February 15, 2013

There's hope for the survival of frogs

Leopard running frog, Kassina arboricola.
Photo by Duncan Reid.

Amphibians are one of the most threatened animal groups in the world; almost one third of all species are under severe threat. One of the main reasons for this is a nearly worldwide distribution of a chytrid fungus that causes a highly-lethal disease in frogs, called Chytridiomycosis. The fungus attacks the skin and blocks respiration in infected frogs, eventually killing the animal.

Chytrid is particularly widespread in Africa, with new positive records reported from countries in southern, eastern, and central Africa each year. One hypothesis is that the chytrid fungus originated in Africa and dispersed globally via the pet trade.

In a recent study published in the science journal PLOS ONE, Burke Museum researchers collaborated with biologists and herpetologists from across the globe and tested nearly 1,000 amphibians belonging to 62 species in seven African countries to see if they have the disease.

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, over 40 different species, were collected on this 17-day Burke expedition.

McElroy conducted genetic and histological tests on more than 100 individual frogs in the study, but did not detect the chytrid fungus. Other tests in the study produced similar findings. Remarkably, the fungus was not found in West Africa despite environmental factors that clearly show the fungus would find suitable conditions there.

“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. One explanation for this, 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.

It 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. Though, according to many experts, future destruction of natural habitats in West Africa could easily rival the devastation of chytrid on amphibians.

In the study, researchers suggest various precautionary measures to prevent chytrid from spreading into West Africa through the trade of frogs for the food market. For example, regional transport of potential fungus-infected materials should be controlled and 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 protect the amphibians of West Africa, and be utilized by conservationists to help other amphibian populations across the globe.

All of the amphibians collected by Burke researchers for this study are a permanent part of the Burke Museum's herpetology collection and are available for future research.

Study Information:
Johannes Penner, Gilbert B. Adum, Matthew T. McElroy, Thomas Doherty-Bone, Mareike Hirschfeld, Laura Sandberger, Ché Weldon, Andrew A. Cunningham, Torsten Ohst, Emma Wombwell, Daniel M. Portik, Duncan Reid, Annika Hillers, Caleb Ofori-Boateng, William Oduro, Jörg Plötner, Annemarie Ohler, Adam D. Leaché & Mark-Oliver Rödel (2013) Title: West Africa - A Safe Haven for Frogs? A Sub-Continental Assessment of the Chytrid Fungus (Batrachochytrium dendrobatidis). PLOS ONE http://dx.plos.org/10.1371/journal.pone.0056236.