9701148 Jarosz Most organisms live in variable environments. For example, nearly all plants experience frequent temporal fluctuations in temperature, light, moisture, and nutrients during their lifetimes. Only recently have biologists begun to address the significance of this environmental heterogencity with regard to natural selection. A general expectation is that environmental heterogeneity will favor plants that are phenotypically plastic. An adaptively plastic plant expresses a phenotype appropriate for the environmental conditions in which it occurs. For example, a plant growing in shade might produce large thin leaves to efficiently harvest the limited light, while the same plant growing in full sun might produce smaller, thicker leaves to minimize water loss. Each leaf phenotype allows the plant to be more fit, i.e., to produce more seeds, than if the alternate phenotype were expressed. Despite the ubiquity of phenotypic plasticity of most traits, the ecological meaning and adaptive relevance of phenotypic variation in natural populations have seldom been investigated. The PIs will characterize the genetic basis of phenotypic responses to three light environments by studying individuals of known genetic relationship in a natural population of the winter annual wildflower, Collinsia verna (blue-eyed Mary). The PIs will examine the fitness consequences of light-induced phenotypic changes by studying traits known to respond to different light levels and/or to be closely related to fitness (e.g., germination date, size at overwintering, leaf size and shape, plant size and branching pattern, date of first flowering, number of flowers, number of seeds, and seed size). Human activity is causing unprecedented environmental change at all scales from local habitat fragmentation to global climate change, with far reaching consequences for earth's biodiversity. The results of this research will contribute to our understanding of many important questions about biodiversity and it s management: What are the determinants of species ranges? What constitutes a stressful environment for a species? How do individuals and species respond to novel and changing environments? When can species be reasonably expected to adapt to change, as opposed to going extinct? By assessing the adaptive nature of phenotypic responses to light, and by quantifying the potential for the further change in plastic traits, this study will make an important contribution to our understanding natural selection in heterogeneous or changing environments.
