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

本论文项目将研究能量是如何分配给人类相互竞争的生物需求的。男性生殖努力和免疫功能之间的权衡是关于人类生物学进化的几种理论的基础。研究人员将通过测试个体生理(包括男性的睾丸激素)如何与寄生虫感染的免疫反应相关联，以及生活方式变化如何影响这种关系，在一个寄生虫病负担较高的人群中来探索这些理论。这项研究中确定的感染模式可能有助于通过测量个人生理(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，从而为治疗方案提供信息。此外，这些分析将通过教育和感染治疗来改善研究地点个人的健康。该项目将支持STEM研究中的本科生和研究生培训和指导。这个项目评估了舒阿尔人中男性生殖努力和免疫功能之间的预测生活史妥协。生命史理论(LHT)试图解释能量资源分配到关键的物理和生殖功能的时机和上下文敏感。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，可以预测物理和生殖投资的不同方面之间的权衡。这些权衡是生理调节的，包括通过激素水平。例如，荷尔蒙睾酮(T)被认为在生殖努力和免疫之间起到了权衡作用。对非人类动物的研究表明，T在抑制免疫功能的同时，通常会增加对与男性生殖相关的身体特征(例如肌肉结构)的投资。然而，这种权衡并没有在人类身上得到很好的测试。Shuar经历了相对较高的病原体环境，随后免疫激活成本增加。此外，病原体暴露在他们的领土上各不相同，与他们获得经济资源的机会有关。这一设定为检验T谱、免疫力和生殖投资之间的假设关系提供了极好的机会。为了测试这些相关性，将收集几项指标，包括新鲜粪便样本中是否存在可观察到的寄生虫种类和每克虫卵；唾液样本中的T水平；被认为与发育T水平有关的体格指标(身高、握力、胸部挤压、上臂周长和2D：4D手指比率)；来自干血点的免疫标记物；以及家庭经济、饮食和生活方式问卷数据。此外，这项研究将评估传统生活和城市化的舒阿尔人之间的T谱是否与病原体暴露的差异有关。因此，通过记录生殖和免疫反应之间的权衡，这项工作将有助于我们理解人类的生活史、男性生殖和健康，这两项功能是耗费能量的。

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.