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Giant Galápagos tortoises; molecular genetic analyses identify a trans-island hybrid in a repatriation program of an endangered taxon

Michel C Milinkovitch1*, Daniel Monteyne1, Michael Russello2, James P Gibbs3, Howard L Snell4, Washington Tapia5, Cruz Marquez6, Adalgisa Caccone2 and Jeffrey R Powell2

Author Affiliations

1 Laboratory of Evolutionary Genetics, Institute for Molecular Biology & Medicine, Université Libre de Bruxelles, Rue Jeener & Brachet 12, 6041 Gosselies, Belgium

2 Department of Ecology & Evolutionary Biology, Yale Institute for Biospherics Studies ECOSAVE, Yale University, New Haven, CT 06520-8106, USA

3 College of Environmental Science and Forestry, State University of New York, Syracuse, NY 13210, USA

4 Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA

5 Galápagos National Park Service, Puerto Ayora, Galápagos Islands, Ecuador

6 Charles Darwin Foundation, Puerto Ayora, Galápagos Islands, Ecuador

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BMC Ecology 2007, 7:2  doi:10.1186/1472-6785-7-2

Published: 15 February 2007



Giant Galápagos tortoises on the island of Española have been the focus of an intensive captive breeding-repatriation programme for over 35 years that saved the taxon from extinction. However, analysis of 118 samples from released individuals indicated that the bias sex ratio and large variance in reproductive success among the 15 breeders has severely reduced the effective population size (Ne).


We report here that an analysis of an additional 473 captive-bred tortoises released back to the island reveals an individual (E1465) that exhibits nuclear microsatellite alleles not found in any of the 15 breeders. Statistical analyses incorporating genotypes of 304 field-sampled individuals from all populations on the major islands indicate that E1465 is most probably a hybrid between an Española female tortoise and a male from the island of Pinzón, likely present on Española due to human transport.


Removal of E1465 as well as its father and possible (half-)siblings is warranted to prevent further contamination within this taxon of particular conservation significance. Despite this detected single contamination, it is highly noteworthy to emphasize the success of this repatriation program conducted over nearly 40 years and involving release of over 2000 captive-bred tortoises that now reproduce in situ. The incorporation of molecular genetic analysis of the program is providing guidance that will aid in monitoring the genetic integrity of this ambitious effort to restore a unique linage of a spectacular animal.