Recognition of dominance status by chemoreception in the red swamp crayfish, Procambarus clarkii

We tested the hypothesis that chemical signals play a role in the recogniti on of dominance status in the red swamp crayfish, Procambarus clarkii. Domi nance was judged on the outcome of dyadic interactions in all male or femal e groups of three individuals. This resulted in a dominant, intermediate, a nd subordinate individual within each population. A choice paradigm in a fl ow-through Y maze was used to judge whether crayfish were able to recognize dominance through chemical cues alone. Both individuals that interacted wi th the animal producing the odor and naive individuals were tested. Irrespe ctive of sex and previous experience, individuals increased their rates of locomotion in the presence of conspecific odor. Naive males investigated th e dominant arm first, spent more time at the dominant nozzle, and responded more aggressively (as measured by meral spread) to dominant male odor and subordinate female odor. Intermediate males spent more time at the dominant male nozzle and responded more aggressively to dominant male odor. Naive f emales spent more time at the dominant nozzle. These results show that male s recognize dominant animals. Since both naive and experienced males respon d to water from dominant animals, we concluded that this is recognition of dominance and not just individual recognition. This signal may be important for the formation or reinforcement of dominance relationships. Based on th e change in behavior between odors, we suggest that crayfish can use chemic al cues to recognize the dominance status of conspecifics.