Population density drives the local evolution of a threshold dimorphism.

摘要: Evolution can favour more than one reproductive tactic among conspecifics of the same sex. Under conditional evolutionarily stable strategy, individuals adopt that generates highest fitness return for their status: large males guard females, whereas small sneak copulations. Tactics change at status which benefits switch from favouring to alternative. This 'switchpoint' is expressed in many species as a threshold between divergent morphologies. Environmental and demographic parameters influence relative male tactics are predicted determine population's switchpoint consequently whether population monomorphic or dimorphic. Here we show evolution forceps dimorphism European earwig Forficula auricularia document transition completely classical male-dimorphic populations over distance only 40 km. Because superior fighting ability dominant morph will be frequently rewarded high encounter rates, density likely key determinant alternative tactics, threshold. We that, predicted, correlates strongly with shift threshold, this factor drives local these island populations. Our data provide evidence origin phenotypic diversity within populations, through strategy has responded density.