Social insect colonies, like those of ants and bees, are divided into castes based on distinct tasks such as reproduction, foraging, defense, and nest maintenance. Individuals belonging to different social castes show distinct molecular, physical, and behavior characters. These are usually established at the larval stage.
But Indian jumping ants (Harpegnathos saltator) are unique. Unlike other ants, Indian jumping ants can switch castes when the reproductive queen dies. In these cases, about 70 percent of non-reproductive workers fight for dominance. Some successfully become reproductive queen-like ants, called gamergates, to ensure the continuation of the colony. This worker-gamergate transition incurs dramatic brain structural remodeling.
New research published in Science Advances has looked more closely at how the brains of gamergates compare to worker Indian jumping ants. By measuring gene expression changes in the brains of these ants at single-cell resolution, scientists discovered that the number of ensheathing glial cells — supportive neuronal cells essential to brain health and homeostasis — increases by 40 percent during the worker-gamergate transition.
Not only that, when the scientists injured the brains of young Indian jumping ants (from stable or non-transitioning colonies) using needle punctures or antenna ablation, these same cells activated and expressed injury-responsive genes at a higher rate to cope with brain damage.
In ant colonies, reproductive queens live about ten times longer than workers, and gamergates about five times longer than workers. This study found that even older gamergates (~120 days in age) contained significantly more ensheathing glial cells than workers of the same age. (To put this into perspective, 120 days of Indian jumping ant life would translate to about 57 years on a human-age scale.) Older gamergates also expressed higher levels of injury-responsive genes after brain injury. Thus, scientists suggest that ensheathing glial cells protect gamergates from brain damage even in old age.
Yet, Indian jumping ants of all castes are genetically the same, so what makes them inherently distinct? The answer could be epigenetics: the inheritance of biological variation independent of the genetic sequence. Ants — and other social insects — provide a great example to study epigenetics and to explore the relative influence of nature and nurture on their lives.