly for Pteromalidae, which appear paraphyletic with respect to all other families sampled in that lineage, is decisively rejected (P < 10(-14)). Within Pteromalidae, monophyly was strongly supported for nearly all tribes represented by multiple exemplars, and for two subfamilies. All other multiply-represented subfamilies appeared para- or polyphyletic in our trees, although monophyly was significantly rejected only for Miscogasterinae, Ormocerinae, and Colotrechninae. The limited resolution obtained in the analyses presented here reinforces the idea that reconstruction of pteromalid phylogeny is a difficult problem, possibly due to rapid radiation of many chalcidoid taxa. Initial phylogenetic comparisons of life history traits suggest that the ancestral chalcidoid was small-bodied and parasitized insect eggs.