Geography and Genetics of Ecological Speciation in Pea Aphids

During ecological speciation, divergent natural selection drives evolution of ecological specialization and genetic differentiation of populations on alternate environments. Populations diverging onto the same alternate environments may be geographically widespread, so that divergence may occur at an array of locations simultaneously. Spatial variation in the process of divergence may produce a pattern of differences in divergence among locations called the Geographic Mosaic of Divergence. Diverging populations may vary in their degree of genetic differentiation and ecological specialization among locations. My dissertation examines the pattern and evolutionary processes of divergence in pea aphids (Acyrthosiphon pisum) on alfalfa (Medicago sativa) and clover (Trifolium pretense). In Chapter One, I examined differences among North American aphid populations in genetic differentiation at nuclear, sequence-based markers and in ecological specialization, measured as aphid fecundity on each host plant. In the East, aphids showed high host-plant associated ecological specialization and high genetic differentiation. In the West, aphids from clover were genetically indistinguishable from aphids on alfalfa, and aphids from clover were less specialized. Thus, the pattern of divergence differed among locations, suggesting a Geographic Mosaic of Divergence. In Chapter Two, I examined genomic heterogeneity in divergence in aphids on alfalfa and clover across North America using amplified fragment length polymorphisms (AFLPs). The degree of genetic differentiation varied greatly among markers, suggesting that divergent natural selection drives aphid divergence in all geographic locations. Three of the same genetic markers were identified as evolving under divergent selection in the eastern and western regions, and additional divergent markers were identified in the East. In Chapter Three, I investigated population structure of aphids in North America, France, and Sweden using AFLPs. Aphids on the same host plant were genetically similar across many parts of their range, so the evolution of host plant specialization does not appear to have occurred independently in every location. While aphids on alfalfa and clover were genetically differentiated in most locations, aphids from alfalfa and clover were genetically similar in both western North America and Sweden. High gene flow from alfalfa onto clover may constrain divergence in these locations.

The Literature of Disaffection: Political Dysphoria and British Modernism after 1930

This dissertation argues that “disaffection” is an overlooked but foundational posture of mid-twentieth-century British and Anglophone literature. Previously misdiagnosed as quietism or apathy, disaffection instead describes how many late modernist writers mediated between their ideological misgivings and the pressure to respond to dire political crises, from the Second World War to the creation of new postcolonial nations. Stylists of disaffection—such as Henry Green, Virginia Woolf, Elizabeth Bowen, and V. S. Naipaul—grappled with how limiting cultural assumptions, for instance, about class and nation, seemed to inhere in particular aesthetic techniques like stream of consciousness or realism. Disaffected literature appeals to but then disrupts a given technique’s projection of these assumptions and the social totality that they imagine. This literary “bait-and-switch” creates a feeling of dysphoria whereby readers experience a text unnervingly different from what they had been led to expect. Recognizing the formative work of literary disaffection in late modernism offers an original way to conceptualize the transition between modernist and postmodernist literature in the twentieth century.

Characterization and analysis of the exogenous application of selected phytohormones on C. reinhardtii metabolism

Gemstone Team Genes to Fuels