Data from: Flexible mate choice may contribute to ecotype assortative mating in pumpkinseed sunfish (Lepomis gibbosus)

Gene flow is expected to limit adaptive divergence but the ecological and behavioural factors that govern gene flow are still poorly understood, particularly at the earliest stages of population divergence. Reduced gene flow through mate choice (sexual isolation) can evolve even under conditions of subtle population divergence if intermediate phenotypes have reduced fitness. We indirectly tested the hypothesis that mate choice has evolved between coexisting littoral and pelagic ecotypes of polyphenic pumpkinseed sunfish (Lepomis gibbosus) that have diverged in morphology and resource use and where intermediate phenotypes have reduced performance. We assessed the ecotype of nesting males and females using stable isotope estimates of diet and a divergent male morphological trait, oral jaw width. We found positive assortative mating between ecotypes in a common spawning habitat along exposed lake shorelines, but contrary to expectations, assortative mating was variably expressed between two sampling years. Although the factors that influence variable assortative mating remain unclear, our results are consistent with mate choice being expressed by ecotypes. Despite being variably expressed, mate choice will reduce gene flow between ecotypes and could contribute to further adaptive divergence depending on its frequency and strength in the population. Our findings add to a growing body of evidence indicating mate choice behaviour can be a plastic trait, an idea that should be more explicitly considered in empirical studies of mate choice as well as conceptual frameworks of mate choice evolution and adaptive divergence.

基因流（gene flow）通常被认为会限制适应性分化，但调控基因流的生态与行为机制仍未得到充分阐释，尤其是在种群分化的早期阶段。若中间表型的适合度下降，即便种群仅存在细微分化，通过配偶选择实现的基因流降低（即性隔离（sexual isolation））仍可演化形成。本研究间接验证了如下假说：在形态与资源利用模式已发生分化、且中间表型表现性能下降的多型南瓜籽太阳鱼（*Lepomis gibbosus*）的共存沿岸与远洋生态型之间，配偶选择已经演化形成。本研究通过日粮的稳定同位素估算结果以及雄性特有的分化形态性状——口颌宽度——对筑巢雌雄个体的生态型进行了判定。我们在沿暴露湖岸线的共同产卵生境中发现了生态型间的正选型交配（positive assortative mating）现象，但与预期相悖的是，该选型交配模式在两个采样年份间表现出显著差异。尽管调控该可变选型交配的具体机制仍不明确，但本研究结果支持生态型会表现出配偶选择行为这一推论。尽管配偶选择的表现存在变异性，但它仍可降低生态型间的基因流；且根据其在种群中的发生频率与强度不同，该过程还可能进一步推动适应性分化。本研究结果进一步佐证了日益增多的相关证据，表明配偶选择行为可作为一种表型可塑性性状；该观点应在配偶选择的实证研究以及配偶选择演化与适应性分化的概念框架中得到更明确的考量。