Being a good-looking female baboon might bag you the most handsome male, but the latest study suggests that beauty has its drawbacks.
Scientists have found that the most desirable females the ones that are on heat are much more likely to be bullied than females that aren't ready to mate. What's more, it's the other females in the troop that do the persecuting.
The study also shows that if you're a good catch, and you're guarded by an alpha male, you're twice as likely to be tormented by your female peers as others that aren't guarded.
"Sexually-receptive female baboons get a lot more stick from their female colleagues than any other females do," says Dr. Elise Huchard from the German Primate Center, lead author of the study. "Our study highlights the dramatic relationship between the reproductive state of the female and the amount of aggression she faces."
The research, recently published in Behavioral Ecology reveals that sex is much more important than previously thought in shaping relationships between females in large primate groups.
"We were surprised at this finding, because it goes against the traditional view," says Huchard.
While the causes of aggression between male primates have been well studied, conflicts between females have, until now, been largely overlooked.
"The traditional view was that females mainly fight over access to food, while males fight over sex," Huchard explains. "This is because carrying young during pregnancy and feeding them is costly and takes up a lot of energy, so it's reasonable to expect the females to fight over food."
But in the last few years, a number of studies have suggested that females from many species do indeed compete over sex.
To find out exactly what female baboons fight over, Huchard and Dr. Guy Cowlishaw from the Zoological Society of London decided to test three ideas.
Firstly, they predicted that if food is important, pregnant or breast-feeding females would clash the most. But if getting dad to help raise the kids is important, they guessed that there would be lots of fallouts between breast-feeding females. Finally, if access to the best males mattered most to females, they reckoned there would be more aggression among females on heat.
Tsaobis Leopard Park
They recorded the number of aggressive exchanges between 27 wild female chacma baboons from two different groups in Tsaobis Leopard Park in central Namibia over 18 months.
In total, they analysed 1027 interactions, which included a range of aggressive behavior between females like threats, displacements and attacks.
They found that pregnant baboons start the most fights, which partly backs up the idea that aggression arises because of competition for food. But they found that these baboons aren't subjected to much bullying at all. And all the other interactions suggest that the animals don't compete just for food: females on heat and mate-guarded baboons are subjected to the most violent behaviour, but don't themselves bully. Suckling mothers were much less likely to be attacked, or to attack.
"You could interpret this as competition over mating, but we don't think it's as simple as that," Huchard says.
"If this was true, you might expect females on heat to be aggressive towards others. But they weren't; they were the victims," she adds.
One explanation could be that females that are ready to mate are particularly vulnerable: stress is likely to delay conception, so these baboons are best off not getting involved in fights if they can help it.
Huchard says that females probably fight over both food and mates depending on where they are in their reproductive cycles. It's clear that further research is needed to unpick exactly what's going on.
"The most logical next step would be to see if aggression towards sexually receptive females really does mean they have trouble conceiving," Huchard says.
Explore further: Horse behavior in the field
More information: Elise Huchard and Guy Cowlishaw, Female-female aggression around mating: an extra cost of sociality in a multimale primate society, Behavioral Ecology, First published online: June 21, 2011, doi: 10.1093/beheco/arr083