Behavioral responses to “alarm odors” in potentially invasive and non-invasive crayfish species from aquaculture ponds.

Two North American crayfish species, the Eastern white river crayfish, Procambarus acutus acutus, and the red swamp crayfish, P. clarkii, were studied in the laboratory for their responses to food odors and to cues released by injured conspecifics and heterospecifics. The two species differ in that only P. clarkii is known to behave as an invasive species. All the test individuals were collected from aquaculture research ponds, in which they had had no prior contact with the other species and predation risks, excluding cannibalism, were reduced. The experimental design consisted in subjecting 20 crayfish per species to (1) a 3-min control phase after the injection of 20 ml of water and (2) a 3-min test phase after the injection of 20 ml of one of three test solutions (food odor, conspecific odor plus food odor, heterospecific odor plus food odor). We found that the two species differ on one hand for their background behavior and on the other for the intensity and quality of their responses to the three types of cues. Firstly, P. clarkii appeared more active than P. acutus acutus during the control phase and responded in a stronger fashion to the injection of the solutions. Secondly, we recorded an increased locomotion in P. acutus acutus with food and heterospecific cues (by moving crayfish maximize the chance of finding food), but not with conspecific odors (by not moving, crayfish reduce their exposure to visual predators). To the contrary, at the injection of the three test solutions P. clarkii displayed clear feeding-related activities (although less intense with conspecific odors) as opposed to the danger reactions shown in a previous study on individuals from a naturalized population of the same species. This result suggests that crayfish reared in an environment where predation risks are reduced (e.g. in aquaculture ponds) may respond differently to cues that in other, more risky habitats inform of a danger.