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Floral morphology can affect levels of fruit set by influencing both the likelihood of autogamous self-fertilization (i.e., pollination in the absence of an external pollinator) and pollinator efficiency (i.e., removal and deposition of pollen). For wild species that are self-compatible, developmental mechanisms that enhance autogamy, such as close proximity of the stigmatic surface to anthers at the time of dehiscence, are important to ensuring successful fruit set. Autogamy may also be of increasing agroecological relevance given recent reductions in the abundance of pollinators servicing some crop species. For self-incompatible species, floral morphologies that enhance pollinator efficiency could improve fruit set. Although many studies have examined the quantitative genetics of floral traits, very few have tested for developmental flexibility in these traits in response to different environments. The number of floral parts (e.g., number of petals, pistils, or stamens) is comparatively invariant, and has been used in taxonomic analyses. The relative constancy of floral organ number, however, does not translate into constancy of organ size. We have shown that flowers of the selfing species Arabidopsis thaliana are highly plastic to both photoperiod and levels of red:far-red wavelengths (R:FR), an aspect of light quality that varies with plant density. More specifically, mean pistil, stamen, and petal lengths varied between long (16-hr) vs. short (8 hr) photoperiod environments, as well as between high (˜1.0) vs. low (˜0.4) R:FR environments simulating sunlight and foliar-shade conditions respectively. Ongoing studies are comparing the direct effects of light on floral morphology vs. the potential indirect effects of circadian rhythm, which is itself determined in part by photoperiod and R:FR. |
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Developmental responses of flowers to photoperiod are ecologically relevant in Arabidopsis, because this species occurs over a wide latitudinal gradient (see adjacent map of ~100 natural populations in Europe ), and plants in natural populations therefore flower under different photoperiods. Similarly, because many crop species are cultivated over a wide latitudinal gradient, plants of a given crop will likely mature under different photoperiod environments and may differ in the expression of floral traits. Cultivated fields also vary in plant density due to both microsite variation in germination success and local cultivation practices, thereby affecting the levels of R:FR light within a stand. We are currently looking at the genetic and physiological mechanisms of variation in floral morphology, as well as the fitness consequences of this variation. Experimental work uses both the genetic model Arabidopsis thaliana , and the natural species Brassica rapa and Mimulus guttatus . |
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