Hargreaves A L, Bailey S F, Laird R A
Department of Biology, Queen's University, Kingston, ON, Canada.
Bioinformatics Research Centre, Aarhus University, Aarhus C, Denmark.
J Evol Biol. 2015 Aug;28(8):1489-501. doi: 10.1111/jeb.12669. Epub 2015 Jul 14.
Dispersal ability will largely determine whether species track their climatic niches during climate change, a process especially important for populations at contracting (low-latitude/low-elevation) range limits that otherwise risk extinction. We investigate whether dispersal evolution at contracting range limits is facilitated by two processes that potentially enable edge populations to experience and adjust to the effects of climate deterioration before they cause extinction: (i) climate-induced fitness declines towards range limits and (ii) local adaptation to a shifting climate gradient. We simulate a species distributed continuously along a temperature gradient using a spatially explicit, individual-based model. We compare range-wide dispersal evolution during climate stability vs. directional climate change, with uniform fitness vs. fitness that declines towards range limits (RLs), and for a single climate genotype vs. multiple genotypes locally adapted to temperature. During climate stability, dispersal decreased towards RLs when fitness was uniform, but increased when fitness declined towards RLs, due to highly dispersive genotypes maintaining sink populations at RLs, increased kin selection in smaller populations, and an emergent fitness asymmetry that favoured dispersal in low-quality habitat. However, this initial dispersal advantage at low-fitness RLs did not facilitate climate tracking, as it was outweighed by an increased probability of extinction. Locally adapted genotypes benefited from staying close to their climate optima; this selected against dispersal under stable climates but for increased dispersal throughout shifting ranges, compared to cases without local adaptation. Dispersal increased at expanding RLs in most scenarios, but only increased at the range centre and contracting RLs given local adaptation to climate.
扩散能力将在很大程度上决定物种在气候变化期间能否追踪其气候生态位，这一过程对于处于收缩（低纬度/低海拔）范围边界的种群尤为重要，否则这些种群将面临灭绝风险。我们研究了在收缩范围边界处的扩散进化是否受到两个过程的促进，这两个过程可能使边缘种群在气候恶化导致灭绝之前就能够体验并适应其影响：（i）气候导致的适合度向范围边界下降；（ii）对不断变化的气候梯度的局部适应。我们使用一个空间明确的、基于个体的模型模拟了一个沿着温度梯度连续分布的物种。我们比较了气候稳定与定向气候变化期间全范围的扩散进化，比较了均匀适合度与适合度向范围边界下降的情况，以及单一气候基因型与局部适应温度的多个基因型的情况。在气候稳定期间，当适合度均匀时，扩散向范围边界减少，但当适合度向范围边界下降时，扩散增加，这是由于高度扩散的基因型在范围边界维持着汇种群，较小种群中的亲缘选择增加，以及出现了有利于在低质量栖息地扩散的适合度不对称性。然而，在低适合度范围边界处的这种初始扩散优势并没有促进气候追踪，因为它被灭绝概率的增加所抵消。局部适应的基因型受益于靠近其气候最适点；与没有局部适应的情况相比，这在稳定气候下不利于扩散，但在整个变化范围内有利于增加扩散。在大多数情况下，在扩张的范围边界处扩散增加，但只有在局部适应气候的情况下，在范围中心和收缩的范围边界处扩散才会增加。
