IS GLOBAL WARMING CAUSING FROGS TO CROAK?

In the past few years, global warming has become the focus of much attention by many concerned citizens and scientists. Changes to climate worldwide affects plants, animals and people on many different levels. Understanding those changes, and deciphering clues as to their causes, has been the work of scientists in a variety of different disciplines. At the Sam Noble Oklahoma Museum of Natural History, herpetology curator Janalee P. Caldwell studies amphibians around the world, most particularly in the Amazon River basin in Brazil. Caldwell has been surveying frog populations in Oklahoma since 1990. Amphibians, such as frogs, are very sensitive to environmental changes and are often early indicators of imbalances in the environment that can lead to larger problems later on. Changes to worldwide frog populations are of concern among scientists. Here, Caldwell explains how frogs provide clues to global climate changes around the world.

In 1989, a small group of scientists began voicing concerns about frog disappearances in many types of habitats. Soon after, the Declining Amphibian Populations Task Force (DAPTF) was formed to investigate the problem. The task force found that, of the 5,362 species of frogs that are currently known, thousands have declined in numbers, and more than 400 species are listed as “Critically Endangered” in a recent global assessment. Of all amphibians, 122 species are possibly extinct, meaning that they have not been observed in nature by any herpetologist for many years.

Causes of these declines have puzzled herpetologists. Of course, habitat destruction or degradation is a factor in declines of all kinds of animals and plants, not just frogs. Other factors that cause local populations to disappear are increased levels of UV-B radiation, introduced species such as certain fish that feed on tadpoles and eggs, and chemical contaminants such as pesticides and herbicides. But, the puzzling part is that many frogs are dying in remote areas that have not been touched by civilization, and currently, many of the species that are dying occur at higher elevations. For example, a herpetologist from Illinois, who studied frogs in a mountainous area in Panama, found many species and many individuals for two field seasons. She returned for a third year to find almost no frogs of any species; in addition, she found many dead and dying frogs in the now silent rainforest.

Within the last few years, scientists have begun to put together pieces of this puzzle. Much research is now showing that a fungus, called chytridiomycosis (pronounced “kit-rid” for short), is spreading throughout the world and is deadly for frogs. Frogs breathe through their porous skin, and the fungus attacks through this route. A major question regarding this fungus is “why did it suddenly begin affecting frogs?” Scientists have recently traced the cause to global warming.

In the tropics, warm air increases cloud cover, which in turn provides a more moderate climate (cooler days and warmer nights), especially at mid-elevation localities. This change in climate has allowed the fungus to spread rapidly and appears to explain why frogs in mountainous areas from the western United States to the Andes in South America have declined precipitously in numbers.

What about frogs in Oklahoma? Dr. Caldwell and Dr. Laurie Vitt, curators of herpetology at the museum, are currently surveying amphibians and reptiles throughout the state of Oklahoma under a project funded by the Oklahoma Department of Wildlife Conservation. This work is partly intended to determine if populations of these species are declining. Frogs that occur in Oklahoma have declined in other parts of their range. For example, Blanchard’s Cricket Frog is one of the most common frogs in Oklahoma—its call sounds like rubbing two marbles together and is one of the most common sounds heard on summer evenings. Once widespread throughout the eastern part of the United States, this frog has now disappeared throughout most of the northern states. Current work suggests that a “decline front” is progressing from north to south, and if this trend continues, could affect Oklahoma frogs. Although the cause of the decline of this species is not understood, Dr. Caldwell hopes to be able to detect whether Oklahoma frogs are being affected.

Why should we care if frogs die throughout the world or here in Oklahoma? Both esthetic and practical reasons come to mind. Frogs are a unique, beautiful and melodious group of animals. In addition, benefits that frogs may provide to humans have barely been explored. Frogs have dense glands throughout their skin and produce many specialized chemicals. One of these chemicals is being tested as a potent painkiller and another has strong gluelike characteristics. Two species of frogs from Australia swallow their fertilized eggs, and tadpoles develop in their stomachs. To keep from digesting her offspring, the female frog secretes a chemical that stops the production of stomach acid. This chemical could have implications for gastric problems (for example, ulcers) in humans; unfortunately, these frogs have not been seen in the wild since 1979 and are thought to be extinct.

A much more ominous reason exists for us to worry about amphibian declines. Frogs and salamanders have inhabited the earth for about 200 million years—dinosaurs came and went while amphibians roamed around under their feet! The fact that many amphibians are suddenly dying sends a strong message that something is seriously wrong with the environment that we all share. Think about it—frogs drifted around with the continents during the middle Mesozoic, survived the mass extinction of dinosaurs at the end of the Cretaceous, , and made it through all of the global climate changes associated with Pleistocene glaciations. They inhabited the earth during the entire evolutionary history of mammals, birds, and most of the reptiles that we see today. If these declines in frog populations are the result of human impacts on the environment (a very real possibility), these same impacts could have far-reaching consequences for many other animals, including humans.

Frogs and other amphibians need our help. To find out what frogs occur in Oklahoma and other states and to learn more about why frogs are disappearing and how you can help, please visit the following Web sites: www.nwf.org/frogwatchUSA and http://amphibiaweb.org/declines/declines. And take time to enjoy the beautiful sounds of Oklahoma’s melodious frogs.

The Sam Noble Oklahoma Museum of Natural History is a research division of the University of Oklahoma. The museum employs 13 curators who conduct research in the life, earth and social sciences in the U.S. and around the world. Additional information about the museum is available by calling (405) 325-4712, or online at www.snomnh.ou.edu.

###