Amphibians have made the headlines again in the last few weeks, for the same unfortunate reason as last time and the time before: because they are dying. A recent study published in the journal Nature found that there is an association between global warming, the spread of a pernicious fungus, and the worldwide decline of frogs and their kin. Specifically, the study found a correlation between climate change and the disappearance of species of harlequin frogs from Central America. Pounds et al. (2006) suggest that the warming environment has created favorable conditions— increased cloudiness, which makes for cooler days and warmer nights— for the chytrid fungus, which has wiped out many amphibian populations. Because this was an observational study based on describing correlations among data sets, it does not necessarily prove that global warming is causing the fungus to spread and kill amphibians, but it does suggest that something is going on and that this phenomenon needs further study. The scenario described by Pounds et al. (2006) seems plausible and, if true, is an example of the complex roles that infectious diseases play in the loss of Earth’s biodiversity.
Regardless of whether global warming is helping the chytrid fungus spread, the latter is doing serious damage. Karen Lips and her colleages published a study this month on the rapid decimation of numerous frog and salamander populations in Central America by the fungus (Lips et al, 2006)
A study by Tyrone Hayes (Hayes et al, 2006) found that the herbicide atrazine and an assortment of other chemicals, when mixed together at concentrations typically found in ponds near agricultural fields, kill more than a third of exposed tadpoles and cause adults to suffer a variety of maladies. Harmful effects were more pronounced when chemicals were combined rather than administered individually. These results are important because they show that amphibians suffer high mortality when exposed to man-made chemicals in realistic concentrations and mixtures that are common in some environments. Most earlier studies had shown that these chemicals kill amphibians when administered independently in high concentrations. (Surprise, surprise. Dunk me in a vat of atrazine and see if I don’t develop some problems.)
Times are hard for frogs and salamanders. These ancient and delicate creatures represent lineages that survived the world-shattering End-Permian and End-Cretaceous mass extinctions— lineages which are now being inadvertently snuffed out by an uppity species of ape. Boo!
Hayes, T., et al. 2006. Pesticide mixtures, Endocrine disruption, and amphibian declines: Are we underestimating the impact? Environmental Health Perspectives Online.
Lips, K., et al. 2006. Emerging infectious disease and the loss of biodiversity in a Neotropical amphibian community. Proc. Natl. Acad. Sci. USA
Pounds, J., et al. 2006. Widespread amphibian extinctions from epidemic disease driven by global warming. Nature 439, 161-167