Data from: Thermal regime drives a latitudinal gradient in morphology and life history in a livebearing fish

Within-species diversity is often driven by changing selective regimes along environmental gradients. Here, we provide a direct test of the environmental factors underlying phenotypic diversity across the wide native distribution of eastern mosquitofish (Gambusia holbrooki). We investigated life-history and body-shape divergence (including multiple measures of body size) across more than 14 degrees of latitude in North America, and used Akaike’s information criterion-based model selection to determine the relative contributions of thermal regime, population densities and habitat productivity as potential drivers of latitudinal phenotypic variation. We found thermal regime to be the most important driver of large-scale latitudinal phenotypic patterns: populations in colder climates with greater seasonality and range in temperature exhibited larger body size, larger reproductive investment coupled with smaller offspring size, and shallower bodies with a smaller head and more anterodorsally positioned pectoral fins. Nonetheless, population density and habitat productivity also influenced trait divergence, but independent of latitudinal patterns, and some variation in body shape was due to apparent covariation with life histories. Our study confirms thermal regime as an important driver of latitudinal phenotypic differentiation even in ectotherms, but also uncovers multiple additional factors that shape phenotypic diversity, emphasizing the importance of the multivariate approach we employed here.种内多样性往往由沿环境梯度变化的选择模式（selective regime）所驱动。本研究针对东部食蚊鱼（Gambusia holbrooki）广泛的原生分布范围，对其表型多样性背后的环境驱动因子开展了直接检验。我们调查了北美境内跨越14个以上纬度的多个种群的生活史与体型分化特征（包含多项体型大小测量指标），并采用基于赤池信息准则（Akaike’s information criterion）的模型选择方法，明确了热环境模式（thermal regime）、种群密度以及生境生产力作为纬度梯度表型变异潜在驱动因子的相对贡献程度。 研究结果显示，热环境模式是驱动大尺度纬度梯度表型格局的最核心因子：在季节性更强、温度波动更大的寒冷气候环境中，种群表现出更大的体型、更高的繁殖投入伴随更小的后代体型，同时躯体更浅、头部更小且胸鳍位置更靠前背侧。尽管如此，种群密度与生境生产力同样会影响性状分化，但其作用模式与纬度梯度无关；此外，部分体型变异源于与生活史特征的明显协同变化。 本研究不仅证实了热环境模式即使在变温动物（ectotherms）中也是驱动纬度梯度表型分化的重要因子，同时还揭示了多种其他塑造表型多样性的因子，凸显了本研究采用多变量分析方法（multivariate approach）的重要意义。