Male and Female Fertility Variation in Wild Radish, a Hermaphrodite

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Abstract
We estimated male and female fertilities in a naturally occurring population of 41 hermaphroditic wild radish plants. Male fertilities were estimated by analyzing the paternity of 2,428 seeds (from 39 of the plants), coupled with a maximum-likelihood method to estimate fertility from the paternity data. Female fertilities were estimated as the fraction of the seed yield of the population produced by each individual. We detected a 15-fold range in mean male fertility, nearly a 200-fold range in female fertility, and a 25-fold range in total fertility. Male fertility was correlated with the distance among mates and with a number of phenotypic features of the plants: the total number of flowers produced, flower color, peak flowering time, whether the peak flowering times of the male and female parents overlapped, and some of the interactions of these variables. An additional portion of the variance of male fertility, however, was accounted for by a class variable denoting each male parent, suggesting that unmeasured features of the plants influenced male fertility. Female fertility was distinctly bimodal. Within mode, most of the variance of female fertility was accounted for by the number of flowers produced by each plant and its peak flowering period. Male and female fertilities were only weakly correlated, permitting a wide range of functional genders, 0.03-0.91 (possible range, 0-1), to be expressed. Because wild radishes are annuals, the lifetime fertility variation that we report must have important fitness consequences. In addition, contrary to many researchers'' expectations, in this population the variance of female fertility exceeds that of male fertility. Consequently, phenotypic selection would have been greatest on traits correlated with female fertility or total fertility in this 1986 population.