Social dominance and biology: investigating female hormonal response to non-physical competition

Abstract

Within the broad framework of evolutionary theory it is possible to develop a sustainable foundation for social dominance-hormone relationships in women. However, whilst providing an important contribution towards understanding the role of biology in social dominance, hormone-competition interactions have received considerably less attention in females than in males. Consequently, the thesis explores the relationship between salivary testosterone (T), Cortisol (F), and non-physical competition in women.petition in women. In order to address widely acknowledged difficulties with determining levels of female T, particularly the biologically active 'free' fraction as measured in saliva, a highly sensitive 'in-house' enzyme-linked immunosorbant assay (ELISA) was optimised and validated. Assay sensitivity was 0.5pg/mL; intra and inter-assay coefficients were 2.1% and 6.7% respectively; recovery ranges were between 96-105%; cross reactivity with related compounds was minimal - i.e. androstendione <8%. A modest correlation with a commercially available T assay kit is discussed in relation to the limitations inherent in direct enzyme assays. The ability to measure salivary free T at levels below those easily available to users of commercial kits is fundamental to the work in this thesis.In the absence of reliable information on the daily profile of female free T, biobehavioural studies have tended to formulate salivary sampling strategies taken directly from research involving male subjects. However, this approach may be inappropriate. Accordingly, by determining a comprehensive picture of the circadian activity of salivary T in 36 healthy female subjects, it was possible to demonstrate that T follows a circadian rhythm, the relative levels of which differ over two non-consecutive days. Moreover, throughout the course of the day T levels were highly variable, with episodic fluctuation of individual data points exceeding 83% of 9am levels. These findings highlight the necessity of collecting multiple samples in bio-behavioural research involving T and women.Incorporating methodological refinements in both the measurement of T and sampling protocol, an experimental study sought to examine the dynamic relationship between T, F, and non-physical dyadic competition. Twenty-two females (ages 19-24 years) competed in a knockout tournament involving the wood-block game 'Jenga'. They collected comprehensive salivary samples for baseline, pre- and post-competition phases. Subjects additionally reported mood states and answered questions concerning their participation in the competition. Whilst the comprehensive hormonal data resist easy interpretation, compared against baseline levels, pre-comp T and F appeared un¬ responsive in anticipation of competition. However, at 3 hrs post-competition, T levels rose 35% in winners and fell 4% in losers. F levels, conversely, fell in both losers and winners, although in winners this drop was much more pronounced. These results suggest that, similar to males, women experience a dynamic endocrine response following competition. However, the extent to which T is implicated in female social dominance is likely to be extremely small. The findings further illustrate how choice of competitive task and hormonal sampling regimens used in previous studies may, to a large extent, account for the equivocal findings in the literature. Additional research is required to ascertain ifthis pattern of endocrine response holds under a wider variety of competitive situations and also to explore more fully the psychological processes mediating hormonal responses to competition.