On the role of hybridisation in evolution - the case of Eurasian Passer sparrows

In this project the focus has been on hybridisation and its role in evolution, using Passer sparrow species as model system. The last year of the project our main focus has been to investigate the potential role of hybridisation in facilitating adaptation. When species hybridise one result is that genetic variation is generated through the admixture of differentiated genomes. This may facilitate adaptation because selection will have more genetic variation to act upon. On the other hand hybridisation involves recombination of divergent genomes and many gene combinations derived from two different species are likely to function poorly and be selected against, thus constraining adaptive evolution. We have tested these hypotheses in populations f the Italian sparrow, a species that originated through hybridization between the house and Spanish sparrow. We do find evidence for local adaptations to local climate and in genes affecting beak morphology. However, the genes that have responded to selection are not differentiated between the parent species. Hence, we find no evidence that hybridisation has facilitated adaptive evolution.

Post doc ansatt på prosjektet, Mark Ravinet har nå fått fast vitenskapelig stilling Ved University of Nottingham. Resultater oppnådd i løpet hans tilknytning til prosjektet har vært sterkt medvirkende til dette. Prosjektet har resultert i internasjonalt forskningssamarbeid som vil bli videreført i fremtidige prosjekter.

We propose to address three urgent challenges in evolutionary biology: 1) How does hybridization affect genome evolution? 2) How does reproductive isolation evolve between a homoploid hybrid lineage and the parental populations? 3) What are the consequences of hybridization for adaptation and diversification? Using Passer sparrow species as the model system and a unique combination of state-of-the-art technology in genomics and morphometrics, we will address the first challenge by reconstructing the evolutionary history of genome evolution in a homoploid hybrid speciation event. We will investigate whether hybridization occurred independently in different locations and if so, whether recombination and selection have fused the parental genomes in similar or differing ways. This can reveal to what extent genome evolution following hybridization depends on historic contingency, or on deterministic and predictable evolution. The second challenge will be addressed by investigating how reproductive isolation has evolved between the hybrid species and its parents. Using cline analysis of candidate genetic incompatibilities we will investigate to what extent the reproductive barriers that isolate the hybrid species differ from those that isolate the parents. This can reveal to what extent transgression in phenotype and/or genome organization is a prerequisite for the development of reproductive isolation in the face of gene flow. The third challenge will be addressed by investigating how hybrid speciation alters the response to selection at the genomic and phenotypic level and to what extent the historic course of genome stabilization can lead to the development of genetic incompatibilities between populations within the hybrid species. In short, the proposed project will result in novel understanding on the modularity of the genome, on the processes of adaptation and speciation and on the question of how biodiversity is organized.