By Dennis T. and alex a. avery
Thursday, May 18, 2006
Scientists around the world are worried about frogs. Many frog populations are in decline, and we don't know why. We've found some small clues: something called the ranovirus is hampering efforts to restore leopard frog populations in alberta, Canada, where they were once abundant. The chytrid fungus, which has caused frog die-offs in australia, africa, and Central america, has also been found in the United States.
Some false leads have also been run down. When Minnesota school kids found deformed frogs in some local ponds, the finger of accusation was pointed at pesticides. Now, the deformities have been traced to a natural parasite, the trematode, which burrows into the just-forming leg joints of tadpoles.
The absence of yellow-legged frogs in some California mountain lakes had been blamed on pesticide-laden dust rising from the intensively farmed San Joaquin Valley. However, when the fish management teams stopped stocking the mountain lakes with hungry trout, the frogs returned in large numbers.
Pesticides are still a favorite bogyman of concerned frog lovers on Internet blogs, however, and there's no shortage of funding--or publicity--or researchers blaming frog declines on farm chemicals. Guilt is a powerful human motivator, and we love to flog ourselves over the ways in which the modern world feeds itself.
That may explain the latest in a long string of publications by Tyrone Hayes from the University of California/Berkeley. Hayes' article in Environmental Health Perspectives, april, 2006, is titled: "Pesticide Mixtures, Endocrine Disruption, and amphibian Declines: are We Underestimating the Impact?
Hayes tested Boston-pedigree frogs with the extremely low-concentration mix of nine pesticides (each at only 0.1 part per billion) that they might encounter in midwestern farming areas. He says in the abstract of the paper that frogs exposed to his dilute pesticide cocktail took longer to metamorphose to adults (by about two weeks), but "most significantly" that frog larvae "that took longer to metamorphose were smaller than their counterparts that metamorphosed earlier."
That sounds ominous. Hayes suggests this could be a big factor in frog declines.
Hayes' previous ominous suggestions have been enough to get him interviewed on National Public Radio, filmed by the BBC, quoted by the New York Times, and featured in the Los angeles Times.
In the body of this paper, however, Hayes reveals that the relationship between the time to complete metamorphosis and the frogs' size at emergence was either not statistically significant (when measured by length) or only barely so (weight)!
It gets worse. Hayes has no real-world evidence for any breeding-related conclusions. Why not? Neither he nor anyone else has ever solved the mystery of getting frogs to reproduce in a laboratory without injecting them with artificial hormones that would automatically ruin Hayes' hormone-centered experiments.
Worst of all for Hayes' argument: He found frogs "present by the thousands" in 2001 in a drainage ditch between two irrigated cornfields in York County, Nebraska. That's where he also found the pesticide mixture he says causes problems. Hayes then shows a photo of the same ditch two years later, after the farmer stopped planting corn and therefore stopped irrigating the field--"causing 100 percent failure of the [frog] population at this site."
Hmm. Hayes says exposing Boston-pedigree frogs to a super-low concentration of nine pesticides in a lab delays their development and might make them smaller, all of which might add up to population crash in the real world. But the real-world Nebraska frogs thrived in the pesticide-tinged irrigation ditch until the farmer cut off the water. Meanwhile, frogs have been disappearing in lots of remote places where no pesticides are used.
Do we need a new theory on frog declines?
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