The common wall lizard, Podarcis muralis, is a small, diurnal, lizard that is wide spread throughout southern Europe, from sea level to high altitude with many island populations and isolated populations at range margins. It is often closely associated with human constructions, such as stone walls and dwellings. Fortunately, they appear to be particularly common in places where there tends to be good patisseries, wine and, in Italy, pizza. However, they are not solely restricted to areas of human habitation also occuring at lower density throughout forests.
Our interest was initially drawn to wall lizards because they are introduced into many places where the species is not native, including tens of populations in England. Studying non-native species allow us to study evolutionary processes as they happen. For example, animals introduced from Tuscany or southern France to England will encounter a very different climate to what they are used to. But wall lizards have coped with, and even adapted to, their new environments. For example, non-native lizards lay eggs with more advanced embryos that develop faster at cooler temperatures than native lizards. Non-native females have also decreased their investment in 2nd and 3rd clutchs compared to native lizards, because these clutches have far smaller probability of hatching.
Our research on the wall lizards has now extended beyond their non-native confines to their native range. Here they form disjunct genetic and geographic distributions across most of Europe. Of particular interest to us are regions where divergent genetic lineages have come back into secondary contact and hybridised. In these regions we find that strong differences in their phenotypic traits, as a result of divergent sexual selection during periods of isolation, strongly impact the outcome of interactions between the two lineages. This has resulted in interesting patterns of gene flow and ultimately provides the basis from the emergence of phenotypic novelty. We are currently exploring multiple lines of enquiry with respect to the causes and consequences of these processes.
Our research on wall lizards is a collaborative effort that involves teams from several countries, including Sweden, Italy, France, Germany, Portugal and Spain .