Data from: Predation drives morphological convergence in the Gambusia panuco species group among lotic and lentic habitats

Fish morphology is often constrained by a trade-off between optimizing steady vs. unsteady swimming performance due to opposing effects of caudal peduncle size. Lotic environments tend to select for steady swimming performance, leading to smaller caudal peduncles, while predators tend to select for unsteady swimming performance, leading to larger caudal peduncles. However, it is unclear which aspect of performance should be optimized across heterogeneous flow and predation environments and how this heterogeneity may affect parallel phenotypic evolution. We investigated this question among four Gambusia species in northeastern Mexico, specifically the riverine G. panuco, the spring endemics G. alvarezi and G. hurtadoi, and a fourth species, G. marshi, found in a variety of habitats with varying predation pressure in the Cuatro Ciénegas basin and Río Salado de Nadadores. We employed a geometric morphometric analysis to examine how body shapes of both male and female fish differ among species and habitats and with piscivore presence. We found that high-predation and low-predation species diverged morphologically, with G. marshi exhibiting a variable, intermediate body shape. Within G. marshi, body morphology converged in high-predation environments regardless of flow velocity, and fish from high-predation sites had larger relative caudal peduncle areas. However, we found that G. marshi from low-predation environments diverged in morphology between sub-basins of Cuatro Ciénegas, indicating other differences among these basins that merit further study. Our results suggest that a morphological trade-off promotes parallel evolution of body shape in fishes colonizing high-predation environments and that changing predation pressure can strongly impact morphological evolution in these species.鱼类形态常受尾柄（caudal peduncle）大小的相反效应制约，需在优化稳态游泳与非稳态游泳性能间权衡取舍。流水生境通常倾向于筛选出稳态游泳能力更强的类群，对应更小的尾柄；而捕食压力则会筛选出非稳态游泳能力更佳的类群，对应更大的尾柄。然而，在异质性的水流与捕食环境中，究竟应优化哪一类游泳性能，以及这种异质性如何影响平行表型演化，目前仍不明确。我们以墨西哥东北部的4种食蚊鱼（Gambusia）属鱼类为研究对象，探究上述问题：分别为河生生境的帕努科食蚊鱼（G. panuco）、泉水特有种阿尔瓦雷兹食蚊鱼（G. alvarezi）与乌尔塔多食蚊鱼（G. hurtadoi），以及栖息于夸特罗锡埃内加斯盆地与纳达多尔斯盐河各类生境、捕食压力存在差异的第四种——马尔什食蚊鱼（G. marshi）。我们采用几何形态测量学（geometric morphometric analysis）方法，分析雌雄个体的体形在物种间、生境间以及是否存在食鱼捕食者时的差异。研究发现，高捕食压力与低捕食压力的类群在形态上存在分化，其中马尔什食蚊鱼呈现出可变的中间型体形。在马尔什食蚊鱼内部，无论水流流速如何，高捕食压力环境下的种群体形均趋于趋同，且高捕食压力采样点的个体相对尾柄面积更大。但我们发现，低捕食压力环境下的马尔什食蚊鱼种群，其体形在夸特罗锡埃内加斯盆地的不同子盆地间存在分化，这表明这些盆地间还存在其他有待进一步研究的差异因素。本研究结果表明，形态权衡驱动了拓殖高捕食压力环境的鱼类体形的平行演化，而捕食压力的变化可对这些物种的形态演化产生强烈影响。