MBE Advance Access published online on October 16, 2008
Molecular Biology and Evolution, doi:10.1093/molbev/msn235
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Research Article |
Candidate genes and adaptive radiation: Insights from transcriptional adaptation to the limnetic niche among coregonine fishes (Coregonus spp., Salmonidae)
Département de Biologie, Université Laval, Québec, QC, Canada, G1V 0A6
1 Québec Océan, Département de Biologie, Université Laval, Québec QC, G1V 0A6, Canada
2 Zoological Institute, University of Bern, CH-3012 Bern, Switzerland
3 Norwegian College of Fishery Science, University of Tromsø, N-9037 Tromsø, Norway
Corresponding author: Julie Jeukens, 1030, Avenue de la Médecine, Université Laval, Québec (QC) G1V 0A6 Canada, Phone: 1 418 656-2131 (8455), Fax: 1 418 656-7176, julie.jeukens.1{at}ulaval.ca
Received for publication August 23, 2008. Revision received October 9, 2008. Accepted for publication October 10, 2008.
In the past forty years, there has been increasing acceptance that variation in levels of gene expression represents a major source of evolutionary novelty. Gene expression divergence is therefore likely to be involved in the emergence of incipient species, namely in a context of adaptive radiation. In the lake whitefish species complex (Coregonus clupeaformis), previous microarray experiments have led to the identification of candidate genes potentially implicated in the parallel evolution of the limnetic dwarf lake whitefish, which is highly distinct from the benthic normal lake whitefish in life history, morphology, metabolism and behavior, and yet diverged from it only 
15 000 YBP. The aim of the present study was to address transcriptional divergence for 6 candidate genes among lake whitefish and European whitefish (C. lavaretus) species pairs, as well as lake cisco (C. artedi) and vendace (C. albula). The main goal was to test the hypothesis that parallel phenotypic adaptation towards the use of the limnetic niche in coregonine fishes is accompanied by parallelism in candidate gene transcription as measured by quantitative real-time PCR. Results obtained for 3 candidate genes, whereby parallelism in expression was observed across all whitefish species pairs, provide strong support for the hypothesis that divergent natural selection plays an important role in the adaptive radiation of whitefish species. However, this parallelism in expression did not extend to cisco and vendace, thereby infirming transcriptional convergence between limnetic whitefish species and their limnetic congeners for these genes. As recently proposed (Lynch 2007, Nature Reviews Genetics 8:803), these results may suggest that convergent phenotypic evolution can result from non-adaptive shaping of genome architecture in independently evolved coregonine lineages.
Key Words: Coregonus • parallel evolution • adaptive radiation • convergence • fish • gene expression
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