Trouble in love town for the faithful Sierra Nevada yellow-legged frog

Sierra Nevada yellow-legged frog. (Photo/Devin Edmonds, http://www.amphibiancare.com)

Most people consider loyalty an admirable trait, but for the Sierra Nevada yellow-legged frog, faithfulness to a compromised breeding ground just might spell doom for the species. In many places, the frog’s habitat is drying up or swarming with ravenous introduced trout. A new study released by the USDA Forest Service in the Canadian Journal of Fisheries and Aquatic Sciences details the extent of this troubled relationship, and provides insights key to giving the frog a chance at survival.

Mountain yellow-legged frogs, (of which there are two species), adapted to live in high alpine lakes, in environmental extremes too cold and harsh for most amphibian species. This specialty helped the frogs thrive, but in the past century, the once common Sierra Nevada yellow-legged frog has disappeared from more than 90 percent of its range. In 2003, the U.S. Fish and Wildlife Service ruled that the mountain yellow-legged frog “warranted” endangered species listing, but was precluded due to the need to list more high priority species.

Likely culprits for the frog’s decline include the usual suspects like disease and contamination, but new research shows that the periodic drying up of habitat and predation from introduced trout coupled with the frog’s loyalty to specific breeding spots is pushing the animal ever closer to extinction.

Yellow-legged frogs need up to four years for their tadpoles to mature. So if a pond dries up, the species could lose up to four year-classes of offspring, issuing a serious blow to that particular population. The study also found that for some of the best ponds left for the frog, introduced trout then threaten the species. Offer a trout a yellow-legged frog and it won’t turn you down, no matter what the life stage of the dangling amphibian.

Kathleen Matthews and Haiganoush Preisler, scientists with the USDA Forest Service’s Pacific Southwest Research Center, conducted a 10-year study to measure the fidelity of yellow-legged frogs in Kings Canyon National Park, east of Fresno, Cali. They used mark-recapture techniques, and observed frog tendency to return to lakes even for locations that tended to dry up in low snowpack years, or where frogs had previously encountered predatory fish.

Fish removal appears to be a strong restoration technique, and projects underway show a rebounding in the order of tens of thousands of frog and tadpole populations in lakes where non-native fish have been eradicated. There may just be a little bit of hope yet for the garrulous hoppers, especially if restoration efforts incorporate knowledge of site fidelity into their tactics.

You can learn more about the natural history and restoration efforts behind this little frog at MYLfrog, or download the USDA Forest Service study here.

The high fidelity of alligator love

Two American Alligators (Photo/Matthew Field)

Oh alligator love, it’s not as fickle as you might think. Get on a gator’s good side and you may just have found a friend for life, if you’re another alligator of course.

In a study that combines field science with molecular biology, researchers from the Savannah River Ecology Laboratory found that alligators were surprisingly loyal partners and akin to birds in their mating habits. The discovery offers new insights into evolutionary links and behavior of crocodilians, birds and dinosaurs – and certainly, at least where one science writer is concerned, proving there is a lot more going on behind those alligator eyes than a cold reptilian stare.

Researchers trapped and re-trapped alligators at Louisiana’s Rockefeller Wildlife Refuge, 76,000 acres of alligator dream real estate bordering the Gulf of Mexico. “Given how incredibly open and dense the alligator population is at RWR, we didn’t expect to find fidelity,” said researcher Stacey Lance. “I don’t think any of us expected that the same pair of alligators that bred together in 1997 would still be breeding together in 2005 and may still be producing nests together to this day.”

Crocodilians have already proven to be more invested in the care of their offspring than most other reptiles, actively nurturing young and defending nests. Crocodiles are even known as considerate egg-layers. As a female drops the egg, she will blindly catch it with a hind leg before it hits the ground and gently place it in the nest. But up until now alligators were thought to be polygamous, mating with several different partners and leading to many fathers for a single nest.

After ten years of following alligators at the refuge, scientists Lance, Travis Glenn, Ruth Elsey and Tracey Tuberville discovered that 70 percent of female alligators stick with who they like. Even if they have multiple partners, the same bachelors get picked year after year, regardless of whether females encounter a new slew of potential suitors.

The study marks the first time fidelity has been observed in any crocodilian species. “In this study, by combining molecular techniques with field studies, we were able to figure something out about a species that we never would have known otherwise,” said Lance. “Hopefully future studies will also lead to some unexpected and equally fascinating results.”

Results of the study were published in the October 7 issue of Molecular Ecology.