Artificial selection on flowering time: influence on reproductive phenology across natural light environments


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1. Flowering time is frequently under selection due to a combination of abiotic, biotic and intrinsic factors. Evolution in response to this selection is likely to have broad effects, altering not only flowering time but reproductive phenology and, potentially, traits throughout the life cycle. We know little about the broader phenotypic changes associated with evolutionary shifts in flowering time, and the extent to which expression of these changes depends on local environmental conditions.

2. After three generations of selection for early- and late-flowering, we grew plants of the herb Campanulastrum americanum in contrasting light environments (light gap and understorey) in its home population.

3. Response to selection on flowering time and correlated responses in reproductive phenology were expressed across light environments with the reproduction of early-flowering lines being over 2 weeks ahead of late-flowering lines. Plants in the understorey delayed initiation of flowering but accelerated flower deployment, fruit maturation and the end of reproduction, resulting in a condensed reproductive period.

4. Timing of seed dispersal influences whether offspring grow as annuals or biennials in C. americanum. Because evolution of flowering time shifted reproductive phenology, it is likely to alter life history frequency. In contrast, understorey habitats both delayed flowering and accelerated reproductive phenology, yielding no expected life history change.

5.Synthesis. Evolution of flowering time altered the phenology of all subsequent reproductive traits and is also likely to affect offspring traits. This ripple effect of changes in flowering time indicates that it is essential to recognize genetic and functional linkages among traits to understand potential life cycle consequences of selection on a single character.