Bats keep it in the family
Female bats share mates with relatives, but without close inbreeding.
Sharing the same sexual partner with your mother or grandmother may sound odd, but female greater horseshoe bats (Rhinolophus ferrumequinum) in Britain do it all the time.
This ensures that the bats in the colony are closely related to each other, says Stephen Rossiter at Queen Mary, University of London, lead author of a study appearing this week in Nature1. Researchers believe that such close family ties encourage cooperation, such as food sharing, between colony members.
University of London
Rossiter's team studied a colony of 45 female bats living in the attic of Woodchester Mansion in Gloucestershire, UK, over a period of ten years. In that time they found a much higher rate of related female bats sharing partners than expected: 11 pairs of mothers and daughters shared mates at least once, for example, along with 7 pairs of grandmothers and granddaughters. Yet amidst all this partnering, there was only one case of a female mating with her own father. How the females avoid mating with close relatives is unclear; they might use smell as a cue, Rossiter says.
Like mother like daughter
For ten years, Rossiter and his colleagues caught females in early summer when their one offspring was still suckling, making it easy to match mothers and children. To determine the father, the researchers used the same paternity test as courts use for humans: analyzing highly variable and repetitive sequences in the DNA of the offspring and the possible fathers - in this case, all the males in caves up to 30 kilometres away.
Many females mated with the same male for several years - a surprise, because most bats are thought to be polygamous. "We were quite shocked," says Rossiter. "Nearly 60% of the females mated with the same male more than once."
The decade-long study is one of the most thorough analyses of the relationships of bats, says Maarten Vonhof, a bat researcher at Western Michigan University in Kalamazoo, Michigan. Mating behaviour has been studied in only ten of the some 1,000 known bat species, he adds, and most such studies lasted only a few years. "This is the only study that could ever even hope to run these analyses," Vonhof says.
Smells like home
It's not clear how a female might find the same male time and again. Each year, typically in autumn, they fly to caves to mate. Perhaps mothers teach daughters where the caves are, Rossiter says. Mated female bats store sperm until they ovulate in April, then return to the attic in summer to give birth and raise the young.
For females, sticking with a male who sires healthy offspring might make evolutionary sense. As might good neighbourly relations: female bats spend much of their 30-year lives in the same colony , sharing feeding sites and roosting in close quarters to stay warm. So a genetic incentive to co-operate might be an advantage.
Rossiter plans to next study the genetics behind the bats' sense of smell, to see if he can determine how the females avoid choosing a close relative as a mate.
- Rossiter S. J., Ransome R. D., Faulkes C. G., Le Comber S. C. & Jones G. I. et al. Nature, 437. 408 - 411 (2005).