Foraging in complex odor landscapes: chemical orientation strategies during stimulation by conflicting chemical cues

The concept of trade-offs and the decisions organisms make regarding them have become a driving force in ecological research. One well-studied trade-off, maximizing growth while minimizing mortality, affects decisions an organism makes regarding activity levels, habitat selection, and refuge use Our study addressed how complex odor cues (e.g., a predation event and food combined) and their physical properties (e.g., concentration and spatial distribution) can affect foraging. Experiments were carried out using the crayfish Orconectes virilis in an artificial stream. A 2 x 2 factorial design was used with 2 odor treatments (food and food + alarm) and 2 shelter treatments (shelter and no shelter). Crayfish in the alarm treatment found the food source less often. They also took significantly longer to find the food source and spent more time in shelters. Crayfish in the presence of alarm stimuli used side shelters significantly more than shelters in the center of the flume, whereas crayfish in the control did not show a preference. Also, concentration of the alarm odor significantly affected the alarm response of the crayfish. Electrochemical recordings showed that the dopamine tracer was present in high concentrations down the center of the flume but in very low concentrations or absent along the sides of the flume for both the food and alarm trials. Our study illustrated the importance of chemical signals in aquatic systems for both locating food and avoiding predators. Complex odors influenced habitat use as well as foraging efficiency and success. The content, concentration, and distribution of complex chemical signals appear to be an important part of risk assessment during foraging, and may provide the necessary information to facilitate ecological interactions.