Altered behaviour and transmission ecology of fluke-infected zombie ants
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Date
2025
Authors
Edison, Lauren M.
University of Lethbridge. Faculty of Arts and Science
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Lethbridge, Alta. : University of Lethbridge, Dept. of Biological Sciences
Abstract
Parasites can induce changes in the colour, morphology, and behaviour of their hosts. In some cases, the induced changes are extraordinary in their expression. In an iconic example, Formicid ants infected with the lancet liver fluke, Dicrocoelium dendriticum, attach their mandibles to a plant for hours or days. I described patterns of infection in two species of ants infected with D. dendriticum in a region of parasite emergence in southern Alberta and found that ants recruit parasites in clumps from their first intermediate host, terrestrial snails. Overall, infected ants contain, on average 27±25 (mean ± standard deviation) encysted metacercariae (n = 677). In a departure from classic examples of parasite manipulation, infected ants do not die on the plant. Rather, they detach, resume normal ant activities, then re-attach. This bizarre ‘attach/detach/repeat’ sequence of altered behaviour likely facilitates transmission into grazing mammals while also preventing desiccation of the ant hosts and their parasites. I conducted a field study monitoring the behaviour of infected ants and found that the timing of attachment and detachment of ants on plants is closely linked with environmental factors such as light intensity, relative humidity, temperature, and also with ant circadian rhythm. Additionally, I completed a spatiotemporal analysis of the distribution of infected ants on plants in the field and found that infected ants are often aggregated on plants adjacent to the nest that they originated from, representing the first reported case of “super aggregation” of parasites. Whereas a pattern of strong aggregation on plants was spatially and temporally consistent for one species of Formicid ant in this region of parasite emergence, the behavioural processes leading to aggregation are enigmatic, as are the consequences of aggregation for rates of fluke transmission from ants into definitive hosts.
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Keywords
zombie ants , lancet liver flukes , altered behaviour , infected ants , environmental factors , host manipulation , reversible host manipulation