Giant step forward in Aldabra giant tortoise conservation |22 October 2022

The only surviving tortoises in the wild can be found on the Aldabra Atoll

In a giant step forward to protect Aldabra giant tortoises, researchers at the University of Zurich (UZH) have decoded the entire genome of Aldabrachelys gigantea, one the largest species of tortoise on Earth.

According to the Red List of the International Union for Conservation of Nature, Aldabra giant tortoises are vulnerable to extinction meaning that the species faces a high risk of extinction in the wild.

The only surviving tortoises in the wild can be found on the Aldabra Atoll, a Unesco World Heritage Site in the Seychelles.

The tortoises play a central role in maintaining healthy island ecosystems, and as such, have been successfully employed in rewilding projects on several Western Indian Ocean islands whose endemic giant tortoise species are now extinct.

In other words, Aldabra giant tortoises act as ecosystem engineers to restore degraded island habitats.

Having more tools and resources, especially genetic information, is one of the best ways to ensure the long-term success of the wild and rewilded populations.

Assembling the species’ full genetic code makes it possible to determine genetic differences between individual Aldabra giant tortoises in the wild or in captivity. “This genomic information is crucial in order for breeding programmes in zoos to represent the genetic diversity found in the wild,” says Gözde Çilingir, first author of the study said in a press release from UZH.

Moreover, the data could be used to monitor the genetic diversity of rewilded or restored giant tortoise herds in the Seychelles.

“Being able to measure genetic diversity between individuals within a population is essential as we start to repopulate islands with tortoises in the Seychelles,” Rich Baxter, director of the Indian Ocean Tortoise Alliance commented.

“By mixing and matching tortoises with different genetic makeups, we can ensure the highest possible level of genetic diversity of tortoises on islands, reducing potential harmful effects of inbreeding. Having high genetic diversity also matters for enabling a population's ability to respond to changes such as the effects of climate change.”

The reference genome will also allow researchers to determine the genetic differences between populations on the Aldabra Atoll but also determine from which population a specific tortoise originates from, which could have further use in tracking tortoises in the pet trade.

“We found that most of the genome is similar to other known genomes of tortoises,” says Çilingir. “This means our data will help the conservation efforts for other tortoise species across East Africa and Madagascar.”

The next steps from this work by researchers at UZH, will be to investigate how DNA can be used to determine the age of animals that are still alive, as the exact age of such extremely old tortoises is often unknown, and potentially reveal the secret on how tortoises live so long.

Literature:

Çilingir, F.G., A’Bear, L., Hansen, D., Davis, L.R., Bunbury, N., Ozgul, A., Croll, D., Grossen, C.1. Chromosome-level genome assembly for the Aldabra giant tortoise enables insights into the genetic health of a threatened population. GigaScience, 12 October 2022. DOI: 10.1093/gigascience/giac090

Press release by Indian Ocean Tortoise Alliance/University of Zurich