Pandas are typically thought of as a lost cause. They're one of the most endangered species on the planet; just 2500 giant pandas live in the wild. They're notoriously difficult to breed; zoos keep them around primarily to attract tourists rather than for any ostensible conservation benefit. At least, that's the perception.
Until as recently as the 1990s, efforts were indeed plagued by low rates of conception and high rates of disinterest among matched pairs. Even when a panda cub was born, they were not likely to survive very long. Only 30 percent of captive giant pandas successfully reproduced, and of those cubs, more than 60 percent died in infancy.
But two important innovations allowed for recent successes in panda breeding. The first was artificial insemination, either with freshly collected or with frozen and thawed sperm. The process is now routine at panda breeding centers, both in China and abroad. Second, the care for newborn pandas has improved tremendously. A large proportion of neonatal deaths can be attributed to the intentional "discard" of one of two twins by a panda mother. More recently, however, husbandry techniques have been developed for the successful rearing of panda cubs by humans. In 2002, neonatal survival had increased to 71%.
A 2010 study revealed that while 52 bird, mammal, and amphibian species creep their way closer to extinction each year (that is, they get more dire classifications according to IUCN criteria), that rate would could be as much as twenty percent worse if not for active conservation-related efforts. In fact, that study identified 68 threatened species whose conservation status was improved, thirteen of which were due to breeding and reintroduction programs. Despite the contentious nature of captive breeding, for some species at least, they seem to work. Like pandas.
There are three large Giant panda (Ailuropoda melanoleuca) breeding centers: Chengdu Research Base of Giant Panda Breeding, China Research and Conservation Center for the Giant Panda at Wolong, and Shaanxi (Louguantai) Rescue and Breeding Center for Rare Wildlife. Combined with the Beijing Zoo, the four centers are responsible for maintaining genetically healthy panda populations, both in the wild and in captivity; China even oversees the majority of captive panda work even in US institutions like the San Diego and National Zoos.
By the late 1990s, the captive panda population included more captive-born individuals than those born in the wild. By 2012, there were 341 giant pandas in captive breeding programs.
That relative success means that researchers are finally beginning to plan the strategic release of captive-born pandas back into their wild habitats. But the success of a release program depends not just on "a large population, but also ample genetic variation as a genetic resource bank for wild populations." That's according to conservation biologist Lei Shan of the Chinese Academy of Science's Institute of Zoology.
Above: San Diego Zoo panda Zhen Zhen (Nathan Rupert/Flickr)
As part of the preparation for a reintroduction plan, Shan and colleagues set out to determine whether the population of captive pandas has sufficient genetic diversity. It is a common belief, they say, that the pandas in the four breeding centers suffer from severe inbreeding, and there is little information on whether there is any gene flow between the four centers. To address the question, the researchers assessed genetic variation and inbreeding levels in 240 individuals, which represents nearly two thirds of the entire captive panda population.
Happily, the captive panda population turns out to harbor quite a bit of genetic diversity! In fact, the diversity in the captive populations is comparable to previous estimates for wild panda populations. The genetic diversity in the captive panda population is actually even higher than that of captive populations within other high-profile reintroduction programs, like black-footed ferrets and the California condors. In other words, the captive population is sustainable; it doesn't need an influx of new genetic material from wild individuals. It also means that is reasonable to transfer individuals from the breeding population back into the wild.
Left: A juvenile San Diego Zoo panda, Yun Zi (Nathan Rupert/Flickr)
That's all great news, but everything isn't perfect. While the captive population as a whole is genetically healthy, some issues did arise when the individual breeding centers were considered on their own. The Shaanxi (Louguantai) Center, for example, has only 19 individuals and is itself at risk of serious inbreeding. However, the solution isn't as simple as encouraging more transfers among the centers. That's because the wild animals that founded each of the captive populations may have had important evolutionary adaptations that allowed them to survive just a bit better in their slightly different environments.
The "Qinling" population, for example, of which the Shaanxi pandas are members, diverged from the rest of the species a third of a million years ago. Since then, the Qinling evolved unique anatomical features that distinguish them from other pandas. If the Shaanxi center traded individuals with the Chengdu center, from a genetic perspective, it would effectively represent a trade between the Qinling and non-Qinling wild populations. How would non-Qinling individuals survive if reintroduced into the Qinling environment, and vice versa? What about hybrid offspring? "This exchange may disrupt patterns of local adaptation established over hundreds of thousands of years, and thus would result in an unpredictable impact on wild populations if captive individuals were reintroduced into their original environments," writes Shan.
Rather than the traditional route towards avoiding inbreeding, which involves trading individuals or sperm between centers, the researchers advocate that the Shaanxi center be managed on its own, to retain the genetic uniqueness of that sub-population. On the other hand, they recommend that the remaining three centers increase their trade of individuals or of sperm in order to maintain current levels of genetic diversity.
The most comprehensive survey of the captive giant panda population ever attempted, this study reflects the effectiveness and success of China's giant panda captive breeding program. But Shan's research also underscores the supreme importance of considering not just population-wide genetic diversity but also the genetic compatibility of candidates for release with the environment and community into which they are to be released. Not all pandas, it seems, are created equal.