There are always "surprises" that cross my desk concerning the cognitive and emotional lives of nonhuman animals (animals). For example, among the numerous recent fascinating discoveries are included recent research that shows fish-are-sentient-and-emotional-beings-and-clearly-feel-pain">fish displaying that they are sentient beings, fish and crocodiles using tools, fish using referential communication to tell other fish where there's food, bees getting depressed, and - related to the study discussed below - parrots dying very young when they're forced to live alone (please see "Captive Grey Parrots Suffer From Social Isolation Loneliness").
Now we know that an invertebrate, namely carpenter ants, also suffer from social isolation. In a landmark paper published in the journal Behavioural Ecology and Sociobiology by researchers Akiko Koto, Danielle Mersch, Brian Hollis, and Laurent Keller called "Social isolation causes mortality by disrupting energy homeostasis in ants," we learn that young ants who are forced to live alone die much younger than group-living ants. The abstract for this paper reads as follows:
Social deprivation can have negative effects on the lives of social animals, including humans, yet little is known about the mechanisms by which social withdrawal affects animal health. Here we show that in the carpenter ant Camponotus fellah, socially isolated workers have a greatly reduced life span relative to ants kept in groups of ten individuals. By using a new tracking system, we found that social isolation resulted in important behavioral changes and greatly increased locomotor activity. The higher activity of single ants and their increased propensity to leave the nest to move along the walls suggested that the increased mortality of isolated ants might stem from an imbalance of energy income and expenditure. This view was supported by the finding that while isolated ants ingested the same amount of food as grouped ants, they retained food in the crop, hence preventing its use as an energy source. Moreover, the difference in life span between single and grouped individuals vanished when ants were not fed. This study thus underlines the role of social interactions as key regulators of energy balance, which ultimately affects aging and health in a highly social organism.
A good review of this paper can be found in an essay called "Lonely ants die young and hungry" by Karl Gruber (for more coverage please click here). When ants get lonely "They're unable to digest their food properly and walk themselves to an early death ..." The results show that isolated ants lived only six days, whereas group-living ants lived up to ten times as long (averaging 66 days of life).
Group-living and food sharing may be important for survival
Researchers are unsure about why young socially isolated ants die young.
"The scientists say their results show that ants simply don't know how to behave when alone. 'Isolated ants exhibited a much higher activity after social isolation, continuously walking without any rest,' says study co-author Dr Laurent Keller, an entomologist from the University of Lausanne. This behavior is a recipe for trouble as the ants don't get enough energy to back it up, explains study co-author Dr Koto Akiko of the University of Tokyo. 'Because of this hyperactivity, isolated ants faced an increased energy demand', says Akiko. 'Isolated ants ingest as much food as their grouped nest mates, but the food is not processed fully by the digestive tract', he adds."
One hypothesis proposed by this team of researchers suggests
"that sharing of regurgitated food, a process called trophallaxis, may be a way for morsels of food to become more digestible. Alternatively, it may be that social interaction affects some neural pathways that promote gastrointestinal activity, notes Keller. But Dr Ken Cheng, a behavioral biologist at Macquarie University has another explanation in mind, involving gut microbes. 'It would not surprise me if gut bacteria, which would be passed around with the exchange of food, played a role as well in the adverse effects of isolation,' says Cheng, who was not involved in the research."
This study on ants shows that social isolation and health are closely related and much more research is needed in this area. It's notable that "even ants" show a negative reaction to loneliness, as do many other species, including humans. It should also be noted that because ants show such negative responses to social isolation, they should not any longer be forced to live alone.