It’s a story as old as time. Star-crossed lovers enjoy stolen moments before returning to their separate worlds. Only there’s a twist. One is a bull. The other is a male donkey. Their unlikely bromance is described in Current Biology.
Achille the bull and Patroclo the donkey live on the Ethiopian plateau. The animals have different owners and spend their nights apart, but their herds come together to graze the same pasture during the day. Once reunited, the pair waste little time in each other’s company. They lick, nuzzle and rub against one another, and the bull repeatedly mounts the donkey.
Now researchers believe the unlikely pair have something important to teach us about animal sexuality – that it is sometimes less binary and more complex than many people have believed.
Researchers stumbled across the relationship when they were studying gelada monkeys in Ethiopia. “The sexual interactions between Achille, the bull, and Patroclo, the male donkey, were not isolated events,” says Elisabetta Palagi, from the University of Pisa. “What really caught our attention was that these interactions were embedded in a very selective and consistent social relationship between the two individuals.”
Intrigued, the researchers decided to study the pair in detail, recording their behaviour over four days when they were both in the same pasture, and four days when only one of the animals was present.
Altogether, Achille mounted Patroclo 51 times. Patroclo didn’t try to avoid Achille or escape his advances. “They repeatedly chose to stay close to each other and engaged in many different affiliative behaviours,” says André da Cruz, also from the University of Pisa.
Intriguingly, licking and rubbing happened both before and after mounting. This suggests these actions weren’t simply associated with sexual arousal, but may also have played a social role, perhaps helping the animals to maintain their close bond.
Both animals had access to partners of the same species and the opposite sex, but they repeatedly chose each other. Neither Achille nor Patroclo was observed mounting a member of their own species of either sex, although Achille did make some overtures towards some female cattle.
At first glance, sexual encounters that cannot produce offspring might seem puzzling from an evolutionary perspective. But same-sex sexual behaviour is surprisingly widespread in the animal kingdom. It has been documented in more than 1,500 species, including 261 mammals, where it’s thought to sometimes play a role in maintaining social relationships and managing conflict.
Nor are Achille and Patroclo the first to break the species barrier. A male snow monkey was seen trying to have sex with a female sika deer, and an Antarctic fur seal was observed trying to mate with a king penguin.
But none of these encounters match the apparent bonhomie of Achille and Patroclo. As Palagi told ScienceAlert, “Animal behaviour is not a picture painted in black and white: It uses the whole palette, with all the colours of the rainbow.”
