Effects of visual, chemical and tactile cues of fish on the behavioural responses of tadpoles

Abstract

Abstract. The anti-predator behaviour of two closely related species of tadpoles, Rana lessonae and Rana esculenta, was examined in response to tactile, visual and chemical cues of a fish predator, pike Esox lucius, alone and in all combinations. Tadpoles were hatched and reared in the laboratory to eliminate any experience from natural habitats. The chemical cue decreased swimming and increased the use of areas of the test chambers furthest away from the fish significantly more than tactile or visual cues. The combination of chemical and tactile cues yielded the strongest responses for swimming, resting and use of the edges of the test chambers, while responses to the tactile cue alone did not differ significantly from the control treatment. It is suggested that the tactile cues used, simulating the movement of water by a fish, give tadpoles additional information about the location and the distance of the predator that is not present in chemical cues alone. The visual cue alone or in combination with the tactile cue produced weak responses that did not differ from the control treatment. It may be that tadpoles have poor vision or that visual cues may not be reliable in benthic aquatic habitats with limited view caused by vegetation, suspended sediments, or phytoplankton. The two species responded differently: R. lessonae used the refuge significantly more than did R. esculenta; conversely R. esculenta used the open water significantly more than did R. lessonae. The lack of significant species by treatment interactions indicates that these responses do not reflect differential behaviour towards predator cues, but rather are inherent species differences.