Role of olfactory appendages in chemically mediated orientation of blue crabs

Abstract

Benthic crustaceans such as the blue crab Callinectes sapidus use various sensory appendages to navigate chemical plumes. We characterized the role of different sensory structures in blue crabs during olfactory search by deafferenting (i.e. removing or rendering inactive) particular sensor populations and by quantifying odor-plume structure and flow dynamics. Our results indicate that blue crabs use both cephalic and thoracic appendages for olfactory-mediated orientation. Cephalic chemosensor deafferentation decreased search success, reduced walking speed and increased the duration of stationary periods. All these deficiencies are manifestations of the inability of crabs to sustain upstream progress. Crabs subjected to deafferentation of thoracic sensilla failed to correctly track the narrowing plume and showed an increased frequency of large course-corrections. Whereas cephalic sensors clearly function in motivating upstream movement during the search process, thoracic receptors aid in source localization. The differing functional roles of these 2 sets of appendages may be associated with different signal characteristics impinging on their chemosensor populations. Intermittent but intense signals received by the cephalic appendages may enable the crabs to identify attractive odors and sustain searching. Chemical signals impinging on legs are more homogeneous and may allow the crabs to acquire better information on the spatial patterns of chemical signal structure that are important for navigation. The simultaneous use of chemical signals at differing heights in the plume suggest that the 3D structure of these plumes is important for foraging success, and that different populations of neural receptors may be tuned to operate optimally in particular signal environments.