Extremely polymorphic genes of major histocompatibility complex (MHC) play a significant role in the function of immune system by recognizing heterogeneous particles, mainly pathogenic origin. Previous research on various vertebrate species indicates that MHC influences individual body odour and mate choice preferences. Many individuals tend to prefer MHC dissimilar partner so that warrants them an offspring resistant against wider spectrum of infections. Research on MHC-related mate preferences in humans, however, is inconclusive to date. Several studies indicate that women not taking hormonal contraceptives prefer the smell of MHC dissimilar partners while other studies have not come to this conclusion. This can be caused by the absence of potentially influencing factors like the menstrual cycle phase. The aim of this study was to test MHC-similarity mate choice preferences in odour, facial and vocal modalities. In particular, we focused on a potential effect of hormonal contraception. Furtermore, we tested preferential shifts across the menstrual cycle by comparing women's preferences in the follicular and the luteal phase in pill and non-pill users. A group of 52 women in different phases of their menstrual cycle rated odour samples, photos and vocal recordings taken from 51 men. All...

Studies of the evolution of the major histocompatibility complex (MHC) have been central to the understanding sexual selection and pathogen-mediated selection. The European badger Meles meles is well suited for exploring such questions because of its life history characteristics, reproductive biology and mating system. In this thesis, I examined both MHC class I and class II genes. Seven putatively functional sequences were found for class I genes and four for class II DRB genes. Evidence of past balancing selection of both genes was demonstrated by the d_Nd_S ratio, by positive selection at the antigen-binding site (ABS) and by trans-species polymorphism of alleles within other mustelids and carnivores. MHC class I genes also showed evidence of concerted evolution, but domains showed different evolutionary histories. MHC genes may influence microbiota and odour of an individual and influence mating preferences. I examined the bacterial community of the subcaudal gland secretion and demonstrated a high number of bacterial species (56 operational taxonomic units), which cubs exhibited a higher diversity than adults. The microbiota may lead to an individual-specific odour as a cue signaling the MHC genotype of potential mating partners. I report the first evidence for a MHC- based mating preference in carnivores. Female badgers showed a MHC-assortative mate choice towards breeding with males that had functionally similar MHC genes, for MHC class II DRB genes. This applied to neighbouring-group matings. I also found considerable annual fluctuation in the occurrence of MHC-based mate choice. Based on genome-wide background in the same mating randomizations I found no evidence of inbreeding, which indicated that MHC similarity was apparently the actual target of mate choice. In line with MHC-assortative mate choice, MHC heterozygosity had no influence on the co-infection status. Individual MHC alleles did, however, associate with resistance and susceptibility to specific pathogens, suggesting that MHC diversity may be driven and maintained by pathogen-mediated selection through rare-allele advantages and/or fluctuating selection. My study of genetic characteristics, mate choice and pathogen pressures in a wild population revealed past and contemporary evolutionary process of the MHC genes. This increases knowledge of how the MHC may affect mating behaviour and sexual selection, ultimately influencing population processes.