Ants swap spit to help them live for longer

Some ants may live for longer at the expense of others, as less valuable individuals produce anti-aging compounds for more useful ants. 

A study by Swiss researchers found that nurse ants have higher than normal levels of antioxidants in their trophallactic fluid - a liquid that is passed mouth-to-mouth by ants. The authors believe that other ants sacrifice their longevity for the good of the colony, prioritising nurses that look after the colony's young. 

The research adds further weight to suggestions that ant colonies act like a single creature known as a 'superorganism' even though they are composed of many individuals. 

Lead author Dr Sanja Hakala says, 'We explored whether the proteins ants exchange are linked to an individual's role in the colony or the colony's life-cycle and found that some colony members can do metabolic labour for the benefit of others.' 

The findings of the study, conducted by researchers at the University of Fribourg, was published in eLife.

Enter the 'superorganism' 

Ants are a group of animals which form part of the Hymenoptera. Within this order are the social insects, which also include bees and wasps. 

Many of these insects are eusocial, meaning individuals specialise into certain roles within a colony. Juvenile ants tend to care for the colony's young, and switch to foraging later in life. However, they don't have offspring themselves, with the queen alone laying the eggs for all of the colony. 

This division of labour has led some to describe eusocial colonies as collectively behaving like a single organism. In this analogy, trophallactic fluid would be the colony's blood, carrying nutrients, hormones and other useful compounds between individuals. 

With carpenter ants, individual ants pass the fluid from mouth to mouth, as author Dr Adria LeBoeuf explains, 'Individual ants have two stomachs – one for digesting their own food and another social stomach that comes before it. They use this stomach to store fluids that they share with other ants in their colony.  

'These fluid exchanges allow ants to share food and other important proteins that the ants themselves produce.' 

The researchers wanted to assess which compounds were in the fluid and how that changed over time. They did this using carpenter ants, whose colonies change structure depending on their age. 

Wild-caught specimens were brought into the lab and raised under the same conditions before the scientists took samples of their 'spit'. 

The generation gap 

The researchers found that the trophallactic fluid contains a complex cocktail of proteins which vary between colonies and individual ants. Overall, 519 proteins were identified, of which just 27 were core compounds found in every sample. 

The rest were a mixture of proteins associated with a variety of roles. Hexamerins are a group of molecules that are used to store up amino acids, the building blocks of protein, for use in growth and reproduction. Meanwhile, smell receptor proteins were also present, which may help ants recognise other individuals from their colony. 

While some proteins were much more common than others, in some samples usually rare proteins were in fact dominant which suggest they may have an important role in specialised ants. 

For instance, workers specialised for nursing had higher levels of antioxidants than foragers. It has been suggested that the high levels of these antioxidants may reduce the effects of ageing and environmental stress on the nurse ants.

They also had higher levels of proteins which help break down food, ensuring they can feed themselves and the colony's young. 

This may help to secure the colony's future during lean times by ensuring nurse ants are always likely to be available to care for offspring. 

Those colonies that have survived a long time also have different proteins from those that are just starting out. Young colonies prioritise growth with higher levels of sugar processing proteins, while older colonies tend to have more storage molecules so they can store their resources away for a rainy day.  

The researchers now want to dig further into identifying the roles of each protein in the fluid, including some which appear to be unique. They also want to know how different ants know which molecules to produce, and who they should be given to. 

Dr LeBoeuf says, 'Having a better understanding of how ants share metabolic labour may help us learn more about the ways that other creatures, like humans, distribute metabolic tasks between different tissues or different cells in their bodies.'