Young cricket characters shaped by 'song'

Gryllus integer field crickets

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The experiences of youth can change the adult personalities of crickets, a new study has found.

Scientists discovered that juvenile males that did not hear a cricket chorus while young grew into more aggressive adults.

It suggests that the animals can pick up behavioural traits while young which then become fixed in adulthood.

The scientists believe that personality may play a crucial role in ecology and evolution.

The findings of the team from the University of California, Davis, US are published in the journal Animal Behaviour.

In conducting the experiment the team captured juvenile field crickets that had not yet developed a tympanum, the equivalent to an ear, which grows on the cricket's front legs.

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"We isolated them all effectively before any of them could hear anything," said lead author Nicholas DiRienzo.

While one group of crickets were reared in silence, another were played a looped recording of five calling males.

"In the sound treatment there was a chorus of five different crickets playing back, calling, to mimic just what you would hear on a summer night, lots of different crickets calling and singing."

The silence was similar to the conditions experienced by juveniles hatching in spring when the cricket population tends to be at a low density, and hence quieter. Any juveniles born later tend to find a denser population of crickets, which is louder.

According to Mr DiRienzo, the team's results suggested that juveniles use cricket song as an indicator for population numbers. This awareness appeared to make an impression on the young crickets, shaping their behaviour.

"The more that are calling, the more could be present in an environment," explained Mr DiRienzo.

"This backs a lot of other studies which show when you raise individuals actually in physical contact with higher density groups, they tend to be less aggressive."

Scientists have theorised that if population density is low and females are few and far between, aggression could prove a more beneficial strategy than if numbers are high.

"The general idea is that fighting costs energy, there's the potential for injury," Mr DiRienzo told BBC Nature.

"So it might actually be beneficial to not be as aggressive because maybe you're going to hurt yourself for no good reason."

The assessments of aggressive behaviour for the species were based on established personality tests, which involved recording males' behaviour once they were introduced to a new environment and to each other.

Gryllus integer field cricket Field crickets may not be big but their fights involve grappling and flipping.

"Some individuals only show low levels of passive aggression. So they'll make aggressive calls, they'll fence with antennae, that kind of thing and so it never really escalates into this big battle."

"Some other individuals will actually get to the point where they're fighting, they're grappling, they're flipping one another," he said.

Mr DiRienzo told BBC Nature that almost every aspect of aggression was affected by hearing the chrous.

Size matters

The study also discovered that the sound of calling affected the growth of the crickets.

Large juvenile crickets, which were reared with the sound grew to be larger than all the other crickets in the study.

According to Mr DiRienzo, the study showed that researchers need to be careful to factor these rearing conditions into their work to prevent them from skewing results.

"If we were always testing aggression in crickets that we had in our lab when there were no other crickets calling, we would actually have these very aggressive crickets and we would say these are all really aggressive."

"Another laboratory a couple of doors down could be actually having lots of calling in their lab, they might not be aggressive at all," he said.

The biologist indicated that, if rearing conditions do have an effect on both growth and behaviour, this could have widespread consequences for our understanding of field cricket ecology.

"It's a mechanism that could influence other processes such as dispersal and things like that," Mr DiRienzo said.

"All these things could [link] with how personality could change based on rearing condition."

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