In our current pandemic, one of the major pieces of advice is to engage in social distancing. This may feel like it goes against your instincts. You may have even wondered if any other species would be able to social distance. In fact, there are some examples of other species who instinctively social distance. The excerpts below come from this Scientific American article. 

Lobsters:

On a shallow reef in the Florida Keys, a young Caribbean spiny lobster returns from a night of foraging for tasty mollusks and enters its narrow den. Lobsters usually share these rocky crevices, and tonight a new one has wandered in. Something about the newcomer is not right, though. Chemicals in its urine smell different. These substances are produced when a lobster is infected with a contagious virus called Panulirus argus virus 1, and the healthy returning lobster seems alarmed. As hard as it is to find a den like this one, protected from predators, the young animal backs out, into open waters and away from the deadly virus.

Ants

Researchers used tiny digital tags to track the movements of common garden ant colonies during an outbreak of a lethal fungus, Metarhizium brunneum. The spores of this fungus are passed from ant to ant through physical contact; it takes one to two days for the spores to penetrate the ant’s body and cause sickness, which is often fatal. The delay between exposure and sickness allowed Stroeymeyt and her colleagues to see whether ants changed their social behaviors in the 24 hours after they first detected fungal spores in their colony but before fungus-exposed ants showed signs of sickness.

To measure how ants respond when disease first invades their colony, the researchers applied fungal spores directly to a subset of the forager ants that regularly leave the colony. The foragers are most likely to inadvertently encounter fungal spores while out searching for food, so this approach mimicked the natural way this fungus would be introduced. The behavioral responses of ants in 11 fungus-treated colonies were then compared with the same number of control colonies, where foragers were dabbed with a harmless sterile solution. Ants in fungus-exposed colonies started rapid and strategic social distancing after treatment. Within 24 hours those forager ants self-isolated by spending more time away from the colony compared with control-treated foragers.

Healthy ants in fungus-treated colonies also strongly reduced their social interactions, but the way they did so depended on their roles. Uninfected foragers, which interact frequently with other foragers that might carry disease, kept their distance from the colony when disease was present. This prevents them from inadvertently putting the reproductively valuable colony members (the queen and “nurses” that care for the brood) at risk. The nurses also took action, moving the brood farther inside the nest and away from the foragers once the fungus was detected in the colony. The cues that the ants use to detect and rapidly respond to fungus exposure are still unknown, but this strategic social distancing was so effective that all queens and most nurses from the study colonies were still alive at the end of the experimental outbreaks.

Guppies:

In work published in 2019 in Biology Letters, Jessica Stephenson of the University of Pittsburgh placed individual guppies that did not yet have worm infections in a central aquarium flanked by two tanks. One was empty, and one contained a group of three guppies that represented potential contagion risk. Many guppies preferred the side of the tank near other guppies, as expected for a social species. But some male guppies strongly avoided the side of the tank near the other fish, and these distancing guppies were later shown to be highly susceptible to worm infections. It makes sense that evolution would favor a strong expression of distancing behavior in those most at risk.

Mandrills:

Strategic social distancing sometimes means maintaining certain social ties even when they raise disease risk. Mandrills, highly social primates with strikingly colorful faces, illustrate this approach. This species can be found in groups of tens to hundreds of individuals in the tropical rain forests of equatorial Africa. Groups typically have a mix of extended family members that frequently groom one another; grooming improves hygiene and cements social bonds. But they adjust their grooming behaviors in particular ways to avoid contagious group mates, Clémence Poirotte and his colleagues noted in a report published in 2017 in Science Advances. The scientists observed the daily grooming interactions of free-ranging mandrills in a park in Gabon and periodically collected fecal samples to learn which animals were heavily infected with intestinal parasites. Other mandrills actively avoided grooming those individuals. The mandrills could detect infection status based on smell alone: mandrills presented with two bamboo stalks rubbed in feces strongly avoided a stalk rubbed with droppings from another mandrill that had lots of parasites.

Why Social Distancing?

This kind of behavior is common because it helps social animals survive. Although living in groups makes it easier for animals to capture prey, stay warm and avoid predators, it also leads to outbreaks of contagious diseases. This heightened risk has favored the evolution of behaviors that help animals avoid infection. Animals that social distance during an outbreak are the ones most likely to stay alive. That, in turn, increases their chances to produce offspring that also practice social distancing when confronted with disease. These actions are what disease ecologists such as ourselves term “behavioral immunity.” Wild animals do not have vaccines, but they can prevent disease by how they live and act.

In their 2020 publication in Biology Letters, the researchers said that maintaining strong and unconditional alliances with certain relatives can have numerous long-term benefits in nonhuman primates, just as in humans. In mandrills, females with the strongest social ties start breeding earlier and may have more offspring over their lifetimes. Such evolutionary gains associated with maintaining some social ties may be worth the risk of potential infection.