Speciation can involve a transition from a few genetic loci that are resistant to gene flow to genome-wide differentiation. However, only limited data exist concerning this transition and the factors promoting it. Here, we study phases of speciation using data from >100 populations of 11 species of Timema stick insects. Consistent with early phases of genic speciation, adaptive colour-pattern loci reside in localized 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. Thus, intermediate phases of speciation are associated with genome-wide differentiation and mate choice, but not growth of a few genomic islands. We also find a gap in genomic differentiation between sympatric taxa that still exchange genes and those that do not, highlighting the association between differentiation and complete reproductive isolation. Our results suggest that substantial progress towards speciation may involve the alignment of multi-faceted aspects of differentiation.
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We thank R. Guillem, R. Kather, J. Stapley and T. Schwander for their advice; the Oakley-, Kuris- and Lafferty-groups at University of California Santa Barbara for their support; L. Jeanson and J. Hosegood for the phenotypic measurements and lab work; R. Marin for drawing all the figures; T. Schwander for providing the genetic crosses used for linkage mapping; the High-Throughput Genomics Group at the Wellcome Trust Centre for Human Genetics (funded by Wellcome Trust grant reference 090532/Z/09/Z and MRC Hub grant G0900747 91070) for generating the whole-genome re-sequencing data; and the National Center for Genome Sequencing (USA) for the GBS data. R.R. was supported by the Human Frontier Science Program, M.M. and K.L. were supported by the Swiss National Science Foundation and P.N. was supported by the Royal Society of London. The work was funded by grants from the European Research Council (grant NatHisGen R/129639 to P.N.) and the Natural Science and Engineering Research Council of Canada (to B.J.C. and G.G.). Computing, storage and other resources from the Division of Research Computing in the Office of Research and Graduate Studies at Utah State University, as well as access to the High Performance Computing Facilities, particularly to the Iceberg HPC cluster, from the Corporate Information and Computing Services at the University of Sheffield, are gratefully acknowledged.
The authors declare no competing financial interests
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Riesch, R., Muschick, M., Lindtke, D. et al. Transitions between phases of genomic differentiation during stick-insect speciation. Nat Ecol Evol 1, 0082 (2017). https://doi.org/10.1038/s41559-017-0082
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