for National Geographic News
Venomous snakes send shivers down many people's spines, but venomous fish are far more common, scientists say.
According to a new evolutionary study, venomous species of fish outnumber not just such snakes, but all other venomous vertebrates combined.
In total, the world's oceans, lakes, and rivers harbor more than 1,200 species of venomous fish, write researchers from the American Museum of Natural History in a recent issue of the Journal of Heredity.
Previously, scientists had estimated that there were only 200 venomous fish. The new additions double the number of known venomous vertebrates to more than 2,000 species.
New Family Tree
Until the new study, scientists had estimated the number of venomous fish species largely from medical records of fish-human encounters, not on biological or evolutionary species surveys.
So the American Museum of Natural History researchers took known venomous specieswhich include stonefish, catfish, lionfish, scorpion fish, toadfish, stargazers, and half a dozen other familiesand tried to determine how they were related to each other and additional fish.
"You have to know how they are related to each other in order to make good, educated statements on whether they are venomous or not," said study co-author Ward C. Wheeler, a curator in the museum's division of invertebrate zoology.
Wheeler's team used DNA sequencing and computer simulations to reconstruct the evolutionary tree of venomous fishall the way back to their common ancestor. (Related news: "Evolution Less Accepted in U.S. Than Other Western Countries, Study Finds" [August 2006].)
That first venomous fish lived much earlier than previously believed, the researchers say. Its family tree therefore contains many additional branches and has resulted in many more modern species than scientists had suspected.
The scientists used their revamped evolutionary tree to predict which species would be venomous and put more than a hundred species to the test by looking for venom-delivery mechanisms.
The physical evidence corroborated the predictions from the DNA tree.
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