In world of amphibians, a rare bright spot
SAN JOSE — Global amphibian news tends to be a downer. Acutely vulnerable to the slightest environmental change, frogs, toads and salamanders are too often described as "disappearing."
But a recent surprise appearance has given scientists something to leap about.
A team from the University of Costa Rica (UCR) recently encountered a new species of dink frog in the Cordillera de Talamanca mountains near the border with Panama. The frog is believed to be endemic to this country, adding a new, roughly 2-centimeter-long member to the nearly 200 types of amphibians known to inhabit Costa Rica. This little nation ranks 19th in the list of countries with the most amphibian species, according to the International Union for Conservation of Nature (IUCN).
The discovery came about like this: Scientists were helping to train local farm workers who want to increase their knowledge of nature in order to secure jobs as tour guides through Costa Rican national parks. During a tour through the jungle of a high elevation valley called Valle del Silencio, on the mountain range’s Caribbean slope, the group heard a whole lot of croaking going on.
"When we arrived at Valle del Silencio we rested up and then took a midnight hike. With flashlights, we went walking and looking around, and suddenly, amid a bromeliad — one of those plants we have in our forests that looks like a pineapple growing out of the ground — we found a female, which is the black one of this species," UCR scientist Gerardo Chavez explained."When I saw the color I immediately said, ‘this is a new species.’
"It was a night of celebration for all the students," he said.
Following confirmation through genetic analysis, Chavez and fellow scientists at UCR co-authored a report on the discovery in Zootaxa, an international journal for animal taxonomists. Not only is this frog unique to Costa Rica, they say, but it appears to be endemic to the very valley in which it was spotted.
The dink or tink frog, of the genus Diasporus, is known by a perhaps more flattering name in Spanish: "rana campana" — or bell frog — "because their song is like a little bell," Chavez said, with fondness. Costa Rica was previously thought to be home to four of the eight species of Diasporus, he said. The newly encountered one would make that five out of nine.
Dubbed Diasporus ventrimaculatus, the frog has several remarkable features that distinguish it from the rest of the family. First, it likes a bit of altitude. The species was spotted at about 2,500 meters (8,202 feet), where average temperatures are about 17 degrees Celsius (62.5 degrees Fahrenheit) — quite cool for a frog in the tropics. Other dink species normally dwell below 2,000 meters (6,651 feet), and most don’t crawl above 500 meters (1,640 feet), Chavez said.
More striking, however, is that their colors vary depending on the sex, which is also unusual for this kind of amphibian. The scientists found black females and orange, reddish and gray males.
"Other variations do exist between male and female amphibians, but color is not common because it’s a group that’s quite nocturnal and normally doesn’t tend to show different coloration between gender. However, this species does," Chavez said. "That’s particular, very striking and highly interesting to investigate."
The Zootaxa editors needed convincing that the males and females did not actually belong to different species. Chavez sought help from UCR biologist Alejandro Leal and his assistant Alejandra Mora, who carried out genetic testing and were able to verify that the males and females belonged to the same species. They also found the species are genetically closer to West Indies frogs than to those on the continent.
Chavez recalled another indigenous amphibian with gender color differences: the golden toad. Mention of this toad — once abundant in north-central Costa Rica’s Monteverde Cloud Forest Reserve — strikes a sore spot for herpetologists, since 20 years have passed since its last appearance.
And the golden toad isn’t alone. Nearly one-third of the world’s amphibian species are globally threatened or extinct, according to the IUCN Red List. The organization assessed about 6,260 amphibians for the list. Scientists believe there are numerous culprits, including humans’ encroachment on amphibian habitats, pollution, climate change and virulent fungi — amphibians are considered important indicators of biodiversity trends and environmental threats that may ultimately affect other wildlife.
In Costa Rica — which is home to 5 percent of the world’s biodiversity and 186 of the planet’s amphibian species — the fate of frogs is a major preocupation among environmental scientists. In 1999, scientist Alan Pounds wrote in the journal Nature that the populations of 20 to 50 frog and toad species in a 30-square-kilometer area of study in Costa Rica had quickly crashed. Last year, the Costa Rican Holdridge’s Toad went extinct, according to the Red List.
However, the IUCN is not quick to place a species into the extinction category — sometimes, long-absent creatures jump back onto the scene. This occurred last May, when a team from the U.K.’s Manchester University and Chester Zoo happened upon a rare tiny female tree frog in the Costa Rican jungle, a cause for cheer (as seen in this BBC video).
With all the bad conservation news, it’s worth pausing over discovered, or rediscovered, species. But even these good times can be fleeting. "It’s not (always) good news," Chavez said, mentioning another recent discovery of a type of Costa Rican atelopus toad that appeared and then disappeared without a trace. "We’re describing a species that we’re almost sure doesn’t exists (any more). We’ve visited the area in which it was discovered and it’s no longer there. We’re giving it a posthumous description."
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