Geographic structuring into vicariant species-pairs in a wide-ranging, high-dispersal plant–insect mutualism: the case of Ficus racemosa and its pollinating wasps

Abstract

Ficus and their mutualistic pollinating wasps provide a unique model to investigate joint diversification in a high dispersal system. We investigate genetic structuring in an extremely wide-ranging Ficus species, Ficus racemosa, and its pollinating wasp throughout their range, which extends from India to Australia. Our samples were structured into four large, vicariant populations of figs and wasps which may correspond to distinct (sub)species, located in India, China-Thailand, Borneo, and Australia. However, the genetically most divergent group was the Indian population for the figs and the China-Thailand population for the wasps, suggesting different evolutionary histories of populations. Molecular dating for the wasps shows that diversification of the pollinator clade is surprisingly old, beginning about 13.6 Ma. Data on both the host fig species and its pollinating wasps suggest that strong genetic flow within biogeographic groups over several hundreds of kilometers has limited genetic and morphological differentiation and, potentially, local adaptation. This is probably due to long-distance dispersal of pollinating wasps. The genetic clustering into large geographic units observed in F. racemosa and its pollinators is reminiscent of what can be observed in some other high-dispersal organisms characterized by morphology that varies little over huge distances. The implications of strong gene flow for diversification processes and adaptation to different ecological conditions in Ficus and their pollinating wasps are just beginning to emerge.