Update on Zombie Ants
Hello, and welcome to all new/returning YCP students! Additionally, welcome to all new BIO230 students–I hope everyone has had a restful and relaxing summer break. I know I sure did; I had fun during summer Micro, had a week long break, and accomplished some important Science in my spare time. One thing I did not do was update this forum. Looking back, it appears I last opened up WordPress back sometime in April. Let’s see if we can do something about that!
I found a news alert on ASM’s Microbe World site, which gives an update on the Zombie Ant story. It summarized work out of the entomology department at Penn State University, which has been studying a fascinating example of symbiosis between an insect and a fungus called Ophiocordyceps. What is most interesting about this relationship is that infection by the fungus causes behavioral changes in the host. These changes are advantageous for the fungus–the ant moves over a greater range, allowing the spores of the fungus to spread further. Obviously, infection of a colony would be a Bad Thing, leading to this observation on the phenomenon of “Social Immunity”.
Social Immunity has been observed in laboratory settings in a variety of insect species. It prevents the spread of diseases within colonies, however it has not been previously observed in field conditions. In a study published recently in PLOS One, researchers placed ants which had been freshly killed by the fungus inside one of two nests; one nest had live ants, and the second nest had no ants. The fungus-killed ants were rapidly removed from the living nest, and no further fungal infection occurred of that colony. This result suggests that effective reproduction of the fungus requires being outside of the colony.
In an expanded study, researchers examined the dynamics between the appearance of infected dead ants outside of colonies (sources of infection) and the position of foraging trails (future hosts) in several colonies over the course of 20 months. The researchers observed a consistent appearance of 14.5 cadaver ants per month per colony. Based on this low rate of infection and the lack of colony collapse, the researchers proposed that this fungal parasite represents a “chronic” infection of these colonies. The authors suggest that the removal of corpses from the colony or ants dying in isolation outside the colony may be an essential step in the development of Ophiocordyceps to a stage that enables the fungus to infect a new host.