It may be ashot in the dark, but freezing sperm is one of the last chances to save the hellbender,North America's biggest salamander, conservationists say.
Hellbenders—also known as snot otters and devil dogs—have dwindled throughout their range, which once encompassed streams from northeasternArkansastoNew York.
The 2.5-foot-long (0.7-meter-long)amphibianshave declined by 80 to 90 percent in most of their traditional watersheds in recent decades, and now haunt only isolated pockets of southern Appalachia (seemap), said Dale McGinnity, curator of reptiles atNashville Zoo.
All of the states in the hellbender's range have listed the animal as a"species of special concern,"and the U.S. Fish and Wildlife Service is currently reviewing whether to add the hellbender to the federal endangered species list, McGinnity said.
The reasons for their decline is unknown, but it's likely environmental contaminants such as pesticides are harming the creatures via their highly permeable skin, he said.
To make matters worse, hellbenders don't seem to be breeding at all in the wild, he said, possibly because human-made pollutants containing synthetic hormones are damaging the amphibians' reproductive systems.
As a result, there are apparently no young wild hellbenders in existence, only aged individuals—the amphibians likely live between 30 and 80 years, McGinnity said.
(Seephotos of vanishing amphibians inNational Geographicmagazine.)
The hellbender's decline spurred an international team to collect sperm from some captive salamanders in September 2009 for cryopreservation, a common zoo practice that freezes sperm without damaging its cell membranes.
Though several zoos have put a"great deal of effort"into breeding the amphibians in captivity, none has been particularly successful, McGinnity added. It's unclear why they're tough to breed, but it may be that it's hard to replicate the exact temperatures of their home streams.
"For the first time, sperm was collected from a living salamander, cryopreserved, and brought back to life,"said McGinnity, who is involved in the sperm-preservation effort with colleagues from Belgium's Antwerp Zoo and Michigan State University.
A sort of"insurance policy"against extinction, the sperm will enable scientists to manage hellbender breeding, according to team memberDalen Agnew,a reproductive pathologist at Michigan State University.
For instance, scientists can use the stored sperm to crossbreed individuals, he said, to ensure that wild hellbenders are genetically diverse, he said. Genetic diversity is important because if closely related salamanders breed, their inbred offspring will be weaker and more susceptible to disease.
(See"Human Sperm Gene Traced to Dawn of Animal Evolution.")
Sperm-Filled Salamanders
Despite their hellish monikers, the"big, flaccid creatures"are actually"very mellow,"Agnew said.
This docile nature certainly helps scientists collect salamander sperm, which is"milked"out of a hellbender by rubbing it between the front legs and tail, said Nashville Zoo's McGinnity.
During mating season, no such coaxing is needed.
"Just by picking the animal up, {sperm} will come pouring out of the animal. ... You need to be ready,"the Michigan State's Agnew said.
(Watch aNational Geographic Channel video of herpetologist Brady Barr"kissing"a hellbender.)
Agnew also found that the hellbender sperm cell—like those of other amphibian species—boasts a ribbon of tissue encircling the tail. Magnified 40 times, it"almost looks like a corkscrew spinning,"Agnew said.
The winding tissue likely adds a jolt of horsepower to the sperm cell, he said. (Related:"Sperm Recognize 'Brothers,' Team Up for Speed.")
So far Agnew and colleagues used a unique"recipe"of preservation ingredients to keep hellbender sperm viable for six months—ideally, the sperm could be stored for hundreds of years.
Snot Otters Unchanged Since Dinosaur Days
Hellbenders haven't changed much since dinosaurs ruled the world, which puts the amphibians in nearly a class of their own, Nashville Zoo's McGinnity noted.
There are only two species related to the hellbender: theChinese giant salamander (picture)and the Japanese giant salamander. (Read about anew giant-salamander breeding centerthat opened in July in Washington, D.C.)
"If we lose it, we lose a whole lot of evolutionary history,"he said."There's nothing similar to it."
Комментариев нет:
Отправить комментарий