Humans can learn a lot from the way vampire bats deal with an infectious disease in a colony
Scientists, public health experts and guidelines have been insisting on social distancing to prevent Covid-19 transmission and humans could probably take some lessons from vampire bats on this. When disease strikes, vampire bats voluntarily socially distance themselves from groupmates in their roost and they do not need any public health advisory, according to a new study.
Researchers gave wild vampire bats a substance that activated their immune system and made them feel sick for several hours, and then returned the bats to their roost. A control group of bats received a placebo. Data on the behavior of these bats was transmitted to scientists by custom-made ‘backpack’ computers that were glued to the animals’ backs, recording the social interactions of the bats. The authors found that compared to control bats in their hollow-tree home, sick bats interacted with fewer bats, spent less time near others and were overall less socially interactive or connected with individuals that were well-connected with others in the roost. Healthy bats were also less likely to associate with a sick bat, reveals the analysis published in the journal Behavioral Ecology. The findings suggest that social distancing while sick comes naturally to vampire bats.
"Social distancing during the Covid-19 pandemic, when we feel fine, doesn’t feel particularly normal. But when we’re sick, it is common to withdraw a bit and stay in bed longer because we're exhausted. And that means we're likely to have fewer social encounters. That’s the same thing we were observing in this study: In the wild, vampire bats, which are highly social animals, keep their distance when they’re sick or living with sick groupmates. And it can be expected that they reduce the spread of disease as a result," explains co-lead author of the report, Simon Ripperger, a postdoctoral researcher in evolution, ecology and organismal biology at The Ohio State University. He is also a visiting scientist at the Museum of National History in Berlin, Germany.
The findings
Individual behaviors when sick can slow the spread of pathogens across a social network. To understand this aspect, the team conducted a field experiment to investigate how this affects individual connectedness over time. For tracking associations among the bats, they used custom-built proximity sensors: miniaturized computers that weigh less than a penny and fall off within a week or two.
The team captured 31 female common vampire bats (Desmodus rotundus) living inside a hollow tree in Lamanai, Belize. They created ‘sick’ bats by injecting 16 bats with the molecule (lipopolysaccharide) that induced the immune challenge but did not cause disease, and 15 (controlled group) with saline, a placebo. After returning the bats to their roost, the scientists analyzed social behaviors in the colony over three days, including a “treatment period” from three to nine hours after the injections during which the researchers attributed behavior changes to the effects of treated bats feeling sick.
The study focused on three measures of the sick bats’ behaviors: how many other bats they encountered, how much total time they spent with others, and how well-connected they were to the whole social network. The investigators found that a control bat had, on average, a 49% chance of associating with each control bat, but only a 35% chance of associating with each sick bat. On average, compared to control bats, the sick bats associated with four fewer groupmates over the six-hour treatment period and spent 25 fewer minutes interacting per partner, and the time any two bats spent near each other was shortest if the encounter involved at least one sick bat.
According to co-lead author Gerald Carter, assistant professor of evolution, ecology and organismal biology at Ohio State, a reason why the sick vampire bats encountered fewer groupmates is because they were lethargic and moved around less.
“In captivity, we saw that sick bats also groom others less and make fewer contact calls. These simple changes in behavior can create social distance even without any cooperation or avoidance by healthy bats. We had previously studied this in the lab. Our goal here was to measure the outcomes of these sickness behaviors in a natural setting,” writes Carter. He adds, “The effects we showed here are probably common in many other animals. But it is important to remember that changes in behavior also depend on the pathogen. We did not use a real virus or bacteria, because we wanted to isolate the effect of sickness behavior. Some real diseases might make interactions more likely, not less, or they might lead to sick bats being avoided.”
The researchers emphasize that they were able to clearly identify each bat’s behavior in the colony’s social network due to the proximity sensors. The latter took measures every few seconds of associations involving sick or healthy bats or a combination of the two. Visualizations of the proximity sensors’ recordings showed growth in the number of connections made in the colony’s social network from the treatment period to 48 hours later. “The proximity sensors gave us an amazing new window into how the social behavior of these bats changed from hour to hour and even minute to minute during the course of the day and night, even while they are hidden in the darkness of a hollow tree,” says Ripperger.