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Researchers at the University of Oxford have discovered that male fruit flies adjust their seminal fluid depending on the levels of competition from other males.

Glowy sperm.jpg

When more rivals are around, they create and add extra protein to their seminal fluid making it extra potent. This boosts the number of offspring their partners produce, but the extra effort comes at a cost: it tires the male out and makes him sluggish to remate.

It previously wasn’t known if sperm and seminal fluid could be changed independent of each other, but this research shows that it can.

Humans also transfer both sperm and seminal fluid during ejaculation and this finding could suggest a new understanding of factors affecting fertility. It may also suggest novel treatment avenues for the current male ‘fertility crisis’, evidenced by human sperm counts declining steeply over the past 40 years.

The researchers’ data, published today in PNAS, suggest that male fruit flies use different rules for changing different parts of semen. If exposed to one or many rivals the researchers observed increases in sperm transfer compared to zero rivals. However, with seminal protein they observed increases in protein transfer in the presence of many compared to one or zero.

Read more (University of Oxford website)