Male Dimorphism as a Consequence of Sexual Selection

Abstract

A number of insect species and red deer possess two forms of males differing from each other in the extent of development of devices involved in competition for females. Such forms may represent genetically based alternative strategies, one form being inferior in combat but wasting little energy in developing expensive weaponry, the other form being superior in combat but burdened with great energy expenditure to achieve this superiority. The return on investment in weaponry for the latter form depends not on the absolute value of investment, but on the extent of investment relative to the other forms present in the population. Such coevolution leads to an escalation of investment in devices of male competition. This costly arms race comes to an end when those investing in weaponry are just as well off as those which have totally opted out of such investment. Such a mechanism could precisely equalize the selective advantages of the two alternatives. Such coevolution is therefore a possible mechanism for the maintenance of a genetic polymorphism.