How humans derailed the sex lives of crickets

Most people have suffered through noise pollution, whether it's the thumping of a jackhammer or a screaming siren. Defined by the EPA as "unwanted or disturbing sound," noise pollution is predicted to become the next public health crisis — an invisible threat to health and well-being.

Noise pollution threatens animals too. In a new study, scientists add another creature to the growing list of animals severely affected by man-made sounds: crickets.

Published Monday in the journal Behavioral Ecology, the study details the impact of human noises on female field crickets (Gryllus bimaculatus). Scientists discovered female crickets become less picky about mate selection when distracted by traffic noise. Picky, typically, is a good thing.

This research "adds to our growing understanding of what seem to be negative compounding effects of anthropogenic noise on the fitness of singing insects," says Robin M. Tinghitella, an associate professor at the University of Denver and specialist in behavioral ecology. Tinghitella was not a part of this study.

How they did it — Researchers placed male and female crickets in temperature-controlled plastic terrariums with normal ambient background noise.

Prior to conducting their courtship tests, the scientists silenced the male insects' natural courtship songs by anesthetizing the insects and cutting their forewings with dissecting scissors.

In lieu of natural songs, the crickets listened to "modified" courtship songs played through a speaker. The scientists played a "high-quality" and "low-quality" version of a male's song.

As male crickets attempted to court the female, the researchers either played the high-quality song, the low-quality song, or no song at all. If the mating was successful, the female would mount the male (a cricket preference).

To test the effects of noise pollution on mating behavior, the scientists played these songs while pumping in ambient noise, white noise, or traffic noise, using speakers placed at both ends of the container.

What's new — The study team did find traffic noise affected the mating rituals — but not in the way that you might think.

Previous studies found low-quality courtship songs have a lower mating success rate than high-quality songs or mating without any song at all. The mating trials conducted in the ambient noise conditions confirmed these prior findings.

But the white noise and traffic noise trials prompted very different results. In these trials, the researchers found no difference between the male's chance of success when mating during a high-quality song, a low-quality song, or no song at all.

The high amplitude of the traffic noise distracted female crickets to the degree they couldn't perceive the differences in quality between the different songs. Song quality is typically a make-or-break for cricket courtship.

"This study shows that even if female crickets can detect and reach singing males under noisy conditions, once in close proximity with males they make less-optimal mating decisions under noise than they do under ambient conditions," Tinghitella says.

Why it matters — The damaging effects of anthropogenic noise — modern, human-generated — sounds — on insects has gained significant attention in recent years, Tinghitella says.

Previous work has found anthropogenic noise "can lead to changes in insect mating songs themselves, and disrupt the ability of females to detect and locate potential mates using their songs," she explains.

Courtship songs have evolved for a very specific evolutionary purpose: to help female crickets select the best mate. If traffic noise causes a female cricket to not pay attention, she might end up reproducing with a male with less advantageous genes.

"Under traffic noise or white noise, the crickets’ typical preference for high-quality song is reduced relative to ambient conditions," Tinghitella says. "They make mating decisions that could lead to reduced fitness."

Anthropogenic disturbances, in turn, could lead to reduced diversity in crickets and even extinction.

What's next — The study also adds to our understanding of the cricket courtship process, providing new details on how females assess the quality of potential mates.

Beyond mate selection, its hypothesized courtship songs may also allow these insects to identify the species of another singing cricket — much like other creatures in the animal kingdom.

However, this area of scientific study requires considerably more research before we can draw any conclusions.

According to the study: "More research is necessary to understand the evolution behind courtship songs in field crickets, which will, in turn, better reveal the function of the song and what information females gain from attending to the signal."

Abstract: By assessing the sexual signals produced by conspecifics, individuals can make informed decisions on the best choice of mate, which can lead to reproductive fitness benefits. However, these communication systems are often vulnerable to disruption by conflicting with stimuli present in the environment. Anthropogenic noise may act as one such disruptive stimulus, leading to inefficient mate choice decisions and, thus, reductions to an animal’s fitness. In this study, the mate choice behaviors of female Gryllus bimaculatus were tested when presented with artificial male courtship songs of differing “quality” under different acoustic conditions. In ambient noise conditions, females significantly preferred mates paired with higher-quality songs, indicated by increased mating rates and reduced latency to mate. However, this mate selection pattern was disrupted in both traffic and white noise conditions. Additionally, “high-quality” courtship songs had an increased mounting latency in traffic and white noise conditions, when compared to ambient noise conditions. Making nonoptimal mating decisions, such as the ones seen here, can lead to deleterious fitness consequences, alter population dynamics, and weaken sexual selection, unless individuals adapt to cope with anthropogenic interference. Female field crickets have different mating preferences when human-generated noise is present. Under ambient noise conditions, females mounted males paired with a “high-quality” song sooner and more frequently than those paired with a “low-quality” song or no song at all. These differences were not apparent when traffic or white noise was present. As acoustic courtships are used by many species, these findings have important implications for mate choice throughout the animal kingdom.