Data from: A test of hybrid growth disadvantage in wild, free-ranging species pairs of threespine sticklebacks (Gasterosteus aculeatus) and its implications for ecological speciation

Ecological speciation is the evolution of reproductive isolation as a direct or indirect consequence of divergent natural selection. Reduced performance of hybrids in nature is thought to be an important process by which natural selection can favour the evolution of assortative mating and drive speciation. Benthic and limnetic sympatric species of threespine stickleback (Gasterosteus aculeatus) are adapted to alternative trophic niches (bottom browsing versus open water planktivory, respectively) and reduced feeding performance of hybrids is thought to have contributed to the evolution of reproductive isolation. We tested this “hybrid-disadvantage hypothesis” by inferring growth rates from otoliths sampled from wild, free-ranging benthic, limnetic, and hybrid sticklebacks from two lakes. There were significant differences in growth rate between lakes, life-history stages, and among years (maximum P = 0.02), as well as interactions between most factors, but not between hybrid and parental species sticklebacks in most comparisons. Our results provide little evidence of a growth disadvantage in hybrid sticklebacks when free-ranging in nature. While trophic ecology per se may contribute less to ecological speciation than envisioned, it may act in concert with other aspects of stickleback biology, such as interactions with parasites, predators, competitors and/or sexual selection, to present strong multifarious selection against hybrids.

生态物种形成（ecological speciation）指生殖隔离（reproductive isolation）作为分歧自然选择（divergent natural selection）的直接或间接后果而发生演化的过程。自然界中杂种适合度下降，被认为是自然选择能够推动选型交配（assortative mating）演化、进而驱动物种形成的关键过程之一。三棘刺鱼（Gasterosteus aculeatus）的底栖与敞水同域物种，分别适应了差异化的营养生态位（trophic niches）——即底层啃食与敞水浮游食性，而杂种摄食能力下降被认为助力了生殖隔离的演化。我们通过采集两座湖泊中野生自由活动的底栖型、敞水型及杂种三棘刺鱼的耳石（otoliths）样本，并据此推断其生长速率，检验了这一"杂种劣势假说（hybrid-disadvantage hypothesis）"。研究发现，不同湖泊、不同生活史阶段以及不同年份间的生长速率均存在显著差异（最大P值=0.02），多数因子间也存在交互效应，但在多数对比中，杂种与亲本刺鱼的生长速率并无显著区别。本研究未发现自由生活的杂种刺鱼存在生长劣势的有力证据。尽管营养生态本身对生态物种形成的贡献可能比此前设想的要小，但它或许可与刺鱼生物学的其他方面（如与寄生虫、捕食者、竞争者的相互作用，以及性选择）协同作用，形成针对杂种的多维度强选择压力。