Romeo and Juliet, Paris and Helen, Myrcella and Trystane. The tale of star-crossed lovers, caught on opposite sides of a great conflict, is one of the most fundamental of human stories. It's not uniquely human, however; mongoose lovers experience the same thing.
Mungos mungos or banded mongooses (but let's just say mongeese) live in packs of up to 40. Most stay within their birth packs for their entire lives, and packs can engage in pitched battles with their neighbors.
Yet as much as these packs may hate each other, love (or maybe lust) overcomes all. A paper in Behavioral Ecology used the DNA of pups born in Queen Elizabeth National Park, Uganda, to show that 18% were the result of cross-clan canoodling.
“Females are capable of refusing mating attempts and it does not appear to be possible for males to force female[s] to mate,” the paper notes. So this isn't a case of victorious packs claiming sex as a spoil of war. Sometimes, males from one pack and females from another break away to form a whole new grouping.
Just as with humans, however, there is plenty of risk involved in looking for love in the tents of the enemy. “Aggressive encounters between packs account for 20% of pup deaths and 12% of adult deaths," says lead author Dr. Hazel Nichols of Liverpool John Moores University.
Of course, there is a huge evolutionary benefit in doing so. "These pups are less likely to be inbred, are heavier and have higher survival chances than their within-pack counterparts,” Nichols notes. The same effect is seen in humans, with crossing tribal and ethnic lines leading to healthier children. As the authors note, “The benefit of seeking compatible genes may be particularly important in species where potential mates are close relatives. In many cooperatively breeding species... potential mates from within the group are often closely related.”
It's one thing to sneak off for a little extracurricular activity during a truce, but Nichols says mongeese take hate sex to new levels. “Banded mongooses are unusual because a lot of mating occurs during these fights, even though it is a dangerous time to decide to mate with one of your rivals!" Some even seem to start fights by entering enemy territory in the hope of meeting a hot date in battle.
The paper notes that for females in other species, "Paternity uncertainty created through polyandrous mating can lead to an increase [in] paternal care," but that doesn't seem to apply to mongeese.
Co-author Dr. Jennifer Sanderson of the University of Exeter says: "The most exciting thing we found is that females are more likely to mate with males from rival packs if they are surrounded by unsuitable mates – such as their brothers and uncles – in their own pack."
No wonder males take so unkindly to discovering a female from their pack looking for love elsewhere – it's a judgment on their own quality as potential mates.
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