The European Wall lizard (Podarcis muralis) is an emerging model system for studying the processes underlying adaptive introgression of sexually selected traits. The two main lineages, referred to as the ‘French’ and the ‘Italian’ lineages, have been separated approximately 2.5 million years ago. During this time, the Italian lineage has evolved a distinct phenotype (green dorsal coloration, black ventral coloration, larger heads) by sexual selection. Roughly 300,000 years ago, the two lineages came into secondary contact and started to hybridize. Since Italian lizards are superior to French lizards in terms of sexual selection, the gene flow is asymmetric with sexually selected genes introgressing into the French genetic background. This process is still ongoing today in a narrow hybridzone on the coast of Liguria in Northwest Italy and provides excellent opportunities to study the dynamics of adaptive introgression.
A high quality genome of the European Wall lizard is available, and RAD-Seq data has been extensively used to reveal genomic differences between the Italian and the French lineages, as well as to characterize the genomic make-up of lizards in the hybrid zone (Yang et al., submitted; Yang et al., in prep). This project aims to complement the analyses on the genomic level and investigate in how far gene expression profiles differ between the two lineages. We will test several predictions, for example if genes that are putatively underlying the exaggerated Italian phenotype are indeed differentially expressed between the two lineages.
Our dataset consists of 24 transcriptomes of lizards from 6 different experimental groups: native Italian lowland, native Italian highland, native French lowland, native French highland. Pregnant females from each group were brought into the lab and their clutches were incubated at two different temperatures (‘cold’, 16˚C; ‘warm’, 24˚C). Embryos were collected at a precisely defined developmental stage and subjected to transcriptome sequencing.