Box 1. Caecilians: Amphibian Enigmas
If it is unusual for us to bump into frogs, toads, and salamanders in our everyday lives, it is even far more unlikely that we would encounter a caecilian, or even know what one was if we were to stumble across one in a tropical forest or an unmarked terrarium in a zoo. Caecilians owe their obscurity to their habit of burrowing underground and remaining out of sight. They are limbless creatures that look like a cross between a snake and an earthworm. Their long cylindrical bodies are clearly snakelike, but upon close examination they lack surface scales and seem to have encircling rings, much like an earthworm. Yet anatomical inspection shows they have a backbone (eliminating any close relation with the earthworms) and the same eye retractor muscle found in other amphibians.
Caecilians diverged from other amphibians well over 200 million years ago, and now occur worldwide in tropical habitats. One hundred sixty-eight species are known, but this number will surely increase as more specimens are unearthed. A few South American species are entirely aquatic, but the rest live underground. They have well-developed bony skulls that allow them to push dirt aside as they burrow. Their eyes are generally covered by a layer of skin or even bone, suggesting that vision is not the primary way in which they sense their subterranean world. They share a unique tentacle located on each side of the head partway between the nostril and eye that presumably allows them to detect prey. Some caecilians lay eggs; others bear live young. In some species, females guard their eggs.
How do scientists find these underground denizens? In tropical rainforests, the enterprising naturalist can sometimes find caecilians deep in the leaf litter or upper soil layers at the base of tree buttresses. Another place to hunt for caecilians is in shade coffee plantations adjacent to forest. They are attracted to the high insect densities found in rotting piles of pulp discarded during the refining process. The terrestrial species cannot withstand saturated soils, so animals can be found on the forest floor after heavy rains or even swimming during floods. Their secretive habits ensure that we still have much to learn about these enigmatic cousins of our more familiar amphibians.
by Roberto Ibá?ez
Box 2. RANA: Catalyzing Amphibian Research
When amphibians began mysteriously disappearing from their habitats in the late 1980s, most field herpetologists were unprepared to study the phenomenon. At the time, most herpetologists concentrated more on studying taxonomy and behavior than demography. Few people thought amphibian diseases were interesting or deserving of much study.
But during the 1990s, it became clear that amphibians in many parts of the world and especially Latin America were in trouble. Potential explanations for the declines included disease, climate change, environmental contaminants, and the effects of introduced species. To sort out these explanations, scientists needed to monitor populations, perform autopsies on dead animals, and analyze weather data in addition to their other studies. The challenge demanded new collaborations with colleagues working in other countries and in other fields.
To catalyze this sea change and better coordinate their research, in 2002 a group of biologists founded the Research and Analysis Network for Neotropical Amphibians—RANA for short. Funded by the U.S. National Science Foundation, RANA’s goals are to promote international collaboration on amphibian decline research and to develop a database on the status of amphibian populations throughout Latin America. To date, over 80 scientists working in 14 Latin American countries have joined the network.
RANA has allowed scientists to examine similarities in how periods of drought correlate with population declines in such distant places as Ecuador, Costa Rica, Venezuela, and Puerto Rico. Another group of RANA scientists is examining the near extinction of harlequin toads, a tropical group in which most of the 77 known species have disappeared from across their range over the last 20 years. And finally, numerous RANA members contributed to this report on the current status of New World amphibian populations. Through these efforts, RANA hopes to hasten the day when we can explain why amphibians are disappearing from pristine habitats and determine what we can do about it.
by Karen R. Lips
Box 3. The IUCN Red List Criteria
The IUCN Species Survival Commission has identified five criteria by which a species can be classified as threatened. For each criterion, species with more severe conditions qualify for higher threat categories. The five criteria are:
- Declining population size. Even abundant species can qualify if their populations are declining fast enough.
- Small, declining geographic range. Geographic ranges typically contract when suitable habitat is systematically destroyed.
- Small and declining population size. Species with small and declining populations are endangered because a single disease or catastrophic climatic event such as a flood could quickly wipe them out.
- Small population size (with no decline). Even stable, small populations are still vulnerable to single catastrophic events.
- Quantitative analysis indicating a high probability of extinction in the near future. These analyses typically use mathematical predictions of population trajectories based on demographic information.
Each criterion is accompanied by guidelines specifying the characteristics a species must display to be classified in a specific threat category. Assessors painstakingly compile all known information about a species before determining which of these criteria apply. The actual criteria are available in English, French, and Spanish on the web, and guidelines for using the criteria are posted (in English only).
Box 4: The Southeastern United States: Hotbed of Salamander Diversity
The United States is the world’s third-largest country, but due to its position well north of the equator it rarely rates so high for biological diversity. Even small tropical countries such as Ecuador typically have many more kinds of virtually every group of organism. Not so for salamanders. With 168 species of salamanders, the United States is tops in the world. Only Mexico, with 127 species, is close.
The southern Appalachian Mountains of western North Carolina and eastern Tennessee is the most salamander-rich area on Earth. Thirty-one species occur within the boundaries of Great Smoky Mountains National Park alone. And on a good day in northeastern Mississippi you could find members of seven of the world’s ten families of salamanders: four aquatic families (Amphiumidae – amphiumas, Cryptobranchidae – hellbenders, Proteidae – waterdogs and mudpuppies, Sirenidae – sirens), two largely terrestrial families (Ambystomatidae – mole salamanders, Plethodontidae – lungless salamanders), and one amphibious family (Salamandridae – newts). Only southern Mexico and Central America, with their great diversity of terrestrial species, rival the diversity in the southeastern United States.
Due to the broad ranges of some of these salamanders and their frequent occurrence in remote mountains, relatively few species are threatened with extinction. Seventeen (16%) of the 106 species that occur in a 13-state region bounded by Virginia, Missouri, Louisiana, and Florida are threatened, but none critically so. The threatened species tend to have small ranges, such as the black warrior waterdog (Necturus alabamensis), which is restricted to a few counties in Alabama’s Black Warrior River drainage. As a group, U.S. salamanders are threatened by habitat loss and degradation caused by logging, atmospheric pollution, and reduced water quality from agricultural, industrial, and residential runoff. Public and private land managers in this extraordinary area shoulder an important responsibility in safeguarding the world’s richest salamander fauna.
by Geoffrey A. Hammerson and David B. Wake
Box 5. Haiti: A Megadiverse Caribbean Country
Known internationally mainly for its political turmoil, Haiti and biodiversity are rarely mentioned in the same breath. Stories about enchanting Haitian wild areas never appear in the nature magazines we read. With its political instability, overcrowding, and few natural attractions, why should conservationists pay attention to Haiti?
The answer is its amphibian diversity. Haiti is home to 50 native amphibian species, second in the Caribbean only to Cuba, which has 58 species in four times the land area. Of Haiti’s total, 26, or more than half, occur in no other country, not even the neighboring Dominican Republic. The largest concentration of amphibian species anywhere in the Caribbean occurs in the Massif de la Hotte, on the tip of the long Tiburon Peninsula that juts westward into the Caribbean Sea in southern Haiti. This small area is home to 32 frog species.
This diversity is all the more remarkable when we consider that Haiti has no taxonomists actively describing species. All Haitian species that have been discovered in the last 50 years have been described by U.S. herpetologists, including Blair Hedges, Albert Schwartz, Richard Thomas, and Ernest Williams, who have visited the country infrequently. So Haiti likely holds (or held) a number of undiscovered species.
Unfortunately, the future for many of these species is grim. Widespread rural poverty has led to the dismantling of natural habitats for firewood and charcoal production. Hillsides are denuded and streams have dried up. The Haitian government has set up an extensive system of protected areas, but park personnel are either nonexistent or powerless to stop rampant extraction of natural resources. Many amphibians have been found only in the tiniest remnants of vegetation that will likely disappear shortly if they have not already. Although establishing effective conservation programs in unstable countries is a challenge, Haiti’s remarkable and unsung diversity merits the effort.
by S. Blair Hedges
Box 6. Telmatobius: A Vanishing Genus of High Andean Frogs
Although many tropical frogs are noteworthy for their spectacular color patterns, the Lake Titicaca frog, Telmatobius culeus, is renowned instead for its bizarre shape. This giant frog—30 centimeters in length—has such baggy skin that it looks like it is wearing a suit three sizes too big. Its looks and restriction to the world’s highest navigable lake have earned the frog attention from Jacques Cousteau and international nature magazines. The Lake Titicaca frog, however, is but one of a group of 51 species in a genus that is threatened in ways that are emblematic of many amphibians.
Telmatobius frogs are aquatic lake and stream-dwelling frogs distributed in the Andes from Ecuador to northern Chile and Argentina at elevations usually exceeding 3,000 meters. The champion is T. marmoratus, which naturally occurs as high as 5,000 meters. To adapt to such elevations, these frogs use their skin to obtain oxygen from the water and highly efficient hemoglobin to bring the oxygen to their body tissues.
Scientists have not found any of the three Ecuadorian species for the last 10 years, despite numerous scientific expeditions to known localities. Museum specimens of T. niger collected before the declines show evidence of Batrachochytrium dendrobatidis, a disease-causing fungus that has devastated amphibian populations worldwide, including Ecuador. This disease, another fungus, and climatic abnormalities may have played a role in the Ecuadorian declines.
In Peru and Bolivia, large Telmatobius frogs from the Andean lakes of Junín, Titicaca, and others are harvested in great quantities for local consumption and to serve in restaurants to adventuresome tourists. In addition, frogs are caught and killed to produce a supposed elixir that is gaining in popularity as an alternative to Viagra. Uncontrolled commercial harvests may have caused dramatic declines in species from this region.
Herpetologists have recently described a number of Telmatobius species from isolated small water bodies in dry desert habitats from the Andes of Chile and Argentina. With large expanses of unsuitable habitat between populations, these species are highly vulnerable to human and agricultural uses of the water where they live. Seventy percent of Telmatobius species occur outside of protected areas. Considering the threat from disease and loss of habitat quality, this is a group that urgently needs habitat protection, population monitoring, and for some species, the establishment of captive populations that can be used as a source of animals for reintroduction into restored habitats.
by Andrés Merino-Viteri
Box 7. Unwelcome Silence: The Lost Frogs of the Brazilian Atlantic Forest
In 1975, Smithsonian Institution herpetologist Dr. Ron Heyer set out to understand the biogeography of frogs in the Atlantic Forest, a formerly continuous strip of rainforest extending along the coast and coastal mountains of eastern and southeastern Brazil. Biogeography is the study of how organisms have diversified, dispersed, and come to occupy the ranges where we find them today. Heyer selected a group of stream-dwelling frogs in the genus Cycloramphus, an obvious choice for the study because the adults are easy to find calling at night along fast-flowing streams. The tadpoles are also conspicuous because they tend to cling to rocks bathed in spray from adjacent waterfalls. At the time, taxonomists recognized 10 species in the genus, all endemic to the Atlantic Forest.
For an introduction to the frogs, Heyer enlisted the help of Rio de Janeiro herpetologist Sergio Potsch de Carvalho e Silva. Carvalho e Silva brought Heyer to a nearby stream one night where male Cycloramphus were calling. Over the next five years, Heyer tramped up and down streams along the length of the Atlantic Forest collecting frogs. By the time he finished, he had doubled the number of known species of the genus Cycloramphus.
In the early 1980s, Heyer returned to Boracéia, a site where he had reliably found two species during his sojourns of the 1970s. To his surprise, both Cycloramphus and several other previously common frogs were nowhere to be found. In the 1990s, Carvalho e Silva began visiting a relative’s mountain retreat near Teresopolis, located in the Atlantic Forest of Rio de Janeiro state near another of Heyer’s original collecting localities. Despite repeated searches of the streams at night, he never could find the populations that Heyer had found so easily two decades previously. Meanwhile, herpetologists Paulo Garcia in Santa Catarina and Magno Segalla in Paraná were revisiting Heyer’s old field sites in their states, finding populations either gone entirely or greatly reduced in abundance. Although one species that disappeared, C. fulginosus, has subsequently rebounded, no one has seen 13 of the 18 stream-dwelling Cycloramphus species in the last 20 years.
What happened to all of these frogs? Without monitoring data for any of the populations, we will never know for sure. However, the observation of montane stream-associated frogs disappearing despite no obvious loss in habitat fits the pattern recorded elsewhere in tropical America. A hypothesis that scientists are currently working on is that a combination of a trend toward dryer weather and disease may have finished off a number of these populations. A particularly harsh frost in 1979 may have caused the disappearances at Boracéia. Whatever the reason, montane streams in the Atlantic Forest are now quieter at night.
by W. Ronald Heyer and Sergio Potsch de Carvalho e Silva
Box 8. Malformed Frogs: Leaping to the Wrong Conclusion?
In 1995, a group of Minnesota schoolchildren made an unsettling discovery at a neighborhood pond. They spied a large number of leopard frogs swimming with horrible deformities, including some with extra hind limbs. The school kids contacted the Minnesota Pollution Control Agency which helped them put their observation on the Internet. The national media picked up the story and finally the Environmental Protection Agency got involved. What could be a more convincing harbinger of environmental collapse than our children finding “Frankenstein frogs” in the ponds near where we live? Could these deformities indicate toxic chemical pollution or dangerous UV irradiation? Are these deformities related to the general collapse of amphibian populations?
It turns out that the likely cause of the deformities was known. In 1990, Dr. Stanley Sessions of Hartwick College and colleague S. B. Ruth described how trematode flatworms can cause extra limbs to grow in developing tadpoles. Subsequent research has confirmed that trematodes are the most likely cause of amphibian malformations in North America. How do these little worms cause such striking changes in their hosts?
The trematode that infects frogs attacks three different hosts during its life cycle. These trematodes (the genus Ribeiroia appears to be the only deformity-causing trematode in North American frogs) need to infect aquatic birds in order to complete their life cycles and produce more adult worms, but they must first undergo embryonic development inside of a pond snail. To do that, the worm’s eggs enter pond water in bird excrement, and the first larval stage, called miracidia, hatches and infects snails. Each miracidium then produces numerous worms of the second larval stage, called cercariae, which develop inside the snail host. The parasite now has a problem: How does it get back into its primary host (birds) to complete its life cycle? These cercariae swim until they find a tadpole where they form cysts (called metacerariae) exactly where limbs will soon form. The cysts disrupt natural limb development causing extra legs and other limb deformities. A frog with extra or badly deformed legs cannot swim or hop well, so it falls easy prey to aquatic birds—exactly what the trematode “wants” in order to finish its life cycle.
Researchers thought at one time that pesticide runoff, particularly retinoid chemicals (such as methoprene, used for mosquito control), caused limb deformities in wild frogs. Although retinoids can cause distinctive deformities in frogs in a laboratory setting, the kinds of deformities seen in the field more closely match those caused by trematode worms.
While deformities can depress frog populations locally, they are unlikely to explain declines globally. Many amphibians that have declined reproduce in fast-flowing streams, temporary pools, or directly in moist leaf litter, all microhabitats where the snail intermediate host does not occur. Observations of mass die-offs of frogs rarely record deformed frogs among the dead. Thus deformities are more a function of local parasite and snail population dynamics (which may be influenced by human-induced degradation of wetlands) and as yet have no connection to global declines.
by Stanley K. Sessions
Box 9. Fish Tale: Introduced Trout in the High Sierra
Intrepid hikers who venture to the high peaks of the Sierra Nevada in Yosemite National Park are rewarded with vistas of pristine lakes and stunning mountain ranges apparently unchanged since the days when John Muir walked those same ridges and was inspired to pen his revolutionary wilderness philosophy. Yet a careful reading of Joseph Grinnell and Tracey Storer’s 1924 classic Animal Life in Yosemite reveals something missing from those lakes today: frogs. Whereas Grinnell and Storer reported that frogs were abundant in many of these lakes, a visitor now is hard-pressed to find a single one.
What happened in these lakes, seemingly in one of the most unspoiled parts of western North America? In the 1990s, scientist Roland Knapp set out to find an answer. Peering into those lakes, Knapp found something that Grinnell and Storer rarely saw: trout. Over the last century, angler groups and the state of California have stocked these historically fishless lakes with trout for recreational fishermen. Following on the pioneer observations of David Bradford, Knapp wondered if the fish might have eaten the frogs to local extinction. He first surveyed 1,700 lakes and ponds for fish and mountain yellow-legged frogs (Rana muscosa), the species historically present there. Bodies of water without fish were three times more likely to have frogs than those with fish, suggesting that Knapp’s hunch was on the mark.
Next, colleague Vance Vredenburg experimentally removed all fish from selected frogless lakes. Within a short time, frogs appeared and successfully reproduced and populated the lakes. Vredenberg also confirmed that trout eat tadpoles as they hatch. These results strongly suggest that introduced trout are the critical factor in the disappearance of mountain yellow-legged frogs from much of the Sierra Nevada. Fortunately, remnant populations remain that can recolonize lakes where trout are removed. With thousands of lakes in the Sierra Nevada, there should be enough for both fisherman and frogs.
by Roland A. Knapp
Box 10. Can Zoos Save our Frogs? The Role of Captive Breeding
With habitats rapidly disappearing and diseases threatening entire species, zoos may seem like our best option for last-ditch conservation of species on the brink of extinction. To successfully fill the roll of Noah’s Ark, zoos have to be able to do two things. First, they must succeed at captive rearing: reproduce animals continually over multiple generations. Second, they must succeed at reintroduction: release animals in the wild to create self-sustaining populations. History has shown that the first task is much easier than the second.
Zoos and governmental hatcheries have been successful at inducing reproduction in a number of threatened species. In Europe, reintroductions of some species such as the Mallorcan midwife toad (Alytes muletensis) have been successful. However, New World amphibians have yet to recover from near extinction due to reintroduction efforts.
- Wild populations of Wyoming toads (Bufo baxteri) are now gone, but 12 zoos and two government facilities rear the species in captivity. Despite annual introductions of tadpoles and toadlets to Mortenson Lake since 1992, the population is still not self-sustaining.
- Western toads (Bufo boreas) have disappeared from many parts of their range in western North America, and they are now on the Colorado state endangered species list. Despite the investment of $14 million on rearing metamorphs (juveniles that have recently grown their legs and absorbed their tails) and adults in captivity, reintroduction efforts failed to establish any new populations.
- The Puerto Rican toad (Bufo lemur) once occurred along the coasts of Puerto Rico as well as in the British Virgin Islands. Today it is restricted to a single population in Guánica National Forest in southwestern Puerto Rico. Although captive rearing has been successful, no reintroduced toads have survived to maturity.
The causes for failure are not clearly understood, but disease and predation are known contributing factors. Reintroductions cannot be successful unless the process that originally threatened a species is stopped before the release of captive-reared animals. Determining what these threatening processes are is clearly a great challenge, but the midwife toad example shows that it is possible.
A less intensive technique called “head starting,” in which eggs laid in the wild are collected, reared to metamorphosis in captivity, and then released in appropriate habitat, is showing some promise. Head starting of three endangered leopard frogs (genus Rana) in Arizona (United States) appears to be working in some areas. Captive rearing is serving our conservation goals by maintaining living populations of gravely threatened animals. The devil is in the details of successfully reintroducing these creatures to the wild.
by Amy J. Lind
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—R. Joglar, personal communication 2004.
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This is a chapter from Disappearing Jewels: The Status of New World Amphibians (e-book).
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