Reported by Ari Daniel Shapiro.

The foothill yellow legged frog has been wiped out from more than half of its historic range along California’s coast and central valley. Many biologists see this tiny amphibian as a canary in the coalmine – an early indication of an ecosystem gone wrong. Jennifer Dever, a biologist at the University of San Francisco, is trying to help the frog make a comeback. By studying the DNA of these frogs, Dever and her graduate student Ryan Peek are examining how big and healthy the remaining populations are. Her fieldwork takes Dever to rivers and creeks all over northern California. When reporting this story, I got to tag along with her on a trip to the Ohlone stretch of Alameda Creek.

Credit: Ari Daniel Shapiro.

Dever and I went to the creek with two other scientists – biologist Sarah Kupferberg and wildlife ecologist Steve Bobzien. The trio was really at home scanning the water for tadpoles and catching them in their hands.

Credit: Ari Daniel Shapiro.

The goal of Dever’s work is to figure out how genetically diverse the frog populations are. When these frogs mate, the male jumps on the female’s back and holds on. It’s called amplexus. With the male hanging onto her back, the female uses her hind legs to clean the surface of a rock until it’s smooth enough to glue her eggs to it. The male fertilizes the eggs in the water. Each of those fertilized eggs gets half its DNA from its mom and half from its dad. The bigger the population, the more different combinations of DNA there are in each generation. That means higher genetic diversity, and a healthier, more resilient population.

Credit: Alessandro Catenazzi

Although Dever didn’t take any samples on the day that I visited, in general she clips off a small tip of tadpole tail and tip of frog toe to get their DNA. Dever puts the samples in ethanol and records their GPS locations, and then she goes back to her genetics lab.

Credit: Ari Daniel Shapiro

Dever puts the DNA through a series of procedures, first copying regions of it over and over again to make a lot more of it. Because DNA has a negative charge, Dever can move it through a square piece of gel (it looks like a clear slab of jello) by applying a positive charge at the other end. Take a look at this photo of two of Dever’s gels. Each column (or lane) corresponds to a different individual frog.

Credit: Jennifer Dever

Each white band is a different fragment of DNA. The DNA in the gel on the left has all moved to pretty much the same vertical positions. That means these frogs have very similar DNA. These frogs are more closely related and come from a smaller, less genetically diverse population. The DNA in the gel on the right has more fragments of different sizes. These frogs have dissimilar DNA, they come from a bigger population, and they’re more distantly related.

By using this technique, Dever’s able to grab the DNA from a handful of frogs or tadpoles in a particular creek and know just how healthy (in terms of genetic diversity) that population is. In the creek, Dever can’t tell how the frogs are related. But in the lab, the answer’s clear. For Dever, every frog counts, and it’s the DNA that adds up.

Credit: Alessandro Catenazzi

Listen to Plight of the Yellow Legged Frog radio report online.

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A Pacific Chorus Frog

I'm sad to say my daughter probably won't share those same experiences I had. I could say it's because we live in San Francisco and cities aren't as amphibian-friendly as the suburbs. But my parents still live in the same house where I grew up. Unfortunately, it has been years since we've seen toads in the garden there. And the quiet singing of the tree frogs seems much lonelier today.

Amphibian decline is happening all over the world. And as depressing as it is not to have those fun childhood experiences of catching, playing with and hearing frogs in the garden, there is a much more serious problem going on. This can have some serious consequences to local food webs. It is also an alarming sign that there is something really unusual happening with the world's environment.

There are many reasons for the decline in the world's amphibian populations. And it seems that each region of the globe, and maybe even each species, may have its own ticking time bomb. Some places may be experiencing rapid habitat decline. There is pollution in the rainwater and chemical run-off in lakes and streams. Some places are seeing a sharp increase in parasites and diseases. Scientists are even looking at increased UV radiation. Or maybe it's a combination of multiple factors. The result is part of what some scientists are now calling the "sixth wave of extinction."

That’s a lot of doom and gloom. Luckily, scientists are racing to understand this decline and hopefully may come up with a means of curbing it before it is too late. We were fortunate to meet some of the best. We joined herpetologists Karen Swaim and Vance Vredenburg out into the field to learn more about what is happening to our local California red-legged frogs. We also visited the laboratory of Professor Tyrone Hayes at UC Berkeley to learn what his team is discovering about the connection between agricultural pesticides and frog decline. (See our additional web-only interview with Professor Hayes) You can test your amphibian knowledge by taking our QUEST quiz. Do you know why my brother and I always put down those toads?

Watch the "Disappearing Frogs" TV Story online, as well as find additional links and resources.

Chris Bauer is a Segment Producer for television on QUEST.

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We scour the web and serve up the best of science, environment and nature content–from the Bay area and beyond–right to our readers.

Today's pick is from YouTube.

National Geographic, via YouTube, brings us the tale of Australia’s water-holding frog. This plucky amphibian rarely sees rain, so when it does, it slurps enough liquid to double its weight. Then it digs a hole and hides in a shell made of its own shed skin. It can hibernate for up to two years, until the rainy season comes 'round again and it's time to look for a mate.Supposedly aboriginals even dig up the frogs when they need a drink–just squeeze and you've got fresh water!Check out the video of this amphibious camel for more on its amazing adaptations:

http://www.youtube.com/watch?v=tuWo_kWMihs

Amber Dance is the Quest Intern and a science communication student at UC Santa Cruz.