THE ECOLOGY AND GENETICS OF FITNESS IN CHLAMYDOMONAS .6. ANTAGONISM BETWEEN NATURAL-SELECTION AND SEXUAL SELECTION

Antagonism between the sexual and vegetative life cycles of eukaryotes is the most fundamental assumption of the theory of sexual selection. A trade-off between sexual competence and vegetative growth rate is expected from life-history theory, which predicts a negative genetic correlation between any two components of fitness that together define total fitness. Alternatively, intra-sexual competition or mate choice may create a positive correlation between vegetative growth and mating success. We have described the nature of the genetic correlation between mating efficiency and vegetative growth rate in the unicellular, facultatively sexual, chlorophyte alga Chlamydomonas reinhardtii. By selecting for mating efficiency and measuring the correlated response in vegetative growth rate, we found a negative genetic correlation between fitness components, as predicted by life-history theory. This is the first demonstration of a net viability cost of sexual selection.