Greater horseshoe bats keep it in the family

The notion of sharing your grandmother’s new sexual partner might seem unappealing to us, but a study of wild greater horseshoe bats reveals that female relatives regularly share male mates, yet nearly always avoid their blood relatives.

The study, published in this week’s Nature, was led by Dr Stephen Rossiter as part of a long-term collaboration between scientists at Queen Mary, University of London, and the University of Bristol. The study used genetic analysis to look at breeding patterns over 10 years in a colony of around 40 greater horseshoe bats, Rhinolophus ferrumequinum, one of Britain’s rarest bats, from Gloucestershire.

The team, funded by the Natural Environment Research Council, found that while a female might mate with the same male as her grandmother, she won’t mate with her own grandfather. As you might expect, things quickly get very confusing, for example, the study revealed several cases in which a female and her maternal half-aunt were also half-sisters on their father’s side!

Why might these breeding patterns evolve? “One possibility is that by increasing kinship, sharing sexual partners strengthens social ties and promotes greater levels of cooperation within the colony,” says Dr Rossiter. “In fact, the study also found another way in which these bats strengthen levels of kinship, with most females returning to the same male over many years.”

This work, based on one of the longest-running and most detailed studies of a wild animal population worldwide, illustrates the hidden complexity that can underlie animal mating patterns in natural conditions, and could have important implications for conservation strategies in a range of important mammalian species.