Of mandrills, lobsters and devils ‒ social distancing in the animal kingdom
Writer and Artist: Patrick Marenda
Editor: Katie Dale
Ever wondered if we are the only ones to isolate ourselves today? Get ready for some tales of social distancing from the animal kingdom, to inspire and ease your own practice towards the end of this year.
Following the coronavirus pandemic, ‘social distancing’ has become omnipresent in our daily lives. We see it in the street, on social media and hear it everywhere. But humans are not the only ones who practise social distancing and self-isolation to reduce infection rates. Indeed, such behaviour has been observed in many other species, such as house finches, who avoid individuals that present general sickness behaviour. Research into the social distancing practices of other social species focuses on the transmission of information and infection, and it isn’t surprising that it saw an uptick in interest this year.
Social living has many advantages for animals, such as improving foraging efficiency and protection against predators. But it comes at a large cost: infections and diseases spread much faster in social species, as the individuals are in closer proximity. While social contact is necessary to establish and reinforce social bonds, it increases the risk of contagion, and as such individuals need to make decisions about whether or not to interact with another group member.
The main anti-pathogenic strategies are avoidance, resistance and tolerance, but they can go as far as self-isolation. Honeybees infected by Varroa destructor, a recently emerged pathogen, are less likely to return to their colony and prefer to die alone to enhance the colony’s survival chances. Such behaviour is mostly found in eusocial insects, such as Temnothorax unifasciatus, where the colony shows a high degree of social structure, segregating tasks like reproduction and foraging to certain individuals. By social distancing in response to the COVID-19 pandemic, we too can protect the more vulnerable bees in our global hive.
In other species, however, infected individuals simply cannot isolate themselves from the rest of the group. For example, Tasmanian devils are threatened with extinction by devil facial tumour disease, a lethal disease transmitted when infected individuals bite others in the group. Aggressive individuals, while having a higher infection risk, also have a higher reproductive output. Although there could be a selection pressure towards placidity, it isn’t clear whether the lower infection rate outweighs the lower reproduction rate. Furthermore, it is unclear if the evolution of social behaviour will suffice to save the Tasmanian devil from extinction.
Many social species have developed strategies to minimise the spread of disease. For example, infected black garden ants are likely to self-isolate, while other group members will not only distance themselves from the infected individual but also from each other, in a natural social distancing measure that minimises disease transmission. Another example can be found in West African mandrills, who can recognise through smell if a group member is infected with a parasite. The infected individual will then be groomed less by other group members, who will distance themselves too. For non-human primates, grooming is a highly social activity crucial to forming social relations and allying oneself with dominant group members. Once the parasite has been treated, the mandrill is again groomed and reintegrated into the group. Other examples of species that perform social distancing include Caribbean spiny lobsters and mice. This lobster avoids dens housing individuals infected by the lethal virus Panulirus argus Virus 1 (PaV1), and instead lives alone in a new den. Immune-challenged mice avoid other group members and reduce their number of social interactions on their own.
While minimising infection risk and limiting the spread of diseases, social distancing can harm social animals, just as it does to humans. In many species, isolation leads to stress, which in turn impacts the immune system, causing serious health consequences and sometimes even death. This is why apes and monkeys in captivity are no longer transported alone. In humans too, isolation can lead to psychological and physical pain. Contrary to animals, we can keep social contact while physically self-isolating, thanks to synchronous virtual communications like Zoom. Indeed, it has been shown that virtual social contact can, to some extent, help to mitigate the negative impacts of social distancing for humans.
Investigating these interactions can deepen our understanding of how natural selection acts on social behaviour and drives the evolution of social systems. More research on the underlying mechanisms allowing for network plasticity is needed in a greater number of species, as it might bring novel solutions relevant to human societies. Furthermore, we should remember that social distancing works since it has evolved over and over in very different animals. So, the next time you need to stay at home, give a thought to those cute and responsible animals, who share with you the burden of isolation. They would probably be jealous of that Zoom call that’s waiting for you.