Even the best pickup line isn't any good if your potential mate doesn't hear it. So scientists have been puzzled that males of many species, including fish and frogs, send mating signals that a female has trouble perceiving. But a new study in this week's issue of Science shows that, during the breeding season, one kind of fish uses hormones to turn a mismatched love call into a match.
The fish in question are called plainfin midshipman (Porichthys notatus). Once a year, they migrate from the deep ocean to shallow water along the Pacific Coast of North America. Here, the males hang out under rocks and invite females to join them by humming endlessly at night. The sound, a sinister A-flat, is well known among people living along the coast, says neuroethologist Joseph Sisneros of the University of Washington, Seattle. Yet earlier studies by his research group had shown that females can't hear sounds this low.
Intrigued by the conundrum, Sisneros and his colleagues caught nonreproductive females and inserted a tiny drug-releasing implant. In some females, the implants slowly released testosterone or estradiol, both commonly found in breeding females. As a control, another group of females were given empty implants. Then, Sisneros placed an electrode in the nerves that lead from the fishes' ears to the brain and recorded their signals while playing a range of notes. He found that the control females' hearing became progressively worse at frequencies above 60 hertz (Hz), and the fish were almost deaf at 250 Hz. But all the hormone-treated females had much more acute hearing for notes up to 300 Hz, nicely encompassing the male's amorous hum, which has base frequency of 100 Hz and harmonics of 200 and 300 Hz.
It's "entirely possible" that the new finding has implications for female mate perception in other organisms, including humans, says neurobiologist Harold Zakon of the University of Texas, Austin. He notes, for example, that a woman's perception of odor and sound changes with the menstrual cycle, which may help her in selecting a mate.