Department of Biology, University of Mississippi Oxford, Mississippi, 38677.
Department of Ecology and Evolutionary Biology, Yale University New Haven, Connecticut, 06520.
Ecol Evol. 2015 Feb;5(3):676-94. doi: 10.1002/ece3.1388. Epub 2015 Jan 13.
Long-term population history can influence the genetic effects of recent bottlenecks. Therefore, for threatened or endangered species, an understanding of the past is relevant when formulating conservation strategies. Levels of variation at neutral markers have been useful for estimating local effective population sizes (N e ) and inferring whether population sizes increased or decreased over time. Furthermore, analyses of genotypic, allelic frequency, and phylogenetic information can potentially be used to separate historical from recent demographic changes. For 15 populations of Galápagos giant tortoises (Chelonoidis sp.), we used 12 microsatellite loci and DNA sequences from the mitochondrial control region and a nuclear intron, to reconstruct demographic history on shallow (past ∽100 generations, ∽2500 years) and deep (pre-Holocene, >10 thousand years ago) timescales. At the deep timescale, three populations showed strong signals of growth, but with different magnitudes and timing, indicating different underlying causes. Furthermore, estimated historical N e of populations across the archipelago showed no correlation with island age or size, underscoring the complexity of predicting demographic history a priori. At the shallow timescale, all populations carried some signature of a genetic bottleneck, and for 12 populations, point estimates of contemporary N e were very small (i.e., < 50). On the basis of the comparison of these genetic estimates with published census size data, N e generally represented ∽0.16 of the census size. However, the variance in this ratio across populations was considerable. Overall, our data suggest that idiosyncratic and geographically localized forces shaped the demographic history of tortoise populations. Furthermore, from a conservation perspective, the separation of demographic events occurring on shallow versus deep timescales permits the identification of naturally rare versus newly rare populations; this distinction should facilitate prioritization of management action.
长期的种群历史可能会影响近期瓶颈的遗传效应。因此，对于受到威胁或濒危的物种，在制定保护策略时，了解过去的情况是相关的。中性标记物的变异水平可用于估计局部有效种群大小 (N e )，并推断种群大小是否随时间增加或减少。此外，对基因型、等位基因频率和系统发育信息的分析可用于将历史变化与近期的种群动态变化区分开来。我们使用了 12 个微卫星位点和线粒体控制区以及核内含子的 DNA 序列，对加拉帕戈斯巨龟 (Chelonoidis sp.) 的 15 个种群进行了分析，以重建浅层（过去∽100 代，∽2500 年）和深层（更新世前，>1 万年前）时间尺度上的种群历史。在深层时间尺度上，三个种群表现出强烈的增长信号，但幅度和时间不同，表明存在不同的潜在原因。此外，对群岛上所有种群的历史 N e 估计值与岛屿年龄或大小均无相关性，这突出表明了预测种群历史的复杂性。在浅层时间尺度上，所有种群都存在遗传瓶颈的特征，而对于 12 个种群，当代 N e 的点估计值非常小（即<50）。根据这些遗传估计值与已发表的种群数量数据的比较，N e 通常代表了种群数量的∽0.16。然而，种群之间的这种比例差异很大。总的来说，我们的数据表明，特殊的、局部的力量塑造了巨龟种群的种群历史。此外，从保护的角度来看，在浅层和深层时间尺度上发生的种群动态变化的分离可以识别自然罕见的种群和新出现的罕见种群；这种区别应该有助于优先采取管理行动。
