Genomic and transcriptomic mechanisms of sympatric divergence in resident forms of Arctic charr Salvelinus alpinus (L.)

This review analyses the genomic and transcriptomic mechanisms of sympatric divergence in resident forms of Arctic charr Salvelinus alpinus (L.) . Classic systems — Thingvallavatn (Iceland), Loch Rannoch (Scotland) and Fjellfrösvatn (Norway) — are examined from biochemical markers to SNP-genomics and transcriptomics. Analysis of 11 sympatric ecotype pairs across two evolutionary lineages shows that phenotypic and transcriptomic parallelism is substantially deeper than parallelism at the level of individual SNPs: only 8 of hundreds of associated loci were shared between lineages (Jacobs et al., 2020). Coalescent modelling of Ice-landic morph pairs (Brachmann et al., 2022) demonstrates that the history of divergence differs between lakes within the same species and the same type of morph pair. A clarification is offered regarding the term «sympatric speciation»: for most of the systems studied, including those of Transbaikalia, complete reproductive isolation has not been demonstrated, and «within-lake adaptive divergence» is the more accurate term. The Editorial Note (2024) concerning Nugent et al. (2019) and the 87k SNP array is noted. Common-garden experiments (Svedäng, 1990; Janhunen et al., 2009) confirm the heritable basis of inter-morph differences while revealing considerable phenotypic plasticity.