García-Verdugo C, Sajeva M, La Mantia T, Harrouni C, Msanda F, Caujapé-Castells J
Departamento de Biodiversidad Molecular y Banco de ADN, Jardín Botánico Canario 'Viera y Clavijo' - Unidad Asociada CSIC, Cabildo de Gran Canaria, Camino del Palmeral 15 de Tafira Alta, 35017, Las Palmas de Gran Canaria, Spain.
Mol Ecol. 2015 Feb;24(4):726-41. doi: 10.1111/mec.13060. Epub 2015 Feb 2.
Ecological and evolutionary studies largely assume that island populations display low levels of neutral genetic variation. However, this notion has only been formally tested in a few cases involving plant taxa, and the confounding effect of selection on genetic diversity (GD) estimates based on putatively neutral markers has typically been overlooked. Here, we generated nuclear microsatellite and plastid DNA sequence data in Periploca laevigata, a plant taxon with an island-mainland distribution area, to (i) investigate whether selection affects GD estimates of populations across contrasting habitats; and (ii) test the long-standing idea that island populations have lower GD than their mainland counterparts. Plastid data showed that colonization of the Canary Islands promoted strong lineage divergence within P. laevigata, which was accompanied by selective sweeps at several nuclear microsatellite loci. Inclusion of loci affected by strong divergent selection produced a significant downward bias in the GD estimates of the mainland lineage, but such underestimates were substantial (>14%) only when more than one loci under selection were included in the computations. When loci affected by selection were removed, we did not find evidence that insular Periploca populations have less GD than their mainland counterparts. The analysis of data obtained from a comprehensive literature survey reinforced this result, as overall comparisons of GD estimates between island and mainland populations were not significant across plant taxa (N = 66), with the only exception of island endemics with narrow distributions. This study suggests that identification and removal of markers potentially affected by selection should be routinely implemented in estimates of GD, particularly if different lineages are compared. Furthermore, it provides compelling evidence that the expectation of low GD cannot be generalized to island plant populations.
生态与进化研究大多假定岛屿种群的中性遗传变异水平较低。然而，这一观点仅在少数涉及植物类群的案例中得到过正式检验，而且基于假定中性标记的选择对遗传多样性（GD）估计的混杂效应通常被忽视了。在此，我们在杠柳（Periploca laevigata）中生成了核微卫星和质体DNA序列数据，杠柳是一种具有岛屿 - 大陆分布区域的植物类群，目的是：（i）研究选择是否会影响不同生境中种群的GD估计；以及（ii）检验长期以来的观点，即岛屿种群的GD低于其大陆对应种群。质体数据表明，加那利群岛的定殖促进了杠柳内强烈的谱系分化，这伴随着几个核微卫星位点的选择性清除。纳入受强烈分歧选择影响的位点会导致大陆谱系的GD估计出现显著的向下偏差，但只有当计算中纳入多个受选择的位点时，这种低估才会很显著（>14%）。当去除受选择影响的位点时，我们没有发现证据表明岛屿杠柳种群的GD低于其大陆对应种群。对从全面文献调查中获得的数据进行的分析强化了这一结果，因为在植物类群（N = 66）中，岛屿和大陆种群的GD估计的总体比较并不显著，唯一的例外是分布狭窄的岛屿特有种。这项研究表明，在GD估计中应常规性地识别和去除可能受选择影响的标记，特别是在比较不同谱系时。此外，它提供了令人信服的证据，表明低GD的预期不能推广到岛屿植物种群。
