Sexual Selection, Sex Ratio and Mating System

Abstract

Sexual selection, competition for mates in the period of independence from the parents, has sometimes resulted in sexual dimorphism. If the dimorphism is a size difference, it may begin to be expressed during the period of parental care, thus requiring differential parental expenditure on offspring of each sex. Accordingly, the primary sex ratio in size-dimorphic species may be skewed from the expected in non-dimorphic forms, unless differential mortality resulting from other factors affects expenditure in the opposite direction. Furthermore, in some cases, the positive correlation found between an unbalanced sex ratio and a polygamous mating system may occur because both the sex ratio and polygamy are possible, independent results of sexual selection.