YEAR OF BIODIVERSITY
Saving Philippine frogs
Saving Philippine frogs
1 How important are frogs in the ecosystem and in the web of life?
Frogs are an excellent indicator of environmental health. One explanation is that the skin of amphibians is semi-permeable, hence is very sensitive to the environment. Amphibians can “breathe” and “drink” through their skin, obtaining oxygen and water from their surroundings. Therefore, polluted environments can directly affect them.
Another explanation is that most species of frogs undergo two phases in their life cycle: an aquatic stage (the tadpole phase) and terrestrial stage (adult metamorph). Both phases involve radically different body forms, ecology and lifestyle. But one thing that is common to both forms is that they are subjected to a wide spectrum of environmental stress and challenges. (Not all frogs, however, have tadpoles. Many Philippine species of frogs skip the tadpole stage and their eggs develop directly into small frogs! This is a mode of reproduction known as direct development.)
Frogs play an essential function in the web of life. In the food chain, for example, they are a major predator of insects and many other invertebrates (animals without backbones). One could just imagine their important role in controlling the population of insect pests that could potentially damage important agricultural crops.
At the same time, frogs are a chief source of food for other animals, both vertebrates (especially birds, monitor lizards, snakes, civet cats and other frogs) and invertebrates. As we all know, many rural Filipinos are also fond of feasting on frog meat come rainy season, when frogs can be seen and caught in great abundance around lakes, ponds, and in flooded rice fields.
2 How many frog species are found in the Philippines?
There are about 105 known species of frogs in the Philippines. But herpetologists (those who study amphibians and reptiles) are aware of the presence of many other species, particularly those that have not been given formal names yet and are now in the process of being “described” to science. When this is done, the Philippines will likely have somewhere between 150 and 200 species of frogs! What is more fascinating is that over 80 percent of the species can only be found in the country.
For a relatively small country, the Philippines is extraordinary in having such a high concentration of biodiversity especially of unique species, the kind that cannot be found on other places of the world.
3 What areas were studied by a US-Philippine research team?
A team of Filipino and American scientists has undertaken field surveys of amphibians and reptiles in the Philippines since 2004. So far, the team has surveyed 20 different places on the islands of Luzon, Lubang, Samar, Leyte, Cebu, Dinagat and Mindanao. The ongoing study is part of a larger, collaborative research program on Philippine biodiversity between scientists from the Philippines and the United States.
The biodiversity research program included a survey of the presence of the chytrid fungus in the Philippines. This was led by scientists from the University of Santo Tomas, University of Kansas and the National Museum of the Philippines in partnership with the San Francisco State University, Silliman University-Angelo King Center for Research and Environmental Management and the Protected Areas and Wildlife Bureau of the Department of Environment and Natural Resources.
Our field surveys were undertaken in forested areas (such as mountains, natural parks, watershed areas) but we also surveyed human-controlled environments (like rice fields, crop plantations, built-up areas and even gardens).
We screened all frogs that we found from those areas for the chytrid fungus. Our initial results show the presence of chytrid fungus in five species of frogs that we found from two localities in Luzon: Mt. Palaypalay (in Cavite province) and Mt. Labo (in Camarines Norte).
4 Are the frog species found infected with the fungus found only in Luzon?
The five species of frogs that tested positive for chytrid fungus were Limnonectes macrocephalus, Limnonectes woodworthi, Rana similis, Rana luzonensis and Occidozyga laevis. Species of Limnonectes are commonly called “fanged frogs.” Both the species of Rana are “stream frogs” and Occidozyga frogs are commonly known as “puddle frogs.”
All these frogs are associated with aquatic environments and are especially found in mountain streams and fast-flowing rivers.
Except for Occidozyga laevis, all species are endemic to the Luzon Pleistocene Aggregate Island Complex or Luzon PAIC. Scientists consider the Luzon PAIC a separate biogeographic region in the Philippines. This means that the species of animals (and also plants) that are found in this region are unique to the region and are usually not found from other places in the Philippines.
Luzon PAIC includes the islands of Luzon, Polillo island group, Catanduanes, Marinduque and other adjacent islands around Luzon. Sometime during the geological past of the Philippines (that is millions of years ago), all these islands were connected to each other and formed one landmass.
5 How does the fungus kill frogs?
First of all, the type of fungus that we are talking about is called chytrid. Chytrid fungi are primarily found in soil and water but are certainly present almost everywhere. So far, only one of the 500 or so species of chytrid has been found to parasitize vertebrates—frogs, specifically—and goes by the scientific name Batrachochytrium dendrobatidis. Let us use the acronym Bd for this fungus.
Studies have shown that Bd causes a pathogenic skin disease in amphibians called cutaneous chytridiomycosis. This disease has been linked to mass mortalities of frogs in many countries in North, Central and South America and in Australia.
Scientists have also found that chytridiomycosis, interacting with other environmental factors, may have triggered the recorded massive decline of many frog populations in those countries, and worse, have caused the extinction of several species.
Bd lives in the skin of frogs. Like other chytrids, Bd produces zoospores (hundreds to thousands of them) in order to reproduce and to disperse. The zoospores are encased inside a structure called sporangium (plural, sporangia), which can be found scattered all over the skin cells of an infected frog. When they mature, the zoospores are ejected from the sporangium through discharge tubes that poke out of the frog’s skin.
Researchers believe that the disease disrupts biological processes in the skin of diseased frogs. Keep in mind that the semi-permeable skin of amphibians plays a critical function in respiration.
Researchers also suspect that Bd produces toxins during the infection stage. The pathogen load weakens the frog and eventually kills it.
6 When did the fungus reach the Philipines?
How is it spread?
We do not know the answer at this point. But the results of recent studies from other countries could provide helpful information.
The studies indicate that Bd might have been introduced along with commercially traded frogs. Frogs are routinely exported or imported as specimens for medical research, animals for the pet trade, as processed meat, or for frog farming.
One study suggested that Bd originated from Africa and was subsequently introduced into other countries through commercial trade of frogs. Another study done in Japan showed that the introduction of an alien species of frog for food and pet trade was the culprit for the appearance of the chytrid fungus in that country.
The results of these studies are highly relevant to us in the Philippines since we know that alien species are commonly traded in the country. In fact, there are now at least five species of alien frogs in the Philippines based on a previous study that we conducted ourselves. One of the five alien species in the Philippines (Rana catesbeiana) is the same species of frog that Japanese researchers found to be a vector of Bd.
On the other hand, Bd may have been in the Philippines for a long time and only recently did it reach pathogenic levels, due perhaps to radical changes in the extent and quality of our forest habitats, the structure, microclimate and so on, brought about by massive deforestation and forest disturbance that are still happening in our country.
But then again, we do not have the data right now to reach a conclusive statement. For example, we even lack baseline information on the population ecology or abundance of frogs from the two mountains where we found the chytrid fungus. Thus, we do not have any historical data to compare the information that we have now.
7 When did it start outside the country?
Scientists were able to identify Bd and the disease it causes in the late 1990s. But researchers working in Central and South America started noticing that something was amiss as early as the 1970s, when the populations of frogs that they were studying and monitoring started to decline and even collapsed.
8 How many countries have been affected by the fungus?
Bd is now known from at least 43 countries and has infected more than 100 different species of frogs.
It has been recorded in countries in North, Central and South America, Europe, Africa, Asia, Southeast Asia and Oceania (Australia and New Zealand).
9 What are the steps being taken to save the frogs?
In other countries, Bd-infected frogs are caught from the wild and are brought into captivity with the aim of preventing the spread of infection to other individual frogs, species or populations. While the diseased frogs are being kept in zoos, veterinarian centers, or research centers, careful observation and monitoring are done. Some groups of researchers have found success in the treatment of diseased frogs using antifungal medications.
But in general, scientists feel that current conservation efforts are insufficient and the available options to control and to combat the spread of the disease are very limited. Scientists are still striving to find more effective and long-term solutions to this global problem.
That is why we believe that it is very important now to establish a monitoring program on chytrid fungus in the Philippines. Among the first steps that should be done are to: (1) Find out which other areas in the country are Bd-positive; (2) Identify which other species of frogs are affected; and (3) Determine and assess the effects of Bd on the frog community.
In the meantime, the two areas where we found the presence of Bd need to be monitored and assessed if the chytrid is causing a decline in their frog populations.
(Arvin C. Diesmos, Ph.D., an ecologist, is a research scientist at the zoology division of the National Museum of the Philippines, Manila and is in charge of the herpetology section; Mae Lowe L. Diesmos, M.Sc., a biologist, is an assistant professor at the Department of Biological Sciences, College of Science of the University of Santo Tomas, Manila.
Rafe M. Brown, Ph.D., an evolutionary biologist, is a curator at the Natural History Museum of the University of Kansas and an assistant professor at the Department of Ecology and Evolutionary Biology of the University of Kansas.)
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