Data from: When Bergmann's rule fails: evidences of environmental selection pressures shaping phenotypic diversification in a widespread seabird

Organisms tend to exhibit phenotypes that can be shaped by climate, commonly demonstrating clinal variations along latitudinal gradients. In vertebrates, air temperature plays a major role in shaping body size in both ectothermic and endothermic animals. However, additional small-scale environmental factors can also act as selection pressures in the marine ecosystem (e.g., primary productivity), evidencing multi-scale processes acting on marine organisms. In this study, we tested Bergmann's rule in a widely distributed seabird, the brown booby (Sula leucogaster), in addition to evaluating the relationship of sea surface temperature and chlorophyll α with phenotypes. We used traits from a morphometric dataset (culmen, wing chord, and tarsus length) and body mass of 276 brown boobies distributed on six breeding sites along a latitudinal gradient in the South Atlantic Ocean (0–27°S). We found significant differentiation among colonies, but phenotypic similarities were observed between colonies located at the extremes of the latitudinal gradient. As the colony nearest to the Equator, Saint Peter and Saint Paul archipelago, had the largest and heaviest individuals, the model containing only air temperature explained <5% of the allometric variation, providing no substantial support for Bergmann's rule. However, when we added the interaction of chlorophyll α and sea surface temperature the deviance explained rose to over 80%. Primary productivity and sea surface temperature do not follow a latitudinal gradient in the ocean and, therefore, the role of small-scale oceanographic processes in shaping body size and the importance of considering additional environmental variables when testing Bergmann's rule in marine organisms are evident.生物往往会展现出受气候塑造的表型，且通常沿纬度梯度呈现渐变群变异（clinal variation）。在脊椎动物类群中，气温对变温动物与恒温动物的体型塑造均起到核心作用。然而，海洋生态系统中还存在其他小型尺度的环境因素可作为选择压力（例如初级生产力（primary productivity）），这证实了多尺度过程会对海洋生物产生影响。本研究针对广泛分布的海鸟——褐鲣鸟（Sula leucogaster），对伯格曼法则（Bergmann's rule）开展了检验，同时评估了海表温度（sea surface temperature）与叶绿素α（chlorophyll α）和表型之间的关联。我们采用了276只褐鲣鸟的形态测量数据集（morphometric dataset）相关指标：喙峰长、翼弦长及跗跖长度，以及体重数据；这些样本分布于南大西洋（0°S至27°S）沿纬度梯度设置的6个繁殖位点。研究结果显示，不同繁殖群体间存在显著的表型分化，但位于纬度梯度两端的繁殖群体却表现出相似的表型特征。作为最靠近赤道的繁殖群体，圣彼得和圣保罗群岛的个体体型最大、体重最重；仅包含气温的模型仅能解释不到5%的异速生长变异（allometric variation），未为伯格曼法则提供实质性的支撑证据。然而，当我们加入叶绿素α与海表温度的交互项后，模型的解释偏差（deviance explained）提升至80%以上。初级生产力与海表温度在海洋中并不遵循纬度梯度分布，由此可见，小型尺度海洋学过程（oceanographic processes）在塑造海洋生物体型中的作用，以及在海洋生物类群中检验伯格曼法则时考虑额外环境变量的重要性均已得到明确证实。