Despite decades of research, the evolution of sex remains an enigma in evolutionary biology. Typically, research addresses the costs of sex and asexuality to characterize the circumstances favoring one reproductive mode. Surprisingly few studies address the influence of common traits that are, in many organisms, obligately correlated with asexuality, including hybridization and polyploidy. These characteristics have substantial impacts on traits under selection. In particular, the fitness consequences of hybridization (i.e., reduced fitness due to interspecific reproductive isolation) will influence the evolution of sex. This may comprise a cost of either sex or asexuality due to the link between hybridity and asexuality. We examined reproductive isolation in the formation of de novo hybrid lineages between 2 widespread species in the ecological model system Boechera. Seventeen percent of 664 crosses produced F1 fruits, and only 10% of these were viable, suggesting that postmating prezygotic and postzygotic barriers inhibit hybrid success in this system. The postmating prezygotic barrier was asymmetrical, with 110 of 115 total F1 fruits produced when Boechera stricta acted as maternal parent. This asymmetry was confirmed in wild-collected lineages, using a chloroplast phylogeny of wild-collected B. stricta, Boechera retrofracta, and hybrids. We next compared fitness of F2 hybrids and selfed parental B. stricta lines, finding that F2 fitness was reduced by substantial hybrid sterility. Multiple reproductively isolating barriers influence the formation and fitness of hybrid lineages in the wild, and the costs of hybridization likely have profound impacts on the evolution of sex in the natural environment.

中文翻译：

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Boechera（Rock Cress）的昂贵杂交缓和了性别的进化

尽管进行了数十年的研究，性的进化仍然是进化生物学中的一个谜。通常，研究涉及性和无性的成本，以表征有利于一种生殖模式的环境。令人惊讶的是，很少有研究涉及在许多生物体中与无性性密切相关的共同特征的影响，包括杂交和多倍体。这些特征对选择的性状有重大影响。特别是，杂交的适应度结果（即由于种间生殖隔离导致的适应度降低）将影响性别的进化。由于杂交和无性之间的联系，这可能包括性别或无性的成本。我们研究了生态模型系统 Boechera 中 2 个广泛物种之间从头杂交谱系形成过程中的生殖隔离。664 个杂交中有 17% 产生了 F1 果实，其中只有 10% 是可行的，这表明后交合前和合子后屏障抑制了该系统中的杂交成功。后交配前的屏障是不对称的，当 Boechera stricta 作为母本时，产生了 115 个 F1 果实中的 110 个。这种不对称性在野生收集的谱系中得到证实，使用野生收集的 B.stricta、Boechera retrofracta 和杂种的叶绿体系统发育。我们接下来比较了 F2 杂种和自交亲本 B.stricta 品系的适合度，发现 F2 适合度因大量杂种不育而降低。