Origin and genetic diversity of an introduced wall lizard population and its cryptic congener

The Common Wall Lizard (Podarcis muralis) has been introduced within large parts of Central Europe, the UK and parts of North America. In an introduced population of this species in Lower Saxony, Germany, we found in addition to mtDNA haplotypes of P. muralis also haplotypes of its congener Podarcis liolepis, a species that hitherto has never been recorded outside its native range. We therefore, (1) wanted to identify the geographic origin of the founder individuals of both non-native populations, (2) test for hybridization between introduced individuals of both species in Germany and (3) compare levels of genetic diversity between native and introduced populations. We sequenced a fragment of the mitochondrial cytochrome b gene and genotyped individuals of the introduced as well as native populations of both species at eleven microsatellite loci. Our results suggest that the founders presumably stem from a region in the eastern Pyrenees, where sympatric populations of P. muralis and P. liolepis are known. No evidence for gene flow between the two species was found in the introduced population. These results are consistent with behavioural observations indicating agonistic interactions of P. muralis towards P. liolepis rather than cross-species attraction. Compared to the native populations, high levels of genetic diversity have been retained in the introduced population of both species and no evidence for a genetic bottleneck was found. The effective population size was high in P. muralis, but substantially smaller in P. liolepis.