The genomes of two giant tortoises - including ‘Lonesome George’ - provide insights into the animals’ size and long lifespans, reports a paper published online this week in Nature Ecology & Evolution.
Lonesome George was the iconic last member of the now extinct Pinta Island tortoises (Chelonoidis abingdonii), from the Galapagos Islands.
Carlos Lopez-Otin, Adalgisa Caccone and colleagues sequenced the genomes of Lonesome George and one Aldabra giant tortoise. The Aldabra giant tortoise (Aldabrachelys gigantea) is the Indian Ocean’s only living species of giant tortoise. Comparing these to the genomes of related species, they find signatures of positive selection for, and expansion of, gene families associated with metabolism regulation and immune response. These, the authors suggest, could be linked to the exceptionally large sizes and long lives of these tortoises.
Long-lived organisms are theoretically at a higher risk of cancer and the authors found that, in turtles, tumour suppressors are expanded compared to other vertebrates, as well as giant-tortoise-specific alterations in two genes whose overexpression is known to contribute to cancer. Although these findings might point to a giant-tortoise-specific cancer mechanism, tumours are very rare in turtles so further studies are needed to determine if these genomic features are associated with tumour development.
These data will help improve our understanding of giant tortoise biology and aid efforts to conserve other giant tortoises in the Galapagos Islands, the authors conclude.