Cost of tokking: the energetics of substrate communication in the tok-tok beetle,Psammodes striatus

Summary

Psammodes striatus, the ‘tok-tok’ beetle, communicates by substrate vibrations produced by tapping its abdomen on the ground. MaleP. striatus responded readily to computer-synthesized vibrations. Oxygen consumption rate ($\dot V_{O_2 }$) of individual male beetles (n=3; mean mass 3.01 g) was continually recorded by computer before, during and after tapping communication with the computer, which also counted the beetle's replies. Standard$\dot V_{O_2 }$ of motionless beetles was also measured, during which time marked discontinuous ventilation was apparent. Since the relation between$\dot V_{O_2 }$ and tapping rate was linear, it was possible to estimate net cost of tapping (0.0279 μl O₂ g⁻¹ tap⁻¹) and minimum cost of tapping (0.0286 μl O₂ g⁻¹ tap⁻¹). Kinematic analysis of trains of taps showed constant intertap period (ca. 150 ms) and distinctive amplitude modulation. The efficiency of muscular movement inP. striatus is 23% of metabolic input, assuming no elastic storage. This figure will drop to ca. 5–10% if significant elastic storage takes place. Minimum cost of searching for a mate via pedestrian locomotion is 340 J kg⁻¹ m⁻², but drops to 33 J kg⁻¹ m⁻² for tapping communication. Similar energetic ratios may play a role in the early stages of the evolution of some communication systems.