Despite a large body of research, little agreement has been reached on the ultimate driver(s) of geographic variation in body size (mass and/or length). Here we use skull length measurements (as a surrogate for body mass) from five Australian marsupial species to test the primary hypotheses of geographic variation in body size (relating to ambient temperature, productivity, and seasonality). We used a revised articulation of Bergmann's rule, wherein evidence for thermoregulation (heat dissipation or heat conservation) is considered supportive of Bergmann's rule. We modeled the skull lengths of four Petaurid glider species and the common brushtail possum (Trichosurus vulpecula) as a function of indices of ambient temperature, productivity, and seasonality. The skull length of Petaurus ariel, P. notatus, and the squirrel glider (P. norfolcensis), increased with increasing winter minimum temperature, while that of T. vulpecula decreased with increasing summer maximum temperature. The skull length of P. ariel decreased with indices of productivity, falsifying the productivity hypothesis. Only P. ariel met the hypothesis of seasonality, as skull length increased with increasing seasonality. Thermoregulation was the most consistently supported driver of geographic variation in body size, as we found evidence of either heat conservation or heat dissipation in four of the five species examined. We found the geographic range of the individual species and the climate space in which the species occurred was integral to understanding the species' responses to climate variables. Future studies should use specimens that are representative of a species' entire geographic range, encompass a variety of climatic regions, and use consistent methodologies and terminology when testing drivers of geographic variation in body size.

中文翻译：

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五只澳大利亚有袋动物体型的地理差异支持伯格曼的体温调节假说

尽管进行了大量研究，但对于身体大小（质量和/或长度）地理差异的最终驱动因素几乎没有达成一致。在这里，我们使用来自五种澳大利亚有袋动物的头骨长度测量值（作为体重的替代物）来测试体型的地理变化（与环境温度、生产力和季节性有关）的主要假设。我们使用了伯格曼规则的修订版，其中体温调节（散热或保温）的证据被认为支持伯格曼规则。我们将四种 Petaurid 滑翔机物种和普通刷尾负鼠 (Trichosurus vulpecula) 的头骨长度建模为环境温度、生产力和季节性指数的函数。Petaurus ariel、P. notatus 和松鼠滑翔机 (P. norfolcensis），随着冬季最低温度的增加而增加，而T. vulpecula 的数量随着夏季最高温度的增加而减少。P. ariel 的头骨长度随着生产力指数的增加而减少，从而证伪了生产力假设。只有 P. ariel 符合季节性假设，因为头骨长度随着季节性的增加而增加。体温调节是身体大小地理变化的最一致支持的驱动因素，因为我们在所检查的五种物种中的四种中发现了热量保存或散热的证据。我们发现单个物种的地理范围和物种出现的气候空间对于理解物种对气候变量的反应是不可或缺的。未来的研究应该使用代表物种整个地理范围的标本，