Opportunistic pollinator shifts among sexually deceptive orchids indicated by a phylogeny of pollinating and non-pollinating thynnine wasps (Tiphiidae)

The thynnine wasp genus Neozeleboria Rohwer is the main pollinating group of the sexually deceptive Australian orchid genus, Chiloglottis R.Br. In a highly specialized interaction, Chiloglottis species attract males from a single or very few Neozeleboria species through the chemical mimicry of the female wasp's sex pheromone. An earlier study examining the historical association among Chiloglottis and Neozeleboria using DNA sequence data found matching phylogenetic patterns suggestive of cospeciation between orchids and pollinators. However, patterns of constraint in Neozeleboria emergence phenology and sex pheromones suggested that the close association among orchid and wasp clades may be due to pollinator switching among closely related wasp taxa that have similar traits. In this study, we further examine the association by incorporating a morphological phylogenetic analysis of non-pollinating as well as pollinating Neozeleboria. The morphological analysis is then compared with DNA sequence data from one nuclear and one mitochondrial gene for an increased sample of outgroup genera. The combined molecular data set finds a monophyletic Neozeleboria, although support for this was not strong in the individual data sets. A high congruence between molecular and morphological analyses was found among higher groupings of Neozeleboria. Neozeleboria species that pollinate Chiloglottis species are not found as a monophyletic group but, rather, are scattered throughout a phylogeny comprising pollinators and non-pollinators. Under the cospeciation model, the presence of related Neozeleboria non-pollinators carries the unlikely implication that the association between plant and pollinator has been repeatedly lost. Instead, we favour the alternative 'preferential pollinator switching' model that accounts for the specialization among orchid and wasp lineages in terms of similarities in traits among related Neozeleboria.