Roughly half of a lizard’s genome consists of transposable elements (TEs). Genome evolution therefore largely depends on the activity of TEs, since these may bring about structural variation, rewire cis-regulatory landscapes, or duplicate/delete parts of the genome. The dynamics between the genome and its TE landscape have been likened to an arms race between host and parasite with the host genome evolving strategies for silencing TEs (preventing from transposing). Wall lizards (Podarcis muralis) are widely distributed across Southern Europe. During the past century, lizards from Italy and France have been introduced to England where they established small, but stable populations. The cool English climate posed a challenge to the newcomers, mostly because incubation of lizard eggs in cool soils compromised the hatching of juveniles. Within only a few decades, the English wall lizards have adapted to the cool climate by increasing their developmental rate and thus shorten the time spent in the cool soil. The current project focuses on the expression patterns of TEs in embryonic wall lizards and addresses two questions: (1) How environmentally sensitive is TE activity? The expression of TEs, and thus their capacity to transpose in the genome, has been reported to be stress-sensitive in a number of organisms. We will investigate how TE expression patterns respond to differences in incubation temperature, an ecologically highly relevant factor. (2) How differ TE expression patterns between native (Italian and French) and introduced (English) populations? The lizard populations in England have experienced a bottleneck during their introduction. It is conceivable that the reduction in effective population size has negatively affected the genome's defense mechanisms against TE activity. We will therefore test if TE expression differs between native and introduced populations. Taken together, our study will provide some answers to how TEs might shape the ecology and evolution of wall lizards.