KINETIC DIALOGS IN PREDATOR-PREY RECOGNITION

Kinetic dialogs are presented in this paper, which may help to deciphe r ambiguous stimuli during interactions of individuals that possess ex tremely antagonistic interests, such as predators and prey. Predators and prey tend not to be perceived by one another because natural selec tion penalizes any signal that announces their presence. Therefore, av ailable 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 o wn ongoing condition of motion immediately before the movement is perc eived. The proposed signalization system is based on the temporal corr elation of movements of the parties (contingency) and on sign (approac h-withdrawal). If, after the animal moves, an object approaches, it sh ould flee. But if the object withdraws, it should attack. I studied th e behaviour of a fish (Brachydanio rerio) in response to a simple stim ulus that approached or withdrew contingently with the fish movements. This was accomplished by means of a closed loop system in which the m ovements of the fish swimming in a glass tank were detected by a high- speed video camera connected to a computer. A real-time operating algo rithm kept track of the movements of the fish. When movement was detec ted, a 4 mm clay ball was directed towards (predator program), or with drawn from (prey program), the fish. Two different measurements of the 'antipredator' behaviour tested (i.e., frequency of turns after the s timulus and number of halts per stimulus) showed significantly higher values under the approaching condition than under the withdrawing cond ition. This differential reaction of the fish to two different values of the predator/prey variable suggests that specific predator/prey cha nnels of communication are being manipulated with this method. (C) 199 7 Elsevier Science B.V.