Vibrational signalling, an underappreciated mode in cricket communication.

Signalling via substrate vibration represents one of the most ubiquitous and ancient modes of insect communication. In crickets (Grylloidea) and other taxa of tympanate Ensifera, production and detection of acoustic and vibrational signals are closely linked functionally and evolutionarily. Male stridulation produces both acoustic and vibrational signal components, the joint perception of which improves song recognition and female orientation towards the signaller. In addition to stridulation, vibrational signalling mainly through body tremulation and/or drumming with body parts on the substrate has long been known to be part of crickets' close-range communication, including courtship, mate guarding and aggression. Such signalling is typically exhibited by males, independently or in conjunction with stridulation, and occurs literally in all cricket lineages and species studied. It is further also part of the aggressive behaviour of females, and in a few cricket groups, females respond vibrationally to acoustic and/or vibrational signals from males. The characteristics and function of these signals have remained largely unexplored despite their prevalence. Moreover, the communication potential and also ubiquity of cricket vibrational signals are underappreciated, limiting our understanding of the function and evolution of the cricket signalling systems. By providing a concise review of the existing knowledge of cricket perception of vibrations and vibrational signalling behaviour, we critically comment on these views, discuss the communication value of the emitted signals and give some methodological advice respecting their registration and control. The review aims to increase awareness, understanding and research interest in this ancient and widespread signalling mode in cricket communication.