Friends or enemies? Chemical recognition and reciprocal responses among invasive Ponto-Caspian amphipods

Abstract

Chemical communication plays a significant role in the aquatic environment, enabling the mutual recognition of mates, predators and food items. Invasive species facing new communities are subjected to a huge variety of new scents. Their ability to recognize and interpret them adequately could be the reason of their successful establishment. We studied reciprocal chemical recognition among invasive freshwater Ponto-Caspian gammarids (Dikerogammarus villosus, Dikerogammarus haemobaphes and Pontogammarus robustoides) that often co-occur in native and invaded areas, to test their ability to avoid via chemical signals possible competitor and/or top intraguild-predator. We used a Y-maze with inflow of water to the Y-arms from two source tanks containing the signal (scent of living animals or the alarm cues released by crushed individuals) or a control (dechlorinated tap water), respectively. Time spent in the Y-maze zones, number of visits to the Y-arms and animal activity were analysed. Only D. villosus was attracted to conspecific and heterospecific alarm cues as well as to living heterospecifics. The other two species avoided the scent of D. villosus. We conclude that D. villosus, as the strongest competitor and intra-guild predator (including cannibalism) among the tested species, perceived various scents as potential food cues and posed a threat to other gammarids.