Investigating Reproductive Senescence in Captive Asian Elephants (Elephas maximus) Through Long-term Hormone Monitoring
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Marcel, Alyssa Catherine
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Abstract
Whether or not elephants experience reproductive senescence, or the decline of reproductive function with age, has been a matter of some debate among researchers. While it has been shown to occur in other non-human species, data on reproductive senescence in both extant species of elephant have produced mixed results. In this study, statistical methods were applied to two previously published data sets on captive Asian elephants (Elephas maximus) to determine if age-related changes in reproductive and metabolic hormones could be detected. Multinomial regression analysis found that younger individuals (15.8-35.8 years old) had significantly higher average progestogen levels than older individuals (45.8-55.8 years old). For a separate subgroup of 11 longitudinally profiled individuals, mean hormone concentrations were profiled on an individual level across approximately 10-20 years. Interestingly, no significant age-associated changes were detected for progesterone, but the levels of several other hormones changed significantly, including that for reproductive hormones FSH and LH, both of which increased with age, and metabolic hormones, namely, cortisol, which has increased, and total T3, which has decreased. These results warrant further attention from researchers seeking to determine how Asian elephants experience reproductive aging, particularly in the North American population that is composed predominantly of post-reproductive females.
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Reproduction, Elephants, Endocrinology, Hormones