Female reproductive investment in response to male phenotype in wall lizards and its implications for introgression

The likelihood that females will breed or how much they invest in reproduction can depend on the characters of their male partners. Such differential allocation may enhance or limit gene flow between hybridizing lineages, in particular when the lineages have diverged in sexually selected characters. Populations of the common wall lizard (Podarcis muralis) in some regions of Italy exhibit striking exaggeration of coloration, morphology and behaviour compared to populations in France. The two forms hybridize in north-western Italy. Gene flow is directional and in concordance with the prediction that the exaggerated sexual characters of lizards of Italian origin give them a mating advantage. To evaluate if differential allocation contributes to asymmetric introgression, we tested experimentally if female reproductive investment is affected by male origin and male secondary sexual characters. Despite the large genetic and phenotypic divergence between males of Italian and French origin, females did not invest more when paired with males of the same origin, nor when paired with males with highly expressed sexual characters. Combined, these results suggest that female responses to male phenotypes in wall lizards are unimportant for explaining the directional pattern of gene flow in regions of secondary contact