The influence of habitat stability on landmark use during spatial learning in the three-spined stickleback

The capacity to learn enables animals to match their phenotypic response to a changing environment on the basis of experience but learning is likely to incur costs such as the cost of making mistakes or the energetic cost of processing information. Little is known about how animals optimize the use of learned behaviour within their natural environments such that potential costs are minimized. We investigated whether the use of local landmarks in learning orientation routes by the three-spined stickleback, Gasterosteus aculeatus, varied in response to the visual stability of their natural habitats. Sticklebacks collected from five fast-flowing rivers and five ponds were trained to locate a hidden reward in a T-maze. Locating the reward required the fish to learn a body-centred algorithmic behaviour (turn left or right) or to follow plant landmarks. Probe trials, in which these cues conflicted, revealed which spatial cue the fish was using. Pond fish appeared to rely more than river fish on visual landmarks, which is consistent with the suggestion that even within a species, learned behaviour is fine-tuned in response to local environmental conditions. Landmarks may be reliable indicators of location only in stable pond habitats. In rivers, turbulence and flow may continually disrupt the visual landscape such that river fish may benefit from learning orientation routes only if learning is constrained so that unreliable visual cues are ignored.