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First published online November 30, 2007
Journal of Experimental Biology 210, 4428-4436 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.011288

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Duration of socialization influences responses to a mirror: responses of dominant and subordinate crayfish diverge with time of pairing

Holly Y. May and A. Joffre Mercier^*

Department of Biological Sciences, Brock University, 500 Glenridge Avenue, St Catharines, ON, L2S 3A1, Canada

View larger version (14K): [in this window] [in a new window]   Fig. 1. Cornering observed during 20 min of observation. (A) Mean frequency of cornering events in the reflective and non-reflective (matte) environments. Dominant (Dom) and subordinate (Sub) crayfish paired for 30 min cornered more frequently on the mirrored side of the tank. After 3 days of pairing, dominant crayfish cornered more frequently on the reflective side. Group-socialized crayfish also cornered more on the reflective side of the tank compared with the non-reflective side. (B) Mean time each crayfish group spent cornering on the reflective and non-reflective (matte) sides of the test aquarium. After 30 min of pairing, both dominant and subordinate crayfish cornered for a longer time on the mirrored side of the tank, but after 3 days of pairing only dominant crayfish did (paired t-test: ***P<0.0001, **P<0.005, *P<0.05; N=20). Error bars depict standard deviation.

View larger version (7K): [in this window] [in a new window]   Fig. 2. Turning behaviour of crayfish observed for 20 min. Mean frequency of turns towards reflective and non-reflective (matte) corners. Dominant and subordinate crayfish that were paired for 30 min both turned more frequently towards reflective corners. After 3 days of pairing, only dominant crayfish turned more often towards corners on the reflective side (paired t-test: **P<0.005, *P<0.05; N=20). Error bars depict standard deviation.

View larger version (14K): [in this window] [in a new window]   Fig. 3. Crossing behaviour of crayfish recorded during 20 min of observation. (A) Mean frequency of crosses towards reflective and non-reflective (matte) walls. Group-socialized crayfish crossed towards reflective walls more than non-reflective walls. Dominant crayfish paired for 30 min and 3 days both crossed towards reflective walls more frequently. (B) The mean frequency of crosses away from reflective and non-reflective (matte) walls. Group-socialized crayfish crossed away from reflective walls more frequently than matte walls. After 30 min of pairing, both dominant and subordinate crayfish crossed away from reflective walls more than non-reflective walls. Dominant crayfish paired for 3 days also crossed away from reflective walls more frequently (paired t-test: **P<0.005, *P<0.05; N=25). Error bars depict standard deviation.

View larger version (8K): [in this window] [in a new window]   Fig. 4. The mean frequency of freezing behaviour recorded during 20 min of observations on the reflective and non-reflective sides (matte) of the test aquarium. Dominant and subordinate crayfish paired for 3 days froze more frequently on the mirrored side of the tank. After 3 days of pairing, dominant and subordinate crayfish also froze more in the reflective environment as opposed to the non-reflective environment (paired t-test: ***P<0.0001, **P<0.005, *P<0.05; N=20). Error bars depict standard deviation.

View larger version (8K): [in this window] [in a new window]   Fig. 5. The mean frequency of reverse walking behaviour observed in crayfish for 20 min on the reflective or non-reflective (matte) sides of the test tank. Group-socialized crayfish reverse walked more on the mirrored side of the tank. Both dominant and subordinate crayfish paired for 3 days also reverse walked more on the reflective side compared with the non-reflective side of the aquarium (paired t-test: **P<0.005, *P<0.05; N=20). Error bars depict standard deviation.

View larger version (9K): [in this window] [in a new window]   Fig. 6. The mean total time each crayfish group spent on the reflective and non-reflective (matte) sides of the aquarium during 20 min of observation. Group-socialized crayfish spent more time overall on the reflective side of the tank. Both dominant and subordinate crayfish paired for 30 min spent more time in the reflective environment compared with the non-reflective environment. After 3 days of pairing, only dominant crayfish spent more time on the reflective side of the test tank (paired t-test: **P<0.005, *P<0.05; N=20). Error bars depict standard deviation.

View larger version (6K): [in this window] [in a new window]   Fig. 7. The mean frequency of crossing at the midline of the aquarium for each crayfish group. Dominant crayfish paired for 3 days crossed the midline significantly more than either dominants or subordinates that were paired for 30 min (ANOVA with Tukey HSD post-hoc analysis: *P<0.05; N=20). Error bars depict standard deviation.