Petridish Spotlight: Fund This Project and Help Solve the Mystery of Animal Cooperation

Why do bats help each other out?

By Gerald Carter|Tuesday, May 15, 2012


Petridish.org is a crowd-funding site for science. Here, we're featuring one of our favorite Petridish projects. To fund this project, or to see more projects, go to Petridish.org.

How does natural selection--the ruthless struggle for genetic survival--produce cooperation, altruism, and empathy?

This question poses an important evolutionary puzzle. If some individuals in a population spend energy helping others, then these helpers can be outbred by non-helping "cheats" that reap all the benefits but don't pay the costs. This is called an evolutionary "tragedy of the commons" because the public good of cooperation is exploited by cheats and eventually disappears. Whenever we see helping behavior in nature, helpers must somehow be preventing cheating such that "nice guys finish first." But how?

I’m studying the vampire bat as a new model to understand how the behavior of individual animals can enforce and stabilize cooperation in a complex society.

I am deeply interested in the evolution of cooperation and I have been obsessively curious about bats since the age of two. In high school, I did my first experiment by testing what bat house designs my backyard bats preferred. As an undergraduate at Cornell University, I created the first noninvasive method for identifying the prey of vampires using DNA from their feces. I later studied vocal communication and how natural selection shapes animal learning. My previous work has led to seven publications. I’m now a Ph.D. candidate and Ford Predoctoral Fellow at the University of Maryland. I'm truly inspired to be working with Professor Jerry Wilkinson, who first reported vampire bat food sharing in 1984.

A hairy-legged vampire bat
Gerald Carter

Why vampire bats?
Like primates, vampire bats are extreme social cooperators. But unlike primates, we can manipulate much of their natural cooperative behaviors in the lab. Vampires bats will naturally share their food with certain partners. Since they drink nothing but blood, which is a nutritionally poor, hard-to-get food, they can starve to death easily. But, they have evolved a vital social safety net. Bats will regurgitate their own food for hungry roostmates, even non-relatives. We think these food donations might represent a social investment which ensures that others will feed them in return. Such complex cooperation might explain why vampire bats (like humans) have a huge brain and neocortex relative to their ancestors.

But what social information do vampire bats use to decide whether to donate to others? Do the bats punish freeloaders by reducing donations to partners who don't reciprocate? Do the bats compete to be the best social partners?

To answer these questions, we are using non-invasive behavioral experiments to test the effects of genetic relatedness, past social experience, and hormones on helping behavior in several colonies of vampire bats.

Filming in a cave in Mexico.
Michelle Nowak

Why this matters
Vampire bats are distantly related to primates, yet they evolved many of the same prosocial behaviors, such as communal food sharing and social grooming. While studying these bats, we have three goals. First, we want to test current and controversial theories about the evolution of cooperation and its consequences for the animal mind. For example, is social experience or genetic similarity a better predictor of helping in vampire bats? Second, we want to gain insight into the mind of an animal that is so alien to us, and yet might be so similar in so many ways. Do vampire bats distinguish an in-group and out-group (like humans)? Finally, we want to understand more generally how genetic relatedness, brain chemistry, and social experience interact to predict prosocial behavior. For example, oxytocin increases trust and generosity in humans, but also exaggerates our tribalistic and xenophobic tendencies. Will it have the same effect on vampire bats or are humans unique in this respect? We hope you find these topics as profound and fascinating as we do!

Potential discoveries
When scientists talk about the social lives of animals, they typically measure genetic structure and the observable patterns of where they live. We want to take things further and closer. In short, we want to use food sharing to understand if and how vampire bats form social bonds. We also want to understand how competition among sharing partners and cooperation between partners might shape the social network.

Our experiments can also help us understand animal cooperation more generally. There has been much work on animal cooperation, but previous studies have either involved relatively simple organisms like microbes, plants, insects, and fish, or cognitively complex animals that have been trained to perform an artificial form of cooperation, like pulling a lever to deliver food. Our study is special because it allows us to conduct controlled experiments on a completely natural form of helping (food sharing) that occurs in the lab but has evolved in the wild.

We expect three important outcomes in the next 3 years. We will measure the extent to which vampire bats care about kinship, past social experience, and the possibilities of alternative partners. We will learn if and how vampire bats deter cheating. And we will gain insight into the role of oxytocin in prosocial behavior.

What your money can do
After years of observations from the field and from captive bats at other institutions, we are finally bringing a colony of vampire bats to our university. We are planning to give them lots of space to fly and socialize, and they will need a gallon of cow blood every week. We are also hoping to support undergraduate students that will help us take care of them. We think it will be a great way to provide research experience for young scientists. Funds will go primarily to caring for the bats, and to analyze sequences of DNA to assess relatedness. We can make this money go a long way!


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