Part Two: In a Fortuitous Turn of Events
By Dr. Kyle Lesack
Parasitism of Cephalotes atratus by Myrmeconema neotropicum
In a fortuitous turn of events, a group of researchers discovered a rare combination of mimicry and host behaviour modification in the nematode-infected Cephalotes atratus, an ant species also known for its gliding behaviour (https://www.youtube.com/watch?v=-YFt2L2GOMg). Among the ant colony members, the researchers discovered individuals with bright red gasters (posterior part of the ant), which they initially believed to be a new species. However, upon dissection, they discovered that these ants were in fact infected by a roundworm, which they named Myrmeconema neotropicum. In their 2008 paper (3), the authors describe how the red gaster likely plays a key role in the parasite’s transmission by mimicking fruit ingested by certain bird species. The study’s lead author, Dr. Stephen Yanoviak stated, "It's phenomenal that these nematodes actually turn the ants bright red, and that they look so much like the fruits in the forest canopy”.[kl1] [kl2] In support of the fruit mimicry hypothesis, they noted that infection was associated with a reduction in ant defences and behavioural patterns that could otherwise deter predation. In the following sections, an overview of the experiments they conducted to explore this parasitic relationship will be described. Examining how the authors tested their hypotheses and supported their arguments provides an excellent example of parasitology fieldwork and the scientific method.
Figure 1: Infected ant with a prominent red gaster.
How are these parasite induced changes discovered?
In 2005, Dr. Yanoviak and his colleagues discovered and published the gliding behaviour of these Cephalotes atratus ants – when the ants fall out of a tree they have some directionality in where they fall. The BBC decided to film the gliding behaviour and Dr. Yanoviak and colleagues need to collect a large number of ants for the film. During the collection process, they found some red gaster ants that they are not sure if it’s a different species. “initially [I] was confused by it like I'm sure a lot of ant people are when you see something like that you think maybe it's a different species.” Dr. Yanoviak then took the ants into the lab and noticed the gasters were easily falling off when handling. Under the microscope, he saw hundreds of nematode eggs pour out, and realized the red gaster is an indication of a nematode infection. “that was the Epiphany, the moment of exciting Discovery where you know you've stumbled onto something interesting and now it's a question of asking the right questions to determine what's really happening.”
References
3. Yanoviak SP, Kaspari M, Dudley R, Poinar G. Parasite-induced fruit mimicry in a tropical canopy ant. Am Nat. 2008;171(4):536–44.
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