Blood parasites in sympatric lizards: what is their impact on hosts' immune system?

Assessment of parasites and their pathogenicity is essential for studying the ecology of populations and understanding their dynamics. In this study, we investigate the prevalence and intensity of infection of haemogregarines (phylum Apicomplexa) in two sympatric lizard species, Podarcis vaucheri and Scelarcis perspicillata, across three localities in Morocco, and their effect on host immune response. We used the Phytohaemagglutinin (PHA) skin testing technique to relate the level of immune response with parasite infection. Prevalence and intensity levels were estimated with microscopy, and 18S rRNA gene sequences were used to confirm parasite identity. All parasites belong to the haemogregarine lineage found in other North African reptiles. There were differences in prevalence between localities and sexes. Overall, infected lizards were larger than uninfected ones, although we did not detect differences in parasitaemia across species, sex or locality. The swelling response was not related to the presence or number of haemogregarines, or to host body size, body condition, sex or species. We found no evidence of impact for these parasites on the circulating blood cells or the hosts' immune system, but more data is needed to assess the potential impact of mixed infections, and the possibility of cryptic parasite species.