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Science Frontiers ONLINE No. 86: Mar-Apr 1993 |
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How A Fly Hears What A Cricket Hears
As we all know, male crickets chirp long and loud for mates from spring until fall. That many males are successful in attracting females is obvious from this insect's population levels. Some of the singing males, however, attract parasitic flies that home in on their songs and deposit their maggots on or near them. Within 10 days, these singers are silent -- they have been consumed by the maggots.
The really interesting part of this tale involves the hearing organs of the crickets and flies. Normally, they are radically different in design and frequency of operation. Crickets usually sing at frequencies above 3 kilohertz, and their ears are attuned to these high frequencies. The usual fly, on the other hand, hums and buzzes at only 100-500 hertz (cycles per second). Their ears are duly optimized at these frequencies. The cricket-hunting flies (genus Ormia), however, would starve to death if they couldn't hear the highpitched cricket songs. Their response was to "evolve" a cricket-type ear so they could home in on their prey. This is a remarkable example of evolutionary convergence.
(Robert, Daniel, et al; "The Evolutionary Convergence of Hearing in a Parasitoid Fly and Its Cricket Host," Science, 258:1135, 1992.)
Comment. How did the parasitic flies survive until they evolved, through small random mutations, just the right sort of ear to tune in on the crickets?