Winner and loser effects of juvenile cricket Gryllus bimaculatus

Agonistic encounters of juvenile male crickets were analyzed behaviourally. In a pairing between adult and juvenile male crickets, the juvenile crickets were usually beaten by the adult males of over 3 days after their final moult. Juveniles, by contrast, won significantly more bouts against young adult males 2 days after their final moult. These findings are good indicators to predict which cricket will defeat which opponent. To examine the effect of previous social experience, two juvenile animals were paired first and then juveniles that became subordinate were paired with day 2 adults, while juveniles that became dominant were paired with day 3 adults 5 min after first pairing. Subordinate juveniles were beaten by day 2 adults, while dominant juveniles tended to win against day 3 adults. This is the first time that winner and loser effects have been demonstrated in juvenile crickets. Similar pairings with day 2 or day 3 adult males were performed 2 h after first pairings. Subordinate juveniles were still beaten by day 2 adults, while the winning rate of dominant juveniles against day 3 adults was decreased significantly. These results suggest that the retention time of loser effect lasted more than 2 h while that of the winner effect disappeared within a shorter period.