Posted: July 18, 2018
This is the 9th of eleven short news articles written by students, during the professional development class. This year we had the students interview their advisor(s), in an effort to help them better understand the larger context of their projects.
Fungus forces ants to die alone: mechanism to avoid defensive nestmates?
By Natalie Imirzian
A zombie carcass silently lurks in a forest nearby, waiting to infect another host. Yet, most of us would likely not notice, as the zombie is much smaller than us--ant-sized to be precise. But not Penn State researcher David Hughes, who is fascinated by these 'zombie ants' as they demonstrate the lengths a parasite might go to avoid the impenetrable fortress of an ant nest.
Hughes and his lab are investigating how ant societies function and how parasites permeate their colonies. Much of Hughes' research focuses on zombie ants, or ants infected by Ophiocordyceps fungi and manipulated by the fungus to die outside the nest.
Ants live in densely packed nests with many of their sisters, making it of utmost importance to defend the colony against predators and parasites. In some colonies, specific ant workers are tasked with standing guard at the entrance, and others with cleaning the nest itself to remove potentially infectious materials. Ant workers programmed to remove disease threats make it difficult for a parasite to survive in the nest.
Ophiocordyceps demonstrates a unique way a parasite might bypass ant colony defenses. The fungus controls the ant to leave the nest, climb up vegetation, and then bite the underside of a leaf. The fungus keeps its ant host alive just enough to control its behavior, leading to the nickname of "zombie ants." When the fungus eventually kills the ant, the fungus grows from the ant body, forming a structure analogous to a little mushroom to release spores for new ants to pick up, continuing the infection cycle. The mechanism of how the fungus manipulates ants to leave the colony and bite a leaf is unknown, motivating much of Hughes' research.
Hughes combines molecular and histological techniques with ecological methods to study how the fungus controls ants. Zombie ants have been found all over the world--from South Carolina to Japan to Australia--but the most diversity is found in the tropical rainforests of Southeast Asia and the Amazon. Lab members perform fieldwork to collect zombie ant samples, as well as observe ant behavior in the field to understand how transmission occurs. In the laboratory, they use microscopy to investigate how the fungus grows inside of ants and genetic analyses explore the evolutionary history of this group of fungi.
Twelve years ago, when Hughes began this research, nothing was known about this parasite. "[Zombie ants] show there is so much more that we don't know than we do know," says Hughes, "We should be uncovering what's on our planet."
As a behavioral ecologist, Hughes emphasizes the importance of observation in the natural world. Observation and exploration of diverse ecosystems promotes discovery of incredible phenomena like zombie ants. Who knows what other crazy parasites might be lingering in the rainforest, waiting to be discovered?
