Browsing by Subject "maternal effects"
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Item Open Access Behavior Genetics and Post Genomics(Behavioral and Brain Sciences, 2012-12) Charney, EThe science of genetics is undergoing a paradigm shift. Recent discoveries, including the activity of retrotransposons, the extent of copy number variations, somatic and chromosomal mosaicism, and the nature of the epigenome as a regulator of DNA expressivity, are challenging a series of dogmas concerning the nature of the genome and the relationship between genotype and phenotype. DNA, once held to be the unchanging template of heredity, now appears subject to a good deal of environmental change; considered to be identical in all cells and tissues of the body, there is growing evidence that somatic mosaicism is the normal human condition; and treated as the sole biological agent of heritability, we now know that the epigenome, which regulates gene expressivity, can be inherited via the germline. These developments are particularly significant for behavior genetics for at least three reasons: First, these phenomena appear to be particularly prevalent in the human brain, and likely are involved in much of human behavior; second, they have important implications for the validity of heritability and gene association studies, the methodologies that largely define the discipline of behavior genetics; and third, they appear to play a critical role in development during the perinatal period, and in enabling phenotypic plasticity in offspring in particular. I examine one of the central claims to emerge from the use of heritability studies in the behavioral sciences, the principle of “minimal shared maternal effects,” in light of the growing awareness that the maternal perinatal environment is a critical venue for the exercise of adaptive phenotypic plasticity. This consideration has important implications for both developmental and evolutionary biologyItem Open Access The Influence of Genetic and Environmental Factors on the Phenology and Life-Cycle Expression of Arabidopsis thaliana(2015) Burghardt, Liana TThis dissertation examines the processes that generate phenotypic variation in life cycles in seasonal environments. Collectively, a life cycle describes the stages an organism passes through during a generation. The timing, or phenology, of these transitions is often influenced by both environmental and allelic variation. Using the model organism Arabidopsis thaliana and both empirical and modeling approaches, I examine how correlations between life-cycle transitions, environment-dependent allelic effects, and epistasis generate patterns of life-cycle variation both within and between generations. In my first chapter, I use experiments to determine that many combinations of genetic, environmental, and developmental factors can create similar germination phenotypes, that maternal effects can influence phenotypes more than genetic differences, and that cross-generational effects can reduce variation in germination timing despite variation in flowering and dispersal time. In my second chapter, I use a modeling approach to consider the entire life cycle. I find that environmental variation is a major driver of phenotypic variation, and that considering the known geographic distribution of allelic variation across the range improves the match of model predictions to phenotypes expressed in natural populations. Specifically, variation in dormancy generated in the previous generation is predicted to cause life-cycle differences within a location, and the geographic distribution of allelic variation in dormancy interacts with local climatic environments to canalize an annual life history across the range. Finally, I test if allelic and environmental variation that affects early life stages can influence the environment experienced during reproduction. This environment determines both the time available for reproduction and the environment experienced during senescence. By implementing simple survival rules for flowering plants in the model, I show that time available for a plant to reproduce depends on earlier phenological traits and varies widely from year to year, location to location, and genotype to genotype. If reproductive trade-offs that underlie the evolution of senescence are environmentally sensitive, these results suggest that genetic variation in earlier life-stage transitions might shape senescence rates and whether they are environmentally responsive. In sum, my dissertation demonstrates the importance of pleiotropy, environment-dependent allelic expression, and epistasis in defining life-cycle variation, and proposes a novel way of predicting these relationships and complex life cycles under seasonal conditions.
Item Open Access Within- and trans-generational plasticity: seed germination responses to light quantity and quality.(AoB PLANTS, 2018-06) Vayda, Katherine; Donohue, Kathleen; Auge, Gabriela AlejandraPlants respond not only to the environment in which they find themselves, but also to that of their parents. The combination of within- and trans-generational phenotypic plasticity regulates plant development. Plants use light as source of energy and also as a cue of competitive conditions, since the quality of light (ratio of red to far-red light, R:FR) indicates the presence of neighbouring plants. Light regulates many aspects of plant development, including seed germination. To understand how seeds integrate environmental cues experienced at different times, we quantified germination responses to changes in light quantity (irradiance) and quality (R:FR) experienced during seed maturation and seed imbibition in Arabidopsis thaliana genotypes that differ in their innate dormancy levels and after treatments that break or reinduce dormancy. In two of the genotypes tested, reduced irradiance as well as reduced R:FR during seed maturation induced higher germination; thus, the responses to light quantity and R:FR reinforced each other. In contrast, in a third genotype, reduced irradiance during seed maturation induced progeny germination, but response to reduced R:FR was in the opposite direction, leading to a very weak or no overall effect of a simulated canopy experienced by the mother plant. During seed imbibition, reduced irradiance and reduced R:FR caused lower germination in all genotypes. Therefore, responses to light experienced at different times (maturation vs. imbibition) can have opposite effects. In summary, seeds responded both to light resources (irradiance) and to cues of competition (R:FR), and trans-generational plasticity to light frequently opposed and was stronger than within-generation plasticity.