The impact of ecological variability on the reproductive endocrinology of wild female African elephants
Save the Elephants, P.O. Box 54667, Nairobi, Kenya; Department of Environmental Science, Policy and Management, University of California at Berkeley, 137 Mulford Hall, Berkeley, CA 94720, United States; Department of Reproductive Biology, German Primate Centre, 37077 Goettingen, Germany; Section of Veterinary Wildlife Studies, Faculty of Veterinary Science, University of Pretoria, 0110 Onderstepoort, South Africa
Non-invasive endocrine methods enable investigation of the relationship between ecological variation and ovarian activity and how this impacts on demographic processes. The underlying physiological factors driving high variation in inter-calving intervals among multi-parous African elephants offer an interesting system for such an investigation. This study investigates the relationship between Normalized Differential Vegetation Index (NDVI), an ecosystem surrogate measure of primary productivity, and fecal progestin concentrations among wild female elephants. Matched fecal samples and behavioral data on reproductive activity were collected from 37 focal individuals during the two-year study. Linear mixed models were used to explore the relationship between fecal 5α-pregnane-3-ol-20-one concentrations and the independent variables of NDVI, calf sex, female age, gestation day, and time since last parturition. Among both non-pregnant and pregnant females, fecal 5α-pregnane-3-ol-20-one concentrations were significantly correlated with time-specific NDVI indicating a strong relationship between ecological conditions and endocrine activity regulating reproduction. In addition, the age of a female and time since her last parturition impacted hormone concentrations. These results indicate that the identification of an individual's reproductive status from a single hormone sample is possible, but difficult to achieve in practice since numerous independent factors, particularly season, impact fecal hormone concentrations. Regardless of season, however, fecal 5α-pregnane-3-ol-20-one concentrations below 1 μg/g were exclusively collected from non-pregnant females, which could be used as a threshold value to identify non-pregnant individuals. Collectively the information generated contributes to a better understanding of environmental regulation of reproductive endocrinology in wild elephant populations, information salient to the management and manipulation of population dynamics in this species. © 2007 Elsevier Inc. All rights reserved.
3beta hydroxy 5alpha pregnan 20 one; animal experiment; article; behavior; birth; controlled study; demography; ecosystem restoration; elephant; endocrine function; evolutionary adaptation; feces analysis; female; genital system; gestation period; groups by age; hormone blood level; independent variable; multipara; nonhuman; ovary function; priority journal; productivity; reproduction; seasonal variation; sex ratio; statistical model; vegetation dynamics; 5-alpha-Dihydroprogesterone; Animals; Animals, Wild; Ecosystem; Elephants; Feces; Female; Gestational Age; Male; Pregnancy; Pregnancy, Animal; Reproduction; Seasons