Drivers and consequences of introgression in evolution

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Background: The importance of introgression, the evolutionary process by which alleles migrate between species via hybrids, was debated for decades. Genome sequencing revealed introgression to be pervasive in eukaryotes. Given its prevalence, we must determine the environmental and genomic factors that regulate its occurrence. Broad, long-term objective: Understanding how species form and persist in nature is a premier goal of evolutionary genetics. Since speciation involves the reduction of introgression between lineages, this question necessitates an understanding of the factors that regulate gene exchange that occurs when species have the chance to interbreed. Our research program on Drosophila hybrid zones has the potential of revealing how species form and what is the importance of introgression in evolution. Questions and approach: As a field, we are aware that introgression is common in nature. The time is ripe to understand what are the factors that determine whether an allele can cross species boundaries and thus serve as raw material for adaptation. The research we are proposing falls into three different categories. First, we will investigate the dynamics of introgressed alleles along space and time in multiple species. We have geolocated and timestamped collections from a hybrid zone which will offer the first evidence of its kind to determine how introgression varies over short periods of time (within 10 years). Second, we will assess whether experimental hybrid populations can inform the composition of naturally occurring hybrid populations. Finally, we will use genetic chimeras to study the phenotypic outcomes of introgressed alleles. My group has expertise in method development to analyze genomic data, genetic analysis of evolutionary processes, and experimental evolution which makes us well-suited to study what factors determine which alleles can cross species boundaries. Relevance to human health: Understanding the source of genetic variation is key to understand how new phenotypes arise. Work from the parent grant demonstrated that introgression is an important source of variation in many organisms, including human pathogens. This renewal proposes comparative approaches to identify introgressed loci in multiple taxa, some of which harbor pathogens or are vector species. Understanding how environmental and human factors influence the exchange of genes for pathogenicity or vector behavior has relevance to human health in a changing climate. Impact: The results from this proposal will generate methods and datasets that will be broadly useful, in addition to helping understand the process of introgression at multiple evolutionary scales. Importantly, the proposed research moves the field from piecemeal assessments of introgression across particular species pairs to a synthetic approach that tries to understand how the process interacts with the environment and whether there are commonalities to across eukaryotes.