Traffic noise makes mating crickets less picky

The research, published in the journal Behavioral Ecology, was carried out at Anglia Ruskin University (ARU), and involved studying the mating choices of female field crickets (Gryllus bimaculatus) under different acoustic conditions.

When a female cricket is nearby, male crickets will perform a courtship song by rubbing their wings together. The song is energetically costly to produce and so contains important information about the male's qualities. Therefore, it would be taken into account by females when making mating decisions.

The researchers paired female crickets with silenced male crickets in ambient noise conditions, artificial white noise conditions, and traffic noise conditions (recorded at a ground level next to the A14 near Cambridge).

Males were then allowed to court the female freely, and an artificial courtship song was played back when the males attempted to sing. Males were either paired with a high-quality courtship song, a low-quality courtship song, or no song at all.

In the control conditions of ambient noise, the females mounted the males much sooner and more frequently when paired with a high-quality courtship song. However, a high-quality courtship song provided no benefit in the white noise and traffic noise conditions, with the researchers finding that courtship duration and mounting frequency were not influenced by the quality or even the presence of a song.

The findings suggest that human-made noise alters how females perceive males when making mate choice decisions. In turn, this could affect individual fitness, as male crickets may attempt to expend more energy to produce an even better courtship song, as well as long-term population viability.

Lead author Dr Adam Bent, who carried out the study as part of his PhD at Anglia Ruskin University (ARU) in Cambridge, England, said: "In the short-term, we found that males paired with high-quality songs in noisy environments are receiving no benefit over those paired with a low-quality song, or no song at all. As a result, males that produce high-quality songs may attempt to expend more energy into their calls to gain an advantage, potentially affecting that individual's survival.

"At the same time, female crickets may choose to mate with a lower-quality male as they are unable to detect differences in mate quality due to the human-made noise, and this may lead to a reduction or complete loss of offspring viability.

"Traffic noise and the crickets' courtship song do not share similar acoustic frequencies, so rather than masking the courtship song, we think the traffic noise serves as a distraction for the female cricket."

Co-author Dr Sophie Mowles, Senior Lecturer in Animal and Environmental Biology at Anglia Ruskin University (ARU), said: "Humans are continually changing the characteristics of environments, including through the production of anthropogenic noise.

"As mate choice is a powerful driving force for evolution through sexual selection, disruptions may cause a decline in population viability. And because anthropogenic noise is a very recent evolutionarily selection pressure, it is difficult to predict how species may adapt."