Data from: Disentangling the drivers of diversification in an imperiled group of freshwater fishes (Cyprinodontiformes: Goodeidae)

Background: One of the most perplexing questions in evolutionary biology is why some lineages diversify into many species, and others do not. In many cases, ecological opportunity has played an important role, leading to diversification along trophic or habitat-based axes. The Goodeidae (Teleostomi: Cyprinodontiformes) are a family of freshwater fishes with two subfamilies: Goodeinae (42 species, viviparous, heterogeneous habitats, Mesa Central of Mexico) and Empetrichthyinae (4 species, oviparous, homogeneous habitats, Great Basin of the United States). These discrepant sets of characteristics and their sister-group relationship make the goodeids amenable to a comparative study of diversification. We gathered lateral body images from more than 1,600 specimens of all extant species in the family. Geometric morphometric, and phylogenetic comparative analyses were used to address whether higher species diversity correlates with higher rates of morphological shape evolution and whether there are differences in functional/habitat modules between the two subfamilies. Results: This study recovered a higher rate of overall body shape evolution in the Goodeinae that is nearly double in magnitude compared to the Empetrichthyinae. A modularity test indicated that the Goodeinae displayed elevated rates of morphological evolution in comparison to the Empetrichthyinae when only trunk (locomotor) regions were compared between subfamilies. No significant differences in evolutionary shape rates were recovered when the trophic (head) regions were compared between subfamilies. Discussion: These results support the hypothesis that Mexican goodeids radiated via an ecological opportunity scenario into a wide-array of novel habitats in the island-like Mesa Central as evidenced by their high rate of shape evolution, relative to the Empetrichthyinae. This study quantitatively unraveled the drivers of evolution and eliminated trophic specialization as a driving force within the Goodeidae.背景：进化生物学中最令人困惑的问题之一，便是为何部分演化支会分化出众多物种，而另一部分却并非如此。诸多案例中，生态机会均发挥了关键作用，推动类群沿营养生态位或生境轴实现分化。胎鳉科（Goodeidae，隶属于真口总纲（Teleostomi）：鳉形目（Cyprinodontiformes））是一类淡水鱼类，包含两个亚科：胎鳉亚科（Goodeinae，42种，胎生，生境异质性强，分布于墨西哥中部台地）以及卵生鳉亚科（Empetrichthyinae，4种，卵生，生境均一，分布于美国大盆地）。二者的特征差异显著且互为姐妹群，使得胎鳉科成为开展分化比较研究的理想类群。本研究收集了该科所有现存物种的1600余份标本的体侧图像，并采用几何形态计量学（geometric morphometrics）与系统发育比较分析，旨在验证物种多样性是否与形态形状演化速率呈正相关，以及两个亚科间在功能/生境模块上是否存在差异。 结果：本研究发现，胎鳉亚科的整体体形演化速率近乎是卵生鳉亚科的两倍。模块性测试表明，仅对躯干（运动）区域进行跨亚科比较时，胎鳉亚科的形态演化速率显著高于卵生鳉亚科；而当比较摄食相关的头部区域时，未检测到两个亚科间演化速率存在显著差异。 讨论：本研究结果支持"墨西哥胎鳉依托生态机会场景，在类岛屿状的墨西哥中部台地辐射演化至多样新生境"的假说，这一结论可通过其相较于卵生鳉亚科的高形体演化速率得到印证。本研究定量阐明了演化驱动因素，并排除了摄食特化作为胎鳉科内部演化驱动力的可能性。