Browsing by Subject "Coevolution"
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Item Characterizing the Roles of Coevolution and Convergence in the Evolution of Venom Resistance in Mammals(2019-08) Drabeck, DanielleThough the study of coevolutionary relationships has been a focus of evolutionary biology, demonstrating true reciprocity at the molecular and functional level in a natural system has remained elusive. Convergent evolution, though a seemingly disjunct phenomenon, has been found to be a fundamental aspect of coevolution particularly in species-rich interactions. While theoretical frameworks have shown that these two processes are intertwined, few empirical examples exist which demonstrate how these processes correlate in a natural system, and none have demonstrated the mode of both molecular and functional evolution in a coevolving trait. In this work I comprehensively review venom resistance as a trait ideal for understanding the biophysical and evolutionary dynamics of coevolution. Subsequently, I use this framework to examine the roles of molecular and biophysical convergence in two such systems hypothesized to be coevolving. Finally, I develop an experimental system which explicitly maps the biophysical and molecular evolution of a trait via direct testing of ancestral phenotypes, to begin to unveil the true mode of evolution as well as the roll of convergent evolution in a trait hypothesized to be coevolving.Item Global biogeography and local adaptation of Streptomyces(2013-10) Schlatter, Daniel CameronStreptomyces play crucial roles in key ecosystem processes including nutrient and plant disease suppression in natural and agricultural systems. Moreover, Streptomyces are major producers of clinically relevant antibiotic compounds. Despite the importance of Streptomyces in natural, agricultural, and clinical settings, we have a limited understanding of Streptomyces ecology and evolutionary biology in natural habitats. Here we characterize the function diversity and biogeography of Streptomyces to shed light on the roles of local adaptation and coevolution in structuring soil Streptomyces communities. Specifically, this work focuses on patterns of antibiotic inhibition, antibiotic resistance, resource use, and phylogeny among sympatric and allopatric Streptomyces communities from across the globe. This work documents the extensive functional diversity of Streptomyces antibiotic inhibitory, resistance, and resource use phenotypes and provides strong evidence that local adaptation, coevolution, and resource competition are crucial drivers of antibiotic inhibition and resistance among Streptomyces.Item The multi-trophic context of plant defense: ecological and evolutionary implications of variation in milkweeds(2014-08) Mohl, Emily KatherinePlants exhibit great diversity in defense-related traits, such as toxins and spines. Most explanations for this variation assume that such traits are costly because they require resources to produce and maintain; however, controlled experiments frequently fail to document costs of plant defenses. One explanation for this pattern is that ecological context matters. I develop the hypothesis that certain plant traits impose ecological costs in a multi-trophic context because they disrupt predation on herbivores. Because milkweed plants are toxic and harbor specialist herbivores that sequester the toxins to defend themselves against generalist predators, I expect plants to incur ecological costs of defense in this system. I investigate the impact of variation among milkweed species on the ecology and evolution of predators that consume herbivores, testing for costs of defense in a multi-trophic context. I show that plants can strongly impact the preference and performance of some predators and generate patterns consistent with ecological costs of defense. However, I also demonstrate that other traits and processes, such as plant tolerance of herbivory and predator tolerance of plant-derived defense, may have the potential to mitigate such ecological costs. Consequently, ecological costs of defense are unlikely to be fixed but are instead subject to coevolutionary dynamics. As introductions, extinctions, and range shifts change the pool of potentially interacting species, a more predictive understanding of the way individual traits affect, and are affected by, the community context in which they occur will improve our ability to prioritize and manage human impacts on these systems.Item The Nature of Defense: Coevolutionary studies, ecological interaction, and the evolution of 'natural insecticides,' 1959-1983(2009-11) Mason Dentinger, Rachel NatalieThe field of "coevolutionary studies" became a vigorous domain of discovery in the 1960s, and its practitioners were direct inheritors of the modern evolutionary synthesis of the 1940s. They were also direct inheritors of a natural environment that seemed increasingly on the decline, thanks primarily to the destructive actions of humans. Thus, in my account, knowing--the pursuit of knowledge about the natural world--is inextricably interwoven with doing--the practical business of interacting with and altering the natural world, for better or worse. In the case of coevolutionary studies, the act of changing nature through technological intervention with chemical insecticides profoundly changed the way that biologists understood the natural world and the way that humans understood our own place in the natural world. In building this argument, I draw from the work of a variety of science studies scholars, especially environmental historians and historians of science who have examined the boundary between nature and technology, and so-called "basic" and "applied" sciences. I find that the values of control and intervention that are implicit in the applied sciences can have a direct, substantive effect on shaping the direction and form that basic science assumes. As a result, coevolutionary theory was, to a large extent, predicated on the role of humans as participants--interactors--in the very natural systems that coevolutionists strove to understand. To understand this dynamic, I analyze how methods, metaphors, and materials derived from the applied sciences of economic entomology and agronomy formed a foundation for coevolutionary studies. It is no coincidence that most of the scientists in this narrative were disciplinarily rooted in entomology or insect physiology, two fields where potent toxins aimed at destroying insects were of significant importance. These insect scientists were intimately familiar with the methods, metaphors, and materials used to intervene technologically in the operation of nature. Moreover, the model of chemical activity, of the causal agency of potent molecular tools, which dominated both insect physiology and economic entomology, shaped the model of biochemical interaction that drove early coevolutionary studies.Item Nutrient competition and coevolutionary antagonistic interactions between Fusarium and Streptomyces in soil(2016-10) ESSARIOUI, AdilPlant impacts on nutrient use profiles among rhizosphere microbes are poorly understood. We examined the effects of plant host and plant species richness on nutrient use profiles of Streptomyces isolated from the rhizosphere of the prairie plants Andropogon gerardii (Ag) and Lespedeza capitata (Lc) growing in communities of 1 (monoculture) or 16 (polyculture) plant species. Growth on 95 carbon sources was assessed over time. Mean niche width and mean growth were significantly greater for isolates from polyculture vs. monoculture plots, and for Streptomyces from Lc vs. Ag. Isolates from high-carbon (polyculture) or high-nitrogen (Lc) soils had larger niche widths than isolates from low-C (monocultures) or low-N (Ag) soils. Isolates from polycultures were significantly more niche (nutrient) differentiated than isolates from monocultures. We also characterized antagonistic phenotypes and nutrient use among sympatric Streptomyces and Fusarium. Streptomyces from monocultures were more antagonistic against sympatric Fusarium populations than isolates from polycultures. In contrast, Fusarium isolates from polycultures were more inhibitory against sympatric Streptomyces than isolates from monocultures. Fusarium isolates from monocultures had greater niche overlap with Streptomyces than those from polycultures, suggesting greater potential for Fusarium to compete with Streptomyces in monoculture plant communities. In contrast, Streptomyces from polycultures had greater niche overlap with sympatric Fusarium than those from monocultures, suggesting that Fusarium experience greater competition from Streptomyces in polyculture than monoculture. These patterns are consistent with selection for Fusarium-antagonistic Streptomyces populations in the presence of strong Fusarium competition in monocultures, and selection for Streptomyces-inhibitory Fusarium populations in the presence of Streptomyces resource competition in polycultures. Finally, we found evidence for local adaptation between Fusarium and Streptomyces populations as evidenced by the presence of significantly greater inhibition among sympatric than allopatric populations in prairie soil. Additionally, for both taxa, there was a significant positive correlation between the strength of inhibition against each taxon and the intensity of resource competition from that taxon, supporting the hypothesis that antibiotics act as weapons in soil communities. Collectively, these results suggest that coevolutionary antagonistic interactions between Fusarium and Streptomyces in soil are driven by resource competition.Item Resource hoarding facilitates cheating in the legume-rhizobia symbiosis and bet-hedging in the soil.(2010-06) Ratcliff, William C.The carbon that rhizobia in root nodules receive from their host powers both reproduction and the synthesis of the storage polyester poly3-hydroxybutyrate (PHB), as well as N2 fixation, which mainly benefits the host. Rhizobia escaping nodules can use stored PHB to survive starvation and reproduce up to 3-fold, but PHB synthesis is energetically expensive and trades-off with N2 fixation. As a result, PHB synthesis is a central mechanism in the evolution of conflict between rhizobia and legumes, and should be included in estimates of rhizobial fitness. Some rhizobia have evolved sophisticated mechanisms to increase PHB accumulation, such as the production of rhizobitoxine, a chemical inhibitor of legume ethylene synthesis. Rhizobitoxine reduces host growth, decreasing rhizobia per nodule for all strains on a plant, but substantially increases PHB accumulation for rhizobitoxine-producing rhizobia. In addition to enhancing reproduction, PHB has a role in bet-hedging: when starved, free-living high-PHB rhizobia divide asymmetrically, forming dormant, high-PHB „persisters‟ that survive long-term starvation and antibiotic treatment, and low-PHB „growers‟ that are sensitive to these stresses. Sinorhizobium meliloti integrates bet hedging and phenotypic plasticity, forming fewer high-PHB persister cells when low competitor density predicts shorter-term starvation. Declining populations may select for delayed reproduction when there is a trade-off between reproduction and longevity, as there is with starving S. meliloti.