Data from: Male competition fitness landscapes predict both forward and reverse speciation

Speciation is facilitated when selection generates a rugged fitness landscape such that populations occupy different peaks separated by valleys. Competition for food resources is a strong ecological force that can generate such divergent selection. However, it is unclear whether intrasexual competition over resources that provide mating opportunities can generate rugged fitness landscapes that foster speciation. Here we use highly variable male F2 hybrids of benthic and limnetic threespine sticklebacks, Gasterosteus aculeatus Linnaeus, 1758, to quantify the male competition fitness landscape. We find that disruptive sexual selection generates two fitness peaks corresponding closely to the male phenotypes of the two parental species, favouring divergence. Most surprisingly, an additional region of high fitness favours novel hybrid phenotypes that correspond to those observed in a recent case of reverse speciation after anthropogenic disturbance. Our results reveal that sexual selection through male competition plays an integral role in both forward and reverse speciation.当自然选择形成崎岖的适合度景观（fitness landscape），使得种群占据被山谷分隔的不同适合度峰时，物种形成过程会得到促进。获取食物资源的竞争是一种强大的生态作用力，可催生此类分歧选择。然而，尚不清楚针对可提供交配机会的资源的性内竞争（intrasexual competition），是否能够形成可促进物种形成的崎岖适合度景观。本研究利用底栖与浮游型三棘刺鱼（Gasterosteus aculeatus Linnaeus, 1758）的高变异雄性F2代杂交个体，对雄性竞争相关的适合度景观进行量化分析。研究发现，破坏性性选择（disruptive sexual selection）会形成两个与两个亲本物种雄性表型高度匹配的适合度峰，进而推动种群分化。最令人意外的是，另有一处高适合度区域青睐于新型杂交表型，这类表型与近期一项人为干扰后发生逆转物种形成（reverse speciation）案例中观测到的表型一致。本研究结果表明，通过雄性竞争介导的性选择，在正向物种形成与逆转物种形成过程中均发挥着不可或缺的核心作用。