Evolution of species interactions in adaptive radiation

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My research program investigates the causes of adaptive radiation, defined as the evolution of ecological diversity in a rapidly diversifying lineage. I propose to carry out experiments to test mechanisms of selection on genes and genomes. My main study organism is threespine stickleback fish, a supermodel organism having many experimental advantages and exhibiting rampant parallel evolution, aiding comparative phenotypic and genomic studies. I describe three major projects. 1) Character displacement and reproductive isolation. Evolution of competitive interactions is a hallmark of adaptive radiation. However, there are as yet no experimental tests of whether resource competition drives evolution in a natural system. The contribution of competition to evolution of reproductive isolation (speciation) is even less well understood. Conflicting theories of adaptive radiation differ by whether character displacement is an integral part of speciation or occurs later. We will use a pond evolution experiment with stickleback to test whether competition leads to divergent evolution in the same regions of the genome already known to underlie niche divergence and assortative mating.  2) The evolution of hybrid genomes. Postzygotic reproductive isolation is hypothesized to evolve more slowly than premating isolation and to play a reduced role early in speciation.  We propose three investigations of the role of gene-gene incompatibilities in hybrids of young stickleback species. First, we will use a pond experiment to test the prediction that gene-gene incompatibilities in F2 hybrids should favor increased heterozygosity genome-wide. Second, we will measure the direction of evolution of minor-parent alleles in wild hybrid populations. Third, we will conduct a multigenerational experimental test of the prediction that that gene-gene incompatibilities should favor major-parent alleles in experimental backcross populations introduced to ponds. Gene-gene interactions are predicted to select against minor parent alleles because they experience more potential antagonistic interactions with major parent alleles regardless of which species is the minor parent. In contrast, ecological adaptation should result in parallel evolution of allele frequencies between populations regardless of major and minor parent allele frequencies. 3) Maintenance of standing genetic variation. The leading hypothesis for the maintenance of standing genetic variation in colonizing populations is that allele frequency is a balance between migration and selection. We will test two unique predictions of this hypothesis for maintaining freshwater alleles in marine threespine stickleback. We will use a bank of 1000 stickleback genome sequences to test if freshwater allele copies in marine individuals have a nearby freshwater source. Second, we will test whether freshwater allele copies found in the sea show a genomic signature of having arrived in the sea only relatively recently.