Movements ofRana catesbeianatadpoles in weak current flows resemble a directed random walk

Abstract

SUMMARYCurrent flow is an important biological stimulus for larval anuran amphibians, but little is known about how it is perceived. We quantified behavioral responses to controlled water flow in the bullfrog tadpole (Rana catesbeiana) at developmental stages prior to metamorphic climax, and examined the contribution of a functioning lateral line system to these behaviors. Tadpoles at these developmental stages show a significant preference for the sides and bottom of a flow tank. In response to water flow at three different rates, they exhibit a significant, time-dependent tendency to move downstream, away from the source of the flow, and to remain in areas where flow is minimized. The consistency of these behaviors at all tested flow rates suggests that the animals are not simply passively pushed by the current; instead, they actively swim away from the current source. Tadpoles do not exhibit positive rheotaxis towards the source of the flow at any flow rate but as a group are randomly oriented. Treatment with cobalt chloride, a known blocker of superficial neuromast function, significantly reduces the tendency to move downstream, but does not alter the preference for the sides and bottom of the tank. Tadpoles' movements under flow are consistent with a model of locomotion based on a directed random walk.

Flow sensing in developing Xenopus laevis is disrupted by visual cues and ototoxin exposure

“…Digitized videos were analyzed off-line using custom-written MATLAB scripts based on DLT (Schmidt et al 2011) that calculated the animal's position in XYZ dimensions and its orientation (direction the head faced in relation to the direction of the flow). Data were sampled in consecutive 30-s time intervals in the 300-s No Flow period, yielding 10 data points beginning at the time of entry of the animal into the tank, and in the 300-s With Flow period, yielding another 10 data points beginning at flow onset.…”

“…A custom-built recirculating flow tank, illustrated in Schmidt et al (2011), was used for behavioral testing. This tank was based on the design and specifications of Vogel and LaBarbera (1978) and is similar to that used by Kanter and Coombs (2003) and Bak-Coleman et al (2013).…”

“…Current flow at different flow speeds was further analyzed using digital particle image velocimetry (DPIV), as previously described (Drucker and Lauder 1999;Schmidt et al 2011). Movements of silver-coated glass spheres (mean diameter 12 μm, density 1.3 g cm −3 ; conduct-o-fil, Potters Industries, Valley Forge, PA, USA) suspended in the flow field were visualized using a pair of 80 mW line lasers (series LBS, Laserglow, Toronto, CA) mounted collinearly above the tank so that they illuminated a single plane.…”

“…Each animal was tested at only one flow speed. Vogel and LaBarbera (1978) and is illustrated in Schmidt et al (2011). a Plan view over the X and Y planes at a Z location of 3 cm.…”

“…Tadpoles of these two species behave differently in a standard assay of superficial neuromast function-rheotaxis, the orientation toward the direction of a flow source. Xenopus tadpoles show positive rheotaxis to a low-velocity current source (Simmons et al 2004) while Rana tadpoles tested under the same conditions are more randomly oriented (Schmidt et al 2011). These behavioral differences may reflect variability in the importance of flow sensing in the natural behavioral repertoire of these animals, perhaps related to the availability of other sensory cues in their habitats.…”