During reproduction, a male can give either an X sperm or a Y sperm, while a female can only give an X egg. A Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female. The part of the Y-chromosome which is responsible for maleness is the sex-determining region of the Y-chromosome, the SRY.
Explanation:
Abstract
Most previous studies of sexual selection have focused on the mechanisms of intrasexual (male) competition and female choice. However, recent work has suggested that, under some conditions, there may be selection for males to allocate their reproductive effort prudently. In Plecia nearctica (Diptera: Bibionidae), most males mate only once, a characteristic which may promote the evolution of such male choice. We found that copulating males were significantly heavier, but no larger, than solitary males. This could result from either male competition or female choice. Copulating females were both larger and heavier than virgin females. This supports the hypothesis that males exercise mate choice, preferring larger females, which are known to contain more eggs, over smaller ones. Contrary to previous studies, assortative mating does occur for body size and weight.
Journal Information
Evolution, published for the Society for the Study of Evolution, is the premier publication devoted to the study of organic evolution and the integration of the various fields of science concerned with evolution. The journal presents significant and original results that extend our understanding of evolutionary phenomena and processes.
