Social interactions predict genetic diversification: an experimental manipulation in shorebirds

Mating strategy and social behaviour influence gene flow and hence affect levels of genetic differentiation and potentially speciation. Previous genetic analyses of closely related plovers Charadrius spp. found strikingly different population genetic structure in Madagascar: Kittlitz’s plovers are spatially homogenous whereas white-fronted plovers have well segregated and geographically distinct populations. Here we test the hypotheses that Kittlitz’s plovers are spatially interconnected and have extensive social interactions that facilitate gene flow, whereas white-fronted plovers are spatially discrete and have limited social interactions. By experimentally removing mates from breeding pairs and observing the movements of mate-searching plovers in both species, we compare the spatial behaviour of Kittlitz’s and white-fronted plovers within a breeding season. The behaviour of experimental birds was largely consistent with expectations: Kittlitz’s plovers travelled further, sought new mates in larger areas, and interacted with more individuals than white-fronted plovers, however there was no difference in breeding dispersal. These results suggest that mating strategies, through spatial behaviour and social interactions, are predictors of gene flow and thus genetic differentiation and speciation. Our study highlights the importance of using social behaviour to understand gene flow, although future work is needed to investigate the relative importance of social structure, intra- and between-season dispersal in influencing the genetic structures of populations.