Sexual selection and asymmetric hybridization between lineages of the European Wall Lizard, Podarcis muralis (#18)
Hybridization has long fascinated biologists as a mechanism for ecological and evolutionary change. Typically, studies of hybrid zones find that gene flow is asymmetric i.e. one taxon acts as the main donor and the other the main recipient of genetic material. However, the mechanisms that dictate the strength and direction of gene flow are often unclear. To gain a clearer understanding of the ecology of hybridization it is valuable to study cases of secondary contact between populations that are in the intermediate stages of divergence and where post-zygotic reproductive isolation is minimal. European wall lizards, Podarcis muralis, from north-central Italy have highly exaggerated male sexual characters compared to other populations in southern Europe. The Italian and Southern European lineages form natural contact zones within their native range and are known to hybridize. We designed an enclosure experiment to examine the drivers of hybridization in this system. Our results show asymmetries in spatial habitat use, male-female interactions, and hybridization upon secondary contact. Italian males monopolized high-quality habitat and defended well-defined territories, while French males tended to adopt a ‘floater’ strategy. Hybridization between lineages was close to unidirectional and primarily occurred between subdominant males of the Italian lineage and French females. Sexual selection was stronger in the dominant lineage and reproductive success was predicted by several characters involved in pre- and post-copulatory male-male competition. These results suggest that the lineage with exaggerated sexual characters should rapidly displace the other lineage ecologically and genetically.