Data from: Habitat segregation and ecological character displacement in cryptic African malaria mosquitoes

Understanding how divergent selection generates adaptive phenotypic and population diversification provides a mechanistic explanation of speciation in recently separated species pairs. Toward this goal, we sought ecological gradients of divergence between the cryptic malaria vectors Anopheles coluzzii and An. gambiae, and then looked for a physiological trait that may underlie such divergence. Using a large set of occurrence records and eco-geographical information, we built a distribution model to predict the predominance of the two species across their range of sympatry. Our model predicts two novel gradients along which the species segregate: distance from the coastline and altitude. Anopheles coluzzii showed a ‘bimodal’ distribution, predominating in xeric West African savannas and along the western coastal fringe of Africa. To test whether differences in salinity tolerance underlie this habitat segregation, we assessed the acute dose-mortality response to salinity of thirty-two larval populations from Central Africa. In agreement with its coastal predominance, Anophels coluzzii was overall more tolerant than An. gambiae. Salinity tolerance of both species, however, converged in urban localities, presumably reflecting an adaptive response to osmotic stress from anthropogenic pollutants. When comparing degree of tolerance in conjunction with levels of syntopy, we found evidence of character displacement in this trait.

阐明趋异选择（divergent selection）如何驱动适应性表型与种群分化，可为新近分化的物种对的物种形成机制提供合理解释。为此，我们针对隐秘疟疾媒介科鲁兹按蚊（Anopheles coluzzii）与冈比亚按蚊（Anopheles gambiae，原文缩写为An. gambiae），探寻介导二者分化的生态梯度，并筛选可能介导该分化的生理性状。我们基于大量物种出现记录与生态地理信息构建了分布模型，以预测两物种在其同域分布区内的优势分布格局。模型结果显示，存在两个可使两物种产生分布分化的全新生态梯度：距海岸线距离与海拔高度。科鲁兹按蚊呈现出‘双峰型’分布格局，在西非干旱稀树草原及非洲西部沿海岸带均占优势。为验证盐度耐受性差异是否为该生境分化的成因，我们对采自中非的32个幼虫种群开展了盐度急性剂量-死亡率响应实验。与该蚊种沿海岸带的优势分布特征相符，科鲁兹按蚊整体的盐度耐受性强于冈比亚按蚊。然而两物种的盐度耐受性在城市生境中趋于一致，这可能反映了它们对人为污染物引发的渗透胁迫产生了适应性响应。当结合耐受程度与同域共存水平进行分析时，我们发现该性状存在性状替换的证据。