Doctoral Dissertation Research: Life history tradeoffs between testosterone and immune function among forager-horticulturalists

这个论文项目将调查能量是如何分配到竞争的生物需求在人类。男性生殖努力和免疫功能之间的权衡是人类生物学进化的几个理论基础。研究者将通过测试个体生理（包括男性睾酮）如何与寄生虫感染的免疫反应相关，以及生活方式的变化如何影响这种关系，在寄生虫病负担高的人群中探索这些理论。通过测量个体生理（激素水平）和生活方式（饮食和住房因素）如何影响寄生虫暴露和传染病风险，本研究确定的感染模式可能有助于告知治疗方案。此外，这些分析将通过教育和感染治疗改善研究地点个人的健康状况。该项目将支持本科生和研究生在STEM研究方面的培训和指导。该项目评估了Shuar人中男性生殖努力和免疫功能之间的预期生活史妥协。生活史理论（Life history theory， LHT）试图解释能量资源对关键生理和生殖功能的时间和环境敏感分配。LHT的一个关键前提是，用于一种功能的资源不能用于另一种功能；因此，预测了物质和生殖投资的不同方面之间的权衡。这些权衡是由生理调节的，包括通过激素水平。例如，睾酮激素(T)被认为是调节生殖努力和免疫之间的权衡。对非人类动物的研究表明，T通常会增加与雄性生殖相关的身体特征（例如肌肉组织）的投资，同时抑制免疫功能。然而，这种权衡并没有在人类身上得到很好的测试。Shuar经历了一个相对较高的病原体环境，随后增加了免疫激活成本。此外，病原体接触情况因其领土而异，并与其获得经济资源的机会有关。这为检验T型基因、免疫和生殖投资之间的假设关系提供了一个极好的机会。为了检验这些关联，将收集一些测量数据，包括可观察到的寄生虫种类和新鲜粪便样本中每克卵的存在；唾液样本中的T水平；被认为与发育T水平相关的物理测量（身高、握力、胸压、上臂围、2D:4D手指比例）；干燥血斑的免疫标记物；以及家庭经济、饮食和生活方式的问卷调查数据。此外，本研究将评估传统生活方式和城市化生活方式之间的T谱是否与病原体暴露差异有关。因此，这项工作将有助于我们对人类生活史、男性生殖和健康的理解，通过记录生殖和免疫反应之间的权衡，这两个能量昂贵的功能。

This dissertation project will investigate how energy is allocated to competing biological needs in humans. Tradeoffs between male reproductive effort and immune function underlie several theories about the evolution of human biology. The investigator will explore these theories by testing how individual physiology (including testosterone in men) is associated with immune responses to infection by parasites, and how lifestyle variation influences this relationship, in a population with a high parasitic disease burden. Infection patterns identified in this study may help to inform treatment protocols by measuring how individual physiology (hormone levels) and lifestyle (diet and housing factors) affect parasite exposure and infectious disease risk. Furthermore, these analyses will improve the health of individuals at the study location through education and treatment of infections. The project will support undergraduate and graduate training and mentorship in STEM research. This project evaluates predicted life history compromises between male reproductive effort and immune function among the Shuar. Life history theory (LHT) seeks to explain the timing and context-sensitive allocation of energetic resources to critical physical and reproductive functions. A critical premise of LHT is that resources used for one function cannot be used for another; thus, tradeoffs are predicted among different aspects of physical and reproductive investment. These tradeoffs are physiologically regulated, including via hormone levels. For example, the hormone testosterone (T) is thought to mediate tradeoffs between reproductive effort and immunity. Work with non-human animals has shown T to generally increase investment in physical traits associated with male reproduction (e.g., musculature) while suppressing immune function. However, this tradeoff is not well-tested in humans. The Shuar experience a relatively high pathogen environment, with subsequent increases in immune activation costs. Further, pathogen exposure varies across their territory, and in relation to their access to economic resources. This setting provides an excellent opportunity for testing the hypothesized relations among T profile, immunity, and reproductive investment. To test these associations several measures will be collected, including the presence of observable parasite species and eggs per gram in fresh fecal samples; T levels from saliva samples; physical measures thought to be associated with developmental T levels (height, grip strength, chest compression, upper arm circumference, and 2D:4D digit ratio); immune markers from dried blood spots; and household economic, dietary, and style of life questionnaire data. In addition, this study will assess if T profiles vary between traditionally-living and urbanized Shuar in relation to differences in pathogen exposure. This work will therefore contribute to our understanding of human life history, male reproduction, and health through documenting tradeoffs between reproduction and immune responses, two energetically expensive functions.