Evolution and assessment of colour patterns in stream-resident and anadromous male threespine stickleback Gasterosteus aculeatus from three regions.

We compared the colour patterns of free swimming, reproductively active male threespine stickleback Gasterosteus aculeatus of the anadromous and stream ecotypes from three geographically distinct regions. Consistent with the hypothesis of environmentally mediated selection, our results indicate ecologically replicated differences in G. aculeatus coloration between anadromous and stream-resident populations, and that G. aculeatus probably have the visual acuity to discriminate colour pattern differences between anadromous and stream-resident fish.