Data from: Host sex modulates the energetics of pathogen proliferation and its dependence on environmental resources

Sex differences in immunity are predicted to underlie much of the
frequently observed sex differences in the prevalence or severity of
infection. We propose the additional hypothesis that differences in the
ability of males and females to acquire and use resources will also affect
how readily a pathogen can convert host energy into transmission stages,
thereby contributing to sex differences in infection dynamics. To test
this we manipulated the resource environment of male and female Daphnia
magna by altering the availability of food and then exposed hosts to a
bacterial pathogen. We measured the production of transmission spores and
virulence via the reduction in life span, together with feeding rates and
changes in mass-independent metabolic rate, as a measure of the intake and
expenditure of energy during infection. When raised in the presence of
high resource levels, females more readily allowed for resources in the
environment to be translated to pathogen exploitation, as represented by
increased spore production, greater virulence, and higher energy use. In
contrast, the traits of infected males were robust to changes in resource
availability. High food availability thus exaggerated the degree of sexual
dimorphism observed between the sexes. It also modified the relationship
between host energy use, virulence, and pathogen spore production for each
sex. These results suggest that a host’s resource environment can affect
how a male or female is exploited by a pathogen and may thus be an
additional factor driving sex-specific patterns of disease susceptibility
or severity.

免疫系统的性别差异被认为是诸多已频繁观测到的感染患病率或严重程度性别差异的核心诱因。我们提出额外假说：雌雄个体获取和利用资源能力的差异，同样会影响病原体将宿主能量转化为传播阶段的难易程度，进而参与塑造感染动态的性别差异。为验证该假说，我们通过调整食物供应量操控大型溞（Daphnia magna）雌雄个体的资源环境，随后令宿主接触细菌性病原。我们通过寿命缩短程度量化传播孢子的产量与病原毒力，同时测定摄食率与体重无关代谢率（mass-independent metabolic rate）的变化，以此作为感染过程中能量摄入与消耗的评估指标。在高资源供给环境下饲养时，雌性个体更易将环境中的资源转化为病原体增殖所需的资源，具体表现为孢子产量提升、毒力增强以及更高的能量消耗。与之相反，受感染雄性的各项性状对资源供应量的变化并不敏感。因此，高食物供给会放大两性间观测到的感染相关性状差异，同时还改变了雌雄个体各自的宿主能量消耗、病原毒力与病原体孢子产量之间的关联。上述结果表明，宿主的资源环境会影响病原体对雌雄个体的利用程度，或可成为驱动疾病易感性或严重程度呈现性别特异性模式的额外因素。