Hugging helps the immune system, cures depression, reduces stress and induces sleep. Gut bacteria also appears to thrive with regular physical contact, suggests new data that shows 'huddling' actions lead to a synchronised microbiome.
Beneficial bacteria in the gut are known to attack pathogens, manufacture vitamins and even act as anti-cancer agents. Recent research has strengthened the scientific understanding that the microbes that live in your gut may affect what goes on in your body.
"When people with different gut microbiomes interact, they share their symbiotic bacteria through touch," said Aura Raulo, lead author and graduate student at Oxford University's department of zoology.
"I might host a bacteria in my gut that is well-behaved, and fits my symbiotic gut community, but might turn out to be an invasive pathogen in another person who is not accustomed to it."
The animal data, published in the Journal of Animal Ecology, have implications for human health as microbes refine immune defence. By sharing microbial allies and enemies infections are reduced by opportunist pathogens in a show of cooperative immunity, the team from Oxford University suggest.
"Understanding that social environment and stress are directly linked to gut microbiome, could go some way to explaining why the western world experiences so many epidemics of autoimmune diseases, and help us to better treat people with them," she said.
"The microbiome is the link between our internal physiology and the external ecosystem. When tackling modern epidemics of autoimmune disease, we cannot ignore the environmental problems our ecosystem is facing, nor the social problems our culture is facing.'
Recent work has found that frequent intimate kissing enhances mutual transmission of mouth microbiota in humans.
Social proximity is also considered a good predictor of gut microbial composition in howler monkeys and baboons (Papio cynocephalus ) regardless of shared environment, diet or relatedness.
Collaborating with scientists from the University of Arizona and the City University of New York (CUNY), the team looked at the gut microbiota within a social network of red-bellied lemurs.
Data were collected from family groups at a time of the year when infants were born and fruit availability was generally low.
Eight groups were observed on a rotating basis with age, sex and identity noted. Data was also collected on behavioural states at five minute intervals.
Social behaviours, such as mutual grooming and huddling were recorded with more than 40 hours of behavioural data used to investigate questions related to social behaviour (total 19 individuals from 5 groups). Faecal samples were also collected from all focal individuals.
Results showed that the gut microbiota of red-bellied lemurs were dominated by the phyla Bacterioidetes , Proteobacteria and Firmicutes.
The lemurs were found to have gut microbiota with slight temporal fluctuations and strong social group-specific composition.
Surprisingly, individual sociality was negatively associated with gut microbial diversity. However, position within the social network predicted gut microbial composition.
"The gut microbiome of red-bellied lemurs most closely resembles that of their group members," said Andrea Baden, co-senior author of the research and assistant professor of anthropology at Hunter College.
"They are extremely cohesive and in contact a great deal, and rarely if ever interact with other groups, so this makes sense.
'This explains a great deal of individual variation, but genetic kinship might explain some as well. We know that infants inherit a suite of microbes from their mother, during birth. Red-bellied lemurs leave their natal groups to form their own groups when they become adults. They might retain some bacteria from their natal family group."
Stress coping mechanisms
The research was unable to answer some key questions such as determining whether the bacteria were good or bad, or even their identity.
The effect of stress on gut microbiome also required further investigation as Raulo acknowledged that "social contact, stress physiology and gut microbiome are all intensely related".
"Your social contact defines how much stress you interact with, and both can influence the cocktail of microbes in your gut."
"People find social situations, such as competition stressful," she added. "People cope with stress through social means, by seeking and giving affection, grooming and touching each other."
"This way, social contact also balances stress. Regardless of whether they are blood relatives, people that live in close quarters, also come to share similar gut bacteria. Synchronized physiological systems make us work more 'as one'."
Journal of Animal Ecology