Browsing by Subject "androgens"

Much of our knowledge of the mammalian immune system comes from laboratory studies of model organisms in highly controlled settings; however, in nature, organisms experience myriad biotic and abiotic pressures that can influence the immune response. Understanding how the immune system operates in natural systems therefore requires studies of animals living in socially and ecologically relevant environments. Here, I investigated the drivers of individual variation in immunocompetence in a wild population of meerkats (Suricata suricatta) living in the Kalahari Desert. The meerkat is characterised by aggressively mediated female social dominance, and although hormonal masculinization is present to varying degrees in all adult, female meerkats, the dominant female in each clan has greater concentrations of total androgens than does any other clan member. I therefore tested if the immunocompetence handicap hypothesis (ICHH), which posits that androgens in males mediate a trade off between reproductive success and immunocompetence, could apply to females and perhaps extend to their offspring. From 2012-2015, I followed and sampled approximately 300 meerkats living in 24 social clans. I related measures of immunocompetence (i.e., gastrointestinal parasite burdens and innate immune function) to environmental, demographic, social, and endocrine variables. I tested for transgenerational effects of maternally derived androgens on offspring immunocompetence by administering an antiandrogen to pregnant dominant dams. For adult meerkats, I found that there is a cost to dominance, in terms of reduced immunocompetence and that those with greater androgen concentrations (either inferred from fecal androgen metabolites or measured directly from blood as androstenedione, A4) had greater parasite burdens and weaker immune responses. Because, in female meerkats, A4 appears to exert the dual effects of promoting reproductive success and compromising immunity, I propose that the ICHH can apply to females. Moreover, the immunosuppressive consequences of female hormonal masculinization extend beyond the dams to their offspring, via prenatal exposure to raised androgens, and therefore may represent a transgenerational consequence of sexual selection operating in females. By studying immune function in natural systems, we can gain a broader perspective on immune function from an ecological and evolutionary context.

As humans continue to introduce stressors into the marine environment, we are obligated to understand how our behaviors impact wildlife. For many cetacean populations, anthropogenic noise poses a significant conservation threat, but the ability to monitor these animals is constrained by their often-remote habitats and limited time at the surface. Researchers have developed innovative solutions to overcome these challenges, including the development of techniques that enable physiological sampling with minimal disturbance. As frontiers, these methods require careful development and validation before they can be used reliably in experimental studies. In this dissertation, I employ one of these innovative techniques, measuring steroid hormones in remote blubber biopsy samples, in short-finned pilot whales (Globicephala macrorhynchus). As modulators of reproduction and stress, steroid hormones provide information that is advantageous for wildlife monitoring. Because a validated method for measuring these compounds in short-finned pilot whale blubber did not yet exist, I adapted a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to simultaneously quantify 11 steroid hormones of interest. Before proceeding with its application, I tested its analytical and biological validity with blubber from three stranded short-finned pilot whales. Next, I applied the validated LC-MS/MS method to an archive of blubber biopsies, collected from free-ranging short-finned pilot whales in the Western North Atlantic. Leveraging the comprehensive nature of LC-MS/MS profiling, I investigated relationships between hormones and characterized steroid hormone profiles across demographic groups and seasons. In the fourth chapter, I conducted an acoustic response study, using the previously established methods to collect and quantify steroid hormones after exposure to simulated mid-frequency active sonar (MFAS). I modeled the responses of cortisol and cortisone over time to gain insight into steroid perfusion rates in cetacean blubber and asked whether demography contributed to these responses. Together, my results demonstrate the reliability of blubber for measuring steroid hormones and reflecting relevant physiological states, like stress and pregnancy. While LC-MS/MS enables extensive steroid measurement, it struggled to detect some steroids of interest in this matrix. This dissertation shows the relevance of multi-steroid profiling and offers reference points for baseline steroid concentrations in analytes relevant to behavior, reproduction, and stress. The observation of post-exposure stress responses confirms a relationship between noise and physiology in short-finned pilot whales and illustrates the ability of blubber sampling to be applied in this context.