Diversity and selection of MHC class II genes in Finnish wolves Alina Niskanen, Jouni Aspi, Minna Ruokonen, Hannes Lohi, Lorna Kennedy, Ilpo Kojola

MHC Major histocompatibility complex (MHC): Gene dense region Vast amount of immune genes Highly polymorphic Associations to parasite infections and immunological diseases MHC has been studied for decades especially on human and mouse The most important immune gene region in the genome Lowered diversity can lead to lowered immunity against diseases and parasites Higher extinction risk

MHC class II MHC genes divided to three classes based on their function Class II genes recognise extracellular antigens Dukkipati et al 2006: ‘Ovar-MHC’ - ovine major histocompatibility complex: structure and gene polymorphism. Gen. Mol. Res. 5: 581-608

MHC class II function MHC class II molecules play associates with components of the pathogen and presents them to specific T helper lymphocytes. Figure: http://www.path.cam.ac.uk/pages/kelly/image/

Selection in MHC Balancing selection maintains polymorphism by: Heterozygote advantage Frequency-based selection Alleles with low frequency are favoured Accumulation of recessive harmful alleles around MHC > Purifying selection against homozygotes Positive selection for new alleles: Excess of non-synonymous mutations compared to synonymous mutations

History of the Finnish wolf population Hunting statistics (Ermala 2003)

History of the Finnish wolf population

Distribution of wolves Finnish population has formerly supposed to be a part of the larger Russian population Moderate differentation between the populations (FST = 0.15)

Objectives What is the level of MHC diversity in Finnish versus Russian wolf population? Is it possible to detect selection in MHC class II loci in wolves? Are there associations between wolf MHC class loci and parasite infections?

Material Finland: 141 tissue samples (exact coordinates) Russia: 43 pelt samples (known locality)

Methods Three MHC class II loci: DLA-DRB1, DLA-DQA1 and DLA-DQB1 Sequenced Neutral autosomal locus 10 microsatellite loci from a previous study

Preliminary results: allelic diversity

Preliminary results: allelic diversity Population Hobs Hexp Reference DRB1 Finland 0.80 0.84 Present study Karjala 0.88 Archangel 0.86 0.77 North America 0.62 0.81 Hedrick et al. 2002 Mexican wolf 0.49 0.38 Scandinavia Seddon & Ellegren 2004 Estonia 0.72 0.56 Latvia 0.87 0.78

Preliminary results: allelic diversity Population Hobs Hexp AR FIS N Reference Microsatellites Finland 0.70 0.69 5.7 -0.006 118 Aspi et al. 2009 Karjala 0.66 0.71 0.094* 29 Archangel 0.63 0.64 4.7 0.051NS 14 MHC 0.78 0.80 6.7 0.033 136 Present study 0.88 0.81 7.3 -0.091 26 -0.236* Differentation between the populations: microsatellites FST = 0.15 Differentation between the populations: MHC loci FST = 0.03

Selection: Ewens-Watterson test

Positive selection at sequence level Sequence level: Tajima’s D and Fu & Li D* and F* sensitive to demographic changes in the population sensitive to recombination DHEW (Zeng et al., 2007) compound test by combining Fay and Wu's H or DH with the Ewens-Watterson (EW) test. DHEW is more robust against the presence of recombination. DHEW test is also relatively insensitive to background selection and demography

Nucleic diversity and selection

Synonumous and non-synonymous mutations

Selection Preliminary results imply balancing selection: Allele frequencies in Finnish wolf population more equal than expected (DRB1 and DQA1) Tajima’s D, Fu & Li D*, F* and DHEW also significantly positive in DRB1 and DQB1 And positive selection: Excess of non-synonymous substitutions in peptide binding regions (DRB1 and DQA1 loci)

Selection: and codon position To find the exact codons under selection in each population, we used a population genetics approximation to coalescent with recombination in Bayesian settings as implemented in OmegaMap (Wilson & McVean 2005). DRB1-locus in Karelian oblast

MHC and association with parasites Finland: 141 samples Echinococcus granulosus examined from 92 individuals; prevalence of infection 16 % (15) Trichinella spp. examined from 99 individuals; prevalence of infection 33 % (33) Less E. granulosus infections in individuals carrying DQA1*00201 (p = 0.034) and DQB*02901 (p = 0.035) alleles Less Trichinella spp. Infections in individuals carrying DRB1*05301 (p = 0.007) allele

MHC and association with parasites Homozygosity of MHC haplotype was associated with Trichinella spp. infection Mean homozygosity No infection Infection

Collaborators and funding Alina Niskanen, Minna Ruokonen University of Oulu, Deparment of Biology Ilpo Kojola Finnish Game and Fisheries Researh Institutute Hannes Lohi University of Helsinki, Lorna Kennedy University of Manchester Academy of Finland Kone Foundation Ministery of Agriculture and Forestry

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