The famous biologist Stephen J. Gould once asked: If we rerun the tape of life, would the outcome of evolution be the same? For years, scientists have questioned whether evolution is predictable, or whether chance events make such predictability unlikely.
A study published online July 23 in the Proceedings of the National Academy of Sciences finds that in the case of insects that developed resistance to a powerful plant toxin, the same adaptations have occurred independently, in separate species in different places and times.
The paper examines 18 insect species across four orders beetles, butterflies and moths, flies, and true bugs that all feed on plants containing powerful toxins called cardenolides.
Common to milkweeds and foxglove, cardenolides are lethal to nearly all insects and function effectively as a defense against pests. Cardenolides work by binding to a cell's sodium pump, one of the most fundamental systems found in all animal cells. The sodium pump works when an essential enzyme (Na,K-ATPase) carries important elements, sodium and potassium, across the cell membrane. Cardenolides bind to the enzyme and disable it, thereby shutting down cells, which results in severe damage.
Among the 18 insects surveyed, the researchers found a few methods that the insects use to resist cardenolides. In monarch butterflies and a species of leaf beetle, for example, resistance is due to a specific mutation called N122H of the Na,K-ATPase gene. The mutation reduces cardenolide binding to the sodium pump enzyme.
"Already knowing how monarchs deal with the toxin, we wanted to see if it was the same molecular solution used by beetles, flies and true bugs that are also resistant to cardenolides," said Anurag Agrawal, a Cornell professor of ecology and evolutionary biology and a co-author on the paper. Susanne Dobler, a professor of molecular evolution at Hamburg University, is the paper's lead author.
|Contact: John Carberry|