in the isopod "paracerceis sculpta" there are three genetically distinct male morphs. alpha males, which represent the largest and most common male morph, tend to defend harems in order to monopolize access to a large number of females. this is the predominant mating strategy in this species. beta males are about the same size as female isopods, and they take advantage of that fact by mimicking female behaviour in order to enter harems and gain access to fertile females. gamma males are the smallest morph. these individuals adopt a sneaking strategy and rely on their small body size to enter harems undetected and remain in them while they seek mating opportunities. these distinct strategies, all determined by a single genetic locus, give equivalent lifetime mating success to each of the three morphs, indicating that natural selection is not acting on one morph more strongly than another. all three alleles expressed in the population will continue to contribute to male morphology as long as the reproductive success granted by each one continues to be as beneficial as the others.