Saving a Giant
To say I feel small sitting next to Dumisha, a two-ton southern white rhinoceros, is an understatement. As I touch her horn, my thoughts shift. The misconception that rhino horn is powerful medicine, despite being no different chemically than fingernails, hooves or hair, is quite persistent.
I wonder how an illusion about something completely unremarkable in its chemistry nearly brought this creature to extinction a century ago. Then I remember an article I read days before reporting the highest levels of rhino poaching in decades. The article suggested that at the current rate white rhinos could be extinct in 15 years.
My thoughts now shift to amazement. As I soak in my first opportunity to touch a southern white, approximately 40 keepers, animal care managers, construction and maintenance workers, veterinarians, technicians and researchers buzz around the sedated animal. They’re an impressive team, working diligently to better understand Dumisha’s lifelong reproductive troubles. In her 28 years, she has never been a mother.
Stories like Dumisha’s are all too familiar. Like her, many female southern white rhinoceros in zoos have reproductive problems. The most striking example is that most females born in zoos never reproduce. We have known of this phenomenon for decades, but its cause still eludes us. The sexual behavior of captive- and wild-born females is similar and both breed regularly. Stress does not appear be a factor. However, there seems to be an unusually high occurrence of tumors, cysts and abnormal hormone cycles. Although diverse, these pathologies share a common thread in that they each result from exposure to high levels of the hormone estrogen.
Actually, estrogen is NOT everywhere, but widespread chemicals, collectively called “environmental estrogens,” can mimic its actions. For example, many plants produce chemicals called phytoestrogens. Literally translated as “plant estrogen,” phytoestrogens are actually not estrogens. But they can cause reproductive harm because the body sees phytoestrogens no differently than its own normally produced estrogen. Biological processes are mistakenly set in motion by phytoestrogens, especially when exposure occurs during fetal development, resulting in a myriad of damaging outcomes. The list is noticeably similar to the well-documented reproductive issues in southern white rhinos.
We were interested in determining if white rhinos get phytoestrogens in their diet and if they might be responsible for rhino reproductive problems. After five years we have made great progress and know the answer to both questions is yes. Zoo diets typically contain soy and alfalfa, which both contain phytoestrogens. Many species thrive on these diets, but white rhinos may be an exception.
Our most exciting discovery is that phytoestrogens are better at deceiving white rhino hormone function than even that of the closely related greater one-horned rhino, which reproduce well in captivity. We are now applying our results by working with staff nutritionists to find new low-phytoestrogen feeds.
Back at the Safari Park, a monitor relays video of Dumisha’s reproductive tract taken with an endoscopic camera. We believe she has leiomyomas, which are estrogen, or perhaps phytoestrogen, dependent benign tumors in her uterus. The connection between dietary phytoestrogens and these uterine anomalies is one additional piece of the puzzle that I desperately want to solve. I’m astounded that after saving the white rhino once, extinction again is possible, and it highlights the urgency to revive once successful breeding colonies by removing them from threats like poachers.
Although her age precludes Dumisha from ever reproducing, hope is not lost for her counterparts. And as I continue working with people like those helping Dumisha today, I know we share the passion and determination to protect this species. Plus, that would mean more baby white rhinos running around…who wouldn’t want to see that?
Christopher Tubbs, Scientist, Reproductive Physiology Division, San Diego Zoo Institute for Conservation Research.