Evolutionary Ecology Of Arabidopsis Thaliana

Author : Mark Alan Taylor
Publisher :
ISBN 13 : 9781085787994
Total Pages : pages
Book Rating : 4.7/5 (879 download)

DOWNLOAD NOW!

Download or read book The Evolutionary Plasticity of Life History in Arabidopsis Thaliana written by Mark Alan Taylor and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: As environments change, organisms must change with them. There are a variety of ways by which organisms can accomplish this change. One is through genetic adaptation in which alleles turnover in time or space to enable a population to track changing fitness optima. Another is through plasticity by which an organism changes its phenotype within a single organism’s lifetime. So where does evolution, plasticity, and evolutionary plasticity start and end? In this dissertation, I explore answers to this question using the genetic model plant Arabidopsis thaliana (Brassicaceae) whose wealth of genomic, breeding, and natural diversity resources enabled a variety of analytical and experimental approaches. Though environments ultimately determine the conditions to which an organism is exposed, short-lived organisms like A. thaliana have developed a remarkable strategy to subvert this paradigm and to themselves determine environmental exposure: life history expression. Unlike animals that can migrate to favorable environments within generations, annual plants are stuck in whatever environment they germinate. However, by timing their germination and subsequent life history to match the most beneficial environmental moment, A. thaliana can construct its own niche. This temporal niche construction occurs as both a genetic adaptation to environmental gradients across its natural Eurasian and colonized ranges as well as plasticity to short-term microenvironmental fluctuations. The life history of A. thaliana is an especially useful and experimentally tractable lens through which to view the interplay of adaptation and plasticity to environmental cues like temperature, which has assumed a special relevance and urgency as climate change accelerates in the Anthropocene. In Chapter One, I track recombinant inbred lines of A. thaliana segregating functional and non-functional alleles of major-effect germination and flowering time loci across multiple generations in the field. This was the first study to contrast early and late seed dormancy and flowering time alleles in natural conditions and to gauge their adaptive value for both fecundity and demographic fitness. We found strongly contrasting fecundity effects of dormancy alleles based on their interaction with flowering time alleles. Strong dormancy increased fecundity in an early-flowering background but decreasing it in a late-flowering background. However, demographic fitness calculated as year-to-year growth rates, was not significantly different among the genotypes. This finding explains the previously paradoxical observation that multiple life histories occur in similar locales since, though fecundity may favor particular life history genotypes, long-term demographic trends enable coexistence. In Chapter Two, I used near isogenic lines (NILs) of A. thaliana with temperature-sensitive and –insensitive alleles in major-effect flowering time alleles to determine how flowering time interacts with temperature and competition to affect fitness. I grew these NILs in two simulated seasonal environments (summer and fall) and under two temperature scenarios (contemporary and warmed) and exposed the plants to increasing intra- and inter-genotypic competition. I measured phenology and fitness, and found that the temperature-insensitive NIL was constitutively early-flowering and less fit than the temperature-sensitive NIL except in the summer future climate. The late-flowering NIL was capable of responding plastically to intragenotypic competition by accelerating flowering (likely as an aspect of shade avoidance) as well as to temperature. This NIL showed seasonal dependence in its plastic response to increased temperature since flowering was accelerated in the summer but delayed in the fall. These results show how plasticity is not necessary a panacea to enable a species to survive rapid climate change since the temperature-canalized NIL was more fit than the plastic NIL in the hottest climate. In Chapter Three, I examine A. thaliana genotypes with loss-of-function (LoF) and gain-of-function (GoF) mutations of flowering time genes in five pathways that control responses to the major environmental drivers of A. thaliana phenology. These mutants were grown in five sites and several seasons across A. thaliana’s European climate range and were measured for a variety of morphometric, phenological, and fitness traits. I constructed adaptive landscapes from total branch number, timing of flowering, and fecundity in order to test how LoF and GoF mutations in these pathways shifted genotypes in both phenotypic and fitness space. I found that mutants were often more fit than their wildtype backgrounds, but that these mutations were only conditionally (not constitutively) adaptive since their benefit was exposed only in certain environments. Also, the mechanisms underlying their increases in fitness sometimes involved modifying branching (i.e. plant morphology) and other times through bolting time (i.e. development/phenology). Furthermore, by leveraging A. thaliana’s well-characterized genomic interactome, I showed that mutations in genes with greater network connectedness caused greater phenotypic and fitness deviations, but again in an environment-dependent manner. This study represents a major advance in our understanding of loss-of-function mutations in a macroscopic macroscopic organism since it is the first to replicate them while controlling for genetic background in a macroscopic organism in multiple environments in nature. My study also helps to explain the persistence of loss-of-function mutations that are often considered to be deleterious in natural populations by showing that some may be adaptive under specific environmental conditions. In these studies, I have shown that multiple life histories can coexist in natural conditions and that fitness metrics can result in complex, contradictory conclusions if considered in isolation. I have also demonstrated that warming temperatures are likely to decrease fitness in seasonally contingent ways, though may also open new phenological niches. Finally, I have shown that mutations can be conditionally adaptive and should be tested in multiple, natural conditions. Together, these findings point to the primacy of contingency in determining ecological and evolutionary outcomes. Contingency in development through genetic and environmental interactions render these outcomes highly unpredictable and thus ripe for further empirical study. Thus, testing life history variation and plasticity in the field will become increasingly relevant and urgent as we strive to predict how plant populations will weather the acceleration of change in the world’s climate and biome.