the Seeds of Science

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Are aggressive sperm a barrier to cross species sex?

By Arvid Ågren, EEB

Sperm has been dyed red to show how they have left the uterus and spread throughout the body.
Sperm has been dyed red to show how they have left the uterus and spread throughout the body.

Males often compete fiercely for access to females. A new study shows that the consequences of this competition may extend beyond showy tails and big antlers, and may prevent individuals from different species from breeding with each other.

Think of competition among males for mates and a image of head butting rams come to mind. However, in many species competition continues long after mating. Some males have evolved strategies—from scooping out sperm from other males, to releasing chemicals that prevent the female from mating again—to reduce the chance of another’s sperm reaching an egg.

Now a team, reporting in PLoS Biology, have shown that aggressively competing sperm in nematode worms can occasionally end up escaping a female’s reproductive tract, ending up in other organs, causing females to become sterile and sometimes even die. The team shows that sperm are more harmful when they come from males of different, but closely related species of worm.

Females, the team suspect, are better at limiting the harmful effects of aggressive sperm from their own species than other species. One consequence of this is that it reinforces the barrier to mating between different nematodes species.

Understanding the mechanisms causing these barriers is, according to many evolutionary biologists, the key to unravel ‘the mystery of mysteries’, the origin of new species. This study shows how aggressive sperm is one such barrier.


This entry was posted on August 8, 2014 by in News and tagged , , .