The mechanical leg response to vibration stimuli in cave crickets and implications for vibrosensory organ functions.

We investigate the influence of leg mechanics on the vibration input and function of vibrosensitive organs in the legs of the cave cricket Troglophilus neglectus, using laser Doppler vibrometry. By varying leg attachment, leg flexion, and body posture, we identify important influences on the amplitude and frequency parameters of transmitted vibrations. The legs respond best to relatively high-frequency vibration (200-2000 Hz), but in strong dependence on the leg position; the response peak shifts progressively over 500-1400 Hz towards higher frequencies following leg flexion. The response is amplified most strongly on the tibia, where specialised vibrosensory organs occur, and the response amplitude increases with the increasing frequency. Leg responses peaking at 800 and 1400 Hz closely resemble the tuning of the intermediate organ receptors in the proximal tibia of T. neglectus, which may be highly sensitive to positional change. The legs of free-standing animals with the abdomen touching the vibrating substrate show a secondary response peak below 150 Hz, induced by body vibration. Such responses may significantly increase the sensitivity of low-frequency receptors in the tibial accessory organ and the femoral chordotonal organ. The cave cricket legs appear suitable especially for detection of high-frequency vibration.