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Genetic study will help protect the Aldabra giant tortoise

Experts at the University of Zurich have now decoded the genome of the Aldabra giant tortoise. The research will not only help to secure a future for these tortoises in the wild, but could also help to explain how these remarkable creatures can live for more than 100 years. 

“The Aldabra giant tortoise (Aldabrachelys gigantea) is one of only two giant tortoise species left in the world. The species is endemic to Aldabra Atoll in Seychelles and is listed as Vulnerable on the International Union for Conservation of Nature Red List due to its limited distribution and threats posed by climate change,” wrote the study authors. 

“Genomic resources for A. gigantea are lacking, hampering conservation efforts for both wild and ex situ populations. A high-quality genome would also open avenues to investigate the genetic basis of the species’ exceptionally long life span.”

Aldabra giant tortoises serve as ecosystem engineers that can help restore degraded island habitats. They have been introduced to several Western Indian Ocean islands whose endemic giant tortoises are now extinct. Tools such as genetic information can help to ensure the long-term success of Aldabra tortoise populations.

The Zurich team has now succeeded in sequencing the genome of an Aldabra giant tortoise. This will help to distinguish genetic differences between individual animals. 

“This genomic information is crucial in order for breeding programs in zoos to represent the genetic diversity found in the wild,” said study first author Gözde Çilingir, who noted that the data could be used for studies on other tortoise species. 

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

“We assembled the first high-quality, chromosome-level annotated genome for the Aldabra giant tortoise, resulting in one of the best-assembled chelonian genomes. Chromosomal collinearity analyses revealed a high degree of conservation even among distantly related tortoise species. We showed that the high-quality resources can be combined with low-coverage resequencing to gain crucial insights into the genetic structure within Aldabra, as well as to resolve the exact origin of zoo-housed individuals,” wrote the study authors. 

“Understanding levels of genomic diversity in both native and ex situ populations is crucial to inform rewilding efforts and prioritize conservation efforts.” 

“Furthermore, genome-wide analyses of polymorphism can be used to assess the presence of deleterious mutations endangering the long-term health of populations and will allow high-confidence estimates of inbreeding based on runs of homozygosity. Finally, given the exceptionally long life span and large body size of A. gigantea, the high-quality genome will inform comparative genomics studies focused on the genetic underpinnings of aging and gigantism.”

The study is published in the journal GigaScience.

Image Credit: Dennis Hansen, University of Zurich

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By Chrissy Sexton, Staff Writer

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