Seismic signaling in the New Zealand Deinacrida: substrate-borne vibration mediates agonistic interactions in the Cook Strait giant weta (D. rugosa)

In the last two decades there has been a growing interdisciplinary interest in understanding the functional mechanisms and evolutionary origins of animal communication through substrate-borne vibration. The genus Deinacrida (giant weta) is a clade of nocturnal, herbivorous, apterous Orthoptera belonging to the family Anosostomatidae. Comprised of some of the largest insects described, they are of Gondwanan lineage with eleven endemic species found in New Zealand. While most Deinacrida species are known to produce an acoustic aggression signal in response to heterospecific disturbance, the primary mechanism of intraspecific communication in this terrestrial group has remained a mystery. The purpose of this study was to test the hypothesis that the Deinacrida utilize substrate-borne vibrational signals in communication. We looked first at D. rugosa, the Cook Strait giant weta. We sought to 1) determine if the species uses vibrational signals, and if so 2) describe the social context of vibrational signaling, and 3) describe the characteristics of the signals for use in future comparative analyses across the group. Using laser Doppler vibrometry we show that D. rugosa adults utilize low frequency (33.82 Hz) substrate-borne vibration for intraspecific communication, with males producing a duetting signal (12.8 syllables/pulse; 0.383 pulses/sec.) through dorsoventral tremulation. These signals are targeted to other males while in a female’s presence; solitary individuals, pairs of males in the absence of females, and pairs of females seldom produce vibration. This suggests that the function of vibrational signaling likely evolved as a mechanism for mediating inter-male contests for access to receptive.