title: Standing chromosomal variation in Lake Whitefish species pairs: the role of historical contingency and relevance for speciation.
abstract: The role of chromosome changes in speciation remains a debated topic, although demographic conditions associated with divergence should promote their appearance. We tested a potential relationship between chromosome changes and speciation by studying two Lake Whitefish (Coregonus clupeaformis) lineages that recently colonized postglacial lakes following allopatry. A dwarf limnetic species evolved repeatedly from the normal benthic species, becoming reproductively isolated. Lake Whitefish hybrids experience mitotic and meiotic instability, which may result from structurally divergent chromosomes. Motivated by this observation, we test the hypothesis that chromosome organization differs between Lake Whitefish species pairs using cytogenetics. While chromosome and fundamental numbers are conserved between the species (2n = 80, NF = 98), we observe extensive polymorphism of subtle karyotype traits. We describe intrachromosomal differences associated with heterochromatin and repetitive DNA, and test for parallelism among three sympatric species pairs. Multivariate analyses support the hypothesis that differentiation at the level of subchromosomal markers mostly appeared during allopatry. Yet we find no evidence for parallelism between species pairs among lakes, consistent with colonization effect or postcolonization differentiation. The reported intrachromosomal polymorphisms do not appear to play a central role in driving adaptive divergence between normal and dwarf Lake Whitefish. We discuss how chromosomal differentiation in the Lake Whitefish system may contribute to the destabilization of mitotic and meiotic chromosome segregation in hybrids, as documented previously. The chromosome structures detected here are still difficult to sequence and assemble, demonstrating the value of cytogenetics as a complementary approach to understand the genomic bases of speciation.
authors.affiliation: Département de Biologie, Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, 1030, Avenue de la Médecine, Québec, Québec, Canada, G1V 0A6.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Dion-Côté
authors.affiliation: Research Institute for Limnology, University of Innsbruck, Mondseestraße 9, A-5310, Mondsee, Austria.
authors.forename: Radka
authors.initials: R
authors.lastname: Symonová
authors.affiliation: Ontario Institut for Cancer Research, MaRS Centre, 661 University Avenue, Suite 510, Toronto, Ontario, Canada, M5G 0A3.
authors.forename: Fabien C
authors.initials: FC
authors.lastname: Lamaze
authors.affiliation: Laboratory of Fish Genetics, Institute of Animal Physiology and Genetics, AS CR, vvi, Liběchov, 277 21, Czech Republic.
authors.forename: Šárka
authors.initials: Š
authors.lastname: Pelikánová
authors.affiliation: Laboratory of Fish Genetics, Institute of Animal Physiology and Genetics, AS CR, vvi, Liběchov, 277 21, Czech Republic.
authors.forename: Petr
authors.initials: P
authors.lastname: Ráb
authors.affiliation: Département de Biologie, Institut de Biologie Intégrative et des Systèmes (IBIS), Université Laval, 1030, Avenue de la Médecine, Québec, Québec, Canada, G1V 0A6.
authors.forename: Louis
authors.initials: L
authors.lastname: Bernatchez
mesh_terms: D000818:Animals; D002875:Chromosomes / Q000235:genetics; D049810:Genetic Speciation; D005828:Genetics, Population; D006570:Heterochromatin / Q000235:genetics; D060106:Lakes; D010641:Phenotype; D012487:Salmonidae / Q000235:genetics*; D061350:Sympatry
chemical_list: D006570:Heterochromatin
keywords: 
  Coregonus
  ; cytogenetics; polymorphism; salmonids; speciation; standing genetic variation