MYSTERY OF EXTINCT SPECIES OF COQUÍ BEING SOLVED

by Suzanna Engman
All coquí photos © by Rafael Joglar

PUERTO RICANS HAVE A THING FOR FROGS. We can't help it. They're everywhere, from the mountainous areas of the island, where nearly 25,000 frogs populate a hectare (the highest density of frog population in the world), to developed metropolitan areas, where scarcely a blade of grass can push through the cracks of the sidewalks. They sing us to sleep each night, calling to each other, "co-quí, co-quí, co-quí." And they're featured in the songs, folklore, and artwork of Puerto Rico.

Puerto Rico's love affair with frogs isn't new. Commonly known as coquís, these amphibians have been in the consciousness of island dwellers for thousands of years, evidenced by Taino Indians' petroglyphs and pictographs depicting coquís.

But something has gone wrong. In 25 years, three of the island's 18 endemic, or native, species of frogs have become extinct, and several more species are endangered.

University of Puerto Rico, Río Piedras, biologists Rafael Joglar, Ph.D. and Patricia Burrowes, Ph.D. set out to find out why. Working with a veterinary pathologist, David E. Green, Ph.D. of the National Wildlife Center in Madison, Wisconsin, they theorized the cause: interactions with a deadly fungus.

Declining populations, extinct species

In 1986 when Joglar returned to Puerto Rico after earning his doctorate at the University of Kansas, he noticed that the coquí populations of some species had declined. So he began monitoring the populations in El Yunque, the National Rainforest in northeastern Puerto Rico.

Then in 1990 at the First World Congress of Herpetology (the study of amphibians), herpetologists began discussing declining populations of frogs in places as far away from each other as New Zealand, Panama, and United States. After ten years of intensive investigation, researchers discovered that the common culprit of frog population decline around the world is a chytrid fungus, Batrachochytrium dendrobatidis.

Normally, Burrowes explains, the chytrid fungus is not harmful. "It belongs to a group of fungus that is wonderful because it contributes to the decomposition of dead arthropods, such as cockroaches and other insects. When it was found that the fungus was causing something harmful, it came as a shock to biologists.

"We found the fungus in 2000 by looking at preserved skin of animals collected in Puerto Rico in the 1970s. We found it in the skin of the last Webfooted Coquí that was collected in 1976, so we can trace infections by this fungus at least to that year.

"We have strong reason to believe that the fungus either arrived in Puerto Rico in the mid 1970s or that for some unknown reason it became pathogenic at that time, possibly due to environmental stressors. Perhaps the frogs had been able to cope with the fungus before then, but more recently other factors may be contributing to their inability to continue to cope with it. In this particular case, we have hypothesized that climate change, specifically an increase in dry periods, is responsible," says Burrowes.

"We do very basic field research that consists of monitoring various amphibian populations over measured transects. We're running controlled laboratory experiments in terrariums under strict temperature and humidity regimes. In collaboration with physiologists and molecular biologists, we sample tissue of our frogs to determine via Polimerase Chain Reaction the presence of pathogenic fungal DNA in their epidermal cells. We also collaborate with colleagues in the United States and Latin America, particularly through an organization sponsored by the National Science Foundation called RANA–Research and Analysis Network for Neotropical Amphibians."

To test for the fungus in living frogs, the biologists and students helping with the research clip off a part of the toe and release the frog back into the rainforest. Joglar explains that the cut doesn't draw blood and the toe grows back within three months. Tissue from the toes is then examined to identify the presence of the fungus.

Some species of coquí on the island are not in danger. "Species in lowlands don't seem to be affected at all," says Joglar.

Contributing environmental factors

Burrowes and Joglar began looking at potential climatic changes that could have contributed to the coquís' reaction to the fungus. As they studied the weather patterns, they found that the mean temperature in Puerto Rico has risen significantly. The minimum temperature has increased significantly in the high mountains of El Yunque, according to records from Pico del Este Weather Station, during the past 30 years. They hypothesize a synergistic effect of climate change–an increase in temperatures and increase in drought–with the infection of a pathogenic fungus.

"In the 1970s the mean temperature was 62.6 degrees Fahrenheit (17 degrees Celsius). In 2000 it was 64.4 degrees Fahrenheit (18 degrees Celsius). Most people haven't noticed the temperature increase. We're mammals. We have ways of regulating our body temperature. We can sweat, for example," says Joglar.

"But amphibians can't regulate their temperature," points out Burrowes. "Although one degree centigrade may not sound like much for a mammal, it may be physiologically significant for a small ectothermic animal such as an amphibian. During the past 30 years, there have been clumps of dry years between in the early-to-mid '70s and in the early-to-mid '90s, precisely in the years when species have disappeared. There's also evidence of prolonged dry periods in those years, which is detrimental for amphibian reproduction, since this event is triggered by May rains. We have reason to believe that climatic changes–the combination of less rainfall and higher temperatures–is related to the decline in populations."
Higher temperatures and drought may cause frogs to clump together in humid patches in order to conserve moisture. "It is precisely in those humid patches where we expect the fungus to be. If frogs are stressed because it's dry and hotter, their immune systems may be compromised. Under these conditions of environmental stress –immunological deprivation and clumping–we can expect an epidemic," says Burrowes.

"We have conducted controlled experiments in our laboratory to determine if frogs do, indeed, tend to clump in humid pockets, despite their territorial behavior, during dry spells. We've found that frogs do clump significantly when stressed with lack of water. Our second phase of experiments seeks to find out if frogs that are contaminated with chytrids and stressed with drought tend to die off faster than those that are contaminated but not stressed by drought. We are just starting this phase."

Apparently harmless to humans and not visible to the naked eye, the chytrid fungus can be deadly to frogs. And although researchers aren't sure how it claims its victims, they have postulated several possibilities.

"One hypothesis is that when a frog is attacked by the fungus there's an inflammatory response of the skin. This inflammation may affect a frog's ability to rehydrate and/or breathe effectively. Another hypothesis is that the metabolism of the fungus itself releases toxins that could kill an amphibian. Pathologists at the University of Colorado are investigating how the fungus kills the frogs," says Burrowes.

Introduction of Exotic Species

The worldwide spread of the disease could be caused by introduction of exotic species (species not native to a geographical region). "The exotics compete with endemic populations for food and for environment–places to breed, places to hide from predators. They could even be responsible for introducing the pathogens themselves," says Joglar.

"Scientists have sequenced the entire genome of the fungus. Comparison among strains around the world revealed very little variation," says Burrowes.

"The impression is that this thing is moving faster than it would happen naturally. Most likely, humans or exotic animals are involved spreading the fungus," says Joglar.

Several species of frogs in Puerto Rico are in danger of extinction because of population declines. "The Sapo Concho is in bad shape. Only 80 came out to breed in 2003. This species could be one of the most endangered in the world," says Joglar.

Call for Protected Environment

Conservation biologists investigate the causes of biodiversity deterioration or extinction. They have several methods of helping an endangered species survive and recover, including breeding in captivity. But this approach doesn't always work. While some species don't breed in captivity, others, such as the Sapo Concho, which is being bred in captivity in the United States, do successfully reproduce. However, once they're released they don't survive.

"The best way to help an endangered species is by protecting their natural habitat. We need to buy the land in order to preserve their environment," says Joglar.
A species of coquí in danger of extinction, Coquí Guajón, is a cave-dweller that needs protected land in Sierra Pandura in the area of Yabucoa, Maunabo, and the region between Patillas and San Lorenzo, says Joglar. The surviving members of the species now live on private land in these areas, and it is thanks to the support of the private landowners that biologists are able to conduct research there. But privately owned land is always vulnerable to being developed, and development could push an endangered species into extinction.

Joglar cites several reasons for fighting to protect endangered species. "Amphibians eat a lot of insects, two or three a night. They're also important in the food chain," says Joglar. At least 19 and maybe as many as 70 different species of birds eat coquís. In addition, lizards, snakes, spiders, snails, scorpions, and all kinds of mammals consume coquís. "If we remove this very important part of the food chain, we're harming the ecosystem."

Patricia Burrowes and Rafael Joglar

http://www.cnnet.clu.edu/procoqui