TROJAN SPARROWS - EVOLUTIONARY CONSEQUENCES OF DISHONEST INVASION FOR THE BADGES-OF-STATUS MODEL

An adapted game-theory model for the "badges of status" hypothesis is introduced, and factors influencing the formation of "honest" stable population states are investigated. The stability of these states is then studied when two "dishonest" mutant strategies, "cheat" and "Trojan sparrow," are evoked. The honest population states are stable against invasion by the cheat strategy if social control of deception, in the form of punishment from aggressive individuals, is sufficiently severe. The Trojan-sparrow strategy is found to be successful for invading honest population states under all conditions, which indicates that the conventional badges-of-status model is fundamentally evolutionarily unstable in the absence of constraints limiting phenotypes to honesty. Without honest phenotypic limitation we predict that mixed fighting strategies will evolve but that individuals will not display accurate information regarding their aggressive intent and that dominance hierarchies will be based on true measures of resource-holding potential and not badge size. Hence, the conventional badges-of-status theory can be reduced to the conventional hawk-dove model and cannot be used to explain the evolution of mixed fighting strategies without honest phenotype limitation. We identify the reproductive trade-off, honest "handicap," and/or genetic and/or pleiotropic constraints under which badges of status may prove evolutionarily stable by the limitation of the strategy set to honesty.