Section of Integrative Biology, University of Texas-Austin, TX 78713, USA.
Ann Bot. 2012 Feb;109(3):613-20. doi: 10.1093/aob/mcr159. Epub 2011 Oct 6.
The trailing edges of species ranges are becoming a subject of increasing interest as the environment changes due to global warming. Trailing edge populations are likely to face extinction because of a decline in numbers and an inability to evolve new adaptations with sufficient speed. Discussions of character change in the trailing edge have focused on physiological, exomorphic and phenological traits. The mating pattern within populations has not been part of the discourse, in spite of the fact that the mating pattern may affect the ability of populations to respond to environmental change and to maintain their sizes. In this paper, the case is made that a substantial increase in self-fertilization rates may occur via plastic responses to stress.
Small populations on the trailing edge are especially vulnerable to environmental change because of inadequate levels of cross-fertilization. Evidence is presented that a deficiency of cross-seed production is due to inadequate pollinator services and a paucity of self-incompatibility alleles within populations. Evidence also is presented that if plants are self-compatible, self-fertilization may compensate in part for this deficiency through a stress-induced increase in levels of self-compatibility and stress-induced alterations in floral morphology that elevate self-pollination. Whereas increased self-fertility may afford populations the time to adapt to their changing environments, it can be concluded that increased selfing is not a panacea for the ills of environmental change, because it will lead to substantial reductions in genetic diversity, which may render adaptation unlikely.
随着全球变暖导致环境变化，物种分布的尾缘正成为越来越受关注的话题。由于数量减少和无法足够快地进化出新的适应能力，尾缘种群很可能面临灭绝。关于尾缘特征变化的讨论集中在生理、外形态和物候特征上。尽管交配模式可能会影响种群对环境变化的适应能力和维持种群规模的能力，但种群内的交配模式并没有成为讨论的一部分。在本文中，我们提出了一个观点，即通过对压力的塑性反应，自交率可能会大幅增加。
处于尾缘的小种群由于异交水平不足，特别容易受到环境变化的影响。有证据表明，由于传粉者服务不足和种群内自不亲和等位基因的缺乏，导致异交种子产量不足。也有证据表明，如果植物是自交亲和的，那么自交可能会通过增加自交亲和水平和改变花形态来部分补偿这种不足，从而提高自交授粉率。虽然增加自交能力可以为种群提供适应变化环境的时间，但可以得出结论，增加自交并不能解决环境变化带来的所有问题，因为它会导致遗传多样性的大幅减少，这可能使适应变得不太可能。
