Disease-driven declines in global amphibian biodiversity
Amphibians such as frogs and toads are being driven to extinction by an aquatic fungus. This microbe, commonly called Bd, is spreading rapidly around the world and contributing to the decline in the biodiversity of the animals. In this article in Microbiology Today (pdf) Matthew Fisher believes that if control measures are not implemented, one-third of amphibian species could disappear:
Amphibians became the most ancient class of land-dwelling vertebrates when, 360 million years ago, Ichthyostega first hauled itself onto what was then Greenland. Since then, the amphibia have diversified into over 6,300 species that not only settled all continents except Antarctica, but also survived the catastrophic extinction events that overwhelmed their sister group, the dinosaurs. However, longevity of species is no guarantee of their future success; modern-day amphibians are suffering rates of extinction that far exceed those of any other class of vertebrates, including mammals and birds. Nearly one-third of amphibian species are threatened. The question of why amphibians are becoming extinct at these accelerated rates has puzzled scientists for three decades. While it is now clear that we are heading for a new anthropocene mass-extinction event as a consequence of human-driven planetary degradation, it has not been clear why this should be affecting amphibians more than other taxa. Further, many amphibian declines and extinctions were observed to occur in pristine environments that are relatively untouched by humans, such as rainforests and montane systems. A clue to the mystery came about when scientists working in Central America noted that the declines in amphibian biodiversity appeared to be occurring in a wave-like manner, with the initial losses being observed in Costa Rica, then spreading southwards towards the Panama Canal at rates of up to 43 km per year. These patterns of decline were suggestive of an epidemic, spreading pathogen, and in 1997 an international team of scientists discovered a new organism that appeared to be associated with many previously ‘enigmatic’ amphibian extinctions in two regions: Central America and north-eastern Australia. In 1999, the mycologist Joyce Longcore formally described this organism as new species of aquatic fungus and named it Batrachochytrium dendrobatidis.
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Tags: Biology, Emerging disease, Environment, Fungi, Microbiology, Mycology, Science
