Charlotte Ngo MSc Student, Yakimowski Lab Investigating the evolutionary origin(s) of EPSPS copy number variation in Amaranthus palmeri Agricultural use of herbicides has led to the repeated evolution of herbicide resistance in numerous agricultural weeds, posing significant challenges for food production and agriculture sustainability worldwide. The development of herbicide resistance over contemporary timescales has provided us with a unique opportunity to investigate the origins of this adaptation - has herbicide resistance arisen from de novo mutations or from standing genetic variation? Amaranthus palmeri (A. palmeri), a major agricultural weed originating from southwestern United States and Mexico, has been expanding northward, recently was detected in Canada. Many A. palmeri populations exhibit resistance to glyphosate, a common herbicide, primarily through EPSPS gene copy number variation. Yet it remains unclear whether such variation predated the commercialization of glyphosate in 1974. This project aims to answer an important evolutionary question concerning glyphosate resistance in A. palmeri - did the copy number variation of EPSPS exist as standing genetic variation, or did it evolve rapidly in response to glyphosate selection pressure? To investigate the origins of glyphosate resistance, I collected historic samples from the United States and Mexico from herbaria across the United States, spanning three different time periods (pre-1974, between 1974 and 1995, and post-1995), representing a broad geographic distribution. I extracted leaf tissue samples using a modified CTAB protocol, followed by quantification of EPSPS gene copy number using digital drop PCR (ddPCR). The project unveiled intriguing evolutionary patterns that can be explored further through genomic analyses of whole genomes. Given the expanding range of A. palmeri across North America, understanding the evolutionary mechanisms of herbicide resistance is imperative for unraveling the spread of not only A. palmeri but also other weed species. Moreover, the utilization of historical samples in this research serves as an exemplar for studying rapid adaptation to human-induced environmental changes.
Mia Akbar MSc Student, Colautti Lab Examining phenological trade-offs under biotic and abiotic selection in Lythrum salicaria Studies measuring phenotypic selection on day of first flower or “flowering time” in natural populations commonly observe directional selection for early flowering. Paradoxically, phenological responses to climate change are highly variable and do not demonstrate a unilateral shift to earlier flowering time. The timing of flowering is only one part of the overall “flowering schedule” and may trade-off with other adaptive aspects such as duration and peak flowering time, offering one potential resolution to this apparent contradiction. Furthermore, variation in growing conditions across years may maintain variation in the flowering time phenotype and offer an additional explanation for the lack of evolution in response to selection for earlier flowering. Focusing on the North American invasive plant Lythrum salicaria, I use common garden experiments to investigate whether flowering time correlates with other characteristics of the flowering schedule, how variation in annual growing conditions and insect herbivory have the potential to alter the strength of selection on flowering time and whether these relationships differ by latitude of origin. I discovered that detailed metrics of the flowering schedule vary along a latitudinal gradient and that responses to insect herbivory were highly variable across years of the experiment, demonstrating two potential mechanisms that contribute to the “paradox of evolutionary stasis” in the flowering time trait.
Dr. Steven Brady Professor, Southern Connecticut State University Boulevard of broken frogs: The perils of polluted ponds and life beside the road Human impacts on wild populations are numerous and extensive, degrading habitats and causing population declines across taxa. Residing perhaps in the shadows of climate change, roads and their many contaminants remain a widespread but often overlooked threat to biota, fragmenting landscapes and delivering suites of pollutants to adjacent habitats. In the snowbelt region of North America, deicing salts – used to melt snow and ice on roads and other impervious surfaces – is causing the salinization of many freshwater habitats. There, these added salts join a bevy of other runoff pollutants that threaten environmental health. Simultaneously, roads and their pollutants can act as agents of natural selection. Increasingly, it is becoming clear that road salt and other pollutants are driving population divergence across contemporary timescales. However, the capacity for local populations to adapt to these stressors remains unclear. Here, we consider the effects of road adjacency and road salt exposure on a pair of amphibian species, the spotted salamander (Ambystoma maculatum) and the wood frog (Rana sylvatica), which are found throughout much of North America. At the population level, these two species of spring-breeding amphibians exhibit contrasting responses to polluted roadside ponds. Spotted salamanders show evidence for local adaptation to roadside habitats. Wood frogs present a complex suite of maladaptive traits expressed during aquatic life stages but adaptive traits in terrestrial life stages. For instance, embryonic survival is relatively low for roadside populations yet adults from these populations have increased fecundity and locomotion. Further, recent evidence suggests that temperature has an exacerbating effect on salt toxicity, especially for roadside populations, and that a pair of genes might underlie the differential sensitivity found between populations. Together, this work indicates that exposure to pollution can have complex transgenerational effects, both adaptive and maladaptive, and that life history tradeoffs and potentially negative pleiotropy might mediate these outcomes.
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