Data from: Incipient speciation driven by hypertrophied lips in Midas cichlids fish?

Sympatric speciation has been debated in evolutionary biology for decades. Although it has gained in acceptance recently, still only a handful of empirical examples are seen as valid (e.g. crater lake cichlids). In this study, we disentangle the role of hypertrophied lips in the repeated adaptive radiations of Nicaraguan crater lake cichlid fish. We assessed the role of disruptive selection and assortative mating during the early stages of divergence and found a functional trade-off in feeding behavior between thick- and thin-lipped ecotypes suggesting that this trait is a target of disruptive selection. Thick-lipped fish perform better on non-evasive prey at the cost of a poorer performance on evasive prey. Using enclosures in the wild, we found that thick-lipped fish perform significantly better in rocky than in sandy habitats. We found almost no mixed pairs during two breeding seasons and hence significant assortative mating. Genetic differentiation between ecotypes seems to be related to the time since colonization, being subtle in L. Masaya (1600 generations ago) and absent in the younger L. Apoyeque (<600 generations ago). Genome-wide differentiation between ecotypes was higher in the old source lakes than in the young crater lakes. Our results suggest that hypertrophied lips might be promoting incipient sympatric speciation through divergent selection (ecological divergence in feeding performance) and non-random mating (assortative mating) in the young Nicaraguan crater lakes. Nonetheless, further manipulative experiments are needed in order to confirm the role of hypertrophied lips as the main cue for assortative mating.同域物种形成（Sympatric speciation）在进化生物学领域已争论数十年之久。尽管近年来其认可度有所提升，但目前仅有少数实证案例被视为有效例证（如火山口湖慈鲷）。本研究旨在厘清肥厚唇部（hypertrophied lips）在尼加拉瓜火山口湖慈鲷的重复适应性辐射（adaptive radiations）演化中所扮演的角色。我们对物种分化早期阶段的歧化选择（disruptive selection）与选型交配（assortative mating）的作用进行了评估，发现厚唇与薄唇生态型（ecotypes）在摄食行为上存在功能性权衡（functional trade-off），表明该性状是歧化选择的作用靶点。厚唇慈鲷在应对非逃逸性猎物时表现更优，但代价是在逃逸性猎物的捕食中表现欠佳。通过野外围栏实验，我们发现厚唇慈鲷在岩石生境中的表现显著优于沙质生境。在两个繁殖季中，我们几乎未观察到混合配对，因此存在显著的选型交配现象。生态型间的遗传分化似乎与定居后的时长相关：马萨亚湖（L. Masaya，1600代之前）的生态型间遗传分化较为微弱，而较年轻的阿波耶克湖（L. Apoyeque，<600代之前）则未出现此类分化。相较于年轻火山口湖，古老源湖的生态型间全基因组分化程度更高。我们的研究结果表明，在尼加拉瓜年轻火山口湖中，肥厚唇部可能通过歧化选择（摄食性能的生态分化）与非随机交配（选型交配）推动早期同域物种形成进程。尽管如此，仍需开展进一步的操控实验，以确认肥厚唇部作为选型交配主要诱因的作用。