Abstract:
Knowledge regarding the relationship between endocrine parameters and reproductive activity
can offer important insights into how social and environmental factors influence the
reproductive success of mammals. Although components of both the physical and social
environment affect endocrine regulation of reproduction, less is understood about the
potential role of interactions between different endocrine axes on reproductive activity. We
evaluated temporal patterns of reproductive and adrenocortical steroids in two male and three
female aardwolves (Proteles cristata) housed in captivity at Brookfield Zoo, Chicago, USA.
We found seasonal variation in faecal androgens, estrogens, and progestagens, which provide
support for previous observations of the aardwolf as a seasonal breeder. However, the timing
of peak endocrine activity did not correspond to observations from wild populations. Our
interpretation is that this discrepancy is caused by photoperiodic regulation of reproductive
activity. We found a positive relationship between faecal androgens and faecal glucocorticoid
metabolites in males and a positive relationship between faecal estrogens and faecal
glucocorticoid metabolites in females when housed with conspecifics but not when housed
alone. We also found a positive but asymptotic relationship between faecal progestagens and
faecal glucocorticoid metabolites. We argue that these observations indicate a potential effect
of reproductive endocrine activity on the hypothalamic-pituitary adrenal axis, which could
result in interesting physiological trade-offs in male reproductive tactics and female prepartum
maternal investment because of the negative effects of long-term glucocorticoid
elevation on reproductive performance. Finally, our results suggest that social and
environmental factors interact in regulating many aspects of endocrine fluctuations in this
mostly solitary species.
