Recently, studies have shown that gene exchange occurs between divergent species (i.e natural hybridization).Furthermore, this genetic exchange between different species or sub-species contributes to adaptation and diversification of many organisms (i.e adaptive introgression).Geographic and phenotypic variation have shown that hybridization and introgression are common in animals. However, despite increased evidence of patterns of variation consistent with hybridization in animals, rarely do we understand how those patterns come about and when hybridization will shape the evolution of organisms and their genomes. Therefore, a major challenge for evolutionary biologists is to connect causes of hybridization with their consequences for diversification and adaptation.
Wall lizards (Podarcis muralis), a genetically and phenotypically variable species common in southern Europe, has been shown to exhibit asymmetric hybridization between major genetic lineages. Recent research has suggested that this is driven primarily by differences in by male competitive ability, which results in the transfer of sexually selected characters from one lineage to another (While et al. 2015; MacGregor et al. 2016). However, analyses of Single Nucleotide Polymorphisms (SNPs) and phenotypic variation suggest (i) that introgression of a small part of the genome is responsible for large shifts in phenotype; (ii) that sexually selected introgression is counter-balanced by natural selection at high altitude; and (iii) that this results in sexually antagonistic selection across altitudinal clines. This suggests that the outcome of introgression and hybridisation for phenotypic divergence is influenced by a suite of environmental conditions which mediate the costs and benefits of different phenotypes in a potentially sex-specific manner.
My Ph.D. project will examine the processes that drive these geographic patterns of introgression in the wall lizard and the consequences this has for the evolution of sexual dimorphism. Specifically, my project will have four main aims:
1) Undertake a landscape genomics approach to characterise patterns of asymmetric introgression across altitudinal gradients and identify the environmental parameters that limit adaptive introgression.
2) Generate estimates of ongoing selection on male and female phenotypic traits at the leading edge of the hybrid zone.
3) Test predictions for the sources of potentially sexually antagonistic selection on phenotypic traits.
4) Utilise next generation sequencing to test how predictions from the selective processes identified in first two aims shape variation across the genome.
To addresses these aims my project will combine detailed field studies, laboratory experiments and genomic analyses