Fruit flies, to humans, are an annoying batch of little critters. But to other fruit flies, there is a different picture. A team led by University California researchers has discovered a sensory system in the foreleg of the fruit fly that tells male flies whether a potential mate is from a different species. The work addresses a central problem in evolution that's poorly understood: how animals of one species know not to mate with animals of other species.
Fruit flies, to humans, are an annoying batch of little critters. But to other fruit flies, there is a different picture. A team led by University California researchers has discovered a sensory system in the foreleg of the fruit fly that tells male flies whether a potential mate is from a different species. The work addresses a central problem in evolution that's poorly understood: how animals of one species know not to mate with animals of other species.
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For the common fruit fly, Drosophila melanogaster, the answer lies in the chemoreceptor Gr32a, located on sensory neurons on the male fly’s foreleg.
"In nature, this sensory system would prevent the creation of hybrids that may not survive or cannot propagate, thereby helping the species preserve its identity," said senior author Nirao M. Shah, MD, PhD, a UCSF associate professor of anatomy.
Before mating, the researchers found, the male approaches a prospective female and taps her repeatedly on the side with his foreleg which might be described as a form of courting but is not as it turns out. "As he does so, he is using Gr32a to detect, or actually taste, unpleasant-tasting waxy chemicals on the cuticle, or outer skin, of individuals of other species," said co-author Devanand S. Manoli, MD, PhD, a UCSF postdoctoral fellow in anatomy and fellow in child and adolescent psychiatry.
The researchers also found that if the male fly’s Gr32a neurons are activated directly, courtship with other species can be suppressed in these male flies. "These and other findings show that Gr32a neurons are both necessary, in terms of having this taste receptor, and sufficient, in terms of their activity, to prevent males from courting females of other species," said Manoli.
"Indeed, D. melanogaster males lacking Gr32a will attempt to mate with fruit flies of other species even if these species are two to three times larger and look different to the untrained human eye," Shah said.
Likewise, when the section of the foreleg with Gr32a neurons is surgically removed, said Manoli, the male will court females of other species not being able to tell the difference anymore.
Interestingly, said Shah, males use a mechanism that is "similar, but not identical," to inhibit the courting of other males of the same species. "That system involves additional chemoreceptors and neural pathways, which makes sense," he said, "since if you’re a male, other males of your own species might be competing with you for food, territory and mates, and so you would be identifying them for different reasons, in different circumstances."
Manoli noted that other animals may have equivalent mechanisms for distinguishing members of other species. "Rodents, for example, like flies, primarily use smell to find mates and food, and avoid predators. Some species of fish use electrical impulses. Many primates, including humans, rely on visual and auditory cues."
For further information see Fruit Fly Selection.
