Barking Cats are Sexy
Zoos serve a purpose for educating the public and stimulating interest in conservation. That being said, I do think that zoo animals tend to give the public a false sense of security about the status of endangered species. It’s easy for people to tell themselves that even if habitats are destroyed, at least there are “back-up copies” in captivity. This, of course, is problematic for enough reasons to fill entire books, for scientific reasons well beyond general welfare. One key issue with viewing zoos as holding pens for biodiversity, though, is the difficulty with getting animals to breed in captivity. In general, intelligent animals with complex social structures (such as mammals, especially carnivores) are the most challenging. My undergraduate thesis work is on factors affecting the success/failure of reproduction among captive maned wolves, and digging into the multiplicity of factors that contribute to successful breeding is pretty fascinating. With so many unwanted litters among domestic dogs and cats, who knew that their wild counterparts would be so finicky?
One major factor is that many carnivore species do not ovulate before breeding. In fact, studies have shown that courtship and copulation are actually needed stimulate ovulation. This pattern—known as induced ovulation—is found in cats, camelids, rabbits, and some (not all) other mammals, especially those with multi-male mating systems. (See here for a very readable but thorough explanation of the cycle in alpacas).
In a nutshell, pheromones and/or copulation will send signals to the female’s hypothalamus, stimulating the pituitary to produce luteinizing hormones (LH). These hormones are rushed down to the ovaries, arriving at just about the same time the sperm finally arrives at the egg after an exhausting race up the female’s reproductive tract. The LH jump-starts ovulation, and the whole process is perfectly choreographed so that the follicles are ready for the sperm, just in time.
This causes all kinds of headaches for ex situ conservation programs, because many captive animals are rather awkward when it comes to courtship, and may lack the body language cues and other seduction methods used by their wild counterparts. Females may not be “turned on,” and so even successful intromission may not result in ovulation, which of course is bad news for captive breeding.
Recently, a research group led by Matt Anderson at the San Diego Zoo, has uncovered previously unrecognized signal that male cheetahs use to induce ovulation in their desired mates. Apparently, males will emit a “stutter bark” that has been shown to cause a significant spike in female reproductive hormones. One of the things that makes cheetahs unique among felids (they are a monospecific genus, are the only large cat not included in the genus Panthera), is their lack of ability to roar. Their vocal repertoire is unique among all other cats, you can listen to a sample of their signature “chirp” here and that sexy stutter bark over at National Geographic
While I am skeptical about the ultimate impact of captive breeding without equal or greater efforts to preserve habitat, there are some species which truly do need a population boost. Doing it in captivity may not be ideal, but it’s sometime the only option available. The issue of reproductive success has been especially dire for the cheetah, because both wild and captive cheetahs have miserably low heterozygosity. Hopefully the new discovery can be used to boost cheetah populations, although it will take more than extra cubs to save the species within its ecological context.