Adaptation to contrasting environments occurs when advantageous alleles accumulate in each population, but it remains largely unknown whether these same advantageous alleles create genetic incompatibilities that can cause intrinsic reproductive isolation leading to speciation. Identifying alleles that underlie both adaptation and reproductive isolation is further complicated by factors such as dominance and genetic interactions among loci, which can affect both processes differently and obscure potential links between adaptation and speciation. Here, we use a combination of field and glasshouse experiments to explore the connection between adaptation and speciation while accounting for dominance and genetic interactions. We created a hybrid population with equal contributions from four contrasting ecotypes of Senecio lautus (Asteraceae), which produced hybrid genomes both before (F1 hybrid generation) and after (F4 hybrid generation) recombination among the parental ecotypes. In the glasshouse, plants in the second generation (F2 hybrid generation) showed reduced fitness as a loss of fertility. However, fertility was recovered in subsequent generations, suggesting that genetic variation underlying the fitness reduction was lost in subsequent generations. To quantify the effects of losing genetic variation at the F2 generation on the fitness of later generation hybrids, we used a reciprocal transplant to test for fitness differences between parental ecotypes, and F1 and F4 hybrids in all four parental habitats. Compared to the parental ecotypes and F1 hybrids, variance in F4 hybrid fitness was lower, and lowest in habitats that showed stronger native‐ecotype advantage, suggesting that stronger natural selection for the native ecotype reduced fitness variation in the F4 hybrids. Fitness trade‐offs that were present in the parental ecotypes and F1 hybrids were absent in the F4 hybrid. Together, these results suggest that the genetic variation lost after the F2 generation was likely associated with both adaptation and intrinsic reproductive isolation among ecotypes from contrasting habitats.

中文翻译：

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晚代杂交种中生态上重要的遗传变异的丧失揭示了适应与物种形成之间的联系。

当有利的等位基因在每个种群中积累时，就会对对比环境产生适应，但目前仍不清楚这些相同的有利等位基因是否会产生遗传不相容性，从而导致内在的生殖隔离，从而导致物种形成。位点之间的优势和遗传相互作用等因素使识别适应和生殖隔离背后的等位基因变得更加复杂，这些因素可能对这两个过程产生不同的影响，并掩盖了适应和物种形成之间的潜在联系。在这里，我们结合实地和温室实验来探索适应和物种形成之间的联系，同时考虑优势和遗传相互作用。我们创建了一个混合群体，其四种不同的千里光生态型（菊科）的贡献相同，在亲本生态型重组之前（F1 杂交一代）和之后（F4 杂交一代）产生了杂交基因组。在温室中，第二代（F2 杂交代）植物表现出由于生育力丧失而导致的适应性下降。然而，生育能力在后代中恢复，这表明适合度降低的遗传变异在后代中消失了。为了量化 F2 代失去遗传变异对后代杂交体适应性的影响，我们使用相互移植来测试亲本生态型以及所有四个亲本栖息地中的 F1 和 F4 杂交体之间的适应性差异。与亲本生态型和F1杂种相比，F4杂种适应度的方差较低，并且在表现出更强的本地生态型优势的生境中最低，这表明对本地生态型更强的自然选择减少了F4杂种的适应度变异。亲本生态型和 F1 杂种中存在的适应度权衡在 F4 杂种中不存在。总之，这些结果表明，F2 代后丢失的遗传变异可能与来自不同栖息地的生态型之间的适应和内在生殖隔离有关。