Knock-knock, who’s there: Sex-coding, competition and the energetics of tapping communication in the tok-tok beetle, Psammodes striatus (Coleoptera: Tenebrionidae)

ABSTRACTI describe the abdomino-substratal tapping communication system of a Southern African tenebrionid beetle, Psammodes striatus (Fabricius, 1775) (Coleoptera: Tenebrionidae: Molurini), using computer simulation of tapping signals and computer-assisted acquisition of precise response timing data, augmented with data from natural beetle-beetle communication. Communication consists of trains of 5 - 7 Hz taps in groups or trains separated by 2-3 sec intervals. Male beetles spontaneously produce groups of tap-trains with 8 - 18 taps per train. If other beetles reply, an alternating duet commences. Solitary female beetles do not tap spontaneously but respond to male tapping with short, distinctive tap-trains containing 4 – 6 taps; they ignore female signals. In contrast, extensive communication occurs between male beetles, the nature of which changes significantly if the stimulus call is typical of male or of female beetles. Inter-male communication consists of long tap-trains, but males interacting with females produce shorter tap-trains and engage in phonotactic behavior that is absent in inter-male communication. Females respond highly preferentially to inter-male communication, rather than to the signals produced spontaneously by single males. Finally, I propose a simple model of the selective advantages of this unusual communication system, and calculate its approximate energetic leverage over random locomotion (∼13x).