BACKGROUND 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). RESULTS 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. CONCLUSION 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.

中文翻译：

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加拉帕戈斯巨龟；分子遗传学分析在濒临灭绝的分类单元的遣返计划中确定了跨岛杂交体。

背景技术在超过35年的时间里，密集的圈养繁殖遣返计划一直关注着西班牙埃斯帕尼奥拉岛上的巨型加拉帕戈斯陆龟，这使该分类群免于灭绝。但是，对来自释放个体的118个样本的分析表明，这15个育种者之间的性别偏见和生殖成功的巨大差异严重降低了有效种群数量（Ne）。结果我们在这里报告，对另外473只圈养的乌龟的分析表明，该个体（E1465）具有15个育种者中未发现的核微卫星等位基因。统计分析并结合了主要岛屿上来自所有种群的304名现场抽样个体的基因型，表明E1465最有可能是Española雌龟和Pinzón岛雄性龟的杂交体，由于人类的运输，它们可能出现在Española上。结论保证将E1465及其父亲和可能的（半）兄弟姐妹都搬走，以防止在这个具有特定保护意义的分类单元中进一步污染。尽管发现了这种单一污染，但值得注意的是，要强调这项遣返计划在近40年的成功中所取得的成功，其中涉及释放了2000多只现成繁殖的圈养乌龟。