Sprol

Photo Credit: Yamanaka Tamaki

Most of us have heard stories of some unsuspecting child or fisherman happening upon a frog that seems completely healthy, except for the fact that it has no legs or an extra eye. At one time, these stories were deemed as oddities or unusual, freak occurrences. Now, however, malformed frogs are much more common than once thought and are real life indicators of significant problems in our environment.

It is true that some variations of morphological abnormalities are expected among the world’s vast amphibian population, including more than 4,000 species of frogs and toads. These anticipated abnormalities, however, are typically due to some type of trauma, developmental problems and mutations rather than environmental factors.

The United States is home to roughly 230 amphibian species, which includes 90 frog and toad species. Beginning in the early 90s, in several of Minnesota’s wetlands, malformation rates were found to be between 30 to 50%. With the typical, expected malformation rate between zero and two percent, this finding was cause for concern. Once Minnesota’s frog problems were unearthed, elevated malformation rates were discovered in 56 of the United States’ native species and in 48 states.

While these abnormalities are often referred to as “deformities,” most of the abnormalities found are actually “malformations.” Notably, there is a real difference between the two conditions. Deformation is the process of disfiguring or distorting an already existing body part while malformation is the process of disrupting a normally-formed body part or organ during those vital first stages of development.

The malformations most commonly reported by herpetologists involve missing legs, extra legs and paralyzed or misshapen legs. Also seen are frogs with legs that are fused against the frog’s body, webbed together with extra skin or split into two new legs halfway down.

Images of malformed frogs

Other malformations are also reported. Frogs with missing or extra eyes, as well as eyes that are unusual in size, shape and location have also been found. Misshapen jaws and incomplete tail absorption have also been documented.

Because frogs are extremely sensitive to their environments, they have long been considered the “canary in a coal mine” for environmental disasters. In the past, before better methods had been developed, coal miners commonly relied upon canaries to detect toxic or explosive gases in mines. These delicate birds are more sensitive to toxic gases than we are and would collapse long before any miners were affected. A collapsed canary made the perfect alarm for miners to get out immediately and for management to investigate the noxious problem and fix it.

As with the coalmining canaries, frogs are especially vulnerable to the environment in which they live. Frogs are especially sensitive to pollution and other environmental stressors. They live at the meeting place of two very different environments, the land and the water, and easily absorb damaging pollutants directly through their skin.

As human beings, we breathe through our lungs, which are obviously tucked safely inside our bodies. Our bodies provide much protection from direct contact with polluted air and contaminated water. Although some amphibians do breathe completely through their skin, the majority breathe and receive their oxygen partially through their skin, which is always open to the elements. Whether breathing partially or completely through their skin, the amphibian body is much more vulnerable and susceptible to outside factors, including diseases, toxic chemicals, ionizing radiation (UV-B) from the sun and habitat destruction.

Because of this special vulnerability, we continue to see an increasing numbers of malformed frogs along with a steadily decreasing population of frogs, and amphibians as a whole. Like the coalminers, this should be our alarm to look into and fix this problem. This complex problem, however, will not be easy to remedy because there are several possible contributing causes.

Photo Credit: Hamed Saber

Consider this. Amphibians are such effective indicators of significant environmental variations that many ecological problems may go undetected by our human eyes until significant environmental damage has occurred. The current worldwide amphibian population is declining and the number of bodily malformations is increasing. This may be an early warning to us – an early warning of serious ecosystem imbalances.

WHAT’S TO BLAME

First, consider the extensive use of pesticides across the United States. The chemical runoff collecting in the vast Midwestern farmlands is causing much damage to frog populations. Not only do excessive pesticides and other xenobiotic chemicals affect the sexual development of frogs, but it also makes them more susceptible to often fatal bacterial meningitis as well as some dangerous, parasitic fungi.

Scientists have confirmed that agricultural contaminants may be an important factor in amphibian declines in California. According to an article recently accepted by the journal Environmental Toxicology and Chemistry, a study by scientists of the U.S. Geological Survey and U.S. Department of Agriculture indicates that organophosphorus pesticides from agricultural areas, which are transported to the Sierra Nevada on prevailing summer winds, may be affecting populations of amphibians that breed in mountain ponds and streams.
USGS

Studies at the University of California Berkeley have been conducted on delicate developing tadpoles. The tadpoles were reared in a watery environment contaminated with a mixture of nine pesticides, fungicides and herbicides – chemicals commonly found in ponds located close to Midwestern cornfields.

The evidence showed that polluted tadpoles take longer to complete their metamorphosis into adult frogs. Because of this delay, they are smaller, which makes it harder for them to catch and eat their prey and turns them into easier prey for other animals. Research also showed that these frogs had increased levels of a stress hormone that causes holes to develop in the thymus gland, which likely causes an impaired immune response to disease.

Photo Credit: Stadtwald

Pesticides are just one factor causing the decline of amphibian populations. This problem is the result of a combination of factors. Excessive chemical applications, the introduction of nonnative predators and competitors, increasing levels of ultraviolet light and global warming, acid rain, mercury pollution, eradication of wetlands and overall habitat destruction are all contributing to the decline of the frog.

While it is a natural occurring process for amphibian populations to fluctuate according to environmental conditions, such as rainfall amounts, the human population is the most likely component to the amphibian malformation and population decline.

Humans have the capability to improve or correct environmental problems. We also possess the ability to exacerbate the same ecological problems at local, regional and global levels. It’s up to us!