title: Genetic Variation at Exon 2 of the MHC Class II DQB Locus in Blue Whale (Balaenoptera musculus) from the Gulf of California.
abstract: The genes of the Major Histocompatibility Complex (MHC) play an important role in the vertebrate immune response and are among the most polymorphic genes known in vertebrates. In some marine mammals, MHC genes have been shown to be characterized by low levels of polymorphism compared to terrestrial taxa; this reduction in variation is often explained as a result of lower pathogen pressures in marine habitats. To determine if this same reduction in variation applies to the migratory population of blue whales (Balaenoptera musculus) that occurs in the Gulf of California, we genotyped a 172 bp fragment of exon 2 of the MHC Class II DQB locus for 80 members of this population. Twenty-two putatively functional DQB allotypes were identified, all of which were homologous with DQB sequences from other cetacean species. Up to 5 putative alleles per individual were identified, suggesting that gene duplication has occurred at this locus. Rates of non-synonymous to synonymous substitutions (ω) and maximum likelihood analyses of models of nucleotide variation provided potential evidence of ongoing positive selection at this exon. Phylogenetic analyses of DQB alleles from B. musculus and 16 other species of cetaceans revealed trans-specific conservation of MHC variants, suggesting that selection has acted on this locus over prolonged periods of time. Collectively our findings reveal that immunogenic variation in blue whales is comparable to that in terrestrial mammals, thereby providing no evidence that marine taxa are subject to reduced pathogen-induced selective pressures.
authors.affiliation: Laboratorio de Bioconservación y Manejo, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Mexico City, Mexico.
authors.forename: Diana D
authors.initials: DD
authors.lastname: Moreno-Santillán
authors.affiliation: Museum of Vertebrate Zoology, University of California, Berkeley, California, United States of America.
authors.forename: Eileen A
authors.initials: EA
authors.lastname: Lacey
authors.affiliation: Laboratorio de Ecología de Cetáceos y Quelonios, Centro Interdisciplinario de Ciencias Marinas, Instituto Politécnico Nacional, La Paz, BCS, México.
authors.forename: Diane
authors.initials: D
authors.lastname: Gendron
authors.affiliation: Laboratorio de Bioconservación y Manejo, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Mexico City, Mexico.
authors.forename: Jorge
authors.initials: J
authors.lastname: Ortega
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D050616:Balaenoptera / Q000235:genetics*; D001483:Base Sequence; D002140:California; D005091:Exons / Q000235:genetics*; D005787:Gene Frequency / Q000235:genetics; D056426:Genetic Loci; D014644:Genetic Variation; D059866:HLA-DQ beta-Chains / Q000737:chemistry / Q000235:genetics*; D006239:Haplotypes / Q000235:genetics; D000949:Histocompatibility Antigens Class II / Q000235:genetics; D016013:Likelihood Functions; D008969:Molecular Sequence Data; D010802:Phylogeny; D012641:Selection, Genetic; D016415:Sequence Alignment
chemical_list: D059866:HLA-DQ beta-Chains; C069051:HLA-DQB1 antigen; D000949:Histocompatibility Antigens Class II