Department of Evolution and Ecology, University of California, Davis, CA 95616, USA.
Proc Natl Acad Sci U S A. 2011 Jul 12;108(28):11704-9. doi: 10.1073/pnas.1100404108. Epub 2011 Jun 27.
According to theory, gene flow to marginal populations may stall or aid adaptation at range limits by swamping peripheral populations with maladaptive gene flow or by enhancing genetic variability and reducing inbreeding depression, respectively. We tested these contrasting predictions by manipulating patterns of gene flow of the annual plant, Mimulus laciniatus, at its warm range limit. Gene flow was experimentally applied by using crosses within warm-limit populations (selfed and outcrossed), between warm-limit populations, and between warm-limit and central range populations across two elevational transects. We measured the fitness of offspring in a common garden at the warm-edge species range limit. All sources of gene flow increased seedling emergence at the range limit, suggesting local inbreeding depression at both range limit populations; however, lifetime reproductive success only increased significantly when pollen originated from another warm-limit population. Center-to-warm-edge gene flow was maladaptive by delaying time to development at this warm, fast-drying range limit, whereas edge-to-edge gene flow hastened emergence time and time to reproduction. By empirically testing theory on the effects of gene flow on the formation of geographic range limits, we find benefits of gene flow among populations to be greatest when gene flow is between populations occupying the same range limit. Our results emphasize the overlooked importance of gene flow among populations occurring near the same range limit and highlight the potential for prescriptive gene flow as a conservation option for populations at risk from climate change.
根据理论，基因流向边缘种群可能会停滞或有助于适应范围限制，方法是通过适应性较差的基因流使外围种群陷入困境，或者分别通过增强遗传变异性和减少近交衰退。我们通过在其温暖范围限制处操纵一年生植物 Mimulus laciniatus 的基因流动模式来测试这些相互矛盾的预测。通过在温暖限制种群内（自交和杂交）、在温暖限制种群之间以及在温暖限制和中心范围种群之间的两个海拔横截面对基因流动进行了实验应用。我们在温暖边缘物种范围限制处的普通花园中测量了后代的适应性。所有基因流动的来源都增加了在范围限制处的幼苗出现率，这表明在两个范围限制种群中都存在局部近交衰退；然而，只有当花粉来自另一个温暖限制种群时，终生繁殖成功率才会显著增加。中心到温暖边缘的基因流是适应不良的，因为它会延迟在这个温暖、干燥迅速的范围限制处的发育时间，而边缘到边缘的基因流则会加快出现时间和繁殖时间。通过对基因流对地理范围限制形成的影响进行理论检验，我们发现当基因流在处于相同范围限制的种群之间发生时，种群之间的基因流的好处最大。我们的研究结果强调了在相同范围限制附近发生的种群之间的基因流动被忽视的重要性，并突出了作为气候变化风险下的种群保护选择的规定性基因流动的潜力。
