A new article in Behavioral Ecology, published by Oxford University Press, found that wild vampire bats that are sick spend less time close to others in their community, which slows down how quickly a disease spreads. The research team had already seen this behavior in the laboratory and used field experience to confirm it in nature, advances the EurekAlert portal.
As a pathogen spreads through the population, changes in social behavior can change the way the disease spreads. Transmission rates can increase when the parasites change the host’s behavior or decrease when healthy individuals avoid the sick.
In certain social insects, patients may voluntarily isolate themselves or be excluded by their colony companions. A simpler mechanism that causes reduced transmission is that infected animals usually exhibit unhealthy behavior, which includes increased lethargy and sleep, and reduced movement and sociability. This disease-induced social detachment does not require the cooperation of other people and is probably common among species.
The researchers conducted a field experiment to investigate how unhealthy behavior affects relationships over time, using a dynamic social network created from high-resolution proximity data.
After capturing 31 adult female vampire bats from a perch inside a hollow tree in Lamanai, Belize, the researchers simulated “sick” bats by injecting a random half of bats with the challenging immune substance, lipopolysaccharide, while the control group received saline injections. .
Over the next three days, the researchers pasted proximity sensors onto the bats, dropped them back into their hollow tree and monitored changes over time in the associations between all 16 “sick” bats and 15 control bats under natural conditions .
Compared to control bats, “sick” bats associated with less group mates, spent less time with others, and were less socially connected to healthy group mates when considering direct and indirect connections.
During the six hours of the treatment period, an “sick” bat was associated, on average, with four associates less than a control bat. 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. During the treatment period, “sick” bats spent 25 minutes less associating with each other. These differences narrowed after the treatment period and when the bats were sleeping or foraging outside the roost.
“The sensors gave us an incredible new window into how the social behavior of these bats changed hourly and even minute by minute during the day and night, even while they were hiding in the darkness of a hollow tree,” said lead author of the study, Simon Ripperger. “We move from data collection every day to a few seconds.”