Australasian Science: Australia's authority on science since 1938

Males Make Fast Sperm for Sisters

Inbreeding can be costly to both sexes, so the males and females of many species avoid mating with their siblings. However, a new study published in Biology Letters has added a twist to this story by showing that males produce faster sperm when paired with their sisters.

Prof Jon Evans’ team at The University of Western Australia’s Centre for Evolutionary Biology exposed male guppies to either their full sisters or unrelated females to determine whether their courtship and ejaculate expenditure differed. They found that male guppies (a live-bearing freshwater fish) direct less courtship towards their sisters. However, they also found that males produce ejaculates with faster-swimming sperm when paired with their sisters.

“We interpret this latter finding as evidence for sexual conflict because, in guppies, females exhibit ‘preferences’ for unrelated sperm,” Evans said. “By producing more competitive sperm when mating with siblings, male guppies may potentially circumvent the females’ natural preference to avoid inbreeding.”

The findings may reflect sex-specific responses to inbreeding, whereby males tolerate higher levels of inbreeding than females. The research also shows that male guppies are capable of recognising their kin, and can adjust both their courtship and sperm quality accordingly.