New research from the University of St Andrews has discovered that insects who conceal themselves as leaves also use their leafy camouflage to amplify mating calls, making themselves more attractive to the opposite sex.
Published in Proceedings of the Royal Society B, this is the first demonstration of how impressive leaf mimicry can also be used to enhance the attractiveness of a sexual signal. Katydids create songs by rubbing specialised structures on their wings together but in many tropical species, the leaf-mimicking portion makes up the majority of the wing surface. The researchers found that males are able to use the acoustic properties of these structures to their reproductive advantage.
Previously, it has been theorised that adaptations for survival and for attracting mates function in conflict, particularly if they are physically connected in some way, as is the case with katydids. For example, the flashy tail feathers of a peacock make males more attractive to mates but makes them more detectable to predators, making them less likely to survive. However, these new results demonstrate a rare example of how multifunctionality can be achieved.
Bioacoustic, behavioural, and biophysical experiments revealed that these "leafy" structures do more than conceal, they also enhance the attractiveness of male calls to females.
While the males are the ones that sing, the females indicate their interest by replying with short clicks. Despite living in an extremely noisy rainforest, they produce very short, sporadic and infrequent calls; estimates suggest they call for only a total of 2 seconds in a single night. They also call in the ultrasound which makes it difficult for humans to hear them.
Researchers looked at a species of Katydid called Viadana brunneri and found that if the 'leafy' portions of the male wings were removed, it changed the pitch and loudness of their songs. When these calls were played to females, lower pitch calls from males with their 'leafy' sections intact were preferred.
It was also discovered that these leafy portions of the male katydid wing vibrate so that they amplify the songs males produce, thus making them more detectable to females.
Dr Benito Wainwright, Research fellow in the Centre for Biological Diversity at the University of St Andrews who led the research, said: "Our study provides a rare example of natural and sexual selection acting in harmony, producing traits that simultaneously improve survival and mating success. We are now extremely excited to start exploring how such an interesting interaction evolved in katydids."
