Zoos and aquariums around the world have been conducting research in the field of wildlife endocrinology (studying hormones in exotic wildlife) for a few decades now. We are few and far between, spanning the globe in our efforts to help exotic wildlife. It has been somewhat difficult to share information, ask questions, and gather information among our researchers. A few years ago, the International Society of Wildlife Endocrinology (ISWE) was formed to bring our research to the next level. The mission of San Diego Zoo Global—to bring back species from the brink of extinction—is better served with the existence of ISWE, as its members have been better able to share hormone information. This experience has proved invaluable as both a learning experience and toward advancing our science.
Studying hormones in people has many challenges but only involves one species. Studying hormones in many different species presents unique challenges in that each species may possess different hormone production mechanisms and metabolic pathways. In wildlife endocrinology, one of the many challenges lies in trying to measure the hormone of choice in a noninvasive way—a fancy way to say that we generally study hormones in the urine or feces of our collection animals!
What does all this have to do with cheetah pseudopregnancy? What is cheetah pseudopregnancy? At the 4th annual ISWE conference, I presented data looking at true pregnancy versus pseudopregnancy in cheetahs. Cheetah reproduction is very interesting in that, first, they are induced ovulators. Unlike people, the cheetah ovary experiences follicle (egg) growth that appears to come in waves similar to ours but doesn’t result in ovulation every month (or on any time schedule). Rather, cheetah follicles mature, then dissolve, mature, then dissolve without ovulation.
There are a few different animal species that experience induced ovulation, and the typical mechanism for stimulating actual ovulation of a follicle tends to be the physical act of mating. However, in cheetahs, the physical act of mating does not appear to be the trigger every time. We don’t yet understand what actually triggers a cheetah to successfully ovulate.
The next challenge involves possible pseudopregnancy. I use this term to explain that cheetahs can breed and then ovulate, which is always followed by a rise in the hormone progesterone, but sometimes not produce cubs. Cheetahs are typically pregnant for about 90 days. If they show pseudopregnancy, their progesterone levels tend to fall back to baseline levels between 50 and 60 days of the possible pregnancy. This time frame for determining cheetah pregnancy can present challenges for our animal managers in addition to time lost toward breeding efforts, critical when involved in a breeding program for an endangered species such as the cheetah.
At the ISWE conference, I presented data showing that we believe we can accurately predict true cheetah pregnancy versus pseudopregnancy between days 41 and 46 of a possible pregnancy. This is not a vast improvement over our current technology but is a step in the right direction. In the Behavioral Ecology division at the San Diego Zoo Institute for Conservation Research, we continue to reach into our scientific tool kit and explore all ways to improve the breeding efforts of collection cheetahs worldwide.
Cheetahs are currently experiencing loss of habitat in their natural ranges along with poaching by farmers. To top it off, they breed poorly in zoos. These factors combined paint a bleak picture for the survival of the cheetah. San Diego Zoo Global has worked tirelessly attempting to breed cheetahs since 1972. We have had moderate success, but we always challenge ourselves to do better because the stakes are so high. We are committed to keeping the cheetah away from the brink of extinction and breaking the code to the secrets of cheetah breeding!
Corinne Pisacane is a senior research laboratory technician for the San Diego Zoo Institute for Conservation Research. Read her previous post, Saving Shrikes from Extinction.