Will a ‘frozen zoo’ save the Mexican wolf?

Endangered Mexican wolves roam the wilds of New Mexico, Arizona and Mexico. They also live in captivity. But their future may lie in a “frozen zoo.” That’s the term of endearment scientists use for the bank of frozen wolf sperm and ovaries housed at the St. Louis Zoo in Missouri and Chapultepec Zoo in Mexico City – two cryogenic vaults where some of the most precious genes of the species are being held for future reproductive use. Even as New Mexico continues to fight with the federal government over the U.S. Fish and Wildlife Service’s troubled program to reintroduce Mexican wolves to the wild, the scientists charged with breeding the species back into greater numbers are pushing on with the complex work of preserving the genetic diversity of a captive population that began with just seven wolves. “Right now, our mandate is to preserve genes,” said Cheryl Asa, a reproductive physiologist who led the research program at the St. Louis Zoo for 30 years and now serves as a consultant. “This is looking into the future so that, as animals die who are genetically important to the species, their genes live on.” Since 2007, the quest to preserve Mexican gray wolf genes has included “vitrifying” the ovarian tissue of female wolves that are past reproductive age in hopes of one day being able to impregnate younger females through in vitro fertilization – although the technology does not yet exist to perform this technique in dogs or wolves. But researchers are getting close, Asa said. “The ‘frozen zoo’ is what some of us call it,” said Maggie Dwire, assistant Mexican wolf recovery coordinator with the service. “We aren’t going to find new founders. We need to be very careful about retaining the genetic diversity we do have.” Just before breeding season, during the last two weeks of January, when the wolves’ eggs are close to ovulation, they are spayed like a domestic dog would be spayed – an operation that might happen at one of the 51 institutions that hold captive wolves. The wolf ovaries are wrapped in gauze, kept warm in a saline solution, packed in a container and immediately shipped in the cargo hold of the next passenger plane headed to St. Louis, Asa said. In the St. Louis Zoo lab, scientists use a needle to draw out egg cells from each follicle; the remaining tissue is vitrified and banked, “kept in liquid nitrogen forever, or until they might be used,” she said...more