Contact zone dynamics and the evolution of reproductive isolation in a North American treefrog, the spring peeper (Pseudacris crucifer)

Despite over seven decades of speciation research and 25 years of phylogeographic studies, a comprehensive understanding of mechanisms that generate biological species remains elusive. In temperate zones, the pervasiveness of range fragmentation and subsequent range expansions suggests that secondary contact between diverging lineages may be important in the evolution of species. Thus, such contact zones provide compelling opportunities to investigate evolutionary processes, particularly the roles of geographical isolation in initiating, and indirect selection against hybrids in completing (reinforcement), the evolution of reproductive isolation and speciation. The spring peeper (Pseudacris crucifer) has six well-supported mitochondrial lineages many of which are now in secondary contact. Here I investigate the evolutionary consequences of secondary contact of two such lineages (Eastern and Interior) in Southwestern Ontario using genetic, morphological, acoustical, experimental, and behavioural evidence to show accentuated divergence of the mate recognition system in sympatry. Mitochondrial and microsatellite data distinguish these two lineages but also show ongoing hybridization. Bayesian assignment tests and cline analysis imply asymmetrical introgression of Eastern lineage nuclear markers into Interior populations. Male calls are divergent between Eastern and Interior allopatric populations and show asymmetrical reproductive character displacement in sympatry. Female preference of pure lineage individuals is also exaggerated in sympatry, with hybrids showing intermediate traits and preference. I suggest that these patterns are most consistent with secondary reinforcement. I assessed levels of post-zygotic isolation between the Eastern and Interior lineages using a laboratory hybridization experiment. Hybrid tadpoles showed equal to or greater fitness than their pure lineage counterparts, but this may be countered through competition. More deformities and developmental anomalies in hybrid tadpoles further suggest post-zygotic isolation. Despite evidence for pre-mating isolation between the two lineages, isolation appears incomplete (i.e. hybridization is ongoing). I hypothesize that potentially less attractive hybrids may circumvent female choice by adopting satellite behaviour. Although mating tactics are related to body size, genetic status may play a role. I show that pure Eastern males almost always engage in calling, while hybrids adopt a satellite tactic. An absence of assortative mating, despite evidence of female preference, suggests successful satellite interception possibly facilitating introgression.

From Where Do We Teach? Potential Positions in Public Education

This thesis is a conceptual examination of the positions from which we teach in public education. As it is philosophical in nature, it takes no qualitative or quantitative data. It offers a review of selected relevant literature and an analysis of personal and professional experience, with the intent to pose critical questions about teaching and learning. The framework of this thesis represents the following contentions: First, from its inception, public schooling served capital by preparing skilled labour for emerging industrial markets. This history is the hegemonic shadow that hangs over public education today. Second, movements toward the standardization of funding, curriculum, and evaluation support the further commodification of public schooling. The “accountability” that standardization offers, the “back to basics” that it aims for, is counter to the potential that public education might critically inform citizens and seek social justice. Third, movements toward the privatization of public schooling under the guise of “choice” and “mobility”, brought on by manufactured crisis, serve only to widen socio-economic inequities as capitalist neoliberal interests seek profit in both the product of public schools and in schooling itself. If we recognize and understand the power of public education to inform vast numbers of citizens who will, in turn, either maintain or reform society, we must ask: What do we want public education to be? What are the effects of continuing down historically conventional and increasingly standardized paths? What do progressive pedagogies offer? How might teachers destandardize their pedagogy and pursue equitable opportunities for marginalized students? How might students name themselves and their world, that they might play a part in its reimagining? For whom do we teach, and under what conditions? From where do we teach, and why? For educators to ask these questions, and to employ what they discover, will necessitate taking substantial risks. It will necessitate taking a stand and cannot be done alone. Teachers must seek out the collaboration of their students. They must offer students the time and the space to find their own voices, to create their own selves, and to envision previously uncharted paths on which we might walk together.