Department of Genetics, Evolution, and Environment, University College London, Gower Street, London WC1E 6BT, UK.
CoMPLEX, University College London, Gower Street, London WC1E 6BT, UK.
Genetics. 2024 Jul 8;227(3). doi: 10.1093/genetics/iyae073.
Inversions have been proposed to facilitate local adaptation, by linking together locally coadapted alleles at different loci. Prior work addressing this question theoretically has considered the spread of inversions in "continent-island" scenarios in which there is a unidirectional flow of maladapted migrants into the island population. In this setting, inversions capturing locally adaptive haplotypes are most likely to invade when selection is weak, because stronger local selection (i) more effectively purges maladaptive alleles and (ii) generates linkage disequilibrium between adaptive alleles, thus lessening the advantage of inversions. We show this finding only holds under limited conditions by studying the establishment of inversions in a more general two-deme model, which explicitly considers the dynamics of allele frequencies in both populations linked by bidirectional migration. In this model, the level of symmetry between demes can be varied from complete asymmetry (continent-island) to complete symmetry. For symmetric selection and migration, strong selection increases the allele frequency divergence between demes thereby increasing the frequency of maladaptive alleles in migrants, favoring inversions-the opposite of the pattern seen in the asymmetric continent-island scenario. We also account for the likelihood that a new inversion captures an adaptive haplotype in the first instance. When considering the combined process of capture and invasion in "continent island" and symmetric scenarios, relatively strong selection increases inversion establishment probability. Migration must also be low enough that the inversion is likely to capture an adaptive allele combination, but not so low as to eliminate the inversion's advantage. Overall, our analysis suggests that inversions are likely to harbor larger effect alleles that experience relatively strong selection.
倒位被认为可以通过连接不同基因座上的局部共适应等位基因来促进局部适应。之前从理论上解决这个问题的研究工作考虑了“大陆-岛屿”情景下的倒位传播，在这种情景下，存在从大陆向岛屿种群单向流动的不适宜移民。在这种情况下，当选择较弱时，捕获局部适应单倍型的倒位最有可能入侵，因为更强的局部选择（i）更有效地清除不适宜的等位基因，（ii）在适应等位基因之间产生连锁不平衡，从而降低倒位的优势。我们通过研究在一个更一般的双种群模型中倒位的建立，证明了只有在有限的条件下才能得到这个发现，这个模型明确考虑了由双向迁移连接的两个种群中等位基因频率的动态。在这个模型中，种群之间的对称性程度可以从完全不对称（大陆-岛屿）到完全对称变化。对于对称选择和迁移，强选择增加了种群之间的等位基因频率分歧，从而增加了移民中不适宜等位基因的频率，有利于倒位——与在不对称的大陆-岛屿情景中看到的模式相反。我们还考虑了新的倒位最初捕获适应单倍型的可能性。当考虑“大陆-岛屿”和对称情景下的捕获和入侵的综合过程时，相对较强的选择会增加倒位建立的可能性。迁移也必须足够低，以使倒位有可能捕获到一个适应的等位基因组合，但又不能太低以至于消除倒位的优势。总的来说，我们的分析表明，倒位可能包含经历相对较强选择的较大效应等位基因。
