Vampire bats know that sharing blood with friends is a good way
Vampire bats don’t have the best reputation. On the one hand, they are bats, and despite the value of bats and their great variety – about a quarter of all mammal species – not everyone likes them.
It may have to do with the virus they host, which wouldn’t be much of a problem if we left them alone. Or it may just be that the beating of bat wings at night strikes a chord with most humans. But these are not the bats that we think are the source of the novel coronavirus.
And then there’s the vampire thing. But bats are not Dracula, nor any of his animated blood companions on shows such as Castlevania. Vampire bats are, in fact, the soul of cooperation, with a complex social structure. Like good toddlers, they learned to share. For bats, their life depends on it.
If a vampire bat drinks from a cow’s ankle one night, it will likely share that meal with another bat. They do it by regurgitation, but it’s just a matter of style. Blood meals are hard to find, and they don’t keep you very long. According to one estimate, a bat needs food every 48 hours to survive. It is a good evolutionary incentive to develop food sharing.
Vampire bats generally share what they have drunk with other members of their female-headed family. But they also extend the habit of sharing blood to other bats that they bond closely with, even though they have nothing in common genetically.
Gerald Carter, a behavioral ecologist at Ohio State University who studies cooperation in vampire bats, reported Thursday in Current biology that an experiment in his lab has shown that bats gradually form friendships, while other bats show that they are reliable.
Dr Carter, who has been recording the behavior of bats in his lab for over a year, said they were following predictions from a mathematical model called “raising the stakes”,”In which the favors exchanged gradually increase in size.
The model has been shown to work in testing with humans playing cooperative games. But, said Dr Carter, his experience in a situation that mimics natural conditions shows “how animals move from being aliens to forming a naturally cooperative relationship.”
“It’s a great study,” said Dina Dechmann, behavioral ecologist at the Max Planck Institute for Animal Behavior in Germany, which also studies bats and was not involved in the research. Actions that cost the donor, such as sharing food, were thought to be related to parentage by preserving their own genes. So share with friends was a puzzle.
“But we are increasingly finding that cooperating groups and individuals are not linked – here is an explanation of how this could happen,” said Dr Dechmann.
Dr. Carter has been an avid bat enthusiast since he was a child. Fortunately, vampire bats have proven to be extremely useful for the study of animal cooperation, his favorite field. They are easy to rear in a small space, like rats, but socially complicated, like primates.
In the wild, said Dr. Carter, “Vampire bats spend almost all of their time, like 23 hours a day, inside a space that is perhaps the size of a small closet. He experimented with colonies of females, which also contained young males.
“When we put them in captivity, they do whatever they would do inside a hollow tree,” he said.
Cooperative behavior comes naturally, and experimenters can trigger it, simply by enforcing a fast of the type that vampire bats experience in the wild.
Dr Carter said extending a network of blood donors to non-family people offers no immediate benefit. But, in a pinch, if mom and sister go missing, having a backup can be helpful.
“Individuals who only have a commercial food relationship with a mother, they don’t have backup partners. So we think that’s what these weaker relationships with non-parents are for, ”he said. “It’s basically an insurance policy.
Dr. Carter took vampire bats from the wild and herded them in the lab as aliens with cameras pointed at them.
Some were in a relationship. In other cases, an alien was introduced to a group of three bats who had lived together. And in other cases, two groups of three were formed.
Isolated pairs formed relationships more quickly; groups were slower to bond, like college roommates reunited, Dr Carter said.
But what Dr. Carter’s group was studying was not time, but different behaviors and their cost to a bat. Grooming, in the form of licking your fur, doesn’t cost much in terms of energy, so it’s a small investment in a social bond. But food sharing is expensive, especially when you only have 48 hours to find a meal.
As expected, grooming behavior appeared first, and grooming relationships were more common than food sharing relationships. And the amount of grooming was an indication of the subsequent sharing of the food. The more important the grooming, the more likely it was to share food. They predicted that the grooming would happen first and then move on to blood sharing.
What Dr. Carter would like to study next is what happens if a bat doesn’t delay ending the relationship.
Dr Dechmann, in email comments on the paper, couldn’t help but put a cap on bats and bat lovers around the world: (among other notable things) these very intelligent animals have.