Bad News for Big Babies: The Elephant Fertility Crisis
By Elizabeth Deatrick
BU News Service
Baby elephants are among the most adorable infants of the animal kingdom, with their oversize floppy ears, tiny soft eyes and fuzzy rounded backs. But despite their popularity in American zoos, these babies are all too rare: Captive elephants are facing a population crash. In the early 1990s, instead of importing more elephants from the wild, zoos began breeding their own, and it didn’t take long to realize that only a few elephants were fertile. Even today, researchers are still figuring out why.
For every five Asian elephants that die in captivity today, only three are born. And the birth rates are only slightly better for African elephants. The problem isn’t just one of numbers: each time an elephant dies without reproducing, its genes disappear. American zoos already have a very small population of elephants, and losing any diversity means inbreeding becomes more likely. After too many generations of mating with their close relatives, the elephants’ offspring will eventually become sickly and prone to disease. Zoos have thirty years before the elephants start to become inbred. If the problem isn’t solved in fifty years, elephants in captivity will go extinct.
Zoos often portray themselves as bastions of conservation, so the disappearing elephants represent a failure. When elephants die out in American zoos, they’ll likely be gone from American soil for good. Thanks to international and federal restrictions, no new African importing live elephants have been imported to the U.S. since 2003, when eleven orphaned elephants, which would otherwise have been killed to prevent overcrowding, were shipped from Swaziland. Zoos also generally support the ban on elephant imports: for many, conserving elephants in the wild is just as great a priority as educating visitors using captive elephants. While wild elephants don’t suffer the same fertility problems as captive ones, their populations are faltering from habitat loss and poaching.
So what’s the biological basis for captive elephants’ infertility? “It’s complicated,” says Natalia Prado-Oveido, a doctoral candidate at George Mason University who studies elephant endocrinology. Like humans, female elephants go through hormonal cycles. However, elephants’ cycles are four months long, instead of humans’ one-month menstrual cycles. At certain points in the cycle, female elephants will enter estrous, and become receptive to male elephants’ advances. But for some unknown reason, many captive elephants no longer undergo estrous cycling––and stopping the cycle means no more elephant babies.
Even wild elephants can stop cycling naturally for many reasons: when one female in a herd becomes pregnant, the others will “tamp down” their hormonal cycles for a while, so that the resulting elephant calves are more spaced out. “We do see periods when they stop and start [naturally],” says Prado-Oveido, “the problem is when they stop and don’t start up again. We call those the non-cyclers.”
The question now is why elephants in zoos are becoming non-cyclers. Prado-Oveido believes it’s at least partially explained by a condition called hyperprolactinemia––an excess of a protein called prolactin. When normal hormonal cycles associated with reproduction are “turned off” by too much prolactin, the ovaries no longer release eggs on schedule, and it becomes difficult or impossible for a woman (or female elephant) to become pregnant.
The problem with this theory is that not all non-cycling elephants have hyperprolactinemia: some elephants are infertile, but still have low prolactin levels. Recently, researchers have been testing human medications for hyperprolactinemia on elephants, but they haven’t had much success. This suggests that the problem lies elsewhere.
Prado-Oveido isn’t the only one working on the elephant fertility problem. New research, funded in large part by the Association of Zoos and Aquariums, points to something commonly associated with human infertility: fat. In captive elephants, high body fat strongly correlates with infertility. This is a huge problem, as about forty percent of captive elephants are overweight, despite healthy diets and encouragement to exercise.
It’s likely that there’s some link between hyperprolactinemia, the elephants’ weight, and their lack of regular hormonal cycles: in humans, the same conditions that can cause hyperprolactinemia can also cause weight gain. However, because researchers have only studied elephant endocrinology for about twenty years, the chain of cause and effect remains a mystery.
For now, researchers agree, the best thing that zoos can do for their elephants is to keep them as fit as possible, and to continue working with scientists to research the fertility problem. As Prado-Oveido says, “Saving endangered species has to be a concerted effort, or else it wouldn’t work.”