Kinetic dialogs in predator–prey recognition

Abstract

Kinetic dialogs are presented in this paper, which may help to decipher ambiguous stimuli during interactions of individuals that possess extremely antagonistic interests, such as predators and prey. Predators and prey tend not to be perceived by one another because natural selection penalizes any signal that announces their presence. Therefore, available signals for making adequate decisions may be scarce. I propose that within this impoverished signalization system the way each party reacts to a sudden movement of the other, strongly depends upon its own ongoing condition of motion immediately before the movement is perceived. The proposed signalization system is based on the temporal correlation of movements of the parties (contingency) and on sign (approach–withdrawal). If, after the animal moves, an object approaches, it should flee. But if the object withdraws, it should attack. I studied the behaviour of a fish ( Brachydanio rerio) in response to a simple stimulus that approached or withdrew contingently with the fish movements. This was accomplished by means of a closed loop system in which the movements of the fish swimming in a glass tank were detected by a high-speed video camera connected to a computer. A real-time operating algorithm kept track of the movements of the fish. When movement was detected, a 4 mm clay ball was directed towards (predator program), or withdrawn from (prey program), the fish. Two different measurements of the `antipredator' behaviour tested (i.e., frequency of turns after the stimulus and number of halts per stimulus) showed significantly higher values under the approaching condition than under the withdrawing condition. This differential reaction of the fish to two different values of the predator/prey variable suggests that specific predator/prey channels of communication are being manipulated with this method.