Jensen Evelyn L, Edwards Danielle L, Garrick Ryan C, Miller Joshua M, Gibbs James P, Cayot Linda J, Tapia Washington, Caccone Adalgisa, Russello Michael A
Department of Biology University of British Columbia Okanagan Kelowna British Columbia Canada.
Present address: Department of Biology Queen's University Kingston Ontario Canada.
Evol Appl. 2018 Aug 13;11(10):1811-1821. doi: 10.1111/eva.12682. eCollection 2018 Dec.
Population genetic theory related to the consequences of rapid population decline is well-developed, but there are very few empirical studies where sampling was conducted before and after a known bottleneck event. Such knowledge is of particular importance for species restoration, given links between genetic diversity and the probability of long-term persistence. To directly evaluate the relationship between current genetic diversity and past demographic events, we collected genome-wide single nucleotide polymorphism data from prebottleneck historical (c.1906) and postbottleneck contemporary (c.2014) samples of Pinzón giant tortoises (; =25 and 149 individuals, respectively) endemic to a single island in the Galapagos. Pinzón giant tortoises had a historically large population size that was reduced to just 150-200 individuals in the mid 20th century. Since then, Pinzón's tortoise population has recovered through an ex situ head-start programme in which eggs or pre-emergent individuals were collected from natural nests on the island, reared ex situ in captivity until they were 4-5 years old and subsequently repatriated. We found that the extent and distribution of genetic variation in the historical and contemporary samples were very similar, with the latter group not exhibiting the characteristic genetic patterns of recent population decline. No population structure was detected either spatially or temporally. We estimated an effective population size ( ) of 58 (95% CI = 50-69) for the postbottleneck population; no prebottleneck point estimate was attainable (95% CI = 39-infinity) likely due to the sample size being lower than the true . Overall, the historical sample provided a valuable benchmark for evaluating the head-start captive breeding programme, revealing high retention of genetic variation and no skew in representation despite the documented bottleneck event. Moreover, this work demonstrates the effectiveness of head-starting in rescuing the Pinzón giant tortoise from almost certain extinction.
与种群数量迅速下降的后果相关的群体遗传学理论已相当完善，但很少有实证研究在已知的瓶颈事件前后进行抽样。鉴于遗传多样性与长期存续概率之间的联系，此类知识对于物种恢复尤为重要。为了直接评估当前遗传多样性与过去种群动态事件之间的关系，我们收集了加拉帕戈斯群岛一个岛屿特有的平松岛巨型陆龟（分别为25只和149只个体）在瓶颈事件发生前的历史样本（约1906年）和瓶颈事件发生后的当代样本（约2014年）的全基因组单核苷酸多态性数据。平松岛巨型陆龟历史上种群数量庞大，在20世纪中叶减少到仅150 - 200只个体。从那时起，平松岛的陆龟种群通过一个迁地保育预育计划得以恢复，该计划从岛上的自然巢穴收集龟卵或即将孵化的个体，在圈养环境中迁地饲养至4 - 5岁，随后放归自然。我们发现历史样本和当代样本中遗传变异的程度和分布非常相似，当代样本未表现出近期种群数量下降的典型遗传模式。在空间或时间上均未检测到种群结构。我们估计瓶颈事件发生后种群的有效种群大小（Ne）为58（95%置信区间 = 50 - 69）；由于样本量低于真实的Ne，无法获得瓶颈事件发生前的Ne点估计值（95%置信区间 = 39 - 无穷大）。总体而言，历史样本为评估预育圈养繁殖计划提供了有价值的基准，揭示了尽管经历了记录在案的瓶颈事件，但遗传变异仍高度保留且代表性无偏差。此外，这项工作证明了预育计划在将平松岛巨型陆龟从几乎确定的灭绝中拯救出来方面的有效性。
