Monthly Archives: August 2012

08/25/12

Frogs Are Blue!

Most people think frogs are green, right? And it’s true, most frogs are a greenish, brownish, yellowish color, the better to hide from predators among grass and other vegetation.

But frogs can be many different colors, even bright crayon colors like sky blue.

This three-centimeter-long blue tree frog in a tree in Chofu, western Tokyo. Courtesy of Toba Aquarium, Japan.

Why would a frog species evolve such a bright vivid color that would make it stand out? In most cases the frog, such as the colorful dart frogs, are giving a strong warning to predators: Don’t eat me! I’m poisonous! Either through instinct or through learning the hard way, predators will avoid them. These brightly colored frogs contain poisons that can kill or paralyze an animal that comes into contact with it.

The frog’s skin is not actually blue. The color comes from layers of chromotophores, or pigment-containing and light-reflecting cells between the dermis and epidermis (inner and outer skin layers). A blend of the three types of chromatophores creates the color, or in some cases, even transparency:

melanophores: contain pigments that appear black or brown from melanin

xanthophores: contain yellow colored pigments

iridophores: contain reflective or iridescent pigments

So although most of the time, frogs are green, sometimes Frogs Are Blue!

08/15/12

Live Bullfrog Trade Helping to Spread Deadly Fungus

A Frogs Are Green reader alerted us to a recent Dot Earth (New York Times) blog post by Andrew C. Revkin, “Genetic Study Finds Bullfrog Trade is Prime Pathway For Devastating Amphibian Fungus.”

University of Michigan mycologist Tim James and colleagues conducted a genetic analysis and have found that the global trade of live bullfrogs is helping to spread the deadly chytrid fungus, which has devastated worldwide amphibian populations. The results were published in the journal Molecular Ecology.

As Revkin notes, it isn’t clear why the fungus is devastating to amphibians in some areas, but seems to be harmless to those in other areas. For example, although there are deadly strains in the Northeast, there are no chytrid-related declines reported. Environmental conditions or other issues might account for this.

The researchers examined the role of bullfrog farming in spreading the chytrid fungus between the forests and frog farms of Brazil and then to the United States and Japan. They collected and analyzed bullfrogs sold at Asian food shops in seven U.S. cities and found that 41 percent of the frogs were infected with chytrid fungus, which is harmless to humans. Frogs in these shops are imported live primarily from farms in Taiwan, Brazil and Ecuador and sold as food for their legs.

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“A lot of the movement of this fungus is related to the live food trade, which is something we should probably stop doing,” James said. “We don’t need to have millions of live frogs being shipped from foreign countries into the United States.”

For more information: Press release from the University of Michigan

08/7/12

A Green Frog (at Frogs Are Green)

At Frogs Are Green, we’ve posted about tomato red frogs, blue frogs, and yellow-and-black spotted frogs, but I don’t think we’ve ever written about the Green Frog (Rana clamitans).

Green frog camouflaged in grass. Photo by Mary Jo Rhodes

Recently I visited my sister, who lives in the woods in Connecticut. On our first night, there was heavy downpour. When I woke the next morning, I heard what sounded like someone plucking a loose banjo string. Coming from the city, I was thrilled: it was my welcome call from a Green Frog outside! My sister has built a couple of frog/koi ponds on her property. Although fish and frogs aren’t supposed to co-exist (fish eat the frogs’ eggs), somehow it has worked out.

Frog pond in CT

The Green Frog is mainly aquatic, but they often rest by the side of the pond, leaping in when danger approaches. Males have a tympanum (external hearing structure) twice the diameter of the eye and a bright yellow throat.

Green Frog. Notice the large eardrum behind his eye. Photo by Mary Jo Rhodes.

Green frog in reeds. Photo by Mary Jo Rhodes

You might see Green Frogs in ponds, lakes, and swamps—they are one of the most common frogs in the eastern U.S.

Just in case you’re out in the country this summer, here is what it sounds like: