The interplay between natural selection and migration is predicted to shape the architecture of adaptation in different ways, depending on whether the direction of selection is spatially homogenous or heterogeneous. When different populations experience selection towards a similar phenotypic optimum, there is no tension with migration and "global adaptation" proceeds in manner similar to that predicted for a single population. By contrast, when populations are selected towards different optima, "local adaptation" occurs, which tends to favour architectures driven by fewer, larger, and more tightly clustered alleles than global adaptation. Despite this clear theoretical prediction, there have been few, if any, comprehensive tests in natural populations. Here, we bring together genome sequence data from thousands of individuals from 25 species of plants to compare signatures of repeated selective sweeps (global adaptation) with those of genotype-environment association (local adaptation)...
Using replicate populations evolved under the same environmental conditions, experimental evolution provides the unique opportunity to study polygenic adaptation. I will discuss how genetic redundancy, pleiotropy, epistasis and linkage disequilibrium influence the selection response of polygenic traits.
For over a century, most biologists have been convinced that all aspects of biodiversity have been driven entirely by natural selection, with stochastic forces and mutation bias playing a minimal role. However, this is not the case at the molecular and cellular levels, where diverse traits scale with cell/organism size in ways that cannot be explained by optimization and/or speed vs. efficiency arguments. These include aspects of gene/genome architecture, intracellular error rates, the multimeric nature of proteins, swimming efficiencies, and maximum growth rates.
Although natural selection may be the most powerful force in the biological world, it is not all powerful, and the power of random genetic drift ultimately dictates what selection can and cannot accomplish. Many prokaryotes may reside in population-genetic environments where the limits to selection are indeed dictated only by the constraints of cell biology. However, in the eukaryotic domain, larger organism size is typica...
