Stucki, D., Sundström, L. & Freitak, D.

Caste-specific expression of constitutive and Beauveria bassiana induced immunity in the ant Formica exsecta (Hymenoptera: Formicidae)

One of the distinctive features of eusocial insects is the production of separate castes, each of which specializes in different aspects of colony performance. As a consequence, queens, males, and workers follow different evolutionary trajectories, depending on their life histories and tasks within the colony. The short-lived males and long-lived queens only leave the colony for reproduction, whereas workers experience frequent contact with the surrounding environment. Yet, workers often perform tasks sequentially during their life. Younger workers tend brood, whereas older workers forage for food. Here, we examined the expression of nine candidate genes both at the constitutive level and following challenge with the entomopathogenic fungus Beauveria bassiana (Vuillemin, 1912) in males, young queens, nurses, and foragers of the ant Formica exsecta Nylander, 1846. We found no difference in the survival following an infection between queens and males or between nurses and foragers. However, we found clear caste- and worker class-specific differences in the response to B. bassiana in genes associated with immune functions. In queens and nurses, the expression of antifungal genes increased, which in the queens was coupled to reduced expression of genes not directly involved in immune responses. In contrast, in males and foragers, gene expression did not increase upon infection; instead the expression of antibacterial genes declined.