November 15, 2010
The world's fastest animal, the cheetah has not outpaced a disheartening march toward extinction. Populations have declined from an estimated 100,000 a century ago to about 13,000 today. For years, researchers have pointed to the high genetic similarities among individual cheetahs as the main reason why captive cheetahs don't often get pregnant.
"But if it was truly genetic, then wild cheetahs should have the same problem," the study's lead author, Bettina Wachter of the Leibniz Institute for Zoo and Wildlife Research in Berlin, Germany, told mongabay.com.
Sonography in the bush: Veterinarian Susanne Thalwitzer examines wild Namibian cheetah. Picture credit: Severin Goerss
Wachter and her colleagues captured 18 free-ranging female cheetahs in the open farmlands of Namibia and fitted them with GPS collars for tracking. After immobilizing the animals, researchers examined their reproductive organs with ultra-sonography—the same technique used to view human fetuses. By repeating the process with 15 captive female cheetahs, the scientists compared the reproductive health of both groups.
All of the wild cheetahs were in estrous, pregnant, or lactating: signs of active, healthy reproductive systems. About 40% of the captive adult females had active cycles. In the rest of the females, the team concluded that oestrogens—the hormones that control cycling—were impairing or "wearing out" the reproductive organs. Pregnancy and lactation give the organs a rest and promote fertility.
A sonogram of a pregnant female. It is not very sharp but this is because it is a picture out of a video tape. You can see the embryo as a white structure in the dark, i.e. liquid filled round structure. Picture credit: Susanne Thalwitzer
The team also tested whether the stress of being fenced in makes captive cheetahs breed poorly, a factor proposed by other scientists. Wachter's group measured the sizes of their cheetahs' adrenal glands, which release adrenaline and grow larger when an animal feels chronic stress. The researchers found no difference in the glands of the captive and free-ranging cheetahs.
The combined results point toward early reproduction as the key to keeping cheetahs fertile, regardless of where they live, Wachter said.
"In the wild, cheetahs have their first litter at about three years, while captive cheetahs often are not bred until they are six, seven or eight," she said. "If these animals are intended to be breeders reintroduced to the wild, this will have to change."
Cheetah (Acinonyx jubatus) in Kenya's Maasai Mara. Photo by Rhett A. Butler
A forthcoming independent study also found that a cheetah's reproductive system wears out more quickly if the animal has never been pregnant, said wildlife biologist Adrienne Crosier of the Cheetah Science Facility at the National Zoological Park in Front Royal, Virginia.
"I completely agree that the reason we often fail to reproduce cheetahs in captivity is that we wait too long with the females," Crosier told mongabay.com.
CITATION: Bettina Wachter, Susanne Thalwitzer, Heribert Hofner, Johann Lonzer, Thomas B. Hildebrandt and Robert Hermes. Reproductive history and absence of predators are important determinants of reproductive fitness: the cheetah controversy revisited. Conservation Letters published online 20 September 2010. doi: 10.1111/j.1755-263X.2010.00142.x
Danielle Venton is a graduate student in the Science Communication Program at the Science Communication Program at the University of California, Santa Cruz.
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