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Molecular Genetic Analysis of a Barrier to Gene Flow Between Two Ecologically Divergent Populus Species

Gene locus with lower than expected introgression across hybrid zone, showing a negative departure from neutrality

Barriers to gene flow play a central role in many topics of evolutionary genetics. Species barriers between ecologically divergent forest trees are particularly interesting, because the genes conferring ecological character differences are expected to segregate in interspecific hybrids. Hence, hybrid populations offer a powerful tool for the genetic analysis of adaptively important traits – suites of characters that are especially important in the face of global climate change.

Perhaps the biggest impediment to unlocking the potential of interspecific populations lies in the difficulty of generating multi-generation crosses in long-lived forest trees. Natural hybrid zones offer an attractive alternative: the increased genetic variability and admixture linkage disequilibrium (admixture LD) present in hybrid populations can be utilized for genetic association studies. This approach has been remarkably successful for the study of disease-related genes in admixed human populations. The same methodology is applicable to long-lived forest trees, but evaluating its potential requires a study system with a favourable setting, i.e., extensive interspecific gene flow, pronounced interspecific character differences, and good genomic resources. Members of the genus Populus lend themselves to this purpose.

This project aims to identify and characterise recombinant hybrid genotypes in natural hybrid zones between Populus alba and Populus tremula in Europe, to detect genomic regions that introgress more or less frequently than expected under neutrality, and to study associations between these regions and phenotypic characters. The proposed work will yield important insights into the nature of a barrier to gene flow between two ecologically divergent Populus species, and into the potential of admixture LD mapping as a tool for the genetic analysis of adaptively important traits in trees. This three year project is funded by a NERC New Investigator grant and is expected to result in at least three publications in peer-reviewed international journals. Information arising from the project will be disseminated via appropriate established internet databases, e.g. Dendrome server.

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