Department of Biology, University of Fribourg, Fribourg, Switzerland.
PLoS Genet. 2023 Sep 1;19(9):e1010883. doi: 10.1371/journal.pgen.1010883. eCollection 2023 Sep.
As species expand their geographic ranges, colonizing populations face novel ecological conditions, such as new environments and limited mates, and suffer from evolutionary consequences of demographic change through bottlenecks and mutation load accumulation. Self-fertilization is often observed at species range edges and, in addition to countering the lack of mates, is hypothesized as an evolutionary advantage against load accumulation through increased homozygosity and purging. We study how selfing impacts the accumulation of genetic load during range expansion via purging and/or speed of colonization. Using simulations, we disentangle inbreeding effects due to demography versus due to selfing and find that selfers expand faster, but still accumulate load, regardless of mating system. The severity of variants contributing to this load, however, differs across mating system: higher selfing rates purge large-effect recessive variants leaving a burden of smaller-effect alleles. We compare these predictions to the mixed-mating plant Arabis alpina, using whole-genome sequences from refugial outcrossing populations versus expanded selfing populations. Empirical results indicate accumulation of expansion load along with evidence of purging in selfing populations, concordant with our simulations, suggesting that while purging is a benefit of selfing evolving during range expansions, it is not sufficient to prevent load accumulation due to range expansion.
随着物种扩展其地理分布范围，殖民地种群面临新的生态条件，如新的环境和有限的配偶，并遭受人口变化瓶颈和突变负荷积累的进化后果。自交常常在物种分布范围的边缘观察到，除了对抗缺乏配偶之外，自交被假设为通过增加同型性和清除突变负荷积累的进化优势。我们通过清除和/或殖民化速度来研究自交如何在范围扩展过程中影响遗传负荷的积累。通过模拟，我们区分了由于人口统计学和自交导致的近交效应，并发现无论交配系统如何，自交者的扩张速度更快，但仍会积累负荷。然而，导致这种负荷的变异的严重程度在不同的交配系统中有所不同：更高的自交率会清除大效应隐性变异，留下较小效应等位基因的负担。我们将这些预测与异交植物 Arabis alpina 进行比较，使用来自避难所的异交种群和扩展的自交种群的全基因组序列。实证结果表明，随着自交种群中清除的证据，扩张负荷的积累，与我们的模拟结果一致，这表明虽然自交在范围扩张过程中进化是清除的好处，但不足以防止由于范围扩张而导致的负荷积累。
