Field colonies of leaf‐cutting ants select plant materials containing low abundances of endophytic fungi

Abstract

Endophytic fungi live symbiotically in the tissues of plants. Although a large amount of evidence suggests a mutualistic role for vertically transmitted endophytic fungi in agronomic grasses, the role of horizontally transmitted endophytic fungi as mutualists has been challenged. Recent studies, however, have shown that horizontally transmitted endophytic fungi can act as mutualists to their plant hosts by providing defense against pathogens and defoliators. In particular, several experimental studies have shown that endophytic fungi interact negatively with leaf‐cutting ants and their fungal cultivar, but these studies were performed under laboratory conditions. Using field colonies of Atta colombica in Central Panama, we measured the fungal endophyte content in the forage material of leaf‐cutting ants and compared it to ambient endophyte levels. We then used the collected data to model the area of plant material containing endophytes that enters a mature colony daily. We found that mature colonies collect leaf material that is 20% lower in endophyte abundance than surrounding leaves. A similar pattern was observed for newly emerged colonies. Our model suggests that via ant foraging preferences, leaf‐cutting ants reduce the possible area of material containing endophytes entering the colony by 33%. Our results provide further evidence for a negative interaction between leaf‐cutting ants and horizontally transmitted endophytes, suggesting that fungal endophytes have a defensive role in tropical plants by influencing leaf‐cutting ant foraging preferences.

Keywords

• Atta colombica
• fungal endophytes
• interactions
• mutualism
• Neotropics
• Panama