GENOME-SEQUENCING PROJECT MAY SAVE ONE OF THE WORLD’S LAST SURVIVING SPECIES OF GIANT TORTOISE
The Aldabra giant tortoise is classed as vulnerable, meaning the species is at high risk of going extinct in the wild
Fossil records show that giant tortoises were once widespread. These days, thanks to predation by invasive species such as dogs and cats, and grazing competition from cattle, there are just two species left: the Aldabra giant tortoise, which lives on the Aldabra Atoll in the Seychelles, and the more famous Galápagos giant tortoises, of which there are a number of subspecies. These giant tortoises are considered to be vulnerable to extinction or critically endangered.
Now, an international research team 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, 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].”
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 Zürich Zoo.
By comparing this data with the reference genome, they were able to determine where the zoo-housed animals originally came from.
“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,” said Çilingir.
THE ALDABRA GIANT TORTOISE
The Aldabra giant tortoise can grow to a weight of up to 300kg – half the size of an average dairy cow. Its shell can measure more than 1.2m from front to back.
They are incredibly long-lived. They typically make it into their 100s but one animal that died in a Calcutta zoo in 2006 was reportedly 250 years old. If this is true, it would make it the oldest land vertebrate ever recorded.
Females lay clutches of 10 to 25 eggs between February and May. After incubating for eight months, the hatchlings emerge between October and December.