BERGMAN, Daniel A; MOORE, Paul A: The olfactory role in the fight dynamics of the crayfish, Orconectes rusticus

Dyadic agonistic interactions produce stable dominance relationships among individual crayfish. A variety of factors influence the formation of hierarchical structures, including a crayfish’s intrinsic aggressive state, an ability to physically dominate, and previous agonistic experience. Crayfish, which experienced a recent win, become more likely to also win their next fight, even against new opponents, while future chances of winning decreases in previous losers. Thus, a winner or loser effect will be established. Moreover, chemical communication via urine signals plays a significant role in recognition of aggressive state and may also carry information on dominance status. Olfactory information affects the outcome and duration of agonistic interactions. We investigated how the winner effect was influenced by the presence of chemicals being released during agonistic encounters. After establishing a winner effect, the winning crayfish was introduced to a naive opponent after a 20-minute interval. This opponent was prevented from receiving chemical status cues by blocking its antennae and antennules. This lesion study indicated a difference in fight outcome. Winners that fought against opponents with lesioned chemoreceptors were significantly less likely to win their subsequent encounter than those fought against opponents without lesioned chemoreceptors. When opponents had their olfactory abilities lesioned, fights quickly escalated to higher fight intensity levels and they initiated the fights. This demonstrates that chemical signals perceived by the antennae and antennules play a key role in the outcome of a fight, initiation of agonistic behaviors, and the temporal dynamics of agonistic encounters and suggests that the winner effect is not intrinsic to the winner, but rather results from information communicated via odor.