Contrasting genetic responses to population fragmentation in a coevolving fig and fig wasp across a mainland–island archipelago

Abstract

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.

A comparative study on genetic effects of artificial and natural habitat fragmentation on Loropetalum chinense (Hamamelidaceae) in Southeast China

“…These findings contrast with recent studies in either region, indicating that recent artificial 'islanding' in the TIL region can lead to significant loss of genetic diversity, especially in short-lived herbs (Yuan et al, 2012). Moreover, in the Zhoushan Archipelago, it was recently demonstrated that overwater distance is a significant barrier to contemporary gene flow in both pond frogs (Wang et al, 2014) and fig wasps (Liu et al, 2013), whereby in either instance genetic drift following Holocene island formation likely decreased diversity and increased differentiation among insular populations. By contrast, this study on L. chinense is the first to highlight the importance of gene flow (most likely via seed) in sustaining genetic diversity and preventing inter-population differentiation in the face of habitat 'insularization' in both the TIL region and the Zhoushan Archipelago, that is, at different temporal and spatial scales.…”

“…These islands represent former hilltops that were not flooded by the lake. Although there are numerous studies of genetic diversity on landbridge islands in America (Jordan and Snell, 2008;Barker et al, 2012;Bell et al, 2012), Australia (Furlan et al, 2012;Stankowski and Johnson, 2014) and the Mediterranean Basin (Bittkau and Comes, 2005), relatively little attention has been paid to China (Liu et al, 2013;Wang et al, 2014), despite the fact that China has 410 000 islands, with climates ranging from tropical to cold temperate conditions (Committee ZGHDZ, 2013).…”

One step ahead: a parasitoid disperses farther and forms a wider geographic population than its fig wasp host

“…Liu et al . , ). A major finding of the present study is that parasitoids in this system disperse as far, if not farther, than pollinators.…”

Movements of genes between populations: are pollinators more effective at transferring their own or plant genetic markers?

“…F. pumila populations showed latitudinal and longitudinal gradients in genetic composition, which might be the output of contact of two genetic clusters or caused by dispersal, given the neutral markers used in this study. To infer the potential cause and the most likely direction of dispersal [52], we tested the relationship between genetic and spatial distances to the most southern ( population TC), most northern (population FS), most western ( population LZ) and most eastern population (FQ) using a linear regression in R [53].…”