Fossil records show that giant tortoises were once commonly found scattered throughout Madagascar and other islands across the Indian Ocean. These days, thanks to predation by foreign species such as dogs and cats and grazing competition from cattle, there are just two species left: the Aldabra giant tortoise and the Galápagos giant tortoise. Both are considered to be vulnerable to extinction or critically endangered.
Now, a team of international researchers has made a breakthrough that could help halt the decline of at least one of the species, after producing a highly detailed genome sequence of the Aldabra giant tortoise.
The discovery will help researchers' efforts to breed the animals and strengthen their numbers and while also allowing them to study their biology and anatomy in greater detail.
“Genomic information is important for breeding efforts in zoos to maintain the genetic diversity that is present in the wild,” said lead researcher Dr Gözde Çilingir from the University of Zürich.
“We revealed that most of the genome is similar to other known genomes of Testudines (the order comprising turtles and tortoises).
"Tortoise species are evolutionarily closely related to each other, and therefore our data will be tremendously helpful not only for the Aldabra tortoise but for all east African and Madagascan tortoises."
The genome produced by the team is the most detailed to date and accurately shows the sequence of more than two billion genetic letters. Information of this accuracy and detail will enable researchers to more reliably track genetic variation in wild and captive tortoises.
To test drive the technique, the team sequenced the genomes of 30 tortoises living in the wild in Madagascar and two currently homed in Zurich Zoo.
By comparing this data with the reference genome, they were able to determine where the zoo-housed animals originally came from.
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