Does the evolutionary history facilitate or constrain adaptation and response to changing climates of rear-edge populations?
Characterizing the evolutionary factors affecting adaptation and response to environmental change in range-edge populations is crucial to understand how species’ distributions are shaped, and to predict how these will be altered by climate change. This is most relevant at the rear edge as it often coincides with the warmer range limits. However, the evolutionary factors at play at the rear edge and their effect on adaptive potential remains understudied. These populations often persist from former glacial refugia and thus exhibit high genetic diversity and differentiation. Alternatively, at the rear edge genetic diversity may be constrained by strong genetic drift due to a history of demographic decline and isolation in marginal habitats. Finally, gene flow from core to edge may result in maladaptive variants. This complex evolutionary history is expected to result in a mosaic of adaptive potential at the rear edge.
In this research project, I assess these theories at the rear edge of the North American bellflower Campanula americana. Based on new RADseq SNP datasets and species distribution models, I will infer patterns of genetic diversity, differentiation, demography, migration, and ecological marginality at the rear edge in an integrative framework. I will then perform a large-scale common garden experiment to assess how evolutionary history affects the adaptive potential of rear-edge populations. I expect that in some rear-edge populations, high genetic variation and differentiation result in strong and unique adaptations to warming climates, while other populations experiencing demographic decline, isolation, or maladaptive gene flow will have reduced adaptive potential. Overall, this project will demonstrate the power of integrating evolutionary history for predicting adaptive potential
Characterizing the evolutionary factors affecting adaptation and response to environmental change in range-edge populations is crucial to understand how species’ distributions are shaped, and to predict how these will be altered by climate change. This is most relevant at the rear edge as it often coincides with the warmer range limits. However, the evolutionary factors at play at the rear edge and their effect on adaptive potential remains understudied. These populations often persist from former glacial refugia and thus exhibit high genetic diversity and differentiation. Alternatively, at the rear edge genetic diversity may be constrained by strong genetic drift due to a history of demographic decline and isolation in marginal habitats. Finally, gene flow from core to edge may result in maladaptive variants. This complex evolutionary history is expected to result in a mosaic of adaptive potential at the rear edge.
In this research project, I assess these theories at the rear edge of the North American bellflower Campanula americana. Based on new RADseq SNP datasets and species distribution models, I will infer patterns of genetic diversity, differentiation, demography, migration, and ecological marginality at the rear edge in an integrative framework. I will then perform a large-scale common garden experiment to assess how evolutionary history affects the adaptive potential of rear-edge populations. I expect that in some rear-edge populations, high genetic variation and differentiation result in strong and unique adaptations to warming climates, while other populations experiencing demographic decline, isolation, or maladaptive gene flow will have reduced adaptive potential. Overall, this project will demonstrate the power of integrating evolutionary history for predicting adaptive potential
Schematic depiction of a species distribution and its rear edge
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Campanula americana is an ideal model to study complex evolutionary processes at the rear edge. (A) C. americana occurs across the eastern US, with populations in an Appalachian clade or a larger Western clade. The rear edge of this species is large (lower third of the latitudinal distribution in each clade) and includes the earliest diverging populations of each clade, some of which may have persisted over several glaciation cycles. Some Western rear-edge populations occur in former glacial refugia, as well as marginal and unsuitable habitats. They also occur in distinctly warmer habitats than the rest of the range (B), and include distinct biogeographic regions (C), suggesting a rich evolutionary history.
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Do reproductive cues and phenology adapt to vernalization gradients?
Vernalization – the exposure to cold temperatures in winter – is a common cue to initiate and time reproduction in temperate plants. Species occupying wide climatic gradients, such as Campanula americana, can experience dramatic differences in winter conditions, raising the question of whether differentiation in vernalization cues may serve as an adaptation to these large gradients. I assessed this question in Campanula americana, which occurs over a large latitudinal gradient (~30°N to 45°N) and relies on vernalization to initiate reproduction. I am using a combination of citizen science data, climatic data, greenhouse experiments and transplant experiments to characterize variation in reproductive phenology and vernalization requirements across latitudes.
Vernalization – the exposure to cold temperatures in winter – is a common cue to initiate and time reproduction in temperate plants. Species occupying wide climatic gradients, such as Campanula americana, can experience dramatic differences in winter conditions, raising the question of whether differentiation in vernalization cues may serve as an adaptation to these large gradients. I assessed this question in Campanula americana, which occurs over a large latitudinal gradient (~30°N to 45°N) and relies on vernalization to initiate reproduction. I am using a combination of citizen science data, climatic data, greenhouse experiments and transplant experiments to characterize variation in reproductive phenology and vernalization requirements across latitudes.