Reproductive Traits and Male Fertility in Plants: Empirical Approaches*

Within-population variability in plant reproductive traits can influence both male and female fitness, but research on the male function of flowers has been hindered by the difficulty of measuring male fertility. Here we evaluate studies that employ paternity analysis to examine how specific plant traits affect male reproductive success (RS) in both natural and artificial populations. These studies illustrate the risks of assuming that male RS is correlated with female RS or with components of male fitness, such as the amount of pollen produced per plant. In some studies, paternity was assigned by simple genetic exclusion using unique multilocus allozyme profiles. More powerful methods involve statistical procedures that assign paternity to the most likely father of each offspring. Lack of genetic markers is a common problem in paternity analysis, and we discuss the types of molecular markers that may soon become more widely used in small, natural populations.