CHRONICLE-HERALD (Halifax, Nova Scotia) 11 November 06 For many frog species in the tropics, the first line of defence against predators is poisonous secretions in the skin (Henry Fountain, The New York Times)
For many frog species in the tropics, the first line of defence against predators is poisonous secretions in the skin. Among these alkaloid compounds are a group known as pumiliotoxins that appear to work on contact. Ants and spiders that bite a frog with the toxin let go immediately.
But what about bugs that fly and bite? Paul J. Weldon of the Smithsonian Institution's Conservation and Research Center in Front Royal, Va., and colleagues have now shown that pumiliotoxins function as mosquito repellents, too.
In lab tests reported in The Proceedings of the National Academy of Sciences, the researchers found that a pumiliotoxin called PTX 251D applied to a silicone membrane reduced landing and feeding by Aedes aegypti, the mosquito that carries the yellow fever virus. For those mosquitoes that had the misfortune to land, the compound had a toxic effect: they failed to fly off again. The researchers found that this compound worked at very low concentrations,well below the level found on the skin of most poisonous frogs.
When it comes to courting, the males of many species are show-offs. They like to flaunt some attribute like a colourful fan of plumage or a puffed-out throat - the kind of thing that says "choose me" to a potential mate.
But some courtship displays are not so straightforward. And that of the northern swordtail, a small freshwater fish, is especially perplexing, researchers have found. It's not meant for a female at all, they say, but for other males.
During courtship, a male swordtail swims alongside a female and raises a large sail-like fin on its back. But Heidi S. Fisher and Gil G. Rosenthal of Boston University discovered that in experiments, most females were actually attracted to males with small fins.
So why would males go to all the trouble of displaying something that potential mates wouldn't like? The answer, the researchers report in the journal Biology Letters, lies in the effect on potential competitors. Other males became intimidated in the presence of a male displaying a large fin.
Given that females find large fins unattractive, another option for the male would be to keep its fin completely under wraps. But the researchers suggest a reason they don't: swordtails live in close proximity, with hundreds of males and females in a small area, so it's worthwhile for a male to raise his fin to keep the competition at bay.
Then again, if males with larger fins are more dominant than other males, why aren't females attracted to them? Although a large-finned male may be more successful in competing against other males, that doesn't necessarily translate into advantages for the female. Male swordtails don't care for the offspring and don't hold territory that might be useful for a female to have. And mating with a more aggressive, competitive male may increase the female's risk of being harmed.People of a certain age may remember when barbiturates were the drug of choice for use as sedatives and anticonvulsants. Over the past four decades they have been all but swept aside by safer alternatives like Valium.
But barbiturates can still be found - in surface water, according to researchers in Germany.
Thomas P. Knepper and colleagues at Europa University of Applied Sciences in Idstein developed a method to detect traces of barbiturates in water. They sampled water from several German rivers and found barbiturates in only one, the Mulde, near Leipzig in the east. The findings were reported in the journal Environmental Science and Technology.
The researchers are unsure how the barbiturates came to be there, but suggest a couple of possibilities. Barbiturates are still manufactured, mostly for veterinary use, so the source could be an industrial one. Or they may come from an old contaminated site.