Sympatric speciation through intraspecific social parasitism

Abstract

Sympatric speciation through intraspecific social parasitism has been proposed for the evolution of Hymenopteran workerless parasites. Such inquilines exploit related host taxa to produce their own sexual offspring. The relatedness of inquilines to their hosts has been generalized in Emery's rule, suggesting that social parasites are close or the closest relatives to their host species. If the closest relative of each parasite is its host, then multiple independent origins of the parasite species are implied even within a single genus, probably through sympatric speciation. To test the plausibility of sympatric speciation in inquilines, we conducted a mitochondrial DNA phylogenetic analysis in three inquiline-host pairs of Myrmica ant species. We show that congeneric inquilines have originated independently several times. We also show that two of the inqulines are more closely related to their hosts than to any other species. Our results suggest sympatric speciation of Myrmica inquilines. Sympatric speciation is probably facilitated by the social biology and ecology of Myrmica, with polygyny as a prerequisite for the evolution of intraspecific parasitism.

Fig. 1.

Majority-rule consensus tree of 9,000 Bayesian trees. Bold numbers above branches represent the posterior probability that the clade is correct, given the model of evolution, and numbers above the posterior probabilities are bootstrap proportions; average branch length estimates from the Bayesian analysis are given below the branches (tree length = 1.206). The single most parsimonious tree topology is identical to that of the Bayesian consensus tree. Parasites are given in frames with solid arrow lines pointing to their hosts in this study; other documented karavajevi hosts, rugulosa and sabuleti (43), are shown with dashed lines. The three species groups shown with vertical lines are defined on the basis of worker morphology, excluding the inquilines (47).