Seychelles’ giant tortoises: New genetics study by University of Zurich on Silhouette’s reptiles 

Baxter said that Silhouette is quite an interesting case because this is where some individuals with unique shell shapes are based. (D. Desnousse)

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A team from the University of Zurich has started a project to better understand the genetics of the individual giant tortoises found on Silhouette Island in Seychelles.  

The team is led by Dr Gözde Çilingir, who is undertaking the genetic sequencing.

Every blood sample collected from the giant tortoises at Grand Barbe, Silhouette, will be placed in a database to see if there is a difference from the ones from the Aldabra Atoll.

The data will also be used in the Aldabra giant tortoise census currently conducted by the Ministry of Environment and Indian Ocean Tortoise Alliance representative (IOTA). The samples will be brought to the University of Zurich, Switzerland for analysis.

According to IOTA’s director, Rich Baxter, “Silhouette is quite an interesting case because this is where some individuals with unique shell shapes are based. Unfortunately, one passed away but we have managed to find a saddleback and we have taken the blood sample from him and we’ll be analysing it in due course to see how it fits with the general distribution of the tortoises that we have got blood samples from.”

IOTA is also advising Silhouette Island staff on the behaviour of the captive tortoises that they have, like learning about quarantine before putting them in the wild.

“In the coming years hopefully we can increase the wild population from that captive population and hopefully, in time, we will get a naturally regulated population on Silhouette,” said Baxter.

He added that “we check if it could be a different subspecies or something like that, we have seen it in Mauritius where some individuals have different genetic make-up and they could just be very old ones from Aldabra since there were some giant tortoises that were taken from Aldabra to Mauritius in 1870.”

Another component of the project is to understand how the tortoises age, and for this blood samples will be taken and compared to the sample that the team has already, using a special technique.

Meanwhile, as the work continues to understand the genetics of the tortoises, many people have been looking at the shells of the tortoises saying that there are subspecies.

According to a researcher from the University of Zurich, Dr Dennis Hansen, “whenever you look at the genetics there are no differences, it’s all down to what the tortoises eat. Especially the tortoises that are kept as pets in Seychelles in certain places compared to those kept in the wild. Their variation is even much larger than on Aldabra because you have tortoises living in unnatural conditions, being fed things that they wouldn’t eat in the wild. There have been three studies so far showing that there’s not enough variation to even start thinking of subspecies.”

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