Final Report Summary - NATHISGEN (Species formation from beginning to end: integrative tests of competing hypotheses for the origins of diversity)
The formation of new species (i.e. speciation) can involve a transition from population differentiation at just a few genetic loci to genome-wide differentiation. However, only limited data exist concerning this transition and the factors promoting it. This ERC project studied phases of speciation and genomic differentiation using data from >100 populations of 11 species of Timema stick insects. It used a combination of observational and experimental approaches. Consistent with early phases of genic speciation, adaptive colour-pattern loci were found to reside in localised genetic regions of accentuated differentiation between populations experiencing gene flow. Transitions to genome-wide differentiation are also observed with gene flow, in association with differentiation in polygenic chemical traits affecting mate choice and natural selection acting on many genetic regions. The results support that intermediate phases of speciation are associated with genome-wide differentiation and mate choice, but not growth of a few genomic islands or ‘hotspots’ of adaptation. The core conclusion of the project is that even when speciation involves natural selection, substantial progress towards the formation of new species may require the alignment of multi-faceted aspects of adaptive differentiation.