title: Evolution of the immune system influences speciation rates in teleost fishes.
abstract: Teleost fishes constitute the most species-rich vertebrate clade and exhibit extensive genetic and phenotypic variation, including diverse immune defense strategies. The genomic basis of a particularly aberrant strategy is exemplified by Atlantic cod, in which a loss of major histocompatibility complex (MHC) II functionality coincides with a marked expansion of MHC I genes. Through low-coverage genome sequencing (9-39×), assembly and comparative analyses for 66 teleost species, we show here that MHC II is missing in the entire Gadiformes lineage and thus was lost once in their common ancestor. In contrast, we find that MHC I gene expansions have occurred multiple times, both inside and outside this clade. Moreover, we identify an association between high MHC I copy number and elevated speciation rates using trait-dependent diversification models. Our results extend current understanding of the plasticity of the adaptive immune system and suggest an important role for immune-related genes in animal diversification.
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Martin
authors.initials: M
authors.lastname: Malmstrøm
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Michael
authors.initials: M
authors.lastname: Matschiner
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Ole K
authors.initials: OK
authors.lastname: Tørresen
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Bastiaan
authors.initials: B
authors.lastname: Star
authors.affiliation: Department of Chemistry, Biotechnology and Food Sciences, Norwegian University of Life Sciences, Ås, Norway.
authors.forename: Lars G
authors.initials: LG
authors.lastname: Snipen
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Hansen
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Helle T
authors.initials: HT
authors.lastname: Baalsrud
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Alexander J
authors.identifier: 0000-0001-5539-0999
authors.initials: AJ
authors.lastname: Nederbragt
authors.affiliation: Institute of Fisheries Ecology, Federal Research Institute for Rural Areas, Forestry and Fisheries, Hamburg, Germany.
authors.forename: Reinhold
authors.initials: R
authors.lastname: Hanel
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.|Zoological Institute, University of Basel, Basel, Switzerland.
authors.forename: Walter
authors.initials: W
authors.lastname: Salzburger
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.|Institute of Marine Research, Flødevigen Marine Research Station, His, Norway.|Department of Natural Sciences, University of Agder, Kristiansand, Norway.
authors.forename: Nils C
authors.initials: NC
authors.lastname: Stenseth
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.
authors.forename: Kjetill S
authors.identifier: 0000-0002-8861-5397
authors.initials: KS
authors.lastname: Jakobsen
authors.affiliation: Department of Biosciences, University of Oslo, Oslo, Norway.|Department of Natural Sciences, University of Agder, Kristiansand, Norway.
authors.forename: Sissel
authors.initials: S
authors.lastname: Jentoft
mesh_terms: D000220:Adaptation, Biological / Q000235:genetics; D000818:Animals; D005075:Biological Evolution; D005399:Fishes / Q000145:classification / Q000235:genetics / Q000276:immunology*; D018628:Gene Dosage; D049810:Genetic Speciation; D016678:Genome; D007107:Immune System; D008285:Major Histocompatibility Complex; D010802:Phylogeny; D013045:Species Specificity