Maintenance of species differences in closely related tetraploid parasitic Euphrasia (Orobanchaceae) on an isolated island

提出问题：However, polyploid groups are understudied due to complex sequence homology, challenging genome assembly, and taxonomic complexity. 

主要研究：Here we study adaptive divergence in taxonomically complex eyebrights (Euphrasia), where recent divergence, phenotypic plasticity, and hybridisation blur species boundaries.

研究对象：We focus on three closely-related tetraploid species with contrasting ecological preferences, and which are sympatric on Fair Isle, a small isolated island in the British Isles.

结果1-田间试验：Using a common garden experiment, we show a genetic component to the morphological differences present between these species. 

结果2-全基因组测序：Using whole genome sequencing and a novel k-mer approach we call “Tetmer”, we demonstrate that the species are of allopolyploid origin, with sub-genome divergence of approximately 5%.

结果3-物种形成与分化：Using ～2 million SNPs we show sub-genome homology across species, with very low sequence divergence characteristic of recent speciation. This genetic variation is broadly structured by species, with clear divergence of Fair Isle heathland E. micrantha, while grassland E. arctica and coastal E. foulaensis are more closely related.

结论：Overall, we show tetraploid Euphrasia are a system of allopolyploids of postglacial species divergence, where adaptation to novel environments may be conferred by old variants rearranged into new genetic lineages.