Explanations for the sudden and drastic loss of a large class of animals have included habitat loss through human development, competition with or predation by introduced species, pollution and climate change. Unfortunately, even all these diverse factors cannot adequately explain many of the known cases, which include multi-species extinctions on nature preserves and other relatively pristine lands.
Recently, Collins and other researchers have found evidence that a couple of different pathogens might also be involved -- one an iridovirus and the other a chytrid fungus. Both are from familiar and common groups of organisms.
"The virus is widely distributed and comes from a group that is known in fish and insects. The fungus is from a group of fungi that are cosmopolitan and are generally associated with decaying plant matter. We've known about the chytrids for a long time, but never as pathogens of amphibians until the last 18 months," said Collins.
Collins points out, however, that finding that these pathogens are a big culprit behind a broad disappearance of frogs and salamanders actually raises more questions than it answers: "Are these novel pathogens? Has the physiology of the host changed? Has the biology of the pathogen changed? Has a change in the environment altered the pathogen? Has the environment changed in a way that has caused the immunology of the host to be compromised -- and therefore the amphibian is more susceptible to something that was a natural part of its environment? These are just some of the issues that need to be considered," Collins said.
There is also the problem of the sheer scope of the phenomenon. Large tracts of land are involved, from Saskatchewan to Arizona, through Central America, and across the globe in Eastern Australia. In these areas, dozens of species have become extinct and nume
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Contact: James Hathaway
hathaway@asu.edu
480-965-6375
Arizona State University
13-Feb-2000