Abstract
Flowering is one of the most influential events in the life history of a plant and one of the main determinants of reproductive investment and lifetime fitness. It is also a highly complex trait controlled by dozens of genes. Understanding the selective pressures influencing time to flowering, and being able to reliably predict how it will evolve in novel environments, are unsolved challenges for plant evolutionary geneticists. Using the model plant species, Arabidopsis thaliana, we examined the impact of simulated high and low winter precipitation levels on the flowering time of naturalized lines from across the eastern portion of the introduced North American range, and the fitness consequences of early versus late flowering. Flowering time order was significantly correlated across two environments—in a previous common garden experiment and in environmental chambers set to mimic mid-range photoperiod and temperature conditions. Plants in low water flowered earlier, had fewer basal branches and produced fewer fruits. Selection in both treatments favored earlier flowering and more basal branches. Our analyses revealed an interaction between flowering time and water treatment for fitness, where flowering later was more deleterious for fitness in the low water treatment. Our results are consistent with the hypothesis that differences in winter precipitation levels are one of the selective agents underlying a flowering time cline in introduced A. thaliana populations.
Highlights
When plants are introduced to new habitats, they may become established, and sometimes expand their ranges beyond the area of initial introduction
We examined the effects of winter precipitation on flowering time and addressed two related questions: (1) Is there support for the Samis et al hypothesis that winter precipitation could be a selective agent on flowering time variation in the introduced Arabidopsis range and (2) Do Kenney et al.’s findings of water availability imposing selection on life history hold for a different sample of lines and genotypes, and with water restrictions imposed during simulated winter conditions rather than warm greenhouse conditions?
For the correlation between flowering time in the chamber and the rooftop common garden used by Samis et al (2012), we examined whether the observed correlation coefficients fell into the upper or lower 2.5th percentile of the randomized distribution, which would indicate that it was more extreme than expected by chance alone
Summary
When plants are introduced to new habitats, they may become established, and sometimes expand their ranges beyond the area of initial introduction. Selective pressures can act on plants in different parts of the range, leading to local adaptation. Observing this progression in introduced species offers an excellent opportunity to study evolutionary responses in colonizing populations. Many of the examples of rapid adaptation are from the invasive species literature (Sax et al, 2007), and adaptive evolution is increasingly recognized as an explanation for the ability of some introduced plants to persist and. Confirming major ecological agents of selection is still an active area of investigation, with more manipulative experiments necessary to confirm the forces leading to adaptation in introduced species. We experimentally evaluate a potential selective agent responsible for adaptive evolution of life history in introduced populations of the model plant, A. thaliana
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