Responses to chemical cues indicative of predation risk by the freshwater shrimp Palaemon argentinus (Nobili, 1901) (Caridea: Palaemonidae)

Abstract

Many prey species detect predators through chemoreception, particularly in low-visibility aquatic environments. Moreover, injury-released chemical cues from conspecifics are often perceived as a reliable indicator of predation threat. We examined whether males of the freshwater caridean shrimp Palaemon argentinus (Nobili, 1901) react to different types of infochemicals associated with predation threat. Shrimp were exposed to chemical stimuli from starved individuals of a predatory fish (Australoheros facetus (Jenyns, 1842)) and from crushed conspecific shrimp. Our experiment showed that P. argentinus reacts to waterborne substances associated with predation threat, indicating that chemical cues mediate behavioural antipredator responses. Shrimp adopted an appropriate antipredator behaviour (reduced swimming activity) in response to chemical stimuli from A. facetus, and from crushed conspecifics, relative to a distilled-water control. The chemical stimuli from crushed conspecifics elicited the strongest reduction in swimming activity. Reduced movement, a common response in prey animals to the presence of predators, was not entirely consistent because shrimp increased their walking time in response to the chemical stimuli that were investigated. The ability to alter behaviour based on vision-independent perception of ambient risk would be highly useful for macroinvertebrate prey species such as P. argentinus living in eutrophic shallow lakes where visibility is often reduced. Our results demonstrated chemosensory recognition of predation risk highlighting the important role of chemical cues in the behavioural ecology of this shrimp, especially with regards to predator-prey interactions.