Evolution of nesting behavior and diversification of Ageniellini spider wasps (Hymenoptera: Pompilidae)

A major challenge in evolutionary biology is to explain patterns in traits, phenotypic diversity, and diversification. Spider wasps, especially Ageniellini, are notable for their diverse, unusual, and specialized behavior associated with prey capture, prey transport and nesting. Some Ageniellini amputate the legs of their spider hosts, a few species are cleptoparasites, and some species build mud nests. These nests can be constructed by a single wasp or communally. We reconstructed the phylogeny of Ageniellini from five nuclear markers, and used it to map prey-transport and nest-construction behavior using Bayesian, maximum-likelihood, and stochastic approaches. We reconstructed a single origin for mud nesting in Ageniellini, which is associated with modified morphological features and is correlated with communal nesting. The tribe arose approximately 25.5 Ma, during the late Paleogene – Oligocene. Shifts in diversification were observed around 9 Ma, which corresponds to the origin of the majority of the mud-nesting clades. Our results contradict previous hypotheses of simple to complex, stepwise evolution (ethocline hypothesis) in nesting behavior.