Particle and prey detection by mechanoreceptive copepods: a mathematical analysis

Abstract

When particles move through fluids, they produce far-field pressure differences and near-field fluid deformations. Here we evaluate if a copepod, relying on mechanoreceptive antennulary setal hairs, can detect pressure changes caused by a variety of signal sources. We first provide a correction of the copepod mechanoreception model of Legier-Visser et al. (1986), showing how an object above a minimum size should be detectable. The pressure change ΔP created by an object of this minimum size was 385 dynes/cm², based on biomechanical relationships for a rigid seta bending with respect to the exoskeletal body and using the neurophysiological detection threshold of a 10 nm bend of the sensory seta (Yen et al., 1992). The ΔP for: a 3 μm particle = 0.01 dynes/cm², a 50 μm particle = 0.16 dynes/cm², an escaping nauplius = 78 dynes/cm², a revolving prey = 10⁻⁵ dynes/cm², a 1 mm copepod escaping at 1 m/s at a distance of 1 mm from the mechanoreceptive sensory hairs of its captor = 312 dynes/cm². Only the copepod escaping at high-speed close to the captor would create a pressure difference that could elicit a response. At this point, we conclude that pressure differences are rarely of a magnitude that is perceptible and that additional information must be derived for a copepod to detect prey. Other signals include fluid deformations as well as other types of stimuli (odor, shadows). Like most organisms, a copepod will rely on all sensory modalities to find food, avoid predators, and track mates, assuring their survival in the aquatic environment. It also is possible that the biomechanical model is insufficient for estimating pressure differences causing the cuticular deformation or that further analysis is necessary to improve our certainty of the sensitivity of the copepod seta.