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Reference for tortoise genotype established   |01 June 2023

Reference for tortoise genotype established   

Dr Cilingir addressing the audience (Photos: Louis Toussaint)

 Aldabra tortoises’ genetic information differ from East and West tortoises


Dr Godze Cilingir, a post-doctoral researcher from the University of Zurich, has presented a research done in collaboration with the Seychelles Islands Foundation (SIF), to discover a reference that will be used for future tortoise genotype research, which is to establish the genetic constitution of an individual organism.

A presentation held at the Kaz Zanana on Tuesday, led by Dr Cilingir, outlined the importance of the recently discovered genotype.

She stated that one of the main aims of the project was to come up with genetic tools that will help research understand genetic diversity that remains in the wild population.

“By using this information, we can better manage the future of rewilding projects of Aldabra giant tortoises,” she stated.

SIF’s chief executive, Dr Frauke Fleischer-Dogley, explained that the genotype of a tortoise is like the bible for tortoise research as it reveals everything there is to know about a tortoise. “Seychelles does not have the technology to be able to perform these DNA research so that is why we have to partner with universities from overseas that have the facilities and the labs and the researchers that have worked on similar projects.”

In addition, the genotype will now be used for all future researches to determine any changes or mutations in the genetic molecule structure of a tortoise.

The results from the research show that the Aldabra tortoises do have a difference in their genetic information of East and West tortoises. “This means that there is a certain movement and the way that the information is transmitted so we need to look for what way it has happened,” she explained.

The study started in early 2020 and there was individual sampling which was exported from Aldabra giant tortoises, which originated in 1940’s-1950. This was the reference genome sequencing and assembling it. A total of 30 Aldabra tortoises were sampled which was incorporated in the study which showed the genetic structure of the wild population using the new tool produced.

In addition, there was a genetic bottleneck, which means that there was a loss of genetic diversity due to several reasons such as exploitation or natural causes. The assumption is that something happened causing the number of individuals to decrease significantly.

“This will cause a random loss of genetic diversity,” she explained.

Usually in nature this happens gradually, but with the genetic bottleneck, this happens abruptly and populations and species do not have time to adapt to the loss of diversity. “Mutation rate is not that high in general so the changes in genome do not happen that quickly. In order for species to cope with these changes they need time. This could be detrimental to some species.”

In the Aldabra giant tortoise’s case, the number was close to thousands in the late 19th century and with the restrictive measures, they bounced upwards to 100,000 individuals so there is a stable population of tortoises in Aldabra.

“However, the genetic effects of this bottleneck may remain, because their numbers are high but genetic variation wise, we cannot restore that generation gap, it is lost.” The idea was to create a tool to access this loss and how well to better manage the species.

Dr Cilingir explained that this is the first time she started working with land dwelling tortoises and discussed the fact that there are two types of giant tortoises left in the world. “It is a real adventure for me to start working with tortoises, especially the Aldabra giant tortoises.”

One of the main emphasis is that with the aged tortoises and the referenced genomes, tortoises who are 60 and above, their blood sample can be calibrated to rewind the clock and determine the ages and sex identification of other tortoises.


Sunny Esparon

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