Winter is coming, for the northern hemisphere at least. While many of us dig out our blankets and fleeced socks, some animals go searching for each other.聽Many small mammals huddle together to keep warm when the temperature drops. It now turns out that this huddling behaviour changes the composition of bacteria in the animals鈥� guts 鈥� and it does so in a way that slows down their metabolism and helps them preserve energy.
Huddling is a strategy many animals deploy to maintain body temperature in cold weather. The benefit of such behaviour is obvious: nestling in a group reduces the body area exposed to the cold air, and thus reduces heat loss.
But Dehua Wang at the Chinese Academy of Sciences in Beijing and his colleagues suspected huddling might have additional benefits at a deeper level 鈥� particularly since some studies have found that animals in a huddle have surprisingly similar gut bacteria profiles. This finding suggested to Wang that huddling might influence an animal鈥檚 gut microbiome profile, so he decided to investigate.
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Cold voles
Wang鈥檚 team put voles in a room at a chilly 4 鈩�. They placed some of the voles in a single cage so they could huddle together for warmth, while others were housed individually.
After the voles had endured the chilly temperatures for three weeks Wang and his colleagues extracted gut bacteria from the huddling and isolated voles. They used antibiotics to sterilise the guts of another 12 voles kept at room temperature, and then seeded 6 of them with 鈥榟uddling鈥� vole gut bacteria and the other 6 with 鈥榠solated鈥� vole gut bacteria.
They found those with huddling vole bacteria in their guts consumed 15 per cent less food 鈥� and had a 20 per cent lower resting metabolic rate 鈥� than those with isolated vole bacteria in their guts. This suggests huddling encourages changes to the vole gut flora that then slow down the hosts鈥� metabolism. A slower metabolism will help them conserve energy through cold spells when finding food might be challenging.
Bacteria spike
Digging deeper, Wang鈥檚 team found a greater variety of bacteria in the huddling vole microbiome. They also noticed a spike in the concentration of one particular bacteria group: Lachnospiraceae. These bacteria can generate short-chain fatty acids as they break down dietary fibres.
Wang says these fatty acids can then be reabsorbed into the body, which could explain why voles with these bacteria in their gut don鈥檛 need to consume as much food as normal ones in cold weather.
Sarah Knowles at the University of Manchester, UK, thinks this last conclusion is a bit speculative at the moment. 鈥淭his study doesn鈥檛 have the right experiment to say that short-chain fatty acids played a role here,鈥� she says. 鈥淏ut other than that, their findings on gut bacteria changes are quite robust.鈥�
鈥淭his is the first time we show that huddling behaviour changes animals鈥� gut bacteria,鈥� Wang says. 鈥淏ut the reduction in heat loss in huddling animals certainly has a greater impact on their metabolism than short-chain fatty acids.鈥�
Microbiome
