AROUND MISSISSIPPI — It’s been a good year in the wild and in the lab for one of the world’s most endangered species, the dusky gopher frog.
The rainy spring brought a good hatch at two shallow, rain-fed ponds south of Saucier in the DeSoto National Forest. And new lab projects are underway at Mississippi State University to improve captive breeding of the frog, found only in Mississippi.
More than 500 wild-hatched froglets have been tagged at the two ponds, and more are expected. But only about 10 to 20 percent may reach adulthood, estimates John Tupy, a Western Carolina University researcher studying the amphibians. Most will wind up eaten by bigger critters.
The species, which the International Union for the Conservation of Nature listed last year among the world’s 100 most endangered, is nowhere near recovered.
“One year’s just a little snapshot in time,” said Linda LaClaire, the U.S. Fish and Wildlife Service’s recovery coordinator for the frog. “One of the problems we’ve had in the past has been drought. You never know from one year to the next what’s going to happen.”
At Mississippi State in Starkville, a graduate student and a postdoctoral fellow are refining techniques for inducing females to lay eggs and for freezing and thawing eggs, sperm and embryos, with an eye toward a “frozen zoo” for the endangered amphibians.
“They’ve been doing a terrific job,” said Andy Kouba, director of conservation and research for the Memphis Zoo, which developed the original techniques for freezing gopher frog eggs and getting females to lay them.
Gopher frogs live underground and breed only in ponds too shallow to persist year-round, in longleaf pine forests nearly eradicated by lumbering. Three spots in Mississippi hold an estimated 100 to 200 adults, with hundreds more in zoos and aquariums. “We’ve gone from less than 100 frogs left in the world to now probably over a thousand,” Kouba said.
But eggs and tadpoles have consistently shown up only at a spot called Glen’s Pond, with 10 to 60 breeding adults each year. If 40 survive from this year’s hatch, Tupy said, “that’s pretty good in terms of breeding adults.”
About 380 naturally spawned froglets were tagged at Glen’s Pond before it dried this year, Tupy said: “That’s the second-highest number on record.”
The record was 2,488, in 1998. Scientists don’t know why it was so big, Tupy said. The previous year had the third-largest natural hatch: 221.
But from 1989 to 2007, Glen’s Pond dried before any tadpoles became frogs. In 2000, scientists and the U.S. Forest Service began remodeling nearby Pony Ranch Pond to attract gopher frogs and deepening it to hold water into autumn. In 2002, the year after the U.S. Fish and Wildlife Service declared the frog endangered, scientists began raising some eggs from Glen’s Pond in 300-gallon cattle troughs.
Frogs spawned in Pony Ranch Pond for the first time this spring. That pond still holds water, eggs and tadpoles, many from an experiment to learn whether newly hatched frogs, tadpoles, or tadpoles partway through metamorphosis are most likely to survive.
About 150 froglets have been caught and tagged as they hopped into the forest. Perhaps 25 percent were from eggs laid there, Tupy said. A total of about 2,000 trough-raised froglets and tadpoles have been released, with more to come as frogs develop. Scientists mark them before release: frogs with tiny implanted tags, tadpoles with fluorescent dye injected just under the skin.
Scientists say the work at Mississippi State and the Memphis Zoo is needed because they’ve been unable to get gopher frogs to breed in captivity.
In the forest, winter and spring downpours fill the ephemeral ponds and cue the frogs to leave their solitary burrows to gather at the ponds and breed. Scientists have used sprinklers and changes in light levels to simulate storms for captive frogs. They’ve cooled the rooms. They’ve put the frogs outdoors in large enclosures around ponds. Nothing worked.
“It would be very hard to emulate those conditions, like rain and humidity and atmospheric pressure … without building a very convoluted indoor ecosystem,” said Natalie Calatayud, a postdoctoral fellow at Mississippi State.
After years of unsuccessful attempts at captive breeding, scientists turned to hormone manipulation, said Kouba, who worked out an egg production technique using two hormone treatments four months apart.
MSU graduate student Cecelia Langhorne worked out the technique for freezing frog sperm this spring, Kouba said. Calatayud, whose previous work was on small marsupials in Australia, is working on cryopreservation of eggs and refining the egg production technique.
“A minor tweak” got two females to lay eggs after the first injection, and others have laid eggs within a month or two, Calatayud said. It may have something to do with the animals’ size, she said, “but I’m just starting to analyze that data now.”