While it may not be as socially acceptable among humans, a female choosing to take multiple mates is a common phenomenon in the animal kingdom. But why the practice of polyandry (a female having more than one male mate at a time) is so prominent is still a mystery in most species.
Most theories predict that taking multiple mates would be risky for a female without adding benefits. However, new research finds that in gray mouse lemurs, a type of small primate from Madagascar, healthy females seek out multiple mates in the few hours of one night they are receptive to mating every year. These multiple mates must confer some kind of benefit to the females, though exactly how they benefit is unknown.
"Males get benefits from mating with multiple females, because they can impregnate multiple partners," study researcher Elise Huchard, of the German Primate Center in Göttingen, told LiveScience. "In most species, females only have a few oocytes [eggs], so mating with multiple males will not increase the number of offspring they will have." [Top 10 Swingers of the Animal Kingdom]
During the intense few hours female lemurs mate annually, two things can happen — either different males chase one female up to 100 times an hour, with some chases ending successfully in mating, or one male monopolizes her the whole night.
The females have a choice to make: Either let these males exhaust them while hunting for food, or choose to hide from the males and miss a night of feeding. During their normal breeding season, females are typically smaller than males. To see if size guided the choice and larger females could fight off the males better, the researchers fed the females either a normal food or a reduced-calorie chow.
They then watched the females on their mating nights, in a cage with three male lemurs. They expected to see the larger females push off the unwanted, harassing suitors. Instead, the researchers saw the heavy females scurrying around their cages mating with multiple males. The skinny females were more likely to be monopolized by one male lemur, and had fewer mates overall.
"Polyandry might not respond only to sexual conflicts [harassment], but also provide benefits to females," Huchard said. "That's probably quite general in animal societies; it's been found in multiple studies in invertebrates."
There is some evidence that a type of cryptic choice between different sperm donors occurs in these gray mouse lemurs. Previous studies have found that female lemurs in the wild preferentially use the sperm from mates with certain genes that are different from hers. Researchers don't know how, but after mating with multiple males, the females are able to choose which male fathers her baby lemurs. It's possible she can distinguish between each mate's sperm, and uses only that from the most compatible mates.
In other species, it seems a female's ability to make a cryptic choice can offer benefits to her offspringl. The female can choose males that are better genetic matches, for example those that aren't her close relatives, which would make for healthier offspring.
And so this cryptic choice in mouse lemurs could be one way that taking multiple mates can benefit females in the long run, allowing them to choose the best genetic match, the researchers said.
The study was published Tuesday (Oct. 4) in the journal Proceedings of the Royal Society B: Biological Sciences.
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Jennifer Welsh is a Connecticut-based science writer and editor and a regular contributor to Live Science. She also has several years of bench work in cancer research and anti-viral drug discovery under her belt. She has previously written for Science News, VerywellHealth, The Scientist, Discover Magazine, WIRED Science, and Business Insider.