Multigenerational Effects of Flowering and Fruiting Phenology in Plantago lanceolata

Phenological patterns of flowering and fruiting can be influenced by the effects of reproductive time on seed production. We propose here that these patterns are also influenced by phenological effects on offspring quality. Furthermore, we hypothesize that there are cross-generational trade-offs between parental and offspring components of parental fitness influencing the evolution of reproductive phenology. To test our hypothesis, we examined the multigenerational effects of flowering and fruiting phenology in Plantago lanceolata. Offspring of 30 families were transplanted into field plots to measure the effects of onsets of flowering and fruiting, duration of fruiting, percentage fungal infection, and damage by grasshoppers on total seed production, our measure of the within-generational component of parental fitness. To gather information about cross-generational contributions to parental fitness, we assessed the quality of offspring produced at different times in terms of seed mass and germination. Families significantly differed in flowering and fruiting onsets. Larger plants began flowering earlier, and earlier flowering plants matured fruits earlier and produced fruits for a longer time. Significant family-mean correlations among these traits suggest that selection on any one trait will change all three traits. A negative family-mean correlation between fruiting onset and seed production suggests that we can expect an antagonistic trade-off in response to selection on these two traits. Early fruiting significantly reduced seed predation by grasshoppers and increased seed production. In contrast, late-maturing seeds were significantly heavier and germinated more rapidly than did early-maturing seeds produced by the same plants. The directions of the multigenerational effects support the hypothesis that there are cross-generational trade-offs between parental and offspring components of parental fitness. The experiments indicate that multigenerational fitness effects should be considered in future studies addressing the evolution of flowering and fruiting phenology.