Non-congruent colonizations of remote islands by a specialized pollinating seed-predation mutualism (Phyllanthaceae: Glochidion; Lepidoptera: Gracillariidae: Epicephala)

Pollinating seed-predation mutualisms, such as those between figs and fig wasps, and yuccas and yucca moths, have long served as principal model systems for studies of coevolutionary diversification. However, insights into mechanisms of codiversification are hampered by high sympatric diversity in plants and pollinators, and the difficulty of conducting exhaustive sampling of recently diversified subclades. Here we examine the co-radiation of Glochidion trees (Phyllanthaceae) and their pollinating seed-predatory Epicephala moths (Lepidoptera: Gracillariidae) in Southeastern Polynesia (Cook Islands and French Polynesia) with extensive outgroup sampling from the west Pacific and Asia. We find that both Glochidion and Epicephala have successfully colonized Southeastern Polynesia, but not congruently; e.g., two colonizations of Epicephala are associated with a single colonization of Glochidion. We find evidence that a single, widespread monophyletic morphospecies of Epicephala is associated with 12 species of Glochidion across three archipelagoes; this may represent a recent host shift of the type that has been hypothesized for similar systems on continents. We also present preliminary data examining the phylogeography of Diphtheroptila moths (Lepidoptera: Gracillariidae) which mine Glochidion leaves, and on the network structure of Glochidion-Epicephala trophic interactions on three of the Society Islands (Tahiti, Mo’orea, Huahine). Our results appear to conflict with the paradigm that taxa with highly specialized biotic interactions should be unable to colonize oceanic islands. They also suggest that host-shifts by pollinators may be an important mechanism of diversification in specialized pollination mutualisms, and shed light on the biogeography of Southeastern Polynesia.