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所驱动。本研究针对东部食蚊鱼（Gambusia holbrooki）广阔原生分布区内的表型多样性背后的环境驱动因子开展了直接检验。我们针对北美境内跨越14个以上纬度的种群，调查了其生活史特征与体型分化（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, AIC）的模型选择方法，明确了热环境条件、种群密度以及栖息地生产力作为潜在驱动因子，对纬度梯度上表型变异的相对贡献程度。研究结果显示，热环境条件是驱动大尺度纬度表型格局形成的最核心因子：在季节性更强、温度波动更大的寒冷气候环境中，东部食蚊鱼种群展现出更大的体型、更高的繁殖投入同时伴随更小的后代体型，且躯体更修长（体高更低）、头部更小，胸鳍位置更靠前且偏向背侧。尽管如此，种群密度与栖息地生产力同样会影响性状分化，但这种影响与纬度格局无关；此外，部分体型变异源于与生活史特征的显著协变。本研究不仅证实，即便在变温动物类群中，热环境条件仍是驱动纬度梯度表型分化的重要因子，同时也揭示了多种塑造表型多样性的其他驱动因素，凸显了本研究采用多变量分析方法的重要意义。