Meeting Abstract
Spiders rely on sensing web vibrations for sexual signalling, prey capture and predator evasion. The sensory organs underlying vibration detection are called slit sensilla: they look like cracks in the spider’s exoskeleton and have sensory cells underneath the cuticle. Sensilla crucial to sensing web-vibrations are distributed around leg joints, in collections called lyriform organs. Neurophysiology suggests that lyriform organs are very sensitive to web vibrations but have no frequency selectivity, paradoxically ignoring an important component of information available to them. Neurophysiological measurements, however, effectively ‘disembody’ the spider by removing the contribution of the body’s mechanics to perception. Black widow females have a striking body-form; their long thin legs support an unusually large pendulous abdomen. Here, we show that in their natural posture, the abdominal mass of black-widow females, interacts with the spring-like behaviour of their leg joints and mechanically determines the frequency tuning of different lyriform organs. We use laser Doppler vibrometry to measure the relative motion of leg segments from a live black widow spider on her web. From this relative motion, we infer joint bending. We use multi-body dynamics modeling to build a model black widow spider, which we verify against our data and then use to study the effect of posture on joint bending spectra. We find that adopting different body postures enables females to alter the mechanical tuning of their joints. Thus posture can be used to flexibly and reversibly direct attention to different components of the web’s vibrations. Our results thus emphasize the dynamic loop of interactions between behaviour and perception, i.e. between the ‘brain’ and the body.
