The Adaptive Value and Genetic Basis of Maternal Effects in Competitive Environments

Abstract

Plants rely heavily on environmental cues to direct life-history processes. In many species, the maternal environment is a reliable predictor of environmental conditions in the next generation, and several aspects of progeny phenotype are responsive to environmental cues during seed maturation. The ratio of red to far-red light (R:FR) is one environmental cue that has been widely shown to influence plant phenotypes across generations. Low R:FR are predictive of competitive conditions, because chlorophyll in neighboring leaves absorbs red light but allows far-red light to pass through. It has been suggested that effects of the maternal competitive environment on progeny phenotype are adaptive, but very few studies have convincingly tested this hypothesis. In addition, the genetic basis of environmental maternal effects is poorly understood. In this dissertation, I examine the adaptive value and genetic basis of maternal effects in competitive environments in the plant species Brassica rapa and Arabidopsis thaliana. In chapter 1, I investigate the adaptive value of maternal effects across two generations of competitive environments in B. rapa. Maternal environment effects did not enhance progeny fitness but did influence several other progeny traits, as well as selection gradients in the progeny generation. These results suggest that although environmental maternal effects are not adaptive in this study, they are genetically variable and may evolve or affect the evolution of progeny traits. I further investigate the effects of competition on B. rapa fitness traits in chapter 2, in which I use a quantitative trait loci (QTL) mapping approach to examine how the genetic architecture of multiple components of fitness differs across competitive environments. QTL expression varied across competitive treatments for total fruit production, but QTL were generally conserved in other fitness traits. In addition, I identify environment-specific QTL for seed mass and germination timing in seeds matured under a low R:FR. Lastly, in chapter 3, I investigate if and how phytochrome photoreceptor genes mediate the effects of maternal R:FR on progeny germination. My results suggest that all 5 phytochrome genes in A. thaliana partially mediate progeny germination response to maternal R:FR, and I identify novel roles for individual phytochrome loci in this response. As a whole, this research provides insight into the extent that maternal effects in competitive environments are adaptive and partially elucidates the genetic basis of maternal effects.