Seed dispersal as a maternally influenced character: Mechanistic basis of maternal effects and selection on maternal characters in an annual plant

Maternal influences on progeny characters affect phenotypic correlations be tween characters expressed in maternal and progeny generations and conseque ntly influence evolutionary responses to selection. Net selection on matern ally influenced characters depends on selection birth on the progeny charac ter and on the maternal characters that influence it. I used seed dispersal in Cakile edentula as a system in which to identify the mechanisms of envi ronmentally mediated maternal effects and to determine how selection on mat ernal characters alters the adaptive value of dispersal. In C. edentula, ma ternal morphology responds to conspecific density experienced by the mother . Maternal morphology in turn affects offspring (seed) dispersal and densit y and thereby offspring morphology and fitness. I estimated the magnitude o f density-mediated maternal effects on dispersal and identified their mecha nism by characterizing the plasticity of maternal morphology to density. I also measured density-dependent selection on maternal characters that influ ence dispersal. Maternal plasticity to density was caused by both allometri c and nonallometric variation in morphology, and this plasticity resulted i n a negative correlation between maternal and progeny density. Such negativ e maternal effects are expected to retard responses to selection. Maternal morphology influenced maternal Fitness, in part through the relationship of fitness to maternal plant size and in part through size-independent fitnes s effects. Maternal phenotypes that promote dispersal, and thereby increase progeny fitness, were associated with decreased maternal fitness. Selectio n on dispersal at the level of progeny favors increased dispersal; maternal influences on dispersal, however, not only cause a greatly reduced adaptiv e value of dispersal but lead to the prediction of a slower response to sel ection.