The Quantitative Genetics of Life History and Fitness Components in Raphanus raphanistrum L. (Brassicaceae): Ecological and Evolutionary Consequences of Seed-Weight Variation

Abstract

Natural populations of wild radish harbor 20-fold phenotypic variation in seed weight. Under competitive conditions, the weight of sown seeds is positively correlated phenotypically with final plant stature, lifetime flower production, lifetime fruit production, and seed production. To establish the evolutionary significance of seed-weight variation in a natural population, I conducted reciprocal crosses among individuals chosen from a wild population in Connecticut [USA]. The progeny were sown in an experimental garden, and an analysis of 12 life history and fitness components was conducted on the paternal half sibs. This design provided estimates of the narrow-sense and broad-sense heritabilities of the weight of sown seeds (produced by the parental generation), germination and flowering dates, 7 fitness components, the weight of seeds produced by F1 adults, and lifetime maternal fecundity. The results suggest that natural selection could not operate to effect evolutionary change in seed weight in this experimental population. Maternal environmental effects, non-additive genetic effects, and/or developmental sources of variation are largely responsible for the phenotypic variance in seed weight in wild radish. Additive genetic variance was detected in several life history and fitness components, suggesting that additive genetic variance in total fitness exists within this population.