Impacts of environmental pressures on the reproductive physiology of subpopulations of black rhinoceros (Diceros bicornis bicornis) in Addo Elephant National Park, South Africa.

Black rhinoceros are an icon for international conservation, yet little is known about their physiology due to their secretive nature. To overcome these challenges, non-invasive methods were used to monitor rhinoceros in two sections of Addo Elephant National Park, South Africa, namely Addo and Nyathi. These sections were separated by a public road, and the numbers of elephants, predators and tourists were higher in Addo. Faecal samples (n = 231) were collected (from July 2007 to November 2010) from known individuals and analysed for progestagen and androgen metabolite (FPM and FAM, respectively) concentrations. As biotic factors could impact reproduction, we predicted that demographics, FPM and FAM would vary between sections and with respect to season (calendar and wet/dry), climate and age of the rhinoceros. Mean FPM concentrations from pregnant females were seven times higher (P < 0.05) than samples from non-pregnant rhinoceros. Positive relationships were found between monthly temperatures and FPM from non-pregnant females (r (2) = 0.25, P = 0.03) and the percentage of calves born (r = 0.609, P = 0.04). Although FAM peaked in the spring, when the majority of calves (40%) were conceived, no seasonal patterns in male androgen concentrations were found with respect to month of conception and parturition. Females in Addo had a longer inter-calving interval and were less likely to be pregnant (P < 0.05) compared with those in Nyathi. The biotic stressors (e.g. predators and more competitors) within Addo section could be affecting the reproductive physiology of the rhinoceros negatively. Enhanced knowledge about how black rhinoceros populations respond to environmental stressors could guide management strategies for improving reproduction.

Ovarian cycle activity varies with respect to age and social status in free-ranging elephants in Addo Elephant National Park, South Africa.

Free-ranging African elephants live in a fission-fusion society, at the centre of which is the matriarch. Matriarchs are generally older females that guide their families to resources and co-ordinate group defense. While much is known about elephant society, knowledge is generally lacking about how age affects the physiology of wild elephants. Investigation of the ovarian activity of free-ranging elephants could provide insight into the reproductive ageing process, with implications for population management. Faecal samples were collected from 46 individuals ranging in age from 14 to 60 years for a 2-year period, and progestagen metabolite analyses were used to examine relationships between social status, age, season, and ovarian activity in female elephants in Addo Elephant National Park, South Africa. Social status was the strongest predictor of faecal progestagen metabolite concentrations in non-pregnant elephants, with grand matriarchs (n = 6) having the lowest values compared with matriarchs (n = 21) and non-matriarch females (n = 19). Likewise, social status and age were the strongest predictors of faecal progestagen metabolite concentrations in pregnant elephants (n = 27). The number of years since a non-pregnant female gave birth to her last calf (post-partum duration) was longer for older females with a higher social status, as well as during the dry season. Our results indicate that social standing and age of elephants are related to reproductive function, and that older females exhibit reductions in ovarian capacity. These results expand our understanding of reproduction and fertility throughout an elephant's lifespan, and the factors that impact gonadal function in free-ranging females. Given that possible over-abundance of elephants in areas such as Addo Elephant National Park is fuelling the debate over how best to manage these populations, knowledge about the reproductive potential of high-ranking females can provide managers with biological data to identify the best candidates for controlling growth through translocation or contraception.

Species and fetal gender effects on the endocrinology of pregnancy in elephants.

Quantitative and temporal progestin profiles vary during gestation in the elephant, sometimes making it difficult to determine if a pregnancy is progressing normally. The aim of the present study was to determine if circulating progestin variability was related to species or fetal gender effects. A similar comparison also was conducted for secretory profiles of prolactin, relaxin, and cortisol. Overall mean progestin concentrations during gestation in Asian (n = 19) and African (n = 8) elephants were similar; however, the temporal profiles differed (P < 0.001). Concentrations were higher in African elephants during the first half of pregnancy, but then declined to levels below those observed in Asian elephants (P < 0.05). There also was a fetal gender effect in Asian, but not African elephants. Progestin concentrations were higher in Asian cows carrying male calves (n = 9) as compared to those carrying females (n = 10) (P < 0.001). Overall prolactin concentrations were higher in Asian than in African elephants between 8 and 15 months of gestation ( P< 0.001). There were no species differences in the secretory patterns of relaxin. Cortisol was relatively stable until the end of gestation when significant surges were observed, mainly between 8 and 11 days before parturition, and again on the day of birth. In sum, a comparison of progestin patterns between Asian and African elephants identified notable differences related to species and fetal gender. A role for cortisol in the initiation of parturition also was inferred from these data. From a practical standpoint, understanding the factors affecting gestational hormone characteristics and recognizing what the species differences are will help ensure that data used in diagnosing and monitoring elephant pregnancies are properly interpreted.