38 Scientific American, August 2020
The lobster’s response to disease—seen in both field
and laboratory experiments—is one we have become
all too familiar with this year: social distancing. Peo-
ple’s close interactions with family and friends have
been cut off to reduce the spread of COVID-19. It has
been extremely hard. And many have questioned the
necessity. Yet despite how unnatural it may feel to us,
social distancing is very much a part of the natural
world. In addition to lobsters, animals as diverse as
monkeys, fishes, insects and birds detect and distance
themselves from sick members of their species.
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 con-
tagious diseases. (Just ask any human parent with a
child in day care.) This heightened risk has favored
the evolution of behaviors that help animals avoid
infection. Animals that social distance during an out-
break 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 ani-
mals do not have vaccines, but they can prevent dis-
ease by how they live and act.
Immunity through behavior does come with costs,
though. Social distancing from other members of your
species, even temporarily, means missing out on the
numerous benefits that favored social living in the first
place. For this reason, researchers have learned that
complete shunning is just one approach animals take.
Some social species stay together when members are
infected but change certain grooming interactions, for
example, whereas others, such as ants, limit encoun-
ters between individuals that play particular roles in
the colony, all to lower the risk of infection.
WORTH THE SACRIFICE
The abiliTy of spiny lobsTers to detect and avoid infect-
ed group mates has been key to their persistence in the
face of Panulirus argus virus 1, which kills more than
half of the juvenile lobsters it infects. Young lobsters
are easy pickings for the virus because the animals are
so social, at times denning in groups of up to 20. Safe
homes in sponges, corals or rocky crevices along the
ocean floor—and a mass of snapping claws—help the
group of creatures defend against hungry predators
such as triggerfish. Nevertheless, in the early 2000s
researcher Don Behringer of the University of Florida
and his colleagues noticed that some young lobsters
were denning solo, even though it left them vulnera-
ble. Most of these lonely lobsters, the researchers found,
were infected with the contagious virus. These lobsters
O
n 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 newcom-
er is not right, though. Chemicals in its urine smell different. These
substances are produced when a lobster is infected with a conta-
gious virus called Panulirus argus virus 1, and the healthy return-
ing 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.
IN BRIEF
Despite how unnat-
ural social distanc-
ing may feel to peo-
ple, it is very much
a part of the natural
world, practiced by
mammals, fishes,
insects and birds.
Social animals stay
apart, changing
behaviors such as
grooming to stop the
spread of diseases
that could kill them.
Strategies vary from
shunning a sick ani-
mal to maintaining
interactions with only
the closest relatives.
Dana M. Hawley is a professor at Virginia Tech
who studies social behavior and disease among animals.
Julia C. Buck is an assistant professor at the University
of North Carolina at Wilmington, where she runs a disease
ecology laboratory.
© 2020 Scientific American
