NEWS FEATURE Getting the world’s fastest cat to breed with speed NEWS FEATURE Cheetahs once rarely reproduced in captivity. Today, cubs are born every year in zoos. Breeding programs have turned their luck around—but they aren’t done yet. Amy McDermott, Science Writer Three fluffy cheetah cubs lounge under a tree at the Zoos once tried to breed cheetahs very differently, Smithsonian Conservation Biology Institute, in Front he says, keeping males and females together rather Royal, Virginia. Off exhibit from the public, the 1-year- than mimicking their lifestyle in the wild. Out on the old cats roam a large and grassy enclosure behind a savannah, females are solitary and roam vast distances. high, chain-link fence. They are the newest of 56 cubs Males defend smaller territories and mate when fe- born at this facility since 2007 (1). males pass through (2). Designing exhibits to reflect Breeding cheetahs to produce cubs such as these that natural history has been a major part of breeding was once famously difficult. The biggest problem was success over the last three decades, Saffoe says. that zoos were “not paying attention to natural his- Success has also come from a better understand- tory,” says Craig Saffoe, curator of lions, tigers, and ing of cheetah reproductive physiology (3). Reproduc- bears at the Smithsonian’s National Zoo in Washing- tive studies in the last 30 years have improved ton, DC, who in 2004 led the team that produced breeding by increasing understanding of males’ poor the zoo’s first litter. Tattoos of cheetahs now adorn sperm quality, females’ ovulation cycle, and mate his forearms. choice. Zoos now consistently produce cubs. The Cheetahs have a reputation as stubborn breeders. But the study of cats such as Fatir at the Smithsonian’s breeding facility suggests that a better understanding of natural history and reproductive physiology can dramatically improve captive reproduction. Image credit: Mehgan Murphy/Smithsonian Conservation Biology Institute. Published under the PNAS license. www.pnas.org/cgi/doi/10.1073/pnas.1918672116 PNAS | December 10, 2019 | vol. 116 | no. 50 | 24911–24915 Downloaded by guest on September 30, 2021 they try to balance animal needs, construction costs, and the desires of the public, she says. The breeding setup of large, grassy cheetah yards at the Smithsonian in Virginia would probably look unkempt to tourists. But this kind of attention to natural history is the new guard in zoos. Back in 1983, a landmark study began to explain why cheetahs wouldn’t breed in the typical zoo. It assessed genetic variation in 55 South African chee- tahs at 47 genetic loci and in 155 proteins and showed that cheetahs have unusually low levels of polymor- phisms at these sites, suggesting they have very low genetic variation—compared with not only other cats but with mammals in general. The finding was consistent with a genetic bottleneck, followed by inbreeding, at the end of the Pleistocene some 12,000 years ago (10). ’ Researchers bring males up this lover’s lane at the Smithsonian Conservation In a concurrent analysis of the cheetahs sperm, the Biology Institute to sniff around a potential mate’s enclosure. The approach same study found that 70% was deformed, and sperm mimics some of the cats’ wild behaviors. counts were 10 times lower than in other cats. It’s shocking cheetahs didn’t die out thousands of years ago, Saffoe says. After the 1983 study, “effectively the majority of North American captive cheetahs are man- community said, well there’s your problem, that’s why aged by the Association of Zoos & Aquariums (AZA), they’re not breeding. They’ve got really jacked up whose member institutions include the Smithsonian’s sperm and they’re all identical twins.” National Zoo and other zoos and facilities around the But then in 1992, researchers discovered the cats country. The AZA-managed cheetah population aver- reproduced effectively in the wild despite their ge- ages 43 births per year. netic bottleneck. Cheetahs could breed; they just Despite those successes, breeding programs are weren’t doing it in captivity. An observational study of hitting a wall of sorts, and further progress will be key 20 wild female cheetahs on Tanzania’s Serengeti found to maintaining and expanding the genetic diversity that all but one had cubs (11). Zoos then began to of captive populations. More than one-third of AZA- scrutinize their own breeding programs, Saffoe says, managed captive cheetahs still don’treproduceduetoa asking how their efforts could mimic cheetahs’ natural mix of health, behavior, and reproductive problems (4, history and reproductive biology in the wild. 5). Between 1970 and 2011, more than 70% of females To do so, researchers first needed to know how the and more than 80% of males died cubless (6). cats breed in the wild. Research in the 1980s and Assisted reproduction would help maintain the 1990s found that wild females are solitary and roam diversity of captive populations, but success has been large distances, whereas males live in coalitions of ’ mixed. Artificial insemination hasn t worked well in re- brothers in smaller territories. Females are induced- cent years. Embryo transfer has shown signs of prog- ovulators, meaning they don’t ovulate until after ress, however. This past June, researchers completed mating. Studies in the AZA-managed population have the first-ever successful transfer in cheetahs. also found that females go into estrus every 12 to All these efforts underscore a common theme: When 14 days with occasional months-long periods of ovar- it comes to breeding cheetahs in captivity, natural history ian inactivity, possibly as constant preparation for the — matters a lesson that applies beyond the race to save possibility of mating, to accommodate their solitary, cheetahs to many other rare, captive cats. induced-ovulator lifestyle. Females housed together can suppress ovulation unless the cats know and like Stubborn Breeders each other. And despite their frequent cycles, females People have struggled to breed cheetahs for hun- show few outward signs of estrus unless they’re in- dreds of years. The cats slinked through the ochre terested in mating with a male (12). palaces of the Mughal Empire some 500 years ago as This challenging reproductive biology inspired captive hunting pets. Yet there is only one record of zoos to attempt assisted reproduction beginning in their breeding in captivity before 1956 (7, 8). Zoos the 1990s via artificial insemination or embryo transfer. struggled to reliably breed cheetahs through the Artificial insemination—the introduction of sperm into 1980s, even as wild populations saw steep declines the vagina or through the cervix into the uterus—is the from habitat loss and poaching (9). more straightforward and more common method in Zoos overlooked natural history because of “a lot zoo animals. But it ’s difficult in cats because their of historic baggage,” says Nadja Wielebnowski, con- sperm are propelled through the long horns of the servation and research manager at the Oregon Zoo in wishbone-shaped uterus to the oviducts by muscle Portland. Zoos began as menageries of exotic and contractions. Anesthetized females don’t make these often little-understood species. Although many facilities contractions, so sperm don’t meet eggs (13). Two have made updates, most still have limited resources as breakthrough studies in the 1990s involved directly 24912 | www.pnas.org/cgi/doi/10.1073/pnas.1918672116 McDermott Downloaded by guest on September 30, 2021 inseminating housecat uteruses and cheetah uteruses, transfer cheetahs among their facilities to match successfully producing 15 cheetah pregnancies be- potential mates. tween 1992 and 2003 (14, 15). To breed a female cat in Virginia, Crosier’s team But despite repeated attempts since 2003, it was first moves that target female out of her pen and into a the last successful cheetah artificial insemination ever new yard nearer to the males to stimulate estrus with a conducted, says Bill Swanson, Director of Animal Re- change of scenery. After a few days, the team moves search at the Cincinnati Zoo & Botanical Garden in the female indoors with a treat and brings a male or Ohio. The reasons for the failures remain unclear. One males down lover’s lane to sniff around the female’s possible explanation is a change in the manufacturer now-empty territory. In the wild, he’d smell her before of the hormones that zoos use to induce ovulation he saw her, Crosier explains. If the male stutter barks, a before artificial insemination. But even after changing mating vocalization like a pigeon’s coo, “then he’s hormone sources, cheetahs still aren’t getting preg- allowed to see her,” Crosier says. If he doesn’t bark, “ ” “ nant through artificial insemination. Even surgically then he just goes home. Today, she explains, is not ” putting sperm into the oviducts, onto the eggs— the day. which has yielded pregnancies in ocelots, tigers, jag- But even though the AZA suggests pairing certain uars, and other wild cats—has not worked for chee- males and females to make good genetic matches, tahs, Swanson says. cheetahs are picky, and about one-third of recom- ’ More recent research implies that a female’s age at mended pairs don t breed, Crosier says. One way that first pregnancy strongly influences her reproductive ongoing research attempts to improve reproduction success. For example, a study published this April fol- is through greater understanding of mate choice. A lowed 12 female cheetahs in European zoos through- study published last June, for example, tested scent as out their lives and found that cats with a first pregnancy a possible indicator of mate preference, available before the age of 5 1/2 had higher reproductive before cats meet (17).