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  • Aldabra Riesenschildkröte

    Research at the Zoo: Giant Tortoise Genome Decoded

    Thanks to Hermania, the oldest Aldabra giant tortoise at Zoo Zurich, researchers have succeeded in decoding the genome for this species for the first time. This is a milestone for informing rewilding projects.

    The Aldabra giant tortoise Hermania at Zoo Zurich: she has been living here since 1955, well over 60 years. Hermania probably hatched while still in her natural habitat, the Aldabra Atoll.

    Filling the role of extinct species

    The natural distribution of Aldabra giant tortoises is restricted to the Aldabra Atoll. Today, these tortoises also fulfill an important role in the ecosystem of other islands. These islands were once inhabited by other giant tortoise species that are nowadays extinct. To reinstate ecosystem functioning, Aldabra tortoises have been released to other islands.

    Incorporating genetic management favoring genetically diverse groups of tortoises is important to maintain healthy populations on such projects.

    Video: Zoo Zürich, Nicole Schnyder

    Genome decoded

    Until now, a lack of genome-wide data to genetically distinguish the Aldabra giant tortoises from one another prevented a better understanding of their population genetic structure. Thanks to Hermania, researchers were able to decode the genome of this species. Based on this reference genome sequenced from Hermania, other giant tortoises will be matched in current and future comparisons.

    By comparing thirty individuals from the Aldabra Atoll, researchers were able to identify genetic differences within the Atoll’s islands. In addition, they were also able to determine Hermania’s island of origin.


    To maximize genetic diversity, animals from different genetic groups should be used for reintroductions. Photo: Zoo Zürich, Corinne Invernizzi

    Who will be released where?

    The now available knowledge on the genetic diversity of Aldabra giant tortoises will help future breeding to bring together suitable individuals. The genetic diversity is important to build a healthy population. In this way, the survival of the species can be ensured in the long term.

    Forscherin Gözde Cilingir mit Aldabra-Riesenschildkröte im Zoo Zürich.

    Gözde Cilingir, author of the new study, visits the Aldabra giant tortoises at Zoo Zurich. Foto: Zoo Zürich, Sandro Schönbächler

    Furthermore, the new data can help scientists learn more about the long lifespan of this species and to investigate how the age of animals that are still alive can be determined based on natural molecular processes in the DNA. In the case of long-lived animals like the Aldabra giant tortoises, the exact age of many animals is still unknown.


    Thanks to Hermania, one of the oldest animals at Zoo Zurich, researchers have now decoded the complete genome of the species. Photo: Zoo Zürich, Leyla Davis

    Information on the genome of Aldabra giant tortoises will also help to better understand the genome and genetic variability of other closely related species. More than half of the known turtle species are now threatened with extinction.

    If you want to read more about the study, you'll find the paper here: