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

2. 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

3. 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:

4. MHC class II function
MHC class II molecules play associates with components of the pathogen and presents them to specific T helper lymphocytes.
Figure:

5. 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

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

7. History of the Finnish wolf population

8. 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)

9. 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?

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

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

12. Preliminary results: allelic diversity

13. 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

14. 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

15. Selection: Ewens-Watterson test

16. 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

17. Nucleic diversity and selection

18. Synonumous and non-synonymous mutations

19. 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)

20. 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

21. 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

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

23. 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

24. Thank you for your attention!