Reproductive endocrinology of zoo-housed aardwolves

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.