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.

Three‐dimensional odorant concentration measurements around actively tracking blue crabs

“…This conclusion is supported by a paired t test assuming equal variances (net-to-gross-displacement-ratio (path linearity) equaled 0.856 ± 0.144 (mean ± SD) and 0.814 ± 0.101 for untreated and blindfolded crabs, respectively; p = 0.44, N = 20, 13, respectively; walking speed equaled 7.394 ± 2.010 cm s -1 and 5.713 ± 2.612 cm s -1 for untreated and blindfolded crabs, respectively; p = 0.14, N = 20, 13, respectively). These values are comparable with those observed over many experiments with blue crabs in similar behavioral trials (Weissburg and Dusenbery 2002;Keller et al 2003;Jackson et al 2007). Percent success of crabs with blindfolds was again similar to crabs without blindfolds with untreated crabs achieving 40% success (see Jackson et al 2007) and blindfolded crabs achieving 46% success of finding the stimulus (N = 6 out of 13).…”

“…The attractant had neutral buoyancy and was created by soaking 2.21 g of previously frozen shrimp per liter of seawater (taken from the flume sump) for 1 h. This general preparation has been used in many behavioral assays involving aquatic organisms and, in particular, blue crabs have effectively tracked sources of chemical exudates of shrimp in previous behavioral trials (Keller et al 2003;Jackson et al 2007). The specific concentration of stimulus was chosen as a value in the middle of the dose-response range of blue crabs.…”

“…Based on deafferentation trials, Keller et al (2003) developed the hypothesis that blue crabs used chemosensors located on the antennules to mediate upstream movement. Chemosensors located on the walking appendages facilitate steering and improved orientation with respect to the plume, potentially through bilateral contrast across the crab's body (Weissburg and Dusenbery 2002;Keller et al 2003). Hence, the 3DLIF data collected for this study focused on evaluating concentration data from two primary locations around the tracking crab: near the antennule region and near the walking appendage chemosensors.…”

“…Callinectes sapidus has at least two types of chemosensory organs that are responsible for orientation. Odor stimulus at the antennules (located near the mouth region) apparently is responsible for maintaining upstream movement (Keller et al 2003;Jackson et al 2007). Chemosensors on the legs are spatially separated and allow perception of a contrast between sides of the crab's body.…”

Staying the course: chemical signal spatial properties and concentration mediate cross-stream motion in turbulent plumes

“…This general preparation has been used in many behavioral assays involving aquatic organisms and, in particular, blue crabs have effectively tracked sources of chemical exudates of shrimp in previous behavior trails (Jackson et al, 2007;Keller et al, 2003). The stimulus solution was mixed with a fluorescent dye, Rhodamine 6G, which served as an optically measurable proxy for the relative concentration of the attractive odorant.…”