Australasian Science: Australia's authority on science since 1938

Cologne Critical in Cricket Courtship

By Magdeline Lum

Dominant crickets sing to attract mates, but if they lose a battle and become subordinate they fall silent and rely on body odour.

A male cricket heralds nightfall with his love song to any female cricket nearby who will listen. His skin, or cuticle, glistens in the moonlight with a layer of fatty acids preventing water loss.

As he is about to reach his crescendo, another face appears in front of his, but unfortunately it is not the girl of his dreams. It belongs to the face of another male challenging him to a fight.

Male–male aggressive behaviour is common throughout the animal kingdom, and in many species the dominant male will display a badge of honour. It is a message to other males as a signal of aggressiveness or a sign of resource holdings to minimise conflict.

In birds it may be exotic plumage, but crickets do not have a plumage to exhibit grandiosely. The cricket’s badge of honour is the song it sings to attract females, but it has been discovered that this may not be the only thing used to woo female crickets.

Dr Melissa Thomas and Prof Leigh Simmons from the University of Western Australia’s Centre for Evolutionary Biology found that a dominant male Australian field cricket, Teleogryllus

oceanicus, changes the chemical make-up of fatty acids (cuticular hydrocarbons) on its exoskeleton to resemble the chemical composition of the cuticular hydrocarbons of a subordinate cricket if its social status declines.

These cuticular hydrocarbons are made of different compounds, and provide information on identity, sex and even past mating activity. They also emit a particular scent, with winners smelling different to the losers. The combination of compounds also plays a role in attracting mates.

“Although males cannot force copulations, dominance status does determine a male's ability to attract females via acoustic signals,” Thomas and Simmons wrote in Proceedings of the Royal Society B.

For the study, the researchers first ranked the crickets through a series of fights based on their win/loss result. The social status of the crickets was then forcibly changed by placing two dominant crickets and two subordinate crickets together and letting them fight. The male crickets that were chosen for the study had either won all their bouts or lost all their bouts.

It was easy for the researchers to determine which cricket had won, as it would be the one chirping aggressively while the other cricket would be displaying avoidance behaviour.

Following the outcome, samples of the cuticular hydrocarbons were taken for analysis. Results showed that ousted dominant male crickets had changed the hydrocarbon make-up of their fatty acid coating to resemble a subordinate male.

It turns out that the fatty acid coating of subordinate males contains hydro­carbons that are highly attractive to female crickets. This change in odour could be assisting the previously dominant male to rely on a silent method to attract females to mate.

Subordinate males are unable to produce a song, as a nearby dominant male will then attack them intermittently upon hearing them sing. Unable to sing, these loser crickets lure females away from dominant songsters by secreting cuticular hydrocarbons that females find attractive. It is the equivalent to human males wearing cologne.

“Male dominance status can be frequently challenged, and is therefore a potentially unstable trait,” Thomas and Simmons wrote. “The crickets were tested within 2 hours of losing a fight, suggesting the changes are very rapid.”

Even though the changes are happening in real time, further investigation is needed to determine whether the changes in the hydrocarbon profile of the fatty acid coating are adaptive or by-products of physiological mechanisms.

So the next time the song from a cricket keeps you awake at night, remember that he may be doing so because his potential love interests are being lured away by a silent cologne-wearing competitor.