Inference of evolutionary pattern: diversionary displays of three-spined sticklebacks

In three lakes and one marine lagoon in British Columbia, Canada,groups of three-spined sticklebacks (Gasterosteus aculeatus)cannibalize embryos and fry guarded by conspecific parentalmales. At the approach of these groups, males perform displaysthat divert the groups, often causing them to bypass the male'sterritory. Similar large groups failed to elicit such displaysfrom males in three noncannibalistic populations. The diversionarydisplays in two lakes are similar, apparently attracting conspecificsthrough foraging deception, but sticklebacks in a third lakeand in a marine lagoon perform a more complex array of displaytypes, some of which appear to incorporate ritualized elementsof other behavioral repertoires. Because the freshwater populationsare derived from marine populations of Gasterosteus, the complexdisplay repertoire is apparently ancestral relative to thefreshwater radiation. This inference is strengthened by comparisonwith the diversionary display repertoire in an Atlantic marinepopulation (primitive outgroup). Thus, the absence of the displayin some populations and the relatively limited display formsin others appear to represent a loss of all or part of theancestral display. Loss of the display in noncannibalistic populations may be adaptive because it enhances mating success.The significance of partial loss in some cannibalistic populationsis less clear. Interpretations of these patterns demonstratethe value of accounting for past historical relationships amongpopulations when inferring historical patterns of behavior evolution.