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First published online March 17, 2006
Journal of Experimental Biology 209, 1355-1363 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02126

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The effects of social experience on the behavioral response to unexpected touch in crayfish

Cha-Kyong Song¹, Jens Herberholz² and Donald H. Edwards^1,*

¹ Department of Biology, Georgia State University, Atlanta, GA 30303, USA
² Department of Psychology, University of Maryland, College Park, MD 20742, USA

View larger version (41K): [in a new window]   Fig. 1. A time chart of animal preparation and experiments. Pairs of animals share aquaria (rectangular boxes), where they can be isolated from each other by an opaque barrier (gray vertical bar), kept apart by an open divider that allowed pairs to smell, see and touch each other but not to fight (broken gray bar), or interact freely (gray double-headed arrow). The sequence of treatments is shown vertically, in rows labeled from A to K. Tests are indicated by light coloring of the rectangles. Animals were divided into two groups, Isolates and Social Group. (A) All animals were separated from an aquarium partner by a closed divider (i.e. isolated) for four weeks. (B) (two rows) Isolates were separated for two more weeks and thereafter through the tests. Social pairs were allowed to interact freely and form dominance relationships for 30 min day–1; at other times they were kept apart by an open divider. Dominance status was determined during each 30 min of interaction by scoring the numbers of aggressive and submissive behaviors performed by each member of a pair (see equation in Materials and methods and Fig. 3). (C) At the end of the two weeks, the social pairs were re-isolated overnight (15 h) to prevent further agonistic interactions. (D) On experimental Day 1, Isolates and the socially paired animals were tested while separated. (E) Isolates and socially paired animals remained separated overnight. (F) On Day 2, Isolates remained separated while social pairs were allowed to interact freely with their partners for 30 min. (G) All animals were tested, Isolates while separated and social pairs while in the presence of their partner. (H) Social pairs were kept apart by an open divider for 30 min and then (I) tested over a 2–3 h period. (J) Social pairs were then re-isolated by a closed divider for 30 min and then (K) tested again over 2–3 h while isolated.

View larger version (58K): [in a new window]   Fig. 2. Experimental tests and measures. (A) Response of a subordinate crayfish separated from its dominant partner by an opaque divider. (Ai) Before the stimulus touch. (Aii) After the touch; the animal has turned to face the source of the touch. (B) Response of a subordinate in the presence of its dominant partner. (Bi) Before the stimulus touch. (Bii) After the touch, the animal moved forward away from the touch site. (C,D) Diagrams describing measurements of the HP distance and the angle values in orienting and avoidance responses. The open crayfish outline shows the position of the animal before stimulus; the gray crayfish shows the position of the animal after stimulus. The HP distance is the distance from the head (H) to the point of probe contact (P). is the angle between the body axis and the HP line segment. (C) Orienting responses. (Ci) Both and HP are small when an animal pivots backwards to face the probe. (Cii) is large and HP is small when an animal turns and advances past the probe. (D) Avoidance responses. (Di) becomes small and HP becomes large when an animal walks backwards away from the probe. (Dii) and HP both become large when an animal walks forward away from the probe.

View larger version (13K): [in a new window]   Fig. 3. Dominance index of eight pairs of crayfish recorded during the pairing period (Fig. 1B). All aggressive and submissive behaviors that were recorded during the daily 30 min pairing were scored (attack, +2; approach, +1; retreat, –1; tailflip, –2) and presented as a percentage to show the degree of dominance between each dominant–subordinate pair (see equation in Materials and methods). The degree of dominance was higher in all dominant animals (filled squares) than in subordinate animals (open squares). The dominant animals in pairs 2 and 3 were dominant for shorter periods (2 days and 8 days, respectively, at the end of 14 days) because of status reversals.

View larger version (29K): [in a new window]   Fig. 4. Sequential comparison of the behavioral responses to an unexpected manual touch in socially inexperienced and experienced crayfish. (A) Average response frequencies of Orienting, Avoidance and No Response behavioral responses of Isolates, dominants and subordinates on Day 1 while separated from partners by an opaque barrier (condition as in Fig. 1D). The three behavioral responses of the Isolates and social pairs did not differ significantly (Kruskal–Wallis test, P=0.4570 for Orienting Responses, P=0.7133 for Avoidance Responses, P=0.6163 for No Responses). (B) Average response frequencies of the same animals on Day 2 when the dominant and subordinate crayfish were paired with their partners (condition as in Fig. 1G). The Orienting and the Avoidance responses of dominants and Isolates were significantly different from those of subordinates (for Orienting Responses, overall difference, P=0.0008; Isolates vs subordinates, P=0.0012; dominants vs subordinates, P=0.0002; for Avoidance Responses, overall difference, P=0.0003; Isolates vs subordinates, P=0.0003; dominants vs subordinates, P=0.0002) but were not different from each other (for Orienting Responses, P=0.6126; for Avoidance Responses, P=0.7789). The No Responses were not different in Isolates, dominants and subordinates (overall difference, P=0.2069). (C) Behavioral responses later on Day 2 when the dominants and subordinates were tested while separated by an open divider (condition as in Fig. 1I). The dominants' responses were not different from those of the subordinates (for Orienting Responses, P=0.2786; for Avoidance Responses, P=0.1605; for No Responses, P=0.7984). (D) Dominant and subordinate responses after re-isolation (condition as in Fig. 1K) are not significantly different (for Orienting Responses, P=0.2345; for Avoidance Responses, P=0.3282; for No Responses, P=0.9591). (E) The behavioral responses of the subordinates in the four consecutive social conditions (shown in A–D) significantly changed after pairing experience (Friedman test, P=0.0004 for both Orienting and Avoidance Responses). The subordinate animals when isolated on Day 1 displayed the Orienting Responses significantly more often than when paired on Day 2 (Wilcoxon test, P=0.0078), when semi-separated on Day 2 (P=0.0313) and when isolated on Day 2 (P=0.0313). The subordinate animals when paired on Day 2 displayed the Orienting Responses significantly less often than when semi-separated on Day 2 (P=0.0156) and when isolated on Day 2 (P=0.0156). The average frequency of the orienting response when semi-separated on Day 2 did not differ from those when isolated on Day 2 (P=0.5625). The subordinate animals when paired on Day 2 displayed the Avoidance Responses significantly more often than when isolated on Day 1 (P=0.0078), when separated by the open divider on Day 2 (P=0.0156), and when isolated on Day 2 (P=0.0078). The average frequency of No Responses did not change in the four social conditions examined (overall difference, P=0.0660). *P<0.05, **P<0.01, ***P<0.001. All values are means ± s.d.

View larger version (28K): [in a new window]   Fig. 5. The distribution of the HP distances and the angles of the Orienting (blue circle) Avoidance (red square) and No (green triangle) Responses of all animals tested. (A–D) Isolate and dominant animals displayed Orienting Responses. While separated (A,Bisol,Ddom), while paired (Bdom) and while separated by an open divider (Cdom), most isolate and dominant animals displayed Orienting Responses, although some Avoidance Responses and No Responses were also produced. Note that the Avoidance Responses produced by the isolate and the dominant animals have a small HP distance value (<1). (C) Subordinate animals displayed Orienting Responses when separated but displayed Avoidance Responses when interacting with dominant opponents. The subordinate animals produced Orienting Responses while separated on Day 1 (Asub) similar to the isolate and the dominant animals. While paired (Bsub), the subordinate animals showed Avoidance Responses. Note that the Avoidance Responses produced by the subordinates have a large HP distance value (1<HP distance value<2.5). In a semi-separated condition (Csub), some subordinate animals showed Orienting Responses whereas other subordinate animals continued to show Avoidance Responses and large HP values. While separated on Day 2 (Dsub), most subordinate animals showed Orienting Responses, while three subordinate animals produced Avoidance Responses with large HP values (>1).