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要旨

Adaptive ecotype formation is the first step to speciation, but the genetic underpinnings of this process are poorly understood. While in marine midges of the genus Clunio (Diptera) reproduction generally follows a lunar rhythm, we here characterize two lunar-arrhythmic eco-types. Analysis of 168 genomes reveals a recent establishment of these ecotypes, reflected in massive haplotype sharing between ecotypes, irrespective of whether there is ongoing gene flow or geographic isolation. Genetic analysis and genome screens reveal patterns of polygenic adaptation from standing genetic variation. Ecotype-associated loci prominently include circadian clock genes, as well as genes affecting sensory perception and nervous system development, hinting to a central role of these processes in lunar time-keeping. Our data show that adaptive ecotype formation can occur rapidly, with ongoing gene flow and largely based on a re-assortment of existing and potentially co-adapted alleles.