Recent study shows that rescue behavior in ants is linked to differences in gene activity in the nervous system

Why do some ants help nestmates in distress while others don't? A research team from Johannes Gutenberg University Mainz (JGU) and Tel Aviv University has addressed this question in a new study. The researchers examined worker ants of the species Cataglyphis niger, some of which had shown rescue behavior while others had not. The result, recently published in the Journal of Experimental Biology, suggests that the key difference lies not in body size, morphology, or the animals' energy reserves, but in gene activity in the nervous system.

"Our study shows that, in ants, the willingness to help is linked to measurable differences in gene activity," said Professor Susanne Foitzik of the Institute of Organismic and Molecular Evolution at JGU. "This is exciting because rescue behavior has long been associated primarily with mammals, while this type of behavior has evolved independently in ants."

To investigate what distinguishes helping from non-helping ant workers, the researchers recreated a distress situation in the laboratory. A worker ant was restrained on the floor of a sand-lined test chamber. Individual ants from the same colony were then released into the chamber. The researchers recorded the animals' behavior over a period of 15 minutes. Ants were classified as rescuers if they approached the restrained nestmate and pulled at it or dug around it. Worker ants of this species show similar behavior when attempting to free buried nestmates. The team classified ants as non-helpers if they approached the restrained nestmate but did not attempt to free it.

Genes more active in the brains of helping ants

In the next step, the researchers analyzed in the laboratory whether these behavioral differences were also reflected biologically. To do so, they examined the antennae and various brain regions of the ants that had previously been observed, including the optic lobes and central brain regions. The team focused particularly on the so-called mushroom bodies, central processing centers in the insect brain that integrate sensory information and are involved in learning and behavioral control. From these tissues, the team isolated RNA, molecules that provide information about which genes are active in the respective cells. Using RNA sequencing, the researchers then compared gene activity in rescuing and non-rescuing worker ants.

The differences were particularly clear in the mushroom bodies. "In rescuing animals, 15 genes were more active, including genes associated with odor perception, hormonal regulation, metabolic processes, and immune functions," said Luisa Maria Jaimes-Nino, a member of Foitzik's team and first author of the study. "Across all the tissues examined, we found a total of nine genes that were more active in rescuing ants than in non-rescuing ants."

At the same time, the researchers found no evidence that the rescuing ants were simply stronger or better supplied with energy. "Rather, our results suggest that differences in the processing of sensory stimuli and in certain molecular signaling pathways could influence whether an ant responds to a nestmate in danger," said Susanne Foitzik.

Different behavior is linked to measurable molecular processes

One surprising finding concerns immune genes, which do more than protect insects from pathogens. Previous studies have shown that they can also influence activity, sleep, and the tendency to form groups. The new study suggests that immune functions could also play a role in regulating social responses. It is also possible that rescuing ants face a higher risk of injury or infection because of their behavior and may therefore benefit from stronger activity of immune system genes in such situations.

However, the researchers emphasize that the study does not identify a single trigger for helping behavior. Rescue behavior is therefore likely to arise from the interaction of several processes. These include the perception of alarm signals, the processing of these stimuli in the nervous system, and molecular signaling pathways that influence the ants' readiness to respond.

"Ants are a particularly good model for studying the biological foundations of complex social behavior," said Foitzik. "Our study shows that individual animals within the same colony not only respond differently, but that these differences are also linked to measurable molecular processes."

The project was funded by the German Research Foundation (DFG) and the Israel Science Foundation. In addition to Luisa Maria Jaimes-Nino and Susanne Foitzik from JGU, Bar Adi and Inon Scharf from Tel Aviv University were involved in the study.