Spatial learning ability of the threespine stickleback (Gasterosteus aculeatus) in relation to inferred ecology and ancestry

摘要

Background: Spatial learning is the ability to learn and use features in space to navigate within an environment. In fishes, it is associated with residence in structurally complex habitat, but very little is known about its ancestral condition in adaptive radiations. Goal: To investigate the relationship between foraging mode and spatial learning in derived populations of a well-studied evolutionary model fish species, and to test the importance of experience on spatial learning in an ancestral analogue of this species. Organism: Threespine stickleback (Gasterosteus aculeatus) occur as sea-run (ancestral) and divergent freshwater (derived) forms. Freshwater populations occupy an ecological continuum, with benthic stickleback at one extreme, residing and foraging in shallow, structurally complex lakes, and limnetics at the other, living and feeding in the open water of deep lakes that lack structure. Methods: I used a T-maze to measure spatial learning. In Experiment 1, I compared five benthic andfive limnetic field-caught stickleback populations to explore ecological divergence of spatial learning. In Experiment 2, I used a sea-run population to infer the ancestral condition of spatial learning; I studied laboratory-reared sea-run fish raised inspatially complex or simple aquaria because adequate samples of field-caught sea-run adults proved difficult to attain. Results: In Experiment 1, benthics exhibited better spatial learning than limnetics. These differences were independent of differences in boldness, exploratory behaviour, activity level, or other performance variables that are independent of spatial learning. In Experiment 2, no differences were detected between rearing treatments, but a number of fish from either group still solved the maze, indicating that even fish reared in spatially simple conditions were capable of spatial learning. However, the relative contributions of inheritance and experience remain unclear.