Understanding genetic variation and adaptation in relation to sexual reproduction

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Some of the most prolific plant and animal species reproduce clonally much of the time, using sexual reproduction only rarely. My group will examine the consequences of evolving with little or no sex as well as investigate the conditions favouring the maintenance of sex, using a combination of theoretical, expermimental, and genomic approaches. The empirical work will use two facultatively sexual systems, duckweeds and monogonont rotifers. We will develop theory to understand how asexuals evolve in fluctuating environments, with special emphasis on temporal autocorrelations in selection. We will test these ideas experimentally using obligately asexual clones of the rotifer Brachionus calyciflorus. In another set of experiments, we will build upon our past work demonstrating that adaptation to environmental change can select for higher rates of sex within facultatively sexual populations. Specifically, we will extend and test theory predicting that population subdivision favours higher rates of sex during adaptation. In addition to well-controlled lab experiments with rotifers, we will examine the causes and consequences of sex in a natural system by studying duckweeds. We have already obtained substantial genomic data from two species (Lemna minor and Spirodela polyrhiza) and this will allow us to make progress rapidly. We will extend statistical methods for inferring rates of sex using sequence data and apply these to our duckweed data. Using existing methods of population genetics inference, we will estimate the efficacy of selection from genomic data in different populations and species and relate these measures to inferred rates of sex, testing the prediction that sex increases the efficacy of selection across the genome. Duckweed will also be used to test theory on the evolutionary maintenance of sex. By experimentally creating clonally-derived genotypes as well as sexually-derived genotypes, we will compare the fitness distributions of genotypes from different reproductive modes. This type of data is key to inferring which of two general population genetic mechanisms favour sex. We will assay fitness under several different field-manipulated environments to assess the importance of ecological agents (e.g., natural enemies) that are typically excluded in lab experiments but critical to some hypotheses. Numerous high quality training opportunities will be provided for undergrads, grads, and PDFs.