A parasite turned worker ants into ‘queens’ and extended their lives

The study has shown that the parasite does not simply cause disease, but subtly interferes with the host’s genes, altering metabolism, the immune system and the mechanisms of ageing. The findings help us understand how parasites are able to control the behaviour and physiology of their hosts.

Details

The study focused on Temnothorax nylanderi ants, which are naturally infected by the tapeworm Anomotaenia brevis. The parasite’s life cycle is unusual: the ants serve as intermediate hosts, whilst the parasite completes its development within the bodies of woodpeckers.

Scientists from Johannes Gutenberg University in Mainz compared three groups of insects: healthy worker ants, infected workers and queens.

To do this, the researchers studied gene activity in two important tissues — the brain and the so-called fat body. This is a specialised tissue in the abdomen of insects which performs functions similar to those of the liver and adipose tissue in vertebrates, playing a role in metabolism, immune defence and the storage of nutrients.

It turned out that it is in the fat body that the most striking changes occur. The activity of many genes in infected workers became remarkably similar to that observed in queens.

The changes affected genes associated with metabolism, the immune system, stress resistance and ageing processes.

This helps to explain an unusual phenomenon that scientists had observed previously. Whilst ordinary worker ants of this species live for around one to two years, queens can live for up to 20 years. Worker ants infected with the parasite demonstrate a survival rate that comes very close to that of the queens.

The brains of the infected ants looked quite different. Here, the scientists discovered a reduction in the activity of many neuropeptides — signalling molecules that regulate behaviour, feeding and social activity. This is likely why infected workers become less mobile and are less likely to carry out their usual duties within the colony.

The researchers also tested the widely held hypothesis that the parasite might produce its own molecules that mimic signals from the ant’s body. However, no evidence of this was found.

Instead, the data show that the tapeworm acts differently — it interferes with the host’s own regulatory networks, forcing the ant’s body to switch to a new mode of operation of its own accord.

According to the study’s authors, this state is beneficial to the parasite. The longer an infected ant lives and the lower its risk of dying whilst foraging outside the nest, the greater the likelihood that it will be eaten by a woodpecker — the tapeworm’s ultimate host.

Why this is important

The study demonstrates just how subtly parasites are able to manipulate their hosts’ bodies. Rather than simply causing disease, they can exploit existing biological programmes, altering lifespan, metabolism and behaviour.

The authors believe that the ‘ant–tapeworm’ system could serve as a useful model for studying the mechanisms of ageing, gene regulation and the interaction between parasites and the host organism. However, the findings apply only to this particular species of insect and do not imply that similar mechanisms exist in humans.

Source

The study was published in the journal BMC Genomics.

Title: Cestode infection is linked to transcriptional shifts in neuropeptide signalling and caste-specific ageing pathways in a social insect.