Figs (Ficus spp.) and their pollinators (Hymenoptera: Agaonidae) are a classic example of obligate symbiosis, having evolved completely interdependent life histories. Their symbiosis is exploited by host-specific parasitoid wasps, which kill pollinator offspring and can thus reduce fig pollen transfer. Interactions between the figs, pollinators and parasites play an important role in the coevolution of this system. Pollinator dispersal mediates gene flow of the host fig, and therefore influences fig species boundaries. Furthermore, attack by parasitoids may actually help stabilise the mutualism in the long term by reducing seed predation by pollinator offspring. Previous studies indicate that some fig-pollinating wasps are capable of long-distance dispersal, but little is known about the dispersal and mating systems of their parasitoids. Differential dispersal capacity between pollinator and parasitoid may affect fig – pollinator dynamics in the short term, particularly in isolated fig populations, as well as long-term coevolution. Here, we present the first comparative microsatellite analysis of a fig-pollinator and its parasitoid.

We collected Pleistodontes imperialis sp. 1, a pollinator of Port Jackson figs (Ficus rubiginosa), and its parasitoid (Sycoscapter sp. A) at a series of sites located from about ten to several hundred km apart in eastern Australia, and genotyped all wasps at six microsatellite loci. Preliminary results indicate that P. imperialis sp. 1 comprises two distinct genetic populations, separated geographically by a ~600 km gap between Mackay and Atherton in Queensland. Pairwise F_ST values between sites were lower for P. imperialis wasps (0.003 – 0.031) in the southern population compared to co-sampled Sycoscapter wasps (0.000 – 0.054). This supports the prevailing but untested idea that pollinators disperse further than their parasitoid enemies. Despite this, Bayesian clustering analysis determined that Sycoscapter forms a single genetic population over hundreds of kilometres. Inbreeding was higher in pollinators, consistent with our prediction that fewer pollinator than parasitoid females contribute eggs to each fig, limiting the diversity of mates in the next generation.

Fig-pollinator populations are large and geographically expansive. Fig and pollinator gene flow thus occur over large distances and may prevent the evolution of local genetic adaptation between sites with differing climates. Lower dispersal distances in parasitoids may be more likely to allow local genetic adaptation, and also leave more isolated fig and pollinator populations free from parasites.