Parasites at the Summit: Unexpected Geographic Distribution of the Blood Parasite Lineage Found in the Endangered Giant Lizard of Tenerife

ABSTRACT Host–parasite interactions can have disproportionate consequences in small, isolated populations, particularly on oceanic islands where endemic species face multiple threats. The endangered speckled lizard Gallotia intermedia , endemic to Tenerife (Canary Islands), persists in only two small populations, yet its parasite fauna has remained unexplored. We combined microscopic screening and molecular phylogenetic analyses to characterize blood parasites infecting G. intermedia from the coastal cliffs of Montaña de Guaza and to place these infections in a broader biogeographic context. We detected apicomplexan parasites of the genus Karyolysus infecting 53.6% of G. intermedia and 100% of the syntopic congener Gallotia galloti . All infected G. intermedia harbored a single parasite lineage (haplotype Gi19), and deep amplicon sequencing revealed no evidence of cross‐infection with haplotypes circulating in G. galloti at this locality. Comparative analyses showed that haplotype Gi19 is widespread in G. galloti throughout Tenerife, including extreme high‐elevation sites, but was absent in samples from neighbour islands of Gran Canaria and La Palma. Infection intensity in G. intermedia was low, suggesting effective immune control and a long‐standing host–parasite association. Higher prevalence in immature lizards indicates age‐related vulnerability. The broad geographic distribution of Gi19 relative to the lizard's current restricted range supports the hypothesis that parasite diversity reflects historical host distributions. These results provide the first baseline of blood parasites in G. intermedia and highlight the importance of parasitological data for conservation assessments of threatened insular reptiles.