Thesis (M.S.)--Auburn University, 2007. / Abstract. Includes bibliographic references (ℓ. 139-153)

Thesis (M.A.)--Duquesne University, 2003. / Title from document title page. Abstract included in electronic submission form. Includes bibliographical references (p. 85-94).

Magister Scientiae - MSc / This thesis explores species-level phylogenetic relationships of the African cycad genus Encephalartos, which is one of the eleven genera of cycads. The genus is confined to Africa and comprises approximately 65 species, 38 of which are found naturally in South Africa. The phylogenetic studies on Encephalartos to date still result in many unresolved polytomies so it is not possible to fully understand the relationships between different taxa. In this study, AFLPs were used together with DNA sequencing to reconstruct the phylogenetic relationships of the genus. This study is the first to be presented with aims of resolving the relationships of Encephalartos using AFLPs together with DNA sequences. Total DNA was extracted from accessions sampled from the Kirstenbosch Botanical Garden and the Montgomery Collection, representing the majority of Encephalartos species listed in the most recent world list of cycads. Sequences of the trnL intron, rpoC1, ITS 1, ITS 2, and AFLP profiles from two sets of selective primers were used to reconstruct the phylogenetic relationships within the genus using maximum parsimony methods. As in earlier studies, unresolved polytomies were recovered from the sequencing data. The AFLP trees have some resolution but CI and RI indices were low indicating high levels of homoplasy in the data. The relationships resolved by this study for all the data sets separately and combined were different to those previously suggested for the genus. The biogeography of Encephalartos is also investigated by habitat optimization of the genus to estimate the origin of the genus with respect to its current distribution. / South Africa

No description available.

The pattern of geographic variation in tree-climbing ability of Peromyscus maniculatus was used as a natural experiment to examine the interaction of natural selection, genetic drift, and gene flow. The divergence in climbing behavior among lab-reared mice derived from adults trapped in forest, woodland, and desert habitats was compared with a series of adaptive and non-adaptive hypotheses of evolutionary change. Natural selection was predicted to produce better climbers in forests and woodlands than in deserts whereas divergence due to genetic drift was expected to be independent of habitat type. Gene flow between neighboring habitats was predicted to reduce differentiation in climbing traits. Tree-climbing ability was measured by determining the maximum diameter artificial trunk (rod) that a mouse could climb in escaping from a lighted, confined area. Larger diameter rod scores reflect better climbing abilities (Horner 1954). Comparisons of mean rod climbing scores between subspecies and among forest, woodland, and desert habitats reveal that P. m. rufinus, sampled from forest and woodland, is a better climber than P. m. sonoriensis, sampled from woodland and desert habitats. This is consistent with the hypothesis that natural selection has produced subspecies level adaptation in climbing behavior. However, the climbing ability of P. m. sonoriensis sampled from woodland habitats on isolated mountaintops, although slightly divergent from populations in adjacent desert scrub habitats, has not evolved in response to natural selection to the degree expected from the observed subspecies level adaptation. Additionally, populations of unknown subspecific status sampled from desert grassland habitat, adjacent to woodland P. m. rufinus, have climbing abilities that are not significantly different from woodland forms. Thus, evolution in certain populations is constrained. If gene flow from desert populations into woodland mountaintop populations is constraining evolution, then mountaintop populations should have high trait variances. Analysis of the within population variance does not support this hypothesis. Other lines of evidence that indicate gene flow is low or moderate are reviewed. In conclusion, adaptation to local habitats is constrained, perhaps by restrictive genetic correlations and/or lack of sufficient time to respond to natural selection for climbing ability. As a result, long periods of consistent selection are necessary to produce the pattern of subspecific adaptation in climbing behavior. (Abstract shortened with permission of author.)

No description available.

Antibiotic resistance is generally associated with a cost in terms of reduced competitive fitness in the absence of antibiotics. Despite this 'cost of resistance', the cessation of antibiotic treatment does not result in significant reductions in the prevalence of resistance. The maintenance of resistance, in spite of the costs, has been attributed to the rarity of reversion mutations, relative to compensatory mutations at other loci in the genome. However, the large size of bacteria populations, and the potential for migration, suggest that reversion mutations should occasionally be introduced to resistant populations. In this thesis, I show that additional mechanisms can prevent fixation of reversion mutations even if they do occur. Using an experimental evolution approach, with rifampicin resistance in Pseudomonas aeruginosa as a model system, I measured the costs of resistance in several environments and followed the adaptive dynamics of resistant populations where a sensitive lineage had invaded by migration. The results suggest that several additional mechanisms contribute to the maintenance of antibiotic resistance. Most rifampicin resistance mutations are not unconditionally costly in all environments, suggesting that migration between environments could maintain a resistant reservoir population. In environments where resistance is initially costly, the fixation of a revertant is not guaranteed, even if introduced through migration. Revertant fixation was impeded or prevented by clonal interference from adaptation in the resistant strain. Revertants that did successfully replace the resistant strain were forced to adapt to do so. Contrary to assumptions in the existing literature, fitness in the resistant strains was not recovered by general compensatory mutations, but instead by adaptive mutations specific to the environment. The data challenge several assumptions about the maintenance of antibiotic resistance: that resistance mutations are always costly, that the rarity of back mutations prevents the reversion of resistance, and that resistant strains recover fitness by compensatory mutations.

Human languages are not just tools for transmitting cultural ideas, they are themselves culturally transmitted. This single observation has major implications for our understanding of how and why languages around the world are structured the way they are, and also for how scientists should be studying them. Accounting for the origins of what turns out to be such a uniquely human ability is, and should be, a priority for anyone interested in what makes us different from every other lifeform on Earth. The way the scientific community thinks about language has seen considerable changes over the years. In particular, we have witnessed movements away from a purely descriptive science of language, towards a more explanatory framework that is willing to embrace the difficult questions of not just how individual languages are currently structured and used, but also how and why they got to be that way in the first place. Seeing languages as historical entities is, of course, nothing new in linguistics. Seeing languages as complex adaptive systems, undergoing processes of evolution at multiple levels of interaction however, is. Broadly speaking, this thesis explores some of the implications that this perspective on language has, and argues that in addition to furthering our understanding of the processes of biological evolution and the mechanisms of individual learning required specifically for language, we also need to be mindful of the less well-understood cultural processes that mediate between the two. Human communication systems are not just direct expressions of our genes. Neither are they independently acquired by learners anew at every generation. Instead, languages are transmitted culturally from one generation to another, creating an opportunity for a different kind of evolutionary channel to exist. It is a central aim of this thesis to explore some of the adaptive dynamics that such a cultural channel has, and investigate the extent to which certain structural and statistical properties of language can be directly explained as adaptations to the transmission process and the learning biases of speakers. In order to address this aim, this thesis takes an experimental approach. Building on a rich set of empirical results from various computational simulations and mathematical models, it presents a novel methodological framework for exploring one type of cultural transmission mechanism, iterated learning, in the laboratory using human participants. In these experiments, we observe the evolution of artificial languages as they are acquired and then transmitted to new learners. Although there is no communication involved in these studies, and participants are unaware that their learning efforts are being propagated to future learners, we find that many functional features of language emerge naturally from the different constraints imposed upon them during transmission. These constraints can take a variety of forms, both internal and external to the learner. Taken collectively, the data presented here suggest several points: (i) that iterated language learning experiments can provide us with new insights about the emergence and evolution of language; (ii) that language-like structure can emerge as a result of cultural transmission alone; and (iii) that whilst structure in these systems has the appearance of design, and is in some sense ‘created’ by intentional beings, its emergence is in fact wholly the result of non-intentional processes. Put simply, cultural evolution plays a vital role in language. This work extends our framework for understanding it, and offers a new method for investigating it.

La thèse commence par une ébauche sur l'apparition et l'évolution de la farce, en prenant comme exemple la troupe des Deschiens qui s'en est inspirée, et a créé un théâtre typiquement farcesque, décalé et différent / The thesis begin with a study of appearance and evolution of practical joke, it takes as an example the Deschiens troop, who create a kind of theatre typically based on practical joke

No description available.