title: Diverse MHC IIB allele repertoire increases parasite resistance and body condition in the Long-tailed giant rat (Leopoldamys sabanus).
abstract: BACKGROUND
  Genes of the major histocompatibility complex (MHC) code for key functions in the adaptive immune response of vertebrates and most of them show exceptionally high polymorphism. This polymorphism has been associated with the selection by diverse and changing parasite communities. We analysed MHC class IIB diversity, gastrointestinal parasite load and body condition in the wild ranging tropical rat Leopoldamys sabanus (Thomas, 1887) under natural selection conditions in a highly variable rainforest environment in Borneo to explore the mechanisms that maintain these high levels of genetic polymorphism.
  
  
  RESULTS
  Allelic diversity was determined via SSCP and sequencing, and parasite screening was done through non-invasive faecal egg count. The detected alleles showed expected high levels of polymorphism and balancing selection. Besides a clear advantage for more diverse MHC genotypes in terms of number of alleles, reflected in better body condition and resistance against helminth infection, our data also suggested a positive effect of MHC allele divergence within an individual on these parameters.
  
  
  CONCLUSIONS
  In accordance with the heterozygote advantage hypothesis, this study provides evidence for an advantage of more diverse MHC genotypes. More specifically, the potential negative relation between individual allele divergence and number of parasite species is in line with the 'divergent allele advantage' hypothesis.
authors.affiliation: Department of Animal Ecology and Animal Conservation, University of Hamburg, 20146 Hamburg, Germany. lenz@evolbio.mpg.de
authors.forename: Tobias L
authors.initials: TL
authors.lastname: Lenz
authors.forename: Konstans
authors.initials: K
authors.lastname: Wells
authors.forename: Martin
authors.initials: M
authors.lastname: Pfeiffer
authors.forename: Simone
authors.initials: S
authors.lastname: Sommer
mesh_terms: D000483:Alleles; D000818:Animals; D001893:Borneo; D019143:Evolution, Molecular; D005802:Genes, MHC Class II; D006579:Heterozygote; D006790:Host-Parasite Interactions / Q000235:genetics*; D007113:Immunity, Innate / Q000235:genetics*; D051189:Murinae / Q000235:genetics* / Q000469:parasitology; D010270:Parasite Egg Count; D011110:Polymorphism, Genetic; D018807:Polymorphism, Single-Stranded Conformational; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA