Biogeography of Parasitic Nematode Communities in the Galapagos Giant Tortoise: Implications for Conservation Management

The Galapagos giant tortoise is an icon of the unique, endemic biodiversity of Galapagos, but little is known of its parasitic fauna. We assessed the diversity of parasitic nematode communities and their spatial distributions within four wild tortoise populations comprising three species across three Galapagos islands, and consider their implication for Galapagos tortoise conservation programmes. Coprological examinations revealed nematode eggs to be common, with more than 80% of tortoises infected within each wild population. Faecal samples from tortoises within captive breeding centres on Santa Cruz, Isabela and San Cristobal islands also were examined. Five different nematode egg types were identified: oxyuroid, ascarid, trichurid and two types of strongyle. Sequencing of the 18S small-subunit ribosomal RNA gene from adult nematodes passed with faeces identified novel sequences indicative of rhabditid and ascaridid species. In the wild, the composition of nematode communities varied according to tortoise species, which co-varied with island, but nematode diversity and abundance were reduced or altered in captive-reared animals. Evolutionary and ecological factors are likely responsible for the variation in nematode distributions in the wild. This possible species/island-parasite co-evolution has not been considered previously for Galapagos tortoises. We recommend that conservation efforts, such as the current Galapagos tortoise captive breeding/rearing and release programme, be managed with respect to parasite biogeography and host-parasite co-evolutionary processes in addition to the biogeography of the host.