Infidelity produces faster sperms

Until now, it has been difficult to prove that fast-swimming sperms have an advantage when it comes to fertilizing an egg.

A research team at the University of Uppsala can demonstrate that unfaithful females of the cichlid fish species influence the males' sperms. Increased competition leads to both faster and larger sperms. The findings also show that the speed and the size of sperms are closely related: larger sperms are faster.

These sperms swim faster thanks to the greater power of a larger flagellum, but faster sperms also need to have a larger store of energy, which in turn results in larger sperms. Thanks to new analytical methods, the researchers have also managed to demonstrate the order of this development. The sperms first become faster, then larger, following increased female promiscuity in a species.