Divergence in sexually selected traits in allopatry should affect the degree and direction of hybridization. However, few studies have established the causes and targets of sexual selection during secondary contact. Common wall lizards (Podarcis muralis) from north-central Italy have highly exaggerated male sexual traits compared to populations in Western Europe. Using experimental populations, we show that this creates asymmetries in male dominance, spatial habitat use and reproductive success upon secondary contact. Hybridization occurred almost exclusively between males of the Italian lineage and females of the Western European lineage. We provide evidence to suggest stronger ongoing selection on male sexual traits within the dominant Italian lineage. However, these same characters did not predict hybridization, and hybrid matings contributed little to variance in male reproductive success. Instead, most hybrid offspring were sired by Italian males displaying phenotypes associated with lower within-lineage reproductive success. Thus, highly directional hybridization arises because some Italian males are out-competed within their own lineage but remain competitive relative to males of the other lineage. This pattern of hybridization is consistent with the direction of introgression in natural contact zones, but our data suggest that sexual selection acting through hybridization may be weak at the leading edge of natural hybrid zones. A lay summary is available for this article.
Bibliographical noteFunding Information:
We thank Natalia Zajac, Lindall Kidd and Joseph Williamson for field and laboratory assistance and Robert Heathcote for methodological advice. We also thank Roberto Sacchi, Marco Zuffi and Fabien Aubret for logistical support and two anonymous referees for comments. This work was supported by the British Ecological Society, the National Geographic Society and the Royal Society of London through an early career research grant and a University Research Fellowship (all to TU), a University of Tasmania Graduate Research Scholarship and Holsworth Wildlife Research Endowment (HEAM), an FP7 Marie Curie Fellowship (GMW) and a Funda??o para a Ci?ncia e a Tecnologia postdoctoral grant (SFRH/BPD/94582/2013) (GPL). TU is supported by the Knut and Alice Wallenberg Foundations. All experiments carried out as part of this research comply with UK laws, and the work was approved by the University of Oxford's Local Ethical Review Process and the UK Home Office (PPL: 30/2560). For the relevant fieldwork permits, see Appendix?S1.
© 2016 The Authors. Functional Ecology © 2016 British Ecological Society
Copyright 2017 Elsevier B.V., All rights reserved.
- male–male competition