Genome sequence of the Seychelles giant tortoise


The aldabra giant tortoise (Aldabrachelys gigantea) is one of only two species of these huge reptiles left in the world. It has its habitat in Aldabra – an island in the Seychelles archipelago, in the Indian Ocean – and is found in the list of endangered species. According to the fossil record, giant tortoises existed on every continent except Antarctica and Australia. Today, there are only two species of giant tortoises left: the Aldabra and the Galapagos.

Aldabra giant tortoise

The Aldabra tortoise reaches a weight up to 300 kg and can live for over 100 years, with an individual supposedly reaching 250 years of age. But this gentle giant is “vulnerable”, warns the International Union for Conservation of Nature, meaning the species is at high risk of extinction in the wild. Having more tools and resources, especially genetic information, is one of the best ways to ensure the long-term success of this amazing creature.

Today, an international team of researchers has made a major contribution to the advancement of conservation plans. Gözde Çilingir, a researcher at the University of Zurich (Switzerland), and colleagues from several countries have just completed and published a high-quality genomic sequence, which will help secure the future of this species.

The researchers used several state-of-the-art methods to obtain a “chromosomal scale” representation of the Aldabra giant tortoise genome. Their results were published in the journal open science GigaScience.

According to Çilingir, the book’s lead author, the study reveals that “Most of this turtle’s genome is similar to other known Testudine genomes. —the order which includes tortoises and tortoises—. Turtle species are evolutionarily closely related to each other, so our data will be extremely useful not just for the Aldabra tortoise, but for all turtles. turtles of East Africa and Madagascar », highlighted.

genome sequence

The authors sequenced the genome of the Aldabra giant tortoise at the chromosomal scale. This term is used when the genome sequence data is an almost uninterrupted representation of the sequence of more than two billion genetic “letters”, and the sequences line up in the same order as they appear on the actual chromosomes.

Previous genomic sequences not only had many more gaps, but the sequence data was also placed on what were called “scaffolds”: sequences that are arranged in relative order to each other, but which are not completely anchored in the space referring to the chromosome.

Detailed genetic information

Current chromosomal-scale genomic sequences provide such detailed genomic information that they allow researchers to continue to more accurate genetic variation in wild and captive turtles.

Demonstrate how the new reference genome can be used in practical conservation efforts and breeding, the authors determined the sequence of thirty giant tortoises from the wild population and two individuals from the Zurich Zoo. Using this data in combination with the high-quality reference genome, they were able to determine where the animals housed at the zoo on Aldabra Atoll came from.

Having a high-quality reference genome for this species will help answer a number of biological questions, including why the species grows to such enormous size. With a an appetite proportionate to its size, Giant tortoises play a fundamental role in the formation of a typical island landscape, due to the enormous amount of vegetation they consume.

Indeed, returning giant tortoises to their natural environment and helping them to thrive may allow them to serve as ecological substitutes for extinct giant tortoises on islands in the western Indian Ocean, due to their similar central role in their ecosystems, according to the authors.

Aldabra giant tortoises act as ecosystem engineers restore degraded island habitats, including outside their original range. Restoring natural mechanisms of environmental protection is an essential element to do much more than reduce the risk of extinction of individual species, they conclude.

Character font: SINC Agency

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