Lady Egyptian fruit bats help themselves to food right from the mouths of their bat boyfriends. That has long been observed by the Tel Aviv University department of bat research. But inquiring minds at TAU wondered exactly why the males put up with it. Now they know.
It’s exactly the same reason why human males have been known to spring for dinner and a movie.
As reported in Current Biology on Thursday, “these male Egyptian fruit bats (Rousettus aegyptiacus) are repaid for their tolerance and generosity with sex,” report Prof. Yossi Yovel, Lee Harten, Shachar Ben Cohen and Roi Dor (with participation by Dr. Yosef Porat).
The scientists called the bat who takes food from the mouth of another a “scrounger.” The bat who allows this to happen is called a “producer,” though forager might be a more accurate term.
Anyway, technically, the researchers found a strong correlation between “producer-scrounger feeding interactions” and reproduction, explains lead author Yovel, of Tel Aviv University’s George S. Wise Faculty of Life Sciences.
Meaning? Meaning that the ladies would couple most often with the males they had plundered.
“Three to four months before mating, the females start scrounging for food from several males,” Yovel says. “Then eventually they mate with one of the males — the one with which they forged the strongest bond.”
The fact that the female has the child of her favorite feeder was proven by genetic testing, of the males and pups.
Bats in Shetopian high school
The team at Tel Aviv has been studying fruit bats for many years, on a variety of fronts. At first they couldn’t figure out this habit of stealing fruit from one another’s mouth — until they realized it wasn’t a power play.
“Originally we wondered: Why do the producers of food allow scroungers to take food from their mouths? Maybe they’re stronger? But we found that most of the scroungers are female, and so we considered the possibility that females trade mating for food. This was our hypothesis and, indeed, we found that this is the case,” says Yovel.
Much like our male at the movies, the benefit is likely to be delayed: Scrounging interactions start months before mating season.
It’s not quite a “Shetopia,” but each female clearly forms a clique of her few favorite males, Harten says.
Over the weeks she will eat fruit from their mouths — but eventually will choose one to mate with. Going by the genetic results of the pups and observation, her mate of choice will not couple with another female in that same mating season, Harten adds.
All this goes to show that fruit bats are capable of highly complex relationships, long-term memory and, quite possibly, affection.
Unlike in the movies, this fondness may be transient. The next mating season, part of the clique may find itself replaced, Harten says. Sounds like high school, fruit bat-style. The former fave may well date another female bat, allowing her to feed from his mouth.
But unlike in high school, the females do not compete over the males, though they are the choosers — they choose from whom to scrounge. It isn’t the male who generously confers fruit chunks from his jaws to the lady, Harten says.
Or as TAU put it: “The researchers found that there was almost no overlap between males preferred by each female. It suggests that females choose males to scrounge from based on some form of individual preference. Those personal preferences also changed from year to year.”
Doing it for themselves
Let us be clear that some female fruit bats just go to the dish and eat, upside down of course. The only thing bats do right-side up is relieve themselves: They hang by their wing claws from a branch, bottom down, and doo what they do.
But the majority of females observed in the three different bat colonies set up at TAU were scroungers, Harten told Haaretz.
Some males exhibit “feminine behavior” and scrounge too, but they are very much the minority. Those that do tend to scrounge from females. The smallest group of all is male-on-male scroungers.
No, they have not observed homosexuality in bats, Harten says. Which doesn’t mean it doesn’t happen. Maybe it does.
“I do see friendships. There are social interactions between male bats,” she observes. But they haven’t seen homosexual intercourse in the Egyptian bat. Moving on.
So, again: Why would males allow other bats, primarily females, to literally take food out of their mouths?
“The results were quite clear. Females gave birth to the young of males from which they had scrounged food,” Yovel says. “The findings lend support for the food-for-sex hypothesis in this species.”
No, it isn’t prostitution — it’s reciprocity, a very difficult concept for evolutionary biologists to accept. She gets food, he gets sex, they have a baby.
“Food sharing is evolutionarily puzzling,” the researchers point out. So, could this be some totally bizarre artifact of captivity? Seems not.
“I think it happens in nature,” Harten speculates — based on the fact that the university created three separate bat colonies, of which only in one did the members know each other for years. She then “collected new bats who didn’t know each other, and we observed producing and scrounging from day one,” she says.
Also, the female bat makes a certain vocalization when she scrounges food; the scientists could hear similar sounds in nature, Harten adds.
It may be love
All this leads one to wonder what happens when the males have fed the female assiduously for months, and finally she picks one and gets pregnant. What then?
From the point of inception, Harten says, the female gets very hungry. Or as the scientific community puts it: her energetic needs escalate. A certain change in the batty social interactions starts to appear.
“After birth, while nursing the bat pup, she scrounges a lot and is less specific from who she scrounges,” says Harten. Basically, she will take food from anybody; her priority is meeting her energy demand. Once the pup is weaned, though, the relationships will resume.
Food sharing is not unknown in other species. Wild female chimpanzees have been demonstrated to exchange sex for fruit (papayas), Dr. Kimberley Hockings reported in PLOS One in 2007. The female chimps selected the males by quality of provision.
Which brings us to the best for last in the bat community: it may be love. Of some sort.
Bats, the same TAU group has demonstrated in the past, argue a lot (female bats, it turns out, scold the males regularly over the predictable issues: food, relationships and space). No question about it, one lady bat must have sniffed at another sometime in the past: “What do you see in him?”
“It’s not about male quality. It’s not a popularity contest. It isn’t that the more food they bring, the more popular they are,” says Harten. “The females are not choosing the males that bring the most food. There is no correlation between your food provision and the interest in you.”