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Social Behavior and Disease Risk with Dr. Caroline Amoroso

Written by Sarah McPeek

Dr. Caroline Amoroso never thought she’d live in a world where the questions that motivate her animal behavior research would define daily human life.

Caroline joined the Ecology, Evolution, and Behavior group within the UVa biology department in January as a postdoctoral researcher with Dr. Janis Antonovics, Lewis and Clark Professor of Biology and renowned disease ecologist. Two months later, in-person research at the University shut down in response to the global COVID-19 pandemic. Since then, she’s been working from home with her husband, their six-month-old baby, and their two Boston terriers.

Caroline is a behavioral ecologist by training, a biologist who studies how an animal’s behavior relates to its evolutionary history. Specifically, she’s interested in how animals navigate disease risk in their environment.

Sound familiar?

Like many behavioral ecologists, Caroline’s work hinges on the idea of tradeoffs: behaviors carry both costs and benefits for individuals and social groups. Animals who behave adaptively maximize the benefits of a certain action while minimizing the associated risks.

During her PhD with Dr. Charles Nunn, an evolutionary anthropologist at Duke University, Caroline became fascinated by the intense ecology of red-fronted lemurs (Eulemur rufifrons) in the dry tropical forests of Madagascar. These highly social primates roam the forests as small family troops of four to eighteen individuals. During the prolonged dry season, their lives revolve around travel to ephemeral watering holes puddled on the forest floor. Many lemur troops share the same sparse holes. As a consequence, the shallow pools accumulate fur, urine, feces, and all manner of grime.

The lemurs need water to survive, but drinking from contaminated pools and sharing space with many other lemurs heightens their risk of contracting costly pathogens like parasitic worms. Caroline wanted to know how lemurs weigh this essential tradeoff between dehydration and disease.

To answer this question, she dug pits for experimental water tubs on the forest floor. Some she filled with freshly collected lemur dung that was disinfected to minimize parasite load, others she left pristine. This allowed her to directly test whether lemurs associate dirty water with disease risk. For several weeks, she watched lemurs interact with her experimental tubs and recorded which tubs they used more: the soiled or the clean. Lemurs overwhelmingly avoided the dirty water for the clear, demonstrating that they sense something may be amiss with the mucky water and opt for the cleaner, safer source.

Whether the lemurs realize that dirty water could be infested with pathogens or whether they’re simply disgusted by the soiled, smelly puddles is unclear. In either case, their ability to discriminate between dirty and clean water is adaptive as it reduces their risks of getting sick.

For many wild animals, disease is a constant gnawing danger. Still, disease is only one of the many challenges they face in their environment. Access to essential resources like water, food, and shelter in combination with risks from predators and pathogens all define how animals interact with their world and with each other. In another study that tracked the movements of lemur troops with GPS collars, Caroline found that lemurs prefer watering holes that are closer to their home ranges over watering holes that require long-distance travel to reach. This suggests that in such a parched habitat, disease exposure may be a lemur’s secondary consideration after easy access to vital water sources. Further, the balance of these tradeoffs can shift dramatically over the course of the year. During the brief rainy season when forests are lush with fresh water, lemurs may be more leery of contamination than they are when water is scarce.

The choices Caroline’s lemurs navigate every day are in some ways similar to the difficult decisions we face in the current pandemic crisis. From her research with primates, Caroline recognizes that individual decisions crucially impact group well-being when it comes to the spread of disease. One lemur who drinks contaminated water can not only become infected himself but can go on to infect the rest of his troop. Likewise, one person who flaunts social distancing guidelines risks contracting the coronavirus and spreading it to everyone they encounter, including those who may be at much higher risk for serious illness.

Caroline’s work also shows that effective avoidance is intrinsically linked with successful detection of the disease. Lemurs avoid water that is overtly filthy and foul-smelling. While Caroline and Dr. Antonovics are away from the office, they’re collaborating remotely on mathematical models of host-pathogen coevolution that incorporate avoidance behaviors for hosts, specifically social avoidance of infected individuals. They’re finding that when the infection is detectable and the costs of disease are high, social avoidance behaviors are adaptive and proliferate through the population because the benefits of lowering disease transmission can outweigh the costs of reduced social interaction with infected individuals.

However, when the infection is undetectable and the costs of illness are high, only the highest levels of social avoidance can reduce the spread of the outbreak. Strict social avoidance behaviors minimize the spread of undetectable pathogens from infected to susceptible individuals. Since many carriers of the coronavirus show no signs of illness for long periods of time, detecting who is infected has been an immense challenge with COVID-19. Still, Caroline and Dr. Antonovics’ models show that the adoption of widespread cooperative social avoidance can effectively stamp down disease transmission. Caroline has plans to further extend this research to understand our defensive responses to the current COVID-19 pandemic.

The process of building models helps Caroline identify all the unknowns at play in any disease epidemic, unknowns which have become shockingly apparent in the current crisis. At this point in our encounter with the novel coronavirus, our abilities to detect and isolate infected individuals are low. Thus, concerted avoidance is currently the most viable strategy for stemming the spread of the disease.

Nevertheless, Caroline also recognizes that the costs of our current behaviors are vast. Like lemurs, we are highly social animals that depend on others for comfort, safety, and our very lives and livelihoods. The lack of interpersonal contact takes huge tolls on our mental wellbeing, not to mention the severe economic damage. The balance of tradeoffs between risks from disease and risks from continued social distancing will shift as we learn more about the coronavirus and develop tools to successfully combat COVID-19 in our communities.

We are now in the dry season, but there are promising storm clouds forming on the horizon. Caroline is eager to get back into the field and continue her research when the rains return.

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