Spider leg biomechanics as an information filter for vibration sensing

Substrate-borne vibration sensing is an important sensory modality in arthropods, which use externally generated vibration sources to gather information about their environment. Vibrations are subject to mechanical filtering by the legs and body, which implicates a role for morphology in modulating information flow due to the distributed and embedded nature of arthropod mechanosensors. A general problem with sensing is the separation of signal from noise. While internally generated vibrations can be useful for proprioception, they potentially obscure the small displacements generated by substrate vibrations for exteroception. Here, we use a laser vibrometry dataset quantifying the dynamic response of the tarantula Grammostola pulchra to vibrational input at 50 points across its legs and body to examine relative motion in a single axis, enabling us to infer leg biomechanics and test whether these behave rigidly as vibrations are transmitted through the body. We show that the non-rigid legs may dampen large-amplitude motion from cephalothorax/abdomen resonance-increasing signal-to-noise ratio for exteroception at their distal ends. These properties may also act to increase the robustness of vibration sensing to variation in morphological traits affecting the spider's dynamics. As spider body plans are conserved, we argue the results are generalizable across the mechanosensitive Araneae.