Evolution and community structure of parasites in Galápagos giant tortoises

A central theme in ecology is to understand the distribution and abundance of organisms and the factors influencing these patterns. This thesis investigated the taxonomic identity and biogeography of blood parasites, Amblyomma ticks and gastro-intestinal helminths of Galápagos tortoise, Chelonoidis spp. Blood parasite and ticks were assessed for co-phylogeographic patterns with their tortoise host. The patterns of helminths diversity was examined and whether factor such as host colonization history and local ecology determine their distribution and community composition. Microscope and phylogenetic analysis of 18S rDNA identified the blood parasite as a haemogregarine of the genus Hepatozoon. It was represented by just two haplotypes restricted to the northern volcanoes of Isabela. Thirty-seven tortoise blood samples yielded the same haemogregarine haplotype for Alcedo and Wolf volcanoes, unique to Chelonoidis spp. The only tortoise that was haemogregarine positive from Darwin yielded a different haplotype, related to haemogregarines reported from Galápagos land iguanas. Molecular analysis of the COI gene of Amblyomma ticks revealed 3 different species, one infesting tortoises of Alcedo and Wolf volcanoes, one in tortoises of Santiago and one of tortoises from Pinzón. Galápagos tortoise ticks from Alcedo and Wolf has been described before as A. unsingeri, while tortoise ticks from Santiago and Pinzón have been described as belonging to A. pilosum. The restricted distribution of tortoise haemogregarines impeded testing them for co-phylogeographic patterns. Ticks showed no agreement with the phylogeography of their tortoise host. Coprological and metabarcoding methods revealed the presence of Platyhelminths, Acanthocephala, and Nematoda. Metabarcoding however, exceeded the traditional method in sensitivity for parasite detection and identification. At least seven families of Nematoda were identified with most taxa widespread across the Galápagos archipelago suggesting little effect of host colonisation for the common taxa in their distribution. At least three genera were found only on one or two islands suggesting their potential local acquisition or exclusion. These results are relevant for understanding the diversity and ecology of Chelonoidis spp. parasites, the management andconservation of this reptile and as a model for other wild species.