| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 2006: ¥1,200,000 (Direct Cost: ¥1,200,000)
Fiscal Year 2005: ¥2,100,000 (Direct Cost: ¥2,100,000)
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| Research Abstract |
When the crayfish showed resting posture, mechanical stimulation to the tailfan elicited avoidance reaction in which response pattern was changed from dart to turn response according to the size of the crayfish. Furthermore, when two previously unacquainted crayfish encounter, fighting occurred immediately and dominant-subordinate relationship was determined within several contacts.
I have shown in this study that small crayfish that previously showed dart response in response to mechanical stimulation to the tailfan changed their performance of avoidance reaction when they won the fights with opponents. While they mainly showed dart response (about 92% from 47 crayfish) before fighting, the touching tailfan predominantly elicited turn response (94%). Statistical analysis showed the occurrence probability of the dart response as well as that of the turn response was significantly different between dominant crayfish before and after fighting (p<0.0001: paired t test). After fighting, sub
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ordinate animals were usually observed to run away from the approach of dominant crayfish. The response of the subordinate crayfish to the mechanical stimulation was almost consistent. Touching of the exopodite mainly elicited dart response before (95% from 47 animals) and after (91%) fighting.
To characterize behavioral change of the avoidance reaction in the dominant crayfish, the response of them to the sensory stimulation was continuously tested with 3 different groups. In the 1st group, the dominant and subordinate crayfish were kept to pair for further 8 days. More than half of the subordinates were killed by dominant crayfish within 5 days. Dominant continuously preferred to perform the turn response when the mechanical stimulation was applied. Dominant crayfish of the 2nd group were re-isolated from the subordinates immediately after the test of the 1st day. As days have passed, the probability of the occurrence of the turn response was decreased and that of dart response was increased. Occurrence probability of turn response was still statistically higher than that of dart response in the 2nd and 3rd day. There was no significant preference between turn and dart response in the 4th day, and the dart response was released more often from the 5th day. In the 3rd group, the dominant and subordinate crayfish were separated after the test but both crayfish were paired together for 1 hour from next day. The dominant, crayfish continue to show turn response even in the 8th day. These suggested contact with subordinate is needed to keep the behavioral transition of avoidance reaction. Less
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