Doctoral Dissertation Improvement: Feeding on Phytoestrogens - Implications for Red Colobus Monkey Physiological Ecology

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For millennia, plant species containing chemicals that alter the vertebrate endocrine system have been consumed by humans for nutritional or medicinal purposes. However, the importance of these plant chemicals, such as phytoestrogens, to human and non-human primate ecology and evolution remains unclear and largely unstudied. Phytoestrogens, defined as naturally occurring plant compounds similar in function and/or structure to endogenous vertebrate estrogens, are present in the domesticated crop foods of many cultures and have been shown to impact both reproductive and stress physiology in captive rodents and primates. Yet, little information exists on the prevalence of phytoestrogens in wild plant species and their potential impact on free-ranging, non-human primates. Because more than 99% of human history has relied on a hunter-gatherer subsistence strategy mainly dependent on wild plant-based foods, investigating the prevalence of phytoestrogens in wild plants is necessary to improve our understanding of human origins. Furthermore, the nutritional environment in which human ancestors evolved can be best reconstructed by studying living non-human primates in a natural setting, especially East African primates with a plant-based diet. Since phytoestrogens likely had a significant influence on the evolution of both human and non-human primate physiology and behavior, this project will take a deeper look at the relationship between these plant compounds and the primates ingesting them by examining their role in the physiological ecology of the Uganda red colobus monkey (Procolobus rufomitratus tephrosceles). This will be accomplished by answering three main questions: 1) How prevalent are phytoestrogens in the tropical forest tree community? 2) Does the presence of phytoestrogens influence diet choice in red colobus monkeys? 3) Does the ingestion of phytoestrogens impact stress or sex steroid levels in red colobus individuals? These questions will be addressed by collecting feeding behavior data and fecal samples from one group of red colobus during a 12-month study in Kibale National Park, Uganda. Food and non-food plant species will be screened for estrogenic activity via bioassays and HPLC analysis, and steroid hormone content (estradiol, progesterone, testosterone, and cortisol) of fecal samples from 28 individually known adults will be quantified via immunoassays. Using this data, the relationship between phytoestrogen content of plant items, primate feeding behavior, and steroid hormone levels will be examined. By combining methodology from the fields of primatology, ecology, endocrinology, and nutritional chemistry, this project will provide information that contributes to a deeper understanding of human and non-human primate biology. Additional benefits for society include improved knowledge relevant to the public health issue of the effects of phytoestrogen consumption on human welfare. Discussions of the costs and benefits of phytoestrogen consumption in human diet are currently very popular in the medical literature. Herbal treatments found in drugstores, along with soy and soy-based products, can contain high levels of these compounds. An accurate understanding of the potential impacts of phytoestrogen consumption on public health will be greatly aided by a Darwinian medical approach.