Rapid parallel adaptation despite gene flow in silent crickets

Gene flow is predicted to impede parallel adaptation via de novo mutation, because it can introduce pre-existing adaptive alleles from population to population. We test this using Hawaiian crickets (Teleogryllus oceanicus) in which 'flatwing' males that lack sound-producing wing structures recently arose and spread under selection from an acoustically-orienting parasitoid. Morphometric and genetic comparisons identify distinct flatwing phenotypes in populations on three islands, localized to different loci. Nevertheless, we detect strong, recent and ongoing gene flow among the populations. Using genome scans and gene expression analysis we find that parallel evolution of flatwing on different islands is associated with shared genomic hotspots of adaptation that contain the gene doublesex, but the form of selection differs among islands and corresponds to known flatwing demographics in the wild. We thus show how parallel adaptation can occur on contemporary timescales despite gene flow, indicating that it could be less constrained than previously appreciated. Gene flow is classically thought to impede local adaptation via parallel evolution. However, a genomic study on Hawaiian crickets from different island populations finds evidence of parallel adaptation to the same lethal parasitoid in spite of strong ongoing gene flow.

Automated summary

This study on Hawaiian crickets shows evidence of parallel adaptation to the same lethal parasitoid in different island populations, despite strong ongoing gene flow that was traditionally thought to impede local adaptation via parallel evolution.