麻豆淫院

(麻豆淫院Org.com) -- A new study by a Stony Brook University professor shows that structures that have been evolutionarily lost for hundreds of millions of years can be regained.

A new study by a Stony Brook University professor shows that structures that have been evolutionarily lost for hundreds of millions of years can be regained. The findings are reported in the journal Evolution , in an article entitled "Re-evolution of lost mandibular teeth in frogs after more than 200 million years, and re-evaluating Dollo鈥檚 law".

John J. Wiens, Ph.D., a professor in the Department of Ecology and Evolution, studied the evolution of teeth on the lower jaw in frogs. He combined data from modern frogs, fossils and DNA sequences and utilized new statistical methods to show that frogs lost their teeth on the lower jaw more than 230 million years ago, but that these teeth re-evolved in a single frog species (Gastrotheca guentheri) within the past 20 million years. This means that mandibular teeth were absent for more than 200 million years before re-evolving in Gastrotheca guentheri. Gastrotheca guentheri is a 鈥渕arsupial鈥� treefrog from Colombia and Ecuador, a species in which females carry their eggs in a pouch on their backs.

The study provides strong evidence against 鈥淒ollo鈥檚 law,鈥� the idea that a complex trait that is lost during evolution will not re-evolve again. Dollo鈥檚 law has been controversial among evolutionary biologists. Some scientists have argued that there are now several examples where complex structures have been lost and regained, such as wings in stick insects, coiling in snail shells, and fingers and toes in lizards. Other scientists have suggested that these examples may be invalid. 鈥淭he study of teeth in frogs provides very strong evidence for re-evolution of lost structures, and is unusual in showing that this re-evolution can happen after hundreds of millions of years,鈥� Dr. Wiens said.

This study also suggests how a trait can re-evolve after such a long absence, a mechanism that Wiens calls a 鈥渓oophole鈥� in Dollo鈥檚 law. 鈥淓ven though teeth are absent on the lower jaw in almost all frogs, they are generally present on the upper jaw,鈥� Dr. Wiens said. 鈥淪o the mechanisms for developing teeth are present in most frogs and did not have to re-evolve in Gastrotheca guentheri in order for teeth to re-appear on the lower jaw.鈥� This type of "loophole" may apply to many other cases in which traits appear to re-evolve, such as in the re-evolution of lost fingers and toes in lizards, he said.