Odour recognition learning of multiple predators by amphibian larvae

Many aquatic animals learn to recognize novel predators when they simultaneously perceive the odours of these novel threats paired with alarm cues released by injured conspecifics. Since the odours of several organisms may be present simultaneously in the environment during this process, selection is expected to favour learning mechanisms that allow prey to respond independently to the odour of each species in a mixture of odours. We tested this hypothesis by exposing tadpoles of the edible frog, Pelophylax esculentus, to injured conspecific cues paired with either the odour of two fish species (experiment 1) or one fish and one crayfish species (experiment 2). We subsequently tested the ability of tadpoles to respond to each odour separately. We found clear evidence that tadpoles learned to recognize the odour of individual species in the mixture and that the response to each odour of a mixture was equally strong. However, the learned response was weaker overall in tadpoles conditioned with the mixture of fish and crayfish compared to those with the two fish species. Our study reveals that tadpoles can adaptively handle the presence of multiple predator odours in their environment during conditioned learning, but highlights some constraints that may due to the diversity of predators in the mix.