Body mass affects many biological traits, but its impacts on immune defences are fairly unknown. Recent research on mammals found that neutrophil concentrations disproportionately increased (scaled hypermetrically) with body mass, a result not predicted by any existing theory. Although the scaling relationship for mammals might predict how leucocyte concentrations scale with body mass in other vertebrates, vertebrate classes are distinct in many ways that might affect their current and historic interactions with parasites and hence the evolution of their immune systems. Subsequently, here, we asked which existing scaling hypothesis best-predicts relationships between body mass and lymphocyte, eosinophil and heterophil concentrations—the avian functional equivalent of neutrophils—among more than 100 species of birds. We then examined the predictive power of body mass relative to life-history variation, as extensive literature indicates that the timing of key life events has influenced immune system variation among species. Finally, we ask whether avian scaling patterns differ from the patterns we observed in mammals. We found that an intercept-only model best explained lymphocyte and eosinophil concentrations among birds, indicating that the concentrations of these cell types were both independent of body mass. For heterophils, however, body mass explained 31% of the variation in concentrations among species, much more than life-history variation (4%). As with mammalian neutrophils, avian heterophils scaled hypermetrically (b = 0.19 ± 0.05), but more steeply than mammals (approx. 1.5 ×; 0.11 ± 0.03). As such, we discuss why birds might require more broadly protective cells compared to mammals of the same body size. Overall, body mass appears to have strong influences on the architecture of immune systems.

中文翻译：

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体重对鸟类免疫细胞浓度的影响

体重会影响许多生物学特征，但其对免疫防御的影响尚不清楚。最近对哺乳动物的研究发现，中性粒细胞浓度随体重不成比例地增加（超量测），这是任何现有理论都无法预测的结果。尽管哺乳动物的比例关系可能会预测白细胞浓度如何随其他脊椎动物的体重而变化，但脊椎动物类别在许多方面是不同的，这可能会影响它们当前和历史上与寄生虫的相互作用，从而影响它们的免疫系统的进化。随后，在这里，我们询问现有的比例假设哪个最能预测 100 多种鸟类的体重与淋巴细胞、嗜酸性粒细胞和嗜异性粒细胞浓度（中性粒细胞的鸟类功能等价物）之间的关系。然后，我们检查了体重相对于生活史变异的预测能力，因为大量文献表明，关键生活事件的发生时间影响了物种之间的免疫系统变异。最后，我们询问鸟类的缩放模式是否与我们在哺乳动物中观察到的模式不同。我们发现仅拦截模型最能解释鸟类中淋巴细胞和嗜酸性粒细胞的浓度，表明这些细胞类型的浓度均与体重无关。然而，对于嗜异性生物，体重解释了物种间浓度变化的 31%，远高于生活史变化 (4%)。与哺乳动物嗜中性粒细胞一样，禽类嗜中性粒细胞高度测量（b = 0.19 ± 0.05），但比哺乳动物更陡峭（约 1.5 ×；0.11 ± 0.03）。像这样，我们讨论了为什么与相同体型的哺乳动物相比，鸟类可能需要更广泛的保护细胞。总的来说，体重似乎对免疫系统的结构有很大的影响。