San Diego’s Frozen Zoo Stores Hope for Endangered Species’ Futures

scientist working in lab
Photo courtesy of San Diego Zoo Global

When you hear the phrase “frozen zoo,” you may think of the current cold weather taking hold of your local zoo and its animals — but it's actually a real thing that exists all year long in sunny San Diego, Calif. San Diego Global’s Frozen Zoo is offering hope for the future of conservation by storing genetic material from different animals, many of which are endangered, within its large freezer walls. The zoo’s geneticists collect skin cells and grow them into fibroblasts that can be used to study DNA variations, genetic diversity and more in a range of species.

According to Dr. Oliver Ryder, director of genetics for the San Diego Zoo Institute for Conservation Research, the zoo started collecting material in the 1970s. At that time, the specimens were extremely useful in current studies, but the team knew that as new techniques became available in the future, the applications for the zoo’s contents would increase.

According to Dr. Ryder, “These cells are the same kind of cells that produced Dolly," the sheep cloned by British scientists in 1996. "These may be very helpful for studying health benefits and health management of any species." He adds, "We’re excited about the opportunities that will become available.”

Dr. Ryder has spent 35 years working at the Frozen Zoo, and while it currently acts merely as a library of information, he sees the zoo becoming an important resource for the recovery of species in the future.

Inside the Frozen Zoo

Right now the zoo contains the genetic material of about 10,000 individuals representing more than 1,000 species. The cells are easily collected when an animal has a veterinary exam or after it has died.

The zoo has received samples from hundreds of institutions all over the world. When the cells first arrive, they are stored at room temperature, treated in a suspension and left to grow in flasks. As the number of cells increases, they are divided between different flasks. After a certain number of flasks are made, Dr. Ryder says the cells can then be harvested, treated and stored in frozen liquid nitrogen where they will remain viable. As of now, cells that were frozen 30 years ago are still viable, and there is currently no known limit on how long this stored material will remain useful.

Most of the cells come from vertebrates, primarily mammals, although there are some birds and reptiles. According to Dr. Ryder, there are real advances being made in growing and banking the cells of amphibians, and the scientists have succeeded in storing the cells of a few fish.

“We’re adding to the zoo all the time. In the lab, we just added [the cells of] a ringtail possum and dolphin. We add easily 300 new individuals per year,” he says.

Species that are part of the American Association of Zoos and Aquariums’ Species Survival Plan (SSP) Programs are prioritized for addition to the zoo, as well as those included in major zoo-based conservation efforts. According to Dr. Ryder, each time they add a new species to the zoo, the focus is on capturing a significant representation of the species’ gene pool, which can include keeping material from dozens or even hundreds of individuals, in order to aid conservation efforts for that species. The zoo currently contains material from only one extinct animal, the po’ouli, a bird native to Hawaii.

In order to protect the zoo's research potential, genetic material is kept in more than one location. Multiple samples are frozen; half are stored at the Frozen Zoo while half are stored in a location far away. This dramatically reduces the chance of all the collected material being lost in the event of an accident or disaster.


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