University of Liverpool researchers, in collaboration with Charles University in the Czech Republic, found field mice sacrifice some of their immunity protection in favor of a more rapid fertilization process. That occurs due to the absence of a protein called CD46.

The researchers said field mice have lost their ability to produce the protein -- present in both animals and humans -- resulting in instability of a cap-like structure called the acrosome that's present above the head of sperm cells. The instability allows the acrosome to be shed, creating a surface essential for sperm to be capable of fusing with an egg.

"By improving our understanding of defects in CD46 we may improve treatments for infertility in men," Professor Peter Johnson said. "Humans normally produce a single egg each month and there is no evolutionary necessity to develop rapid sperm reaction to egg fertilization. The process is, therefore, much slower and so any defect in CD46 could result in sperm being destabilized too early."

The study is published in the journal Reproduction.

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