What Influences the Prevalence and Intensity of Haemoparasites and Ectoparasites in an Insular Lizard?

Simple Summary Islands have long been acknowledged as model systems for studying evolution, and within these, lizards and their blood parasites can be an ideal framework to determine how island characteristics, such as size and isolation, correlate with parasite prevalence and intensity. In this study, we assessed haemogregarine parasite diversity within the Aegean wall lizard Podarcis erhardii across the Cyclades islands, using an integrated approach of assessing both blood slides through microscopy and genetic variability using molecular tools. We also recorded the prevalence of ectoparasites, ticks and mites. We identified two unrelated groups of blood parasites, with a species of the genus Schellackia being reported for the first time in this host species. The presence of ticks was associated with haemogregarine prevalence. However, in contrast to an earlier study, we did not find a significant impact of the island age and area on parasite prevalence. Despite the relative simplicity of island systems, untangling the factors underpinning parasite prevalence remains a complex task, requiring integrated approaches. Island biogeography theories predict that characteristics such as island size, age, and isolation interplay in host-parasite dynamics. In this study, we analyzed haemogregarines of the Aegean wall lizard, Podarcis erhardii, to investigate how island characteristics relate to parasite prevalence and intensity. A previous assessment of 19 Greek island populations suggested that isolation time and host population density were key predictors of haemogregarines. Here, by combining microscopy and genetic techniques, we extend this previous study to four additional islands: Syros, Folegandros, Santorini and Nea Kameni. We also recorded the prevalence of ticks and mites, definitive hosts for these parasites. The genetically identified haemogregarines are part of a clade with parasites from other lizard species, including some considered as Karyolysus, but others assigned to Hepatozoon. The prevalence of these parasites differed significantly between islands, while their intensity did not. The presence of ticks was associated with endoparasite prevalence, and males were more frequently infected by haemogregarines than females. Combining our data with that of the previous study, we found no significant impact of the island age and area on parasite prevalence. We also confirmed the presence of the unrelated parasite genus Schellackia through microscopy and DNA sequencing, which is the first record of this genus in this host species. Our results further highlight the complexity of host-parasite systems.