Abstract：
AbstractTerrestrial mammals span seven orders of magnitude in body size, ranging from the <2-g Etruscan pygmy shrew (Suncus etruscus) to the >3,900-kg African elephant (Loxodonta africana). Although body size profoundly affects the behavior, physiology, ecology, and evolution of species, how investment in functional immune defenses changes with body size across species is unknown. Here, we (1) developed a novel 12-point dilution curve approach to describe and compare antibacterial capacity against three bacterial species among >160 terrestrial species of mammals and (2) tested published predictions about the scaling of immune defenses. Our study focused on the safety factor hypothesis, which predicts that broad, early-acting immune defenses should scale hypermetrically with body mass. However, our three statistical approaches demonstrated that antibacterial activity in sera across mammals exhibits isometry; killing capacity did not change with body size across species. Intriguingly, this result indicates that the serum of a large mammal is less hospitable to bacteria than would be predicted by its metabolic rates. In other words, if metabolic rates underlie the rates of physiological reactions as postulated by the metabolic theory of ecology, large species should have disproportionately lower antibacterial capacity than small species, but they do not. These results have direct implications for effectively modeling the evolution of immune defenses and identifying potential reservoir hosts of pathogens.
摘要：
陆地哺乳动物的体型跨越七个数量级，范围从<2-g伊特鲁里亚侏儒（Suncusetruscus）到>3,900公斤的非洲象（Loxodontaafricana）。虽然身体大小会深刻影响行为，生理学,生态学,和物种的进化，对功能性免疫防御的投资如何随着物种的体型而变化是未知的。这里,我们（1）开发了一种新的12点稀释曲线方法来描述和比较对超过160种陆地哺乳动物中三种细菌的抗菌能力；（2）测试了已发表的有关免疫防御规模的预测。我们的研究集中在安全系数假设上，它预测了广泛的，早期免疫防御应随体重高度变化。然而,我们的三种统计方法表明，哺乳动物血清中的抗菌活性表现出等轴测性；杀伤能力没有随物种大小而变化。有趣的是，这一结果表明，大型哺乳动物的血清对细菌的好感不如其代谢率所预测的。换句话说,如果代谢率是生态学代谢理论假定的生理反应率的基础，大物种的抗菌能力应该比小物种低，但他们没有。这些结果对于有效模拟免疫防御的进化和识别病原体的潜在储库宿主具有直接意义。
