Molecular phylogenetics complicating the taxonomic revision of New World ant parasitoids (Orasema coloradensis species group)

The Orasema coloradensis species group of ant parasitoids (Hymenoptera: Eucharitidae) exemplifies the difficulty in species and species group delineation with discordant molecular, morphological, and behavioral data. This is a New World species group with a range from central Argentina to southern Canada. Maximum likelihood and Bayesian analyses of five concatenated gene regions (three ribosomal and two mitochondrial) consistently group nine putative species with a Neotropical grade of six taxa basal to a Nearctic clade of three taxa. Species in this group in the most inclusive sense do not share any distinguishing morphological synapomorphies amongst all members but instead show homoplastic characters with several other species groups in the genus Orasema. Orasema coloradensis Wheeler shows a large amount of size, color, and sculpture variation across its range in North America but shows no distinguishing molecular variation. The problem of too much morphological variation across the species group is juxtaposed with the problem of too little morphological and behavioral variation between some molecularly defined species within the group. The differences between molecular and morphological distances between taxa in this group may have been the result of rapid radiations or host specializations that have reproductively isolated species to different degrees. Redefining the limits of the Orasema coloradensis species group based on shared morphology and using any correlation amongst the three types of data collected (morphological, molecular, and behavioral) to delimit species will create more logical taxonomic groupings.