Department of Biological Sciences, Clemson University, 132 Long Hall, Clemson, SC, 29634, USA.
Heredity (Edinb). 2023 Jun;130(6):347-357. doi: 10.1038/s41437-023-00610-z. Epub 2023 Apr 4.
Climate change has influenced species distributions worldwide with upward elevational shifts observed in many systems. Leading range edge populations, like those at upper elevation limits, are crucial for climate change responses but can exhibit low genetic diversity due to founder effects, isolation, or limited outbreeding. These factors can hamper local adaptation at range limits. Using the widespread herb, Argentina anserina, we measured ecological attributes (population density on the landscape, area of population occupancy, and plant and flower density) spanning a 1000 m elevation gradient, with high elevation populations at the range limit. We measured vegetative clonal potential in the greenhouse for populations spanning the gradient. We combined these data with a ddRAD-seq dataset to test the hypotheses that high elevation populations would exhibit ecological and genomic signatures of leading range edge populations. We found that population density on the landscape declined towards the high elevation limit, as is expected towards range edges. However, plant density was elevated within edge populations. In the greenhouse, high elevation plants exhibited stronger clonal potential than low elevation plants, likely explaining increased plant density in the field. Phylogeographic analysis supported more recent colonization of high elevation populations which were also more genetically isolated, had more extreme heterozygote excess and had smaller effective population size than low. Results support that colonization of high elevations was likely accompanied by increased asexuality, contributing to a decline in effective population size. Despite high plant density in leading edge populations, their small effective size, isolation and clonality could constrain adaptive potential.
气候变化已经影响了全球物种的分布，在许多系统中观察到了向上的海拔迁移。处于主导分布区边缘的种群，如处于海拔上限的种群，对于气候变化的响应至关重要，但由于奠基者效应、隔离或有限的杂交，它们可能表现出较低的遗传多样性。这些因素可能会阻碍分布区边缘的本地适应。本研究使用广泛分布的草本植物阿根廷蓟，测量了跨越 1000 米海拔梯度的生态属性（景观上的种群密度、种群占据面积、植物和花朵密度），其中高海拔种群处于分布区的上限。我们在温室中测量了跨越梯度的种群的营养克隆潜力。我们将这些数据与 ddRAD-seq 数据集相结合，以检验以下假设：高海拔种群将表现出主导分布区边缘种群的生态和基因组特征。我们发现，景观上的种群密度朝着高海拔上限下降，这是分布区边缘的预期趋势。然而，植物密度在边缘种群中升高。在温室中，高海拔植物表现出比低海拔植物更强的克隆潜力，这可能解释了在野外植物密度增加的原因。系统发生地理分析支持高海拔种群的近期殖民，这些种群也更加遗传隔离，具有更强的杂合子过剩，有效种群规模也更小。结果表明，高海拔地区的殖民化可能伴随着无性繁殖的增加，从而导致有效种群规模的下降。尽管处于主导分布区边缘的种群具有较高的植物密度，但它们较小的有效种群规模、隔离和克隆性可能限制了适应潜力。
