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Frogs are dying in alarming numbers worldwide, and now one of the suspects has arrived in Arizona
Big eyes, Betty Davis eyes … legs that go on and on, ending in sculpted, muscular thighs … and that oh-so-smooth and moist skin, skin to die for …
But its skin is not a thing of beauty, rather it is the means by which the frog takes in oxygen so that it can survive. The frog literally breathes through its skin. Some experts say these vulnerable creatures may serve as nature’s “canary”—an early warning system that all is not well in the environment. They’re dying in alarming numbers worldwide. And the suspected cold-blooded killer has arrived here in Arizona.
Frogs belong to the order Anura, tailless amphibians that have an anatomy similar enough to that of humans that they are used in biology classes, namely for dissection and the study of anatomy and physiology. But the word “frog” means much more than an anatomy lesson to many people. To a child, the frog is perceived as a cartoonish solid green, slimy critter that sits on a lily pad, leaps about, and burps out the single syllable “Ribbit.” Most likely, this awkward-looking locomotion is the basis for the child game “leap frog.”
To get an adult view of this creature, a few friends and family members were asked about their “frog perceptions.” Several mentioned the fairy tale stories of a frog that, once kissed by a beautiful young woman, turned into a prince. One said she thought of the word “croaking”—when humans die—when she thought of a frog, while another said she thought of “the French.” (All responses have been included, politically correct or not).
General reference books list several frog uses, everything from a food source (frog legs) to pets, fishing bait, and fashion accessories such as frog-skin purses. There are also some potential medical uses of components found in the toxins of poisonous frogs. Poison arrow frogs (also called poison dart frogs), for example, have a chemical in their skin that is more than 200 times as potent as the narcotic pain killer morphine. Scientific studies of these remarkably complex potions are ongoing ... for as long as the species may be able to survive, that is.
The Oriental fire-bellied toad (Bombina orientalis) inhabits southern China, Korea, Thailand and other southeast Asian countries.
A frog’s life
Frogs are poikilothermic, meaning their body temperature is the same as that of their surroundings. Many are aquatic; some prefer terrestrial quarters in burrows or trees. They can leap great distances, as far as 40 to 50 feet, because of powerful, muscular thighs and webbed feet. But not all of these amphibians leap on the ground. Climbing African frogs (sedge frogs) have special adhesive toe disks that allow them to ascend trees. In addition to variation of appendages, frogs also vary in body length, from the tiny 0.4 inch Brazilian gold frog to the almost foot-long West African Goliath frog. Females are usually larger than males.
The skin of a frog is necessarily thin so that respiration can occur. This adaptation is taken to the extreme in the tropical arboreal frogs—their heart and internal organs can be seen through the thin skin of their underbelly. Frogs emit sounds by forcing air from their lungs over vocal cords and into a vocal pouch, the latter serving as a resonating chamber. Although humans might say a frog simply calls out in monosyllabic monotones, their singing is much more elaborate than this. Usually, the male calls out to attract a mate. In times of distress, frogs emit a higher pitched call.
A closer look at these leaping, climbing, and burrowing creatures reveals some uncanny similarities to the human race. There are the “wall flowers” of the frog species, those whose colors blend into the background so as to not draw too much attention to themselves. And, there is the opposite extreme, the brash bullies—usually a dart frog “feeling its oats” (actually, its skin is full of venomous secretions). These frogs, by the way, are prime examples of the adage “You are what you eat,” for their alkaloid toxins are produced from the insects they eat. When kept in captivity and given an altered diet, oftentimes the skin of these frogs no longer produces potent toxins.
Malaysian horned frogs (Megophrys montana) live in Malaysia, Thailand, Singapore and other southeast Asian countries.
Frogs also have their version of the femme fatale, an iridescent, waif-like creature—yes, the dart frog again. Lest a potential predator do more than simply feast his hungry eyes upon this creature with thoughts of devouring her, only one lick will bring this interlude to a quick ending. A fatal ending.
Like humans, the majority of the frog population is docile and goes about life just trying to stay out of trouble. But when hormones are flowing and it’s mating time, a different animal emerges. Males are known to kick each other, bite and shove one another while in the throes of hormones that have run amuck. Wrestling matches are common and in the case of the Central American strawberry poison dart frog, won only when one male frog tosses the other off of the leaf that serves as their wrestling mat.
The Brazilian gladiator treefrog is a bit more aggressive, wounding its opposing combatant by pulling out a knife—it wounds with its sharp spine of a thumb. Akin to the behavior observed in many a human male, the common rocket frog of Central America seeks out the biggest rock from which to trumpet its attributes. Any challenger must be bumped off the boulder in order for it to hold on to this pinnacle of power. (A more severe form of “voted off the island?”)
It would be sexist and unfair to say that wrestling is exclusive to males, however. The female stream frogs of Trinidad are known to tussle over streambed territory. (Alas, the origins of mud wrestling.)
Frogs also have their own version of the “house husband.” For three different species of frogs in South America, males build nests for eggs and the eventual offspring in riverbank mud. Here, courting, mating, birth of the young, and rearing of the tadpoles occurs. Another species of frog lays its eggs on land, but once the tadpoles hatch, the males carry these young ones on their backs to a body of water. The South American mouth-brooding frog takes this to an extreme, licking up the eggs into its mouth where they will hatch, develop, and then emerge from daddy’s mouth.
For some frogs, a nest in the mud just won’t do. Those of the families Ranidae build ostentatious, in-your-face, so-superfluous-it-borders-on-obscene homes—froth nests. This meringue-like floating castle is created by the male who secretes sperm as his mate produces eggs and then kicks with his back legs until he whips up an airy, fluffy floatation mass. (The human counterpart would be the extreme vacation homes perhaps?)
An aberrant yellow American bullfrog (Rana catesbeiana) sits on a toadstool in Yuma, Ariz.
One frog species has found that when survival needs must be met, sometimes a frog just has to be a bit flexible with the living arrangements. In America, the narrow-mouthed toads Gastrophryne olivacea and G. carolinensis become roommates with tarantulas, cohabiting in the furry-legged creature’s burrow. These unlikely roomies co-habit in—of all places, “red” states—the Midwestern states southward into Texas. The relationship suits both parties and no one gets hurt. In return for the protection and moisture of the burrow, the toad protects the tarantula’s eggs from attack by ants.
So these creatures really do have a lot in common with humans.
They live just about everywhere one finds humans, too. Every continent except Antarctica has populations of frogs. They are most abundant and their diversity is greatest in the tropics. It is here in these exotic lands that one finds the most colorful, exotic-looking frogs.
Probably the most well-known of these colorful frogs are the poison dart frogs. For them, color serves as a warning. From vivid blues to stark oranges and reds, these brightly colored frogs harbor poisons that can cause hallucinations, seizures, cardiovascular collapse, and death. Poisons from these inhabitants of Central and South America are used by native Indians on the tips of arrows. Prey struck by the medicated arrows are immediately paralyzed and are killed.
Want to sound smart to your biology friends? Here’s some frog trivia to impress them.
• The world’s largest frog is the Goliath frog of west Africa. It can grow up to 15 inches long and weigh 7 pounds.
• There are more than 5,000 species of frogs worldwide.
• The world’s smallest frog lives in Cuban frog. It grows less than half an inch long.
• Some frogs lay only a few eggs, while others can lay 30,000 at a time.
• The skin toxins of three species of South American frogs can kill a human if handled or eaten.
Source: The Fernbank Museum
—By Arthur Pignotti
While color can serve to warn, it can also serve to confuse. In some frogs, previously hidden areas of color become suddenly apparent as they move from a still position to one of flight from a predator. This flash of colors is meant to confuse the pursuing predator. Still in other frog species, color helps them to blend in with the background, a survival mechanism.
A good meal to most frogs consists of worms and insects. In the latter case, many frogs have a long tongue that unrolls to catch an unsuspecting insect. For others, a good meal is another frog, rodent, or reptile.
Their value, their danger
Frogs assist with insect control, a function so important that India, for example, no longer exports its bullfrogs, choosing instead to keep this valuable animal within its borders. Frogs are part of a food chain, the upper levels of which risk collapse if this important animal were to cease to exist. In some of the less developed countries, frogs are an important part of the peoples’ diets. Here in America, frog legs from the American bullfrog are popular in southern diets. As mentioned earlier, frogs are used to teach science. And, scientists are nowhere near understanding the possible treasure trove of medicinal agents harbored by these rapidly vanishing creatures.
Because a frog gets its life-giving oxygen through its skin, any disruption in this process compromises its health. In severe cases, it dies. A recently recognized fungus, Batrachochytrium dendrobatidis, commonly referred to as chytrid fungus, infects the skin of a frog and interferes with respiration. Chytrid fungus has been correlated with dramatic declines in frog populations and extinction of some species worldwide, but most notably in Australia and Central American rainforests.
According to Cecil Schwalbe, Ph.D., an ecologist with the U.S. Geologic Survey who resides in Tucson, the fungus has affected 12 frog species in Arizona, about half of the total number of frog species in the state. A recent report from the Global Amphibian Assessment stated that about a third of “amphibian species, now estimated at more than 5,700, have undergone severe declines or extinction.”
It wasn’t until recently that most scientists began to take the declining amphibian populations seriously, Schwalbe says. Previously, it was suggested that the decline was simply part of expected variation in a species’ population. Now, however, things are different. Populations of frogs continue to die and many frog species have become extinct. While researchers search for clues about the origins of this pathogen, why it kills some amphibians but is harmless to others, and what can be done to stop it, field researchers have had to change their standard operational procedures. Equipment must be disinfected with fungicides before it is moved from one location to the next as a way to keep from spreading the fungus to additional susceptible frog populations. After all, the chytrid fungus has done this quite well on its own, so no need to assist its death march.
There are still many unanswered questions about the chytrid fungus and many research needs at this time, but according to amphibian experts, no practical treatments are in sight. In a few cases, researchers have found that transferring infected frogs to warmer waters will clear the pathogen. Schwalbe noted that the fungus prefers temperatures below 28 deg. C, a fact that he has seen borne out in nature. A particular hot springs in New Mexico is free of this pathogen, but only 200 meters away in a cold stream, chytrid fungus is present.
Despite the mounting evidence for the role of the chytrid fungus in amphibian deaths, some say that there are many other factors that could be to blame, things like the introduction of nonnative species, insecticides and other environmental contaminants, acid rain, human encroachment on animal habitat, and climate change. However, some of the declines and extinctions have occurred in sites remote from human influence, in untouched, pristine rainforests.
While this debates continue, nature’s canary is dying.