Is nesting behavior evolving in a stepwise evolution of increasing behavioral complexity in spider wasps? The case of the subfamily Pompilinae (Hymenoptera: Pompilidae)

The evolution of complex behaviors often has been proposed to occur in a stepwise fashion with intermediate states occurring between simple (ancestral) behavioral traits that evolve into more complex (derived) traits. This ethocline hypothesis, however, has rarely been tested in a phylogenetic framework. The subfamily Pompilinae (Hymenoptera: Pompilidae) contains more than 100 genera of spider wasps that exhibit a wide array of nesting behaviors that range from construction of simple burrows to intricate exposed mud nests. There are intermediate states between these nesting types, including species that construct single mud cells in between leaves or wood. To test the ethocline hypothesis, we performed a phylogenetic analysis. We extracted DNA from 100 taxa, belonging to 90% of the genera of the subfamily, and amplified five molecular markers (28S, wingless, long wavelength rhodopsin, elongation factor 1 alpha, and RNA polymerase II. The sequences were aligned using ClustalX, and the model of sequence evolution determined using MrModeltest. The alignments were then concatenated using Geneious. We ran a bayesian analysis for 10 million generations, using partition by gene to model molecular evolution. Ancestral behaviors were inferred using stochastic mutational mapping in SIMMAP. Our results suggest that complex nesting behaviors evolved multiple times in the subfamily, and not necessarily contain intermediate states between simple and complex traits.