Summary from the authors: Polygenic selection drives the evolution of convergent transcriptomic landscapes across continents within a Nearctic sister-species complex

Lake Whitefish (Coregonus clupeaformis)
Adult size benthic (normal) and limnetic (dwarf) sympatric whitefish
Sampled from Cliff Lake, Maine, USA.
Illustration by Paul Vecsei.

The Lake Whitefish (Coregonus clupeaformis) is found in Nearctic post-glacial freshwater lakes, and diverged about 500,000 years ago from its sister species, the European Whitefish (Coregonus lavaretus) found throughout Northern Europe, European Alpine lakes and Russia. These two lineages underwent an adaptive radiation following the last glaciation, resulting in the sympatric occurrence of limnetic and benthic species-pairs. Decades of research has aimed to decipher the process of adaptive divergence and ecological speciation in the Whitefish species complex. Here, we compared independent diverging species-pairs from the two continents to elucidate the genomic and transcriptomic bases associated with the benthic-limnetic diversification. We used a statistical framework to detect polygenic targets of selection associated with phenotypic diversification. We identified a subset of genes that showed convergent patterns of differential expression between limnetic and benthic species across both continents. Those adaptive divergent genes retained a higher degree of shared polymorphism among species-pairs, most likely due to balancing selection, and this genetic variation was associated with changes in levels of gene expression between species. As such, our results indicate that standing genetic variation underlying phenotypes involved in the ecological speciation of the whitefish species-pairs has been partly maintained in parallel across both continents for at least half a million years.

-Clément Rougeux – Postdoctoral Researcher, University of Calgary

Full article: Rougeux C, Gagnaire P‐A, Praebel K, Seehausen O, Bernatchez L. Polygenic selection drives the evolution of convergent transcriptomic landscapes across continents within a Nearctic sister species complex. Mol Ecol. 2019;28:4388–4403. https://doi.org/10.1111/mec.15226

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