By VICTORIA WOOLLASTON
If you think your partner is cheating on you, your sperm may give you and your suspicions away.
According to clinical sexologist Dr. Lindsey Doe, up to 40 per cent of male ejaculate is made up of so-called ‘kamikaze’ or ‘fighter sperm’ designed to prevent another man’s sperm from fertilising the egg.
When a man suspects their partner is being unfaithful, the number of these aggressive sperm increase to tackle this perceived threat.
Speaking to Hank Green on SciShow, Dr. Doe said: ‘Researchers have looked into the microscope and seen that maybe we have what are called kamikaze sperm; killer sperm; fighter sperm.
‘40 per cent of sperm that is in an ejaculate are actually designed to fight off another man’s sperm.’
This means the fighter sperm isn’t designed to inseminate the egg. Instead its included purely to prevent another male’s sperm from doing so.
Dr. Doe describes this method of preventing other sperm from reaching the egg as ‘blocking’.
The fighter sperm use their tails as coils to set up traps by weaving them together to create walls and barricades.
Previous experiments believed these sperm were rigid because they had died or were weak.
Dr. Doe, who regularly presents the Sexplanations YouTube series, additionally said that some fighter sperm will go and attack any it sees as a threat in order to kill them. These particular fighter sperm are referred to as ‘kamikaze sperm’.
When males suspect their partners are not being monogamous, Dr. Doe continued that their body will produce more ‘fighter sperm’ as the threat is perceived to be greater.
This does the job of increasing the level of protection against sperm from other males, however, it can significantly reduce the number of sperm whose job it is to inseminate the egg and therefore reduce the chances of the female getting pregnant at all.
Elsewhere, during ovulation, a woman’s ‘cervical plug’ transforms into channels that are approximately a sperm’s head wide. These then act as channels or 'ladders' for the sperm to climb closer to the egg.
Studying sperm competition is difficult in lab conditions. By genetically engineering sperm of fruit flies to glow in the dark, pictured, researchers have at least been able to confirm the phenomenon takes place in certain species
Dr. Doe said that some of the older, fighter sperm additionally block these channels to stop another man’s sperm from entering.
Or they wait until a number of their own sperm enter the channel before blocking it off, giving those sperms a greater chance.
However, Dr. Doe did explain that this theory, known as sperm competition, is under debate and some deny happens at all.
Earlier this year, Professor John Belote from Syracuse University studied the mating habits of fruit flies by engineering glow-in-the-dark sperm.
In many species, including humans, when a female is promiscuous ejaculates from multiple males may be inside her reproductive tract at the same time, meaning they are competing to fertilise the egg.
This is called postcopulatory sexual selection and is a series of changes that take place in the sperm, and the female body.
However such changes are difficult to study in lab conditions.
By genetically altering the flies, Professor Belote created some with sperm heads that glow red, and others where the heads glow green.
He was then able to closely observe how sperms competed inside the female and times when the female tract rejected or discarded certain sperms to discover that the process does take place.
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