Invasive lizard has fewer parasites than native congener

Invasive species can carry parasites to introduced locations, which may be key to understand the success or failure of species establishment and the invasive potential of introduced species. We compared the prevalence and infection levels of haemogregarine blood parasites between two sympatric congeneric species in Lisbon, Portugal: the invasive Italian wall lizard (Podarcis siculus) and the native green Iberian wall lizard (Podarcis virescens). The two species had significant differences in their infection levels: while P. virescens had high prevalence of infection (69.0%), only one individual of P. siculus was infected (3.7%), and while P. virescens exhibited an average intensity of 1.36%, the infected P. siculus individual had an infection rate of only 0.04%. Genetic analyses of 18S rRNA identified two different haemogregarine haplotypes in P. virescens. Due to the low levels of infection, we were not able to amplify parasite DNA from the infected P. siculus individual, although it was morphologically similar to those found in P. virescens. Since other studies also reported low levels of parasites in P. siculus, we hypothesize that this general lack of parasites could be one of the factors contributing to its competitive advantage over native lizard species and introduction success.