This week I’ve been working with a team of bat researchers in Lamanai, Belize (an archaeological site of the ruins of a Mayan city). We are collecting data for a study on the effects of sickness behavior on social associations in wild vampire bats. Last year, PhD student Sebastian “Basti” Stockmaier and I conducted two projects on how social behavior is affected by lipopolysaccharide (LPS)—a bacterial endotoxin that challenges the immune system and induces sickness behavior. LPS can cause symptoms of sickness such as fever and lethargy, but the effects are temporary and the animal makes a full recovery because there is no actual pathogen. The effect of LPS on social networks was first studied by Patricia Lopes. She injected mice with LPS or saline and tracked their nest-sharing associations. Mice that were injected with LPS were less socially connected to others. This work is important because it shows that sickness behavior can reshape social networks and therefore change how a pathogen might spread.
Basti and I conducted three studies on the effects of LPS on vampire bat social behavior. In one study, we injected vampire bats with either saline (control) or LPS then isolated them and counted how many contact calls they produced. In another study, we individually fasted bats in a large captive colony housed in a flight cage, injected them with LPS or saline, and then looked at whether they received more or less food from their group-mates. We also looked at whether the sick-feeling bats gave or received more social grooming. Finally, to experimentally remove the effect of association, we tested the effects of LPS effects on grooming given and received when bats were forced into constant association by keeping them with one or 3 others in close proximity. We did this test because sickness behavior might have an effect on both social associations (being in the same place at the same time) and social interactions (e.g. mating, fighting, grooming, food sharing) and although people often use associations as a proxy for interactions, they are not the same thing. These studies were all done while I was in Rachel Page’s Lab at the Smithsonian Tropical Research Institute in Panama, and they should be published this year and next.
Next, I thought it would be good to complement these captive studies by looking at effects of LPS on vampire bats in the wild. So Simon Ripperger, my wife Michelle Nowak, and I joined a field trip that Brock Fenton and Nancy Simmons take to Lamanai every year. Simon Ripperger is the only person who could track social associations between more than 30 vampire bats simultaneously. We also teamed up with disease ecologist Daniel Becker who has been banding and monitoring the physiology of the vampire bats at Lamanai the last few years.
Brock knew about a large hollow tree full of insect-eating Saccopteryx bilineata, insect and nectar-feeding Glossophaga soricina, and our target: the blood-feeding Desmodus rotundus. To catch the emerging bats, we strung up mist-nets using a jerry-rigged pulley system. Saccopteryx emerged at dusk, followed by the Glossophaga. Next, we began to capture males going in and out of the tree (see images below taken on previous years at the same roost exit by Brock Fenton).
After a slow period, we began to catch females exiting around 2 am. By the end of the night we had captured more than 40 females and even more males, and we stopped because we ran out of bags and had more than we needed (image below).
We released 34 female vampire bats with proximity loggers, half being injected with LPS and the other half with saline. Daniel Becker banded both males and females and took blood and hair samples for his long-term studies.
Using Simon’s proximity logger system, we could remotely download encounters between bats over the next 4 nights, without having to disturb or recapture them. The loggers document the duration and distance estimates of encounters among up to 60 individuals at distances from touching to 10 meters. My prediction is that the immune-challenged bats will have fewer encounters with others because they will be less active, and that the effects on association will not be as dramatic as what can be seen when observing the actual interactions.