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(1 - 2 of 2)
- Title
- Ecological effects on the evolution of cooperative behaviors
- Creator
- Connelly, Brian Dale
- Date
- 2012
- Collection
- Electronic Theses & Dissertations
- Description
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Cooperative behaviors abound in nature and can be observed across the spectrum of life, from humans and primates to bacteria and other microorganisms. A deeper understanding of the forces that shape cooperation can offer key insights into how groups of organisms form and co-exist, how life transitioned to multicellularity, and account for the vast diversity present in ecosystems. This knowledge lends itself to a number of applications, such as understanding animal behavior and engineering...
Show moreCooperative behaviors abound in nature and can be observed across the spectrum of life, from humans and primates to bacteria and other microorganisms. A deeper understanding of the forces that shape cooperation can offer key insights into how groups of organisms form and co-exist, how life transitioned to multicellularity, and account for the vast diversity present in ecosystems. This knowledge lends itself to a number of applications, such as understanding animal behavior and engineering cooperative multi-agent systems, and may further help provide a fundamental basis for new industrial and medical treatments targeting communities of cooperating microorganisms.Although these behaviors are common, how evolution selected for and maintained them remains a difficult question for which several theories have been introduced. These theories, such as inclusive fitness and group selection, generally focus on the fitness costs and benefits of the behavior in question, and are often invoked to examine whether a trait with some predetermined costs and benefits could be maintained as an evolutionarily-stable strategy. Populations, however, do not exist and evolve in a vacuum. The environment in which they find themselves can play a critical role in shaping the types of adaptations that organisms accumulate, since one behavior may be highly beneficial in one environment, yet a hindrance in another. Ever-changing environments further complicate this picture, as maintaining a repertoire of behaviors for surviving in different environments is often costly. In addition to these environmental forces, the number and composition of other organisms with which individuals interact impose additional constraints. The combination of these factors results in significantly more complex dynamics.Using computational models and microbial populations, this dissertation examines several ways in which ecological factors can affect the evolution of cooperative behaviors. First, environmental disturbance is examined, in which a cooperative act enables organisms and their surrounding neighbors to survive a periodic kill event (population bottleneck) of varying severity. Resource availability is then studied, where populations must determine how much resource to allocate to cooperation. Finally, the effect that social structure, which define the patterns of interactions among the individuals in a population, is investigated.
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- Title
- The influence of general and inducible hypermutation on adaptation during experimental evolution
- Creator
- Weigand, Michael R.
- Date
- 2011
- Collection
- Electronic Theses & Dissertations
- Description
-
Hypermutator (or mutator) strains of bacteria have been observed in a variety of clinical, environmental, and laboratory populations with up to 1000-fold increases in spontaneous mutation rates. Defects in DNA repair machinery responsible for general hypermutation most commonly include the inactivation of methyl-directed mismatch repair that result in constitutive increases in mutation rate. Alternatively, mutagenic DNA repair only transiently raises mutation rates through the activation of...
Show moreHypermutator (or mutator) strains of bacteria have been observed in a variety of clinical, environmental, and laboratory populations with up to 1000-fold increases in spontaneous mutation rates. Defects in DNA repair machinery responsible for general hypermutation most commonly include the inactivation of methyl-directed mismatch repair that result in constitutive increases in mutation rate. Alternatively, mutagenic DNA repair only transiently raises mutation rates through the activation of low-fidelity polymerases in response to DNA-damaging stress conditions. The widespread existence of both general and inducible mutator genotypes suggests that evolutionary strategies of bacteria include mechanisms for increasing mutability. This work investigates the influence of hypermutation on adaptation through experimental evolution with the contextually relevant model organismsPseudomonas cichorii 302959 andP. aeruginosa PAO1. Following ~500 generations of growth, both model organisms exhibited comparable improvements in fitness, independent of mutator status, suggesting that hypermutation does not impede adaptation through mutation accumulation. Both general and inducible hypermutation facilitated genotypic diversification that was not observed in non-mutator lineages. The mechanistic differences underlying general and inducible hypermutation were reflected in unique spectra of nucleotide substitutions but did not restrict access to parallel adaptive traits despite considerable variation in gene expression profiles. The diversity in colony morphologies and gene expression traits observed in mutator lineages may represent a broad exploration of sequence space that is no doubt a favorable strategy for adaptation.
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