Variability of Rheotaxis Behaviors in Larval Bullfrogs Highlights Species Diversity in Lateral Line Function.

Erika E A Brown,Andrea Megela Simmons,Michael L Fine

doi:10.1371/journal.pone.0166989

Erika E A Brown, Andrea Megela Simmons + Show 1 more

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https://doi.org/10.1371/journal.pone.0166989

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Journal: PloS one	Publication Date: Nov 21, 2016
Citations: 3	License type: CC BY 4.0

Affiliation: Brown University, Providence College

Abstract

The morphology and distribution of lateral line neuromasts vary between ecomorphological types of anuran tadpoles, but little is known about how this structural variability contributes to differences in lateral-line mediated behaviors. Previous research identified distinct differences in one such behavior, positive rheotaxis towards the source of a flow, in two tadpole species, the African clawed frog (Xenopus laevis; type 1) and the American bullfrog (Rana catesbeiana; type 4). Because these two species had been tested under different flow conditions, we re-evaluated these findings by quantifying flow-sensing behaviors of bullfrog tadpoles in the same flow field in which X. laevis tadpoles had been tested previously. Early larval bullfrog tadpoles were exposed to flow in the dark, in the presence of a discrete light cue, and after treatment with the ototoxin gentamicin. In response to flow, tadpoles moved downstream, closer to a side wall, and higher in the water column, but they did not station-hold. Tadpoles exhibited positive rheotaxis, but with long latencies, low to moderate accuracy, and considerable individual variability. This is in contrast to the robust, stereotyped station-holding and accurate rheotaxis of X. laevis tadpoles. The presence of a discrete visual cue and gentamicin treatment altered spatial positioning and disrupted rheotaxis in both tadpole species. Species differences in lateral-line mediated behaviors may reflect differences in neuromast number and distribution, life history, or perceptual salience of other environmental cues.

Highlights

In their natural environments, aquatic anamniotes are exposed to current flow, whether from discrete, localized disturbances or as a change from a moving background
We hypothesized that bullfrog tadpoles would not show the robust, accurate rheotaxis exhibited by X. laevis tadpoles, even when tested under the same flow conditions, and that their behaviors would be disrupted by visual cues and by gentamicin treatment
There was a significant interaction between treatment and speed [Pillai’s V = 0.208; F (12,771) = 4.79, P< 0.0001], with univariate tests showing significant effects in all three dimensions. These results indicate that gentamicin affected spatial positioning in XYZ coordinates at some flow speeds

Summary

Introduction

Aquatic anamniotes are exposed to current flow, whether from discrete, localized disturbances (such as in still waters) or as a change from a moving background (such as in flowing waters). Quantitative analyses of flow sensing behaviors in anurans have been limited to two species, the African clawed frog, Xenopus laevis (type 1), during larval and adult stages [6,7,8,9,10,11,12,13] and the bullfrog, Rana (formerly Lithobates) catesbeiana (type 4), during larval stages [14] Tadpoles of these two species differ in their propensity to exhibit rheotaxis, a standard metric of lateral line function which in fishes is mediated by superficial neuromasts [1,15]. We hypothesized that bullfrog tadpoles would not show the robust, accurate rheotaxis exhibited by X. laevis tadpoles, even when tested under the same flow conditions, and that their behaviors would be disrupted by visual cues and by gentamicin treatment

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