Data from: Contrasting genetic responses to population fragmentation in a coevolving fig and fig wasp across a mainland-island archipelago

Interacting species of pollinator–host systems, especially the obligate
ones, are sensitive to habitat fragmentation, due to the nature of mutual
dependence. Comparative studies of genetic structure can provide insights
into how habitat fragmentation contributes to patterns of genetic
divergence among populations of the interacting species. In this study, we
used microsatellites to analyse genetic variation in Chinese populations
of a typical mutualistic system – Ficus pumila and its obligate pollinator
Wiebesia sp. 1 – in a naturally fragmented landscape. The plants and wasps
showed discordant patterns of genetic variation and geographical
divergence. There was no significant positive relationship in genetic
diversity between the two species. Significant isolation-by-distance (IBD)
patterns occurred across the populations of F. pumila and Wiebesia sp. 1
as whole, and IBD also occurred among island populations of the wasps, but
not the plants. However, there was no significant positive relationship in
genetic differentiation between them. The pollinator populations had
significantly lower genetic variation in small habitat patches than in
larger patches, and three island pollinator populations showed evidence of
a recent bottleneck event. No effects of patch size or genetic bottlenecks
were evident in the plant populations. Collectively, the results indicate
that, in more fragmented habitats, the pollinators, but not the plants,
have experienced reduced genetic variation. The contrasting patterns have
multiple potential causes, including differences in longevity and hence
number of generations experiencing fragmentation; different dispersal
patterns, with the host's genes dispersed as seeds as well as a
result of pollen dispersal via the pollinator; asymmetrical responses to
fluctuations in partner populations; and co-existence of a rare second
pollinating wasp on some islands. These results indicate that strongly
interdependent species may respond in markedly different ways to habitat
fragmentation.