Sperm migration and selection in the reproductive tract of female mice is mostly affected by male genotype.

The aim of the present study is to assess the influence of male and female genotypes on the transport of sperm to the site of fertilization. We mated B10.BR, B10.BR-Ydel and BALB/c males with B10.BR and BALB/c females and then analyzed the quality and quantity of spermatozoa found five hours post coitus in three successive parts of the female reproductive tract. We found that B10.BR and B10.BR-Ydel spermatozoa are very effectively selected by the uterotubaljunction and other barriers of the female genital tract. On the contrary, severely deformed BALB/c spermatozoa appeared to be able to cross selective barriers and were present both in oviducts and in cumulus oophorus. It cannot be excluded that these morphologically abnormal male gametes take part in fertilization. B10.BR-Ydel spermatozoa were very rarely observed above the uterotubaljunction. This shows that in vivo they migrate with delay and with difficulties pass the border between uterus and oviducts. This finding is in agreement with previous in vitro analyzes, which revealed many irregularities in movement of B10.BR-Ydel spermatozoa. Sperm quality and quantity in the reproductive tracts of B10.BR and BALB/c females were convergent if they were mated with males belonging to one strain, proving that migration and selection of spermatozoa in the female genital tract depend mostly on male genotype.