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Working with fruit flies, the scientists probed how males manage to pick out members of their own species from the multitude of flies crowding around an overripe fruit. The answer, published this week in the journal Nature, upended long-held beliefs about how evolution works to ensure animals perpetuate their species.
Scientists have long assumed that animals don't interbreed because evolution changed the peripheral parts of their nervous systems, including the sensory organs that detect and process pheromones -- chemical substances that help identify others of the same species. Peripheral changes have been proposed to be essential to allow animals to develop species-specific behaviors, including mating, but it has not been possible to determine whether this was the main or only site of change in the nervous system.
Vanessa - Ruta - Laboratory - Neurophysiology - Behavior
Vanessa Ruta, who heads the Laboratory of Neurophysiology and Behavior, set out with a team from her lab to discover what evolution had done to ensure that two closely related species of fruit flies -- Drosophila melanogaster and Drosophila simulans -- stick to their own kind when mating. Using a host of state-of-the-art genetic and imaging tools, and inventing some new ones, the scientists tracked the electrochemical impulses starting at the sensory neurons in the male foreleg, which they use to "taste" pheromones, all the way to the brain's central-processing center.
The differences between the species, they found, lies deep in the flies' brains, in a small cluster of neurons that controls mating behavior. In fact, the peripheral nervous systems were unchanged, suggesting they play no part in the distinct mating choices of the different species, a finding Ruta hadn't anticipated.
Scientists - Field - Changes - Periphery - Fact
"I think scientists in the field have long thought the changes would most likely be localized to the periphery partially due to the fact that it is the simplest place to look," she says. "People have...
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