Male guppies produce faster sperm with their sisters

In many species, in-built mechanisms are in place to prevent siblings from breeding with each other. Researchers from the University of Western Australia (UWA) have investigated such mechanisms in the male guppy, a live-bearing freshwater fish - with unexpected results.

Writing in the journal Biology Letters, the researchers explained that they exposed male guppies “to either full-sibling or unrelated females and [determined] whether they adjust investment in courtship and ejaculates”. Consistent with expectation, they found that the guppies direct less courtship towards their sisters compared to unrelated females - but they also produce ejaculates with faster swimming sperm when paired with sisters.

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

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

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