Even as recent studies have focused on the construction of larger and more diverse datasets, the proper placement of the hymenopteran superfamilies remains controversial. In order to explore the implications of these new data, we here present the first direct optimization-sensitivity analysis of hymenopteran superfamilial relationships, based on a recently published total evidence dataset. Our maximum parsimony analyses of 111 terminal taxa, four genetic markers (18S, 28S, COI, EF-l), and 392 morphological/behavioral characters reveal areas of clade stability and volatility with respect to variation in four transformation cost parameters. While most parasitican superfamilies remain robust to parameter change, the monophyly of Proctotrupoidea sensu stricto is less stable; no set of cost parameters yields a monophyletic Diaprioidea. While Apoidea is monophyletic under eight of the nine parameter regimes, no set of cost parameters returns a monophyletic Vespoidea or a monophyletic Chrysidoidea. The relationships of the hymenopteran superfamilies to one another demonstrate marked instability across parameter regimes. The preferred tree (i.e., the one that minimizes character incongruence among data partitions) includes a paraphyletic Apocrita, with (Orussoidea + Stephanoidea) sister to all other apocritans, and a monophyletic Aculeata. "Parasitica" is rendered paraphyletic by the aculeate clade, with Aculeata sister to (Trigonaloidea + Megalyroidea).
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