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Genetic and phenotypic variation in resource acquisition and allocation: testing a fundamental model for life-history evolution


One of the major goals of research in evolutionary biology is explaining the biological diversity of organismal life histories. One major explanation of this diversity is that limited resources acquired by an organism must be allocated to various life processes, leading to trade-offs between these processes. In this dissertation, I use a model system-the trade-off between flight capability and reproduction in wing dimorphic insects-to investigate variation in the acquisition of resources and its subsequent allocation to competing processes.

I showed that the pattern of allocation varies in response to temperature in the water strider, Aquarius remigis and that this response has the potential to evolve. In addition, I used a quantitative genetic simulation model to show that the optimal allocation strategy depends on the predictability of resource levels across time. Specifically, this model predicts completely different responses of allocation to resource level variation in environments with low versus high predictability of resource levels across time.

Combining physiological assays with a quantitative genetic breeding experiment, I measured genetic and phenotypic variation in acquisition and allocation in and across several different resource environments in the wing dimorphic cricket, Gryllus firmus. I found a significant genetic variance for both acquisition and allocation, but I also found that independent evolution in different resource environments is constrained. I show that when allocation is measured independently of acquisition, there is evidence for the trade-off even when it may be obscured by variance in acquisition when measured only as the correlation between functions.

Using this data set, I also tested the assumptions and predictions of a theoretical model (the Y model) that predicts patterns of variation in trade-offs. An assumption of the Y model, that acquisition and allocation will be independent of one another, was not supported. However, despite this result, I found strong support for the predictions of the Y model in this system, demonstrating the Y model is robust to violations of the assumption of independence. This study is the first to use estimates of acquisition and allocation to directly test the Y model.

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