Whiskers aid anemotaxis in rats

Abstract

Observation of terrestrial mammals suggests that they can follow the wind (anemotaxis), but the sensory cues underlying this ability have not been studied. We identify a significant contribution to anemotaxis mediated by whiskers (vibrissae), a modality previously studied only in the context of direct tactile contact. Five rats trained on a five-alternative forced-choice airflow localization task exhibited significant performance decrements after vibrissal removal. In contrast, vibrissal removal did not disrupt the performance of control animals trained to localize a light source. The performance decrement of individual rats was related to their airspeed threshold for successful localization: animals that found the task more challenging relied more on the vibrissae for localization cues. Following vibrissal removal, the rats deviated more from the straight-line path to the air source, choosing sources farther from the correct location. Our results indicate that rats can perform anemotaxis and that whiskers greatly facilitate this ability. Because air currents carry information about both odor content and location, these findings are discussed in terms of the adaptive significance of the interaction between sniffing and whisking in rodents.

Keywords: airflow; behavior; hair; navigation; rodents; somatosensory; tactile; vibrissa; vibrissae; wind following.

Fig. 1. Rats were trained to localize airflow or light.

(A) The arena’s entrance door is opposite five fans, placed around the arena circumference. A fence confines the rat. Black solid lines indicate checkpoints. Five holes (black circles) allowed access to tunnels beneath the table (gray shadow) that led to a water reward port (reward 1, black star), activated only for correct trials. A ramp led back to the holding box where a second reward (reward 2, black star) was given for correct trials. (B) Airspeed color map shows that the maximum speed lies approximately along the line connecting fans and the entry door. (C) Five rats’ trajectories (all correct trials before vibrissal removal) superposed on airspeed color map.

Fig. 2. Vibrissal removal degrades performance in airflow but not light localization.

(A) Average (10-day) performance before (blue) and after (red) vibrissal removal for rats trained to localize either airflow or light. Error bars show means ± SEM. ***P < 0.001; *P < 0.05; n.s. (not significant), P ≥ 0.05; Wilcoxon rank sum test; median values are reported in table S2. (B) Average (6-day) localization threshold before (blue) and after (red) vibrissal removal on the two-up/two-down experiment. Data show means ± SD percent maximum airspeed. Dashed lines indicate the fixed airflow speed used in Fig. 2A (87% maximum). (C) Average performance decrement (10-day average) with fixed airspeed is related to localization threshold (12-day average). Data points show mean values; vertical lines indicate ±SEM performance decrement; horizontal lines indicate ±SEM threshold.

Fig. 3. For incorrect trials, vibrissal removal causes rats localizing airflow to deviate more from the straight-line path to an airflow source but not a light source.

(A) Trajectories of all incorrect trials of five rats trained to localize airflow 10 days before vibrissal removal (top row) diverge less than after removal (bottom row). (B) For incorrect trials, deviation of each rat before vibrissal removal (blue) is smaller than after removal (red). Error bars show means ± SEM. ****P < 0.0001; **P < 0.01; *P < 0.05; n.s., P ≥ 0.05; Wilcoxon rank sum test; median values are reported in table S2. (C) The percentage of incorrect trials for which a nonneighboring fan was chosen before (blue) and after (red) vibrissal removal. ***P < 0.001; n.s., P ≥ 0.05; Yates’s corrected χ² test.