FIGURE 5-4 Schematic diagram of factors that mediate the effects of psychological stress on the activity of the hypothalamic-pituitary-gonadal axis.

sible to measure group mean responses to specific stresses and make conclusions about the effect of a stress on a species’ reproductive axis, such a mean assessment may be of little use in determining whether an individual will experience a suppression of reproductive function in response to that stress. An increased understanding of the mechanisms by which psychological and social stresses suppress the activity of the reproductive axis may well be achieved by focusing future studies on these individual differences in response to stress.

SUMMARY AND FUTURE DIRECTIONS

It is becoming clear that to fully understand the multiplicity of factors that come together to regulate and modulate reproductive physiology and reproductive behavior will require integration of demographic and biomedical approaches to these research issues. Many aspects of reproductive biology are difficult to study from the perspective of population biology approaches because of the great variation in function within an individual over a short course of time, such as with fluctuations in hormone levels over the menstrual cycle or even the fluctuation in reproductive hormone levels on an hour-to-hour basis. Biomedical approaches of studying individuals in more detail will be able to define relationships more clearly but are limited by the low power of examining relatively few individuals. What is needed is a twofold approach, first of developing studies that nest demographic and biomedical approaches together and second of using biomedical studies to inform the design of demographic studies.

The first approach would involve performance of large demographic studies to understand the relationships between variables on a global scale, with a select subset of individuals studied in much more detail to test specific hypotheses or to differentiate between possible mechanisms underlying the general relationship. The second approach simply requires further



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