Pregnancy achievement has been shown to be more likely between partners carrying unequal leukocyte antigen (HLA) immunogens. Hence, people are expected to choose HLA unequal reproductive partners. Previous studies have shown that HLA diversity preferences are mediated by body odors rather than facial preferences. However, it has been unclear whether preference for HLA-based mating could occur after sexual intercourse in the female reproductive tract. Researchers from the University of Eastern Finland have now shown that the female reproductive tract is capable of mediating post-mating sexual selection (known as the “cryptic female choice”) to the sperm of HLA-differentiated males. This indicates that the ultimate mating bias to genetically compatible partners only occurs after mating, at the gamet level.
The researchers performed two experiments, in which they activated sperm from multiple men with follicular fluid (the oocyte surrounding bioactive fluid) as cervical mucus from several different women. They then examined sperm motility and other functionally important physiological changes of sperm in all possible male-female combinations. All participants were also genotyped for their human leukocyte antigen (HLA) class I and II alleles.
In both studies, the results showed that the fertility and viability of sperm are strongly dependent on the male-female combination. In other words, the reproductive secretions of women had a stronger effect on the sperm performance of some men than others. Both datasets also showed that sperm performance was better in HLA distinct male-female combinations than in HLA-comparable males and females.
Taken together, the results indicate that the fertility of sperm depends on the immunogenetic compatibility of the reproductive partners and that the fusion of the gametes can be a very selective process.
“These findings may have important implications for a deeper understanding of sexual selection and the fertilization process in humans and other mammals,” says Associate Professor Jukka Kekäläinen of the University of Eastern Finland.
“Since the gametes of some partners may be more immunologically compatible than others, our results may also open up new possibilities for the development of more accurate infertility diagnostics,” adds Annalaura Jokiniemi, MSc.
Human eggs prefer some male sperm over others, research shows
Annalaura Jokiniemi et al. Post-copulatory genetic matchmaking: HLA-dependent effects of cervical mucus on human sperm function, Procedures of the Royal Society B: Biological Sciences (2020). DOI: 10.1098 / rspb.2020.1682
Annalaura Jokiniemi et al. Immunogenetic incompetence of gamete level in humans – to a deeper understanding of fertilization and infertility ?, Inheritance (2020). DOI: 10.1038 / s41437-020-0350-8
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Citation: Partner selection finally happens in the woman’s reproductive tract (2020, August 19) retrieved August 20, 2020 from https://phys.org/news/2020-08-partner-ultately-woman-reproductive-tract.html
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