Intestinal helminths of the Balearic lizard Podarcis lilfordi (Günther, 1874): morphology, genetics and prevalence

Abstract Many insular lacertids represent endemic lineages and are known to harbour unique assemblages of endemic intestinal parasites, making them an interesting system to study host-parasite dynamics. Here, we reassessed the diversity, distribution and prevalence of intestinal helminths infecting the endemic Balearic lizard Podarcis lilfordi across eight insular populations of Mallorca and Cabrera archipelagos. Using a combination of coprological screening, morphological analyses and molecular characterization, we confirmed the presence of two helminth species, Spauligodon cabrerae and Parapharyngodon lilfordi (Oxyuroidea:Pharyngodoninae), both originally described in the late 1980s. No additional helminth taxa were observed, indicating a poorly diverse parasite community compared to historical reports. Phylogenetic analyses based on the cytochrome c oxidase subunit I sequences, obtained from newly designed primers, supported a clear species-level identification and indicated low genetic variation in Par. lilfordi and more pronounced structuring in S. cabrerae across insular populations. Parasite prevalence was high (52%), with Par. lilfordi occurring across all eight islands, whereas S. cabrerae was restricted to the largest islands of Dragonera and Cabrera. Specimen coinfection with both nematode species was observed on both islands. Infection probability was not associated with lizard body size, sex or body condition, which is consistent with a low virulence of these oxyurids, likely favoured by coevolutionary dynamics and temporal stability of the symbiosis in these high-density lizard populations. Overall, this study provides an updated assessment of parasite diversity in Pod. lilfordi and underscores the need for expanded sampling and genomic approaches to better understand host–parasite evolution in insular environments.