Calling in vain - Females sometimes just do not listen

Written by Thomas Hesselberg

Sunday, 24 August 2008

African field crickets (Gryllus bimaculatus). Photographed by Adrian Pingstone (Wikimedia Commons).

Male crickets produce sound at a lower frequency than the females are tuned to and prefer, presumably because the females can better locate the males using lower frequency sounds.

Many animals, like humans, rely on acoustic signals for intraspecific communication. Sound has the advantage of being easier to precisely locate than for instance pheromones and it penetrates the undergrowth and canopy, while at the same time allowing the sender to stay hidden from visual predators.

Acoustic communication is widely used in birds, frogs and in insects such as cicadas, crickets and grasshoppers. Usually, the male (the sender) produces a sound in order to attract the female (the receiver). However, in noisy environments it can be hard to stand out from the background noise, so the sender usually produces sound at a specific narrow frequency range, which the receiver is then selectively tuned to – this is also known as the matched filter hypothesis.

Researchers from the University of Graz in Austria set out to test the matched filter hypothesis in field crickets by studying tuning in individual female neurons and relating that to the choice behaviour in female crickets.

Surprisingly they found that females are tuned to and prefer slightly higher frequencies than are emitted by the males. So why the males not react to that and evolve higher frequency sounds?

The Austrian scientists found evidence of a second matched filter for directional hearing, which operates better at lower frequencies. Thus females in effect have preference for two different sound frequencies – one for selective hearing and one for directional hearing, which may explain the high variance and the relative broad frequency range observed in male sound production.

Source:
Kostarakos K, Hartbauer M, Ro¨mer H (2008) Matched Filters, Mate Choice and the Evolution of Sexually Selected Traits. PLoS ONE 3(8): e3005.doi:10.1371/journal.pone.0003005.

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