Zoo Plays High-Stakes Mating Game, WithÂ Future of Species at Stake
July 7, 2004
Years after his death, Herschel the bull remains a top stud.
In the incestuous world of zoo dating, Herschel's genes are some of the most valuable of any male banteng in North America.
Banteng are one of the rarest species of cattle. With 5,000 or so Banteng clinging to existence worldwide, the 317 thin straws filled with Herschel's frozen sperm at the St. Louis Zoo are helping ensure the species' survival.
Having the most desired genes of your species takes little more than dumb luck. Many species of animals kept in North American zoos have fewer than 100 members in captivity, and many are closely related. Outsider animals bring fresh genes, helping prevent inbreeding and disease.
When Herschel arrived at the St. Louis Zoo in 1982 from a Dutch zoo, he was the hot new bull, soon to grow to 1,500 pounds. Now, 10 offspring later, Herschel's genes are still sought after.
"You need a healthy captive population as a safety net for the wild," said Diane Wilson, a zoological manager at the Zoo. "If you ever want to put the population back into the wild, you want them as healthy as possible. To have Herschel still able to contribute to the population is a great thing."
Keeping the genes fresh is key to how zoos make animal families. Recently the St. Louis Zoo needed a mate for a 3-year-old female tiger named Kalista, whose genes rank the second most valuable in North America. They found him in T.J., an 11-year-old from the Denver Zoo.
Inbreeding is dangerous because it can propagate defective genes. Mating among genetically diverse species tends to wipe out defective genes. In human populations, inbreeding over time leads to genetic diseases such as Tay-Sachs, found most commonly in groups of Ashkenazi Jews.
In zoos, animals are even more likely to be each other's kin. Wilson has seen the effects of inbreeding at the zoo in certain Speke's gazelles, a species of antelope.
Specific zookeepers and conservation scientists around the country are assigned the job of maintaining genetically diverse populations. With an eye toward family planning, each of these matchmakers keeps track of one species. They figure which zoos are best for penguins, which chimps get to mate and which bears should stay on birth control. They consult directories of captive species populations - called "studbooks" in the business - to see who is related to whom. And then they set up matches.
The results are family trees whose arms twist and bend and weave. If a population is dwindling, for example, a zookeeper might have to mate a bear with her uncle. Animals of all stripes, it seems, mate with their cousins. Back in his heyday, Herschel once mated with a cow named Frida. Frida's daughter from another bull, Toppy, was recently artificially inseminated with Herschel's sperm.
"It's her mom's old boyfriend, but it's not her father. They don't much care about that," said Wilson. "You do the best with what you have."
Navigating this world of mating requires the skills of geneticists with computers. A computerized family tree allows geneticists to calculate for each animal a fraction called coefficient of kinship. That number tells zookeepers how related any animal is to the rest of the group.
When Herschel arrived in St. Louis in 1982, for example, his number was zero, because Zoo managers assumed he was unrelated to any of the other captive animals in North America. Now that his descendants are chewing cud in zoos all over the country, his number has risen to .156.
Captive bantengs are a very inbred population. As a whole, the species has a coefficient of kinship of .226. By comparison, a group of first cousins of any animal has a coefficient of kinship of .062.
"You can have an individual who is related to many in their population, but he still may be the least related out there," said Jonathan Ballou, a researcher at the Smithsonian Institution's National Zoological Park.
To play cupid in a zoo, one has to take many factors into account: logistics, zoo capacity and animals' particular social structures, said Steve Bircher, curator of mammals and carnivores at the St. Louis Zoo. And whether animals will actually get along is key. Four-hundred-pound T.J. first met Kalista six weeks ago, on the other side of a chain link fence zookeepers call the "howdy fence."
"He was intimidated by her - maybe because he was the new man on the block," said Bircher. But T.J. has steadily grown fond of the other tiger, and with the howdy fence down, he has been trying recently to get into mating position despite Kalista's shyness.
"Genetics is not the be-all and end-all," said Wilson.
The animals have to be ready to reproduce. The most valuable member of the North American captive antelope species of Guenther's Dik-Diks is an 11-year-old at an American zoo she declined to name. But Wilson, who currently manages the population through the American Zoo and Aquarium Association, worries he might be infertile.
Dr. Cheryl Asa, the Zoo's director of research, recalled proudly that Herschel never suffered that particular problem. Sure, Herschel was a darling bull.
"He was good with the cows, good with the offspring," said Wilson.
But to Asa, an expert in animal fertility, it was the sight of Herschel's sperm surging vigorously under the microscope that warmed her heart. "He had the best sperm of any banteng bull I have ever seen," she said.
Now Herschel's genes sit in liquid nitrogen tanks - roughly the size of beer kegs - in the Endangered Species Research Center and Veterinary Hospital at the Zoo.
For Lisa Wathne, a spokeswoman for People for the Ethical Treatment of Animals, zoos and the efforts they go to arrange mating are cruel and inhuman. Given the choice between the terrors of captivity and extinction, Wathne said, "I think animals would choose to be extinct."
But while Herschel is gone - zookeepers were forced to euthanize him in 1997 because of arthritis - his genes live on.
Herschel's seventh son, a bull named McGwire, was born in 1998 after an artificial insemination procedure, a year after Herschel died. Zookeepers, who named the bull after the retired Cardinals slugger, dubbed him Mac. McGwire now lives with Frida at The Wilds, a zoo in Cumberland, Ohio.
Republished with the permission of the St. Louis Post-Dispatch.
Copyright 2004 St. Louis Post-Dispatch
Courtesy of STLtoday.com