Age- and tactic-related paternity success in male African elephants

Information on age- and tactic-related paternity success isessential for understanding the lifetime reproductive strategyof males and constitutes an important component of the fitnesstrade-offs that shape the life-history traits of a species.The degree of reproductive skew impacts the genetic structureof a population and should be considered when developing conservationstrategies for threatened species. The behavior and geneticstructure of species with large reproductive skew may be disproportionatelyimpacted by anthropogenic actions affecting reproductively dominantindividuals. Our results on age- and tactic-specific paternitysuccess in male African elephants are the first from a free-rangingpopulation and demonstrate that paternity success increasesdramatically with age, with the small number of older bullsin the competitive state of musth being the most successfulsires. However, nonmusth males sired 20% of genotyped calves,and 60% of mature bulls (>20 years old) were estimated tohave sired offspring during the 5-year study period. The 3 mostsuccessful males sired less than 20% of the genotyped offspring.Hence, contrary to prediction from behavior and life-historytraits, reproduction was not heavily skewed compared with manyother mammalian systems with a similar breeding system. Nevertheless,these results indicate that trophy hunting and ivory poaching,both of which target older bulls, may have substantial behavioraland genetic effects on elephant populations. In addition, theseresults are critical to the current debate on methods for managingand controlling increasing populations of this species.     

Predictors of testosterone in zoo-managed male African elephants (Loxodonta Africana)

Reproductive complications for both male and female zoo-managed African elephants (Loxodonta africana) contribute to the rapidly declining population. In zoo-managed bull elephants, few studies have explored the potential physiological, physical, social, and environmental factors that influence bull fertility, particularly, androgen production. Testosterone is the essential steroid hormone for male sexual maturation and inadequate concentrations can be detrimental for spermatogenesis. Testosterone, fecal glucocorticoid metabolites, leptin, glucose, insulin, and triglycerides were analyzed from weekly fecal and blood serum samples taken over 6 months from six zoo-managed African elephant bulls (10–19 years of age). Testosterone levels were compared to endocrine factors, weekly social and environmental variables, daily musth signs, and body condition scores (BCS). The glucose-to-insulin ratio (G:I) was the only physiological biomarker found to be positively associated with testosterone. Predictive physical variables included Musth Score (+) and Moderate Exercise (+). Bulls with BCS signifying overweight (BCS 4) had lower testosterone (36.6 ± 1.6 ng/g fecal extraction [FE]) than bulls with healthy BCS 3; 51.2 ± 4.9 ng/g FE). Numerous social variables influenced testosterone concentrations, including Total Contact Day (+), Female Interaction Day (+), Indirect Contact Day (+), Indirect Contact Night (+) and Total No Contact (−). Both percentage of Time Outdoor and Time Mixed positively influenced testosterone, whereas testosterone decreased for percentage of Time Indoors. Each additional daily browse opportunity increased testosterone by approximately 7 ng/g FE. In managed care, the emphasis should be placed on optimizing these predictors of testosterone production to promote bull reproductive health.