Amphibians are one of the most threatened animal groups in the world; almost one third of all species are under acute threat.
One of the main reasons for their decline is a chytrid fungus (Batrachochytrium dendrobatidis) with a nearly worldwide distribution. In a collaborative effort between Burke Museum researchers and other scientists from across the globe, close to 1,000 amphibians belonging to over 60 species were tested for the disease. The report was recently published in the science journal PLOS ONE.
Chytridiomycosis, the disease caused by the fungus, is known to be highly lethal to frogs and is believed to be responsible for the worldwide amphibian decline. In infected individuals, the fungus attacks the skin and blocks respiration, eventually killing the animal. Chytrid is widespread in Africa, and every year new positive records are reported from countries in southern, eastern, and central Africa. The current study by an international team of biologists and herpetologists did not detect chytrid in West Africa despite extensive tests of 62 species from seven countries. This is especially remarkable because environmental factors clearly show that the fungus would find suitable conditions in West Africa.
Chytrid spread by pet trade?
Two co-authors of the study, Burke Museum Curator of Herpetology Dr. Adam Leaché and University of Washington biology graduate student Matt McElroy, traveled to Ghana in 2011 to collect specimens for the project. Of the nearly 1,000 amphibians analyzed in the study, a significant portion were collected on this 17-day Burke expedition, representing over 40 different species. All are at the Burke Museum and are available to the public for future research. McElroy conducted genetic tests on over 100 individual frogs to detect the chytrid fungus, all of which were negative (no fungus detected).
One hypothesis is that the chytrid fungus originated in Africa and dispersed globally via the pet trade. This makes the study’s finding—that chytrid is not present in West Africa—all the more unusual and interesting.
The researchers used both genetic and histological tests to analyse the samples collected from the field. The consistently negative (chytrid free) results they found stand in stark contrast to what models of environmental parameters might predict. One explanation for this incongruence, according to Johannes Penner, the lead author on the study, is the Dahomey Gap; an arid region in Togo and Benin that naturally divides the rain forests in West Africa from Central Africa and in turn acts as a natural barrier for the dispersal of the fungus.
“Chytrid is having negative impacts on amphibian communities on a global scale, and our study provides hope that at least one highly diverse region of Africa may remain unaffected by this pathogen,” Dr. Leaché said. “Fieldwork and research conducted by Burke graduate students and undergraduates was instrumental to this study. Their efforts made a significant contribution.”
Last of the chytrid-free zones in Africa
It now appears that West Africa is the last tropical region beside Madagascar where chytrid does not exist, potentially sparing West Africa from the great amphibian decline affecting the rest of the world. Unfortunately, according to many experts, destruction of natural habitats, which happen on a large scale in West Africa, can easily rival the devastation of even chytrid.
To prevent chytrid from spreading into West Africa via the trade of frogs for the food market, the researchers suggest various precautionary measures. For example, the transport of potential fungus infected materials between the regions should be controlled and materials prophylactically disinfected. In addition, an early warning system would be useful to detect the appearance of the fungus in Ghana, a potential entry point. These actions could eliminate a significant threat to the amphibians of West Africa, and be utilized by conservationists to help other amphibian populations across the globe.