Vibrations from the crypt: Investigating the possibility of vibrational communication in burying beetles

Communication is fundamental in the animal kingdom, essential to interactions such as mating, defense, and parental care. Vibrational communication has often been overlooked in the past, but in recent decades, it has become clear that insects use substrate vibrations as a communication signal. In burying beetles of the genus Nicrophorus, which are known for their biparental brood care, both parents stridulate. Spending a considerable period of their lives underground, it is very likely the beetles utilize vibrations as part of their communication system. As playback experiments are challenging with this species, this study looked at the physical propagation of the signal of Nicrophorus vespilloides Herbst (Coleoptera: Siliphidae) through three soil types, as well as behavior, to see whether vibrational communication is possible. The aims were to determine: (1) whether the soils used in the laboratory compare to soil from the field, (2) whether the distance of propagation is enough for the range the beetles cover during brood care, (3) whether the two sexes show a difference in stridulation likelihood, (4) whether propagation of defensive signals differs from brood care signals, and (5) whether we can determine a behavior during stridulations that shows a clear and useable reaction to the signal. We manipulated beetles to induce stridulation and then used laser Doppler vibrometers to record the signals using three substrates and various distances, alongside behavioral observations. We showed that the three substrates tested, peat, coconut coir, and forest soil, displayed differences in terms of vibrational propagation, and that burying beetle stridulation signals can be transmitted up to about 25 cm in the soil. We also showed that the location where the animals stridulate exerts a significant influence on the total duration and number of stridulations. Overall, vibrational communication is in principle conceivable in this species, as the signals are transmitted far enough in the natural substrate to allow complex communication, opening possibilities for vibrational communication during this biparental brood care.