Three‐dimensional odorant concentration measurements around actively tracking blue crabs

Abstract

Blue crabs (Callinectes sapidus) and other aquatic organisms locate food and mates by tracking turbulent odorant plumes. The odorant concentration fluctuates unpredictably due to turbulent transport, and many characteristics of the fluctuation pattern have been hypothesized as useful cues for orienting to the odorant source. To make a direct linkage between tracking behavior and odorant signal properties, we developed a laserinduced fluorescence measurement system to quantify the instantaneous three‐dimensional (3D) concentration field surrounding actively tracking blue crabs. The data suggest a connection between upstream walking speed and bursts of odorant concentration arriving at the antennule chemosensors, which are located near the mouth region. Specifically, we note rapid upstream walking speed when high concentration bursts arrive at the antennules location and a decrease in upstream walking speed in the absence of odorant filaments near the antennules. Additionally, we note transverse crab movements in apparent response to the transverse distribution of the odorant concentration field. Specifically, asymmetry of the odorant concentration distribution at the elevation of the leg chemosensors is associated with subsequent crab position adjustments in the transverse direction. The methods described here allow for powerful and direct tests of chemosensory navigation strategies in blue crabs, as well as other macroscopic aquatic animals.

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

“…Unlike in moths, which turn with respect to the wind direction (Arbas et al, 1993), the role of flow here is much more limited. Although crabs move against the flow upon reception of an odorant spike at their cephalic appendages (Dickman et al, 2009;Page et al, 2011), the spatial distribution of odorant mediates cross-stream motion directly.…”

“…Intense laser light is an aversive stimulant to foraging blue crabs, so they were reversibly blinded with electrical heat shrink-wrap, which created no adverse effects (Dickman et al, 2009). Crabs were outfitted with a light-emitting diode (LED) backpack to indicate their position, which was recorded by the CMOS camera simultaneously with the Rhodamine 6G fluorescence data.…”

“…Second, signals very close to the body often were shaded by appendages regardless of the crab orientation. For this reason, the concentration arriving at the outer chemosensors was estimated by evaluating the structure of the approaching plume [see Dickman et al (Dickman et al, 2009) for more details]. Concentration data were extracted in a rectangular region sufficiently upstream to avoid shadow or reflection interference from the leading claw (Fig.2).…”

“…We developed a system for the simultaneous visualization and quantification of odorant signal structure and animal movements during navigation (Dickman et al, 2009) to examine how animals use chemical signal structure to navigate through turbulent odorant plumes. This allows us to define relationships between chemical signal input and the subsequent behavioral output both over an entire tracking event and in different chemical signal environments.…”

Oesophageal chemoreceptors of blue crabs,Callinectes sapidus, sense chemical deterrents and can block ingestion of food

“…In crabs, the aesthetascs also mediate responses to intraspecific signals such as sex pheromones (Gleeson, 1982;Gleeson, 1991). The antennules of crabs play a somewhat different role in chemo-orientation, although ablation of the antennules slows the crabs' upstream progress (Keller et al, 2003;Dickman et al, 2009). Another example of a different organization of the food search is found in the kelp crab Pugettia producta, in which low concentrations of chemical stimuli elicit a local search (e.g.…”