When zombies go vegan: Ophiocordyceps unilateralis hosts are selecting to bite palm leaves before dying?

Abstract

Some parasites that modify hosts' behavior can receive reproductive advantages. For instance, when infected by Ophiocordyceps unilateralis s.l., ants climb understory plants, lock their jaws into the plant tissue, and die in stable microclimatic conditions that favor the reproductive stage of the fungus. However, the so-called “zombie ants” could die on different species of plants, subject to varying environmental pressures. Here, we investigated whether infected ants lock their jaws on particular species of understory plants more often than expected before dying from the infection. We hypothesize that there may be different reproductive advantages to the parasite based on the plant species on which its hosts die. Our findings reveal that 36.3% of the infected ants died on palm trees, specifically Attalea sp. and Euterpe catinga, more frequently than expected by chance. Also, we found that cadavers tend to persist longer on palms than other plants. Our results suggest that there may be a reproductive advantage for the parasite when its hosts die on palm leaves. Palms generally have long leaf durability, which can reduce parasite cadaver loss by foliar abscission and increase cumulative spore dispersal. Furthermore, we propose abundant plant species with no observance of cadavers potentially have traits like trichome coating and antifungal compounds that may influence the arrival and permanence of new zombie ants. Our results show that infected ants dying on certain understory palm species may increase the fungus’ fitness.