Gipson S A Y, Hall M D
School of Biological Sciences and Centre for Geometric Biology, Monash University, Melbourne, Vic., Australia.
J Evol Biol. 2018 Mar;31(3):428-437. doi: 10.1111/jeb.13237. Epub 2018 Jan 22.
The patterns of immunity conferred by host sex or age represent two sources of host heterogeneity that can potentially shape the evolutionary trajectory of disease. With each host sex or age encountered, a pathogen's optimal exploitative strategy may change, leading to considerable variation in expression of pathogen transmission and virulence. To date, these host characteristics have been studied in the context of host fitness alone, overlooking the effects of host sex and age on the fundamental virulence-transmission trade-off faced by pathogens. Here, we explicitly address the interaction of these characteristics and find that host sex and age at exposure to a pathogen affect age-specific patterns of mortality and the balance between pathogen transmission and virulence. When infecting age-structured male and female Daphnia magna with different genotypes of Pasteuria ramosa, we found that infection increased mortality rates across all age classes for females, whereas mortality only increased in the earliest age class for males. Female hosts allowed a variety of trade-offs between transmission and virulence to arise with each age and pathogen genotype. In contrast, this variation was dampened in males, with pathogens exhibiting declines in both virulence and transmission with increasing host age. Our results suggest that differences in exploitation potential of males and females to a pathogen can interact with host age to allow different virulence strategies to coexist, and illustrate the potential for these widespread sources of host heterogeneity to direct the evolution of disease in natural populations.
宿主性别或年龄所赋予的免疫模式代表了宿主异质性的两个来源，这两个来源可能会塑造疾病的进化轨迹。遇到每一种宿主性别或年龄时，病原体的最优利用策略可能会发生变化，从而导致病原体传播和毒力表达的显著差异。迄今为止，这些宿主特征仅在宿主适应性的背景下进行了研究，而忽略了宿主性别和年龄对病原体所面临的基本毒力-传播权衡的影响。在这里，我们明确探讨了这些特征之间的相互作用，发现暴露于病原体时的宿主性别和年龄会影响特定年龄的死亡率模式以及病原体传播与毒力之间的平衡。在用不同基因型的分支巴斯德菌感染年龄结构不同的雄性和雌性大型溞时，我们发现感染会增加雌性所有年龄组的死亡率，而雄性仅最早年龄组的死亡率会增加。雌性宿主允许在传播和毒力之间随着年龄和病原体基因型的不同而出现多种权衡。相比之下，这种差异在雄性中受到抑制，随着宿主年龄的增加，病原体的毒力和传播都会下降。我们的结果表明，雄性和雌性对病原体利用潜力的差异可以与宿主年龄相互作用，从而使不同的毒力策略共存，并说明了这些广泛存在的宿主异质性来源在指导自然种群中疾病进化方面的潜力。
