Some say that opposites attract. Others say that birds of a feather flock together. Conservation biologists often determine which two individuals ought to, err, flock together, simply based on their genes. There’s just one problem: animals are more than sacks of genetic materials. Just because two animals would produce the most genetically valuable offspring doesn’t mean the two critters are actually compatible – at least in the birds and the bees sense of the word. Sure, researchers can combine sperm and egg and implant the developing embryo into a female, but that’s not always the most feasible approach to the problem – and it comes with a hefty price tag. Despite the seeming frequency with which throngs of zoogoers are treated to newborn infants, it turns out that it’s actually quite difficult to coax pandas to mate. A new study finds that giant pandas are more likely to mate and produce offspring – the old fashioned way – if they are simply allowed to choose their own partners.

Of nearly 8,000 vertebrate species listed on the IUCN Red List, “captive breeding played a major role in the recovery efforts of 15% of the species whose threat level has been reduced.” That’s according to Meghan S. Martin-Wintle of San Diego Zoo’s Institute for Conservation Research and PDXWildlife, writing this week in the journal Nature Communications. Together with her colleagues from Portland State University, the Oregon Zoo, and the China Conservation and Research Center for the Giant Panda, Martin-Wintle put together a clever experiment to see whether giant pandas would be more likely to bear offspring if they were allowed to choose their partners.

The experiment was carried out in 2012 and 2013 at the Bifengxia Chinese Conservation and Research Center for the Giant Panda in China’s Sichuan province. Both males and females were allowed visual (but not physical) access pairs of pandas of the opposite sex. The researchers monitored them for pre-mating behaviors, like scent marking, urination, chirping, erection (for males), raising their tail (for females), and so on. They also noted negative interactions such as barking or growling, and attempts at physical aggression. A potential partner was defined as “preferred” if the panda directed the majority of its positive pre-mating behaviors towards one individual and not the other.

Once a pair was allowed to attempt mating, the researchers assessed whether copulation occurred and whether the female became pregnant and produced a cub.

As might have been expected, breeding either sex to a preferred mate almost always increased successful intromission. Copulation occurred as low as 0% of the time when neither partner preferred the other, and as high as 80% when there was mutual preference between the two. And when both members of the copulating duo showed a preference for each other, the likelihood of delivering a healthy cub was a whopping 75%.

Even though loads of money and time have been devoted to panda breeding efforts, the effort to involve the pandas themselves in their own breeding decisions is unique. “Ours is the first study to rigorously examine the effects of mate preference in giant pandas,” write the researchers. It’s also the first to consider male mating preference at all within the scope of a conservation breeding program, since most traditional views assign choosiness to the females rather than the males, at least for species without extensive paternal care. The results of this study, to the contrary, suggest that both sexes have at least some level of preference, and that successful reproduction is a direct consequence of those preferences.

On the face of it, the idea of allowing large, charismatic animals to choose their own partners seems like an obvious move – especially for a species already infamous for its pickiness. But from a biological perspective, captive breeding and reintroduction programs rely upon having a large population of genetically diverse individuals to serve as “founders” of the reintroduced population. At its heart, this is the struggle between thinking of animals as individuals, with individual motivations and complex desires, and thinking of animals as members of a population. Since wildlife conservation is primarily concerned with populations, the evaluation of mate preference is “traditionally underemphasized,” according to Martin-Wintle. She argues that behavioral compatibility ought to be considered on par with genetic compatibility when developing or revising captive breeding protocols for endangered or threatened species. After all, as the researchers point out, “the future of conservation breeding will not take place in a test tube.” Perhaps it’s best to let the pandas sort out their own breeding recommendations. – Jason G. Goldman | 16 December 2015

Source: Meghan S. Martin-Wintle, et al. (2015). Free mate choice enhances conservation breeding in the endangered giant panda. Nature Communications 6, 10125. DOI: 10.1038/ncomms10125.

Header image: Giant panda cubs playing in the panda kindergarten at the China Conservation and Research Center for the Giant Panda (CCRCGP) Bifengxia base in Sichuan, China. Credit: PDXWildlife intern Grace Russell.