Polar bears were listed as threatened by CITES in 2008, meaning that no more wild polar bears could be imported into US zoos. This posed a problem for the zoos, because polar bears do not breed well in captivity. Polar bears have a very high incidence of stillbirths and neonatal death, at least in a zoo setting. Overall, there is only about a 30-40% cub survival rate. Which is obviously not very good. And no matter what your views on zoos are (and I can admit too that my own views on zoos are mixed), I am at least happy that something has sparked an interest in people to look into polar bear reproduction and trying to help save the species.
Currently, there is no way to diagnose of confirm a pregnancy in a polar bear. You can't take a blood sample from a polar bear, and the urine samples are usually so contaminated that they're useless. These are both methods that are used to diagnose pregnancy in humans. We are also able to use ultrasound, something else which is useless in polar bears. You can go ahead and ultrasound a polar bear, but you're not going to see anything. The abdomen is just way too big, and their uterine horns are about the size of a pinky. I don't think that anyone has managed to find them or the uterus on an ultrasound yet. So that left researchers with fecal samples.
When working with fecal samples, researchers are looking for steroid metabolites, or specifically testosterone and progesterone. There does seem to be a way to use these hormones to distinguish between pregnancy and non-pregnancy, but not between pregnancy and pseudo-pregnancy, where the body pretty much acts like it's pregnant without actually being pregnant. Researchers are also trying to figure out where all of the pregnancy loss is occurring within the polar bear's reproductive cycle using these hormones. Knowing where the loss is occurring might lead to a way to have less pregnancy loss.
A polar bear's reproductive cycle is different from ours. For one thing, they are induced ovulators. So unlike humans, who ovulate about once a month regardless of what else is happening, polar bears will only ovulate if actually stimulated by a male to ovulate. They also have a period called diapause, which is a delayed implantation of the fetus in the uterus. Polar bears are seasonal breeders, with the peak breeding season between March and May. The embryo enters diapause throughout the summer, and doesn't implant in the uterus until around September or October. After implantation, there is about a 60 day gestation, with the baby being born around December. Research has found that testosterone spikes in females around ovulation and breeding, and progesterone spikes around the time of implantation and levels remain high until birth. These hormone spikes also occur in pseudopregnant females. A non-pregnant female pretty much just flatlines with her hormones throughout the year, with no spikes.
The next step is trying to use fecal proteins to distinguish between pregnancy and pseudopregnancy. Fecal samples were broken down and the proteins run with gel electrophoresis to separate them, and at the end researchers found that there are 5 proteins that were consistently more abundant in pregnant samples compared to non-pregnancy fecal samples. All of these fecal samples were retrospective, to be sure that it wasn't a case of pseudopregnancy. And 2 out of those 5 proteins have recognized roles in pregnancy- carboxypeptidase B and transthyretin. Transthyretin is produced by the placenta in early pregnancy. This may end up being a way to distinguish pseudopregnancy from an actual pregnancy.
Another method being looked at is actually the use of Sniffer dogs. Dogs are currently used for the detection of a lot of different things- anything from drug dogs to dogs that sniff out allergies and pull their owners away, to dogs who can distinguish people with colon cancer from those without it. So there was an idea to see if dogs could distinguish between pregnant and pseudopregnant females by feces. So far a little beagle named Elvis is distinguishing pregnant from pseudopregnant females with a 95% accuracy rate. He will be traveling around zoos this coming breeding season to try and predict which females are actually pregnant, and then we'll just have to wait and see which bears cub in December. Unfortunately though, there still is no way of telling if the bear is going through pseudopregnancy or if she lost the pregnancy.
Another thing being looked at is semen collection and artificial insemination. In the past, electroejaculation was used on male bears, which works well in other species but not at all in polar bears. It's believed that all of their blubber gets in the way. Now researchers are looking at chem-facilitated collection, where medetomidine is given to the bears, which causes semen to pool in the urethra. This can then be collected by catheterization. There is no urine contamination with this procedure, and it's fast- collection time is only 3-4 minutes. So far there has been really great success with this method. The semen can then be used to artificially inseminate a female, or be frozen for future use.
Researchers are also looking at which drugs to use to induce ovulation in females. On their first female they used ECG (equine chorionic gonadotropin) and porcine LH (luteinizing hormone), which is the standard in tigers. The female this procedure was used on did exhibit nesting behavior, but never produced cubs. No one knows if it was a pseudopregnancy or if she lost the pregnancy.
Recently at Sea World San Diego, one female was bred naturally and another was bred by artificial insemination. The bear was given 2 doses of ECG separated by 4 days and was given GnRH (gonadotropin releasing hormone) at the time of breeding. Sea World has their animals and staff much better trained at collecting samples- their dolphins are trained to pee in cups for urine samples and to present their tail fin for blood collection- so they are able to collect both urine and fecal samples. So far both females are exhibiting nesting behavior, so everyone is waiting to see if there are any cubs this December.
Overall, there has been some really exciting progress. No one had ever artificially inseminated a polar bear before, and even though it was unsuccessful researchers learned a lot about the female reproductive tract in females, when before we had known literally nothing. And with populations continuing to decline in the wild, every effort to help perpetuate the species is important.
Researchers from CREW ultrasounding a polar bear
Researchers at CREW ultrasounding a polar bear
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