Southern white rhinoceros populations, once thriving in zoos, have been showing severely reduced reproductivity among the captive-born population. San Diego Zoo Global researchers have a possible lead into why the southern white rhinoceros population in managed-care facilities is declining: phytoestrogens in their diet might be contributing to reproductive failure in the females.
"Understanding why the captive white rhinoceros population has been dwindling for decades is an important part of protecting the future of this species," said Christopher Tubbs, researcher with the San Diego Zoo Institute for Conservation Research. "Our work is the first step toward determining if phytoestrogens are involved in this phenomenon and whether we need to reevaluate captive white rhino diets."
After elephants, the southern white rhinoceros is the world's second largest land animal. This rhino species also occupies another list—that of the International Union for Conservation of Nature's "near-threatened" species. Wild populations face poaching and sport hunting, but captive populations of this animal are declining due to reproductive problems in the females. These include cystic endometrial hyperplasia; cervical, ovarian, and uterine cancers; and ovarian cysts.
San Diego Zoo researchers believe the diets of the captive population offers much concern. Specifically, phytoestrogens, such as isoflavinoids found in the alfalfa and soy that they eat, activate their estrogen receptors more than those of the greater one-horned rhinoceros, another captive population that receives a similar diet but has better reproductive success.
The study, published in the March issue of Endocrinology, compares populations that are doing well with populations whose reproductivity is placing them at risk, citing diet as a key difference between the two.
The San Diego Zoo Institute for Conservation Research is dedicated to generating, sharing and applying scientific knowledge vital to the conservation of animals, plants and habitats worldwide. The work of the Institute includes onsite research efforts at the San Diego Zoo and the San Diego Zoo Safari Park (historically referred to as Wild Animal Park), laboratory work at the Arnold and Mabel Beckman Center for Conservation Research, and international field programs involving more than 235 researchers working in 35 countries. In addition to the Beckman Center for Conservation Research, the Institute also operates the Anne and Kenneth Griffin Reptile Conservation Center, the Frozen Zoo® and Native Seed Gene Bank, the Keauhou and Maui Hawaiian Bird Conservation Centers, Cocha Cashu Biological Research Station and the Desert Tortoise Conservation Center. The Zoo also manages the 1,800-acre San Diego Zoo Safari Park, which includes a 800-acre biodiversity reserve, and the San Diego Zoo. The important conservation and science work of these entities is supported in part by The Foundation of the Zoological Society of San Diego.
Journal
Endocrinology