Zoological Museum, University of Zurich, , Winterthurerstrasse 190, 8057 Zurich, Switzerland.
Philos Trans R Soc Lond B Biol Sci. 2010 Apr 12;365(1543):1127-38. doi: 10.1098/rstb.2009.0311.
Small and isolated island populations provide ideal systems to study the effects of limited population size, genetic drift and gene flow on genetic diversity. We assessed genetic diversity within and differentiation among 19 mockingbird populations on 15 Galápagos islands, covering all four endemic species, using 16 microsatellite loci. We tested for signs of drift and gene flow, and used historic specimens to assess genetic change over the last century and to estimate effective population sizes. Within-population genetic diversity and effective population sizes varied substantially among island populations and correlated strongly with island size, suggesting that island size serves as a good predictor for effective population size. Genetic differentiation among populations was pronounced and increased with geographical distance. A century of genetic drift did not change genetic diversity on an archipelago-wide scale, but genetic drift led to loss of genetic diversity in small populations, especially in one of the two remaining populations of the endangered Floreana mockingbird. Unlike in other Galápagos bird species such as the Darwin's finches, gene flow among mockingbird populations was low. The clear pattern of genetically distinct populations reflects the effects of genetic drift and suggests that Galápagos mockingbirds are evolving in relative isolation.
小而孤立的岛屿种群为研究有限的种群规模、遗传漂变和基因流对遗传多样性的影响提供了理想的系统。我们使用 16 个微卫星位点评估了 15 个加拉帕戈斯群岛上的 19 个嘲鸫种群内的遗传多样性和种群间的分化情况，涵盖了所有四个特有物种。我们检测了漂变和基因流的迹象，并利用历史标本评估了过去一个世纪的遗传变化，并估计了有效种群规模。种群内的遗传多样性和有效种群规模在岛屿种群之间差异很大，与岛屿大小密切相关，表明岛屿大小是有效种群规模的良好预测指标。种群间的遗传分化显著，且随地理距离的增加而增加。一个世纪的遗传漂变并没有改变整个群岛范围内的遗传多样性，但遗传漂变导致小种群遗传多样性的丧失，尤其是在濒危的弗洛雷纳嘲鸫仅剩的两个种群之一中。与达尔文雀等其他加拉帕戈斯鸟类不同，嘲鸫种群之间的基因流很低。遗传上明显不同的种群的清晰模式反映了遗传漂变的影响，表明加拉帕戈斯嘲鸫在相对隔离的环境中进化。
