Abstracts (first author)
Selection on post-reproductive lifespan in Asian elephants
Among terrestrial mammals, elephants share the features with great apes and humans, of having long lifespan and offspring with long dependency. In humans, these traits combine with female menopause and an extended post-reproductive lifespan. Some have suggested that elephants, too, have a comparable post-reproductive lifespan to women, with survival into 60s in the wild and max. known age >80yrs. However, little data exists on the frequency of post-reproductive lifespan or its fitness benefits in long-lived species except humans. Long lifespan after last birth has been proposed to evolve because of the long offspring dependency and detrimental effects of early mother loss on their fitness. Here we use extensive (n>8000) individual-based multigenerational demographic records on semi-captive Asian elephants in Myanmar to investigate first, the patterns of post-reproductive survival in females and second, the short- and long-term importance of maternal care to offspring survival. We found that first, the age-specific fecundity clearly decreases after age 50, but the pattern does not correspond to the total loss of fecundity in old age found in human females. The elephant post-reproductive phase covers only one tenth of the whole lifespan, in contrast to almost half of that in women. Secondly, maternal death during the first years reduces calf survival considerably, but such effects wane rapidly with age, so that beyond age 5, mother’s death no longer increases calf risk of death. Calves surviving mother’s immediate death do not show long-term effects in later ages. Thus, Asian elephants show decreased fertility in advanced ages, but it differs distinctly from human age-specific fertility and the subsequent post-reproductive survival pattern. Our results imply that the long lifespan in elephants is not sufficiently explained only by long needed maternal care for calves and more generally, that longevity by itself does not necessarily lead to evolution of menopause.