Nuclear DNA variation in Galápagos tortoises: a study on introns and ITS based polymorphisms

The Galápagos giant tortoises, Geochelone nigra, are the largest living tortoises and one of the two remaining species of giant tortoises in the world. Within the archipelago, only 1l of the subspecies survive to the present. Most of the subspecies are endangered. The decline of the populations is primarily due to human impact. Buccaneers and whalers began in the 17th century to remove tortoises from the islands and use them as a source of fresh meat. Introduced ani maIs such as feral goat, pigs, dogs, rats and continued poaching represent more threats to the surviving populations. Although these tortoises have become a symbol of the conservation efforts to preserve the unique fauna of the Galápagos Islands, little is known about the levels of genetic divergence between the different subspecies. Previous work on several mtDNA has produced the first DNA based phylogeny of the group and shown the presence of fixed nucleotide differences between most of the 11 surviving subspecies (Caccone et al., 1999; Caccone et al., in prep.). Here we present data on fast evolving nuclear DNA regions. We assayed variation in five nuclear introns, located in the creatine kinase, actin, calmodulin, and aldolase genes, and in the rDNA ITS region. We compare the levels and pattems of genetic variation in nuclear regions with the ones obtained from the mtDNA ones. Moreover, we address thc finding of diagnostic DNA markers, which coupled with the mtDNA ones help diagnose each subspecies.