Hurston H, Voith L, Bonanno J, Foufopoulos J, Pafilis P, Valakos E, Anthony N
Department of Biological Sciences, University of New Orleans, New Orleans, LA 70148, USA.
Mol Phylogenet Evol. 2009 Aug;52(2):395-405. doi: 10.1016/j.ympev.2009.03.028. Epub 2009 Apr 5.
Landbridge islands offer unique opportunities for understanding the effects of fragmentation history on genetic variation in island taxa. The formation of islands by rising sea levels can be likened to a population bottleneck whose magnitude and duration is determined by island area and time since isolation, respectively. The Holocene landbridge islands of the Aegean Sea (Greece) were formed since the last glacial maximum and constitute an ideal system for disentangling the effects of island area, age and geographic isolation on genetic variability. Of the many reptile species inhabiting this island system, the Aegean wall lizard Podarcis erhardii is an excellent indicator of fragmentation history due to its widespread distribution and poor over-water dispersal abilities. In this study, we utilize a detailed record of Holocene fragmentation to investigate the effects of island history on wall lizard mitochondrial and nuclear microsatellite diversity. Findings show that the spatial distribution of mitochondrial haplotypes reflects historical patterns of fragmentation rather than geographic proximity per se. In keeping with neutral bottleneck theory, larger and younger islands retain more nuclear genetic variation than smaller, older islands. Conversely, there is no evidence of an effect of isolation by distance or effect of distance to the nearest larger landmass on genetic variability, indicating little gene flow between islands. Lastly, population-specific measures of genetic differentiation are inversely correlated with island area, suggesting that smaller islands exhibit greater divergence due to their greater susceptibility to drift. Taken together, these results suggest that both island area and time since isolation are important predictors of genetic variation and that these patterns likely arose through the progressive fragmentation of ancestral diversity and the ensuing cumulative effects of drift.
陆桥岛屿为理解破碎化历史对岛屿生物分类群遗传变异的影响提供了独特的机会。海平面上升形成岛屿的过程可以比作种群瓶颈，其规模和持续时间分别由岛屿面积和自隔离以来的时间决定。爱琴海（希腊）的全新世陆桥岛屿自末次盛冰期以来形成，是一个理想的系统，用于厘清岛屿面积、年龄和地理隔离对遗传变异性的影响。在栖息于这个岛屿系统的众多爬行动物物种中，爱琴海壁蜥Podarcis erhardii因其广泛分布和较差的水上扩散能力，是破碎化历史的一个极佳指标。在本研究中，我们利用全新世破碎化的详细记录，来调查岛屿历史对壁蜥线粒体和核微卫星多样性的影响。研究结果表明，线粒体单倍型的空间分布反映的是破碎化的历史模式，而非地理上的接近程度本身。与中性瓶颈理论一致，较大且较年轻的岛屿比较小且较古老的岛屿保留了更多的核遗传变异。相反，没有证据表明距离隔离效应或到最近较大陆块的距离对遗传变异性有影响，这表明岛屿之间几乎没有基因流动。最后，种群特异性的遗传分化测量值与岛屿面积呈负相关，这表明较小的岛屿由于对漂变更敏感而表现出更大的分化。综上所述，这些结果表明，岛屿面积和自隔离以来的时间都是遗传变异的重要预测因素，并且这些模式可能是通过祖先多样性的逐渐破碎化以及随之而来的漂变累积效应产生的。
