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Pathogen prevalence modulates medication behavior in ant Formica fusca

Citation

Rissanen, Jason (2022), Pathogen prevalence modulates medication behavior in ant Formica fusca, Dryad, Dataset, https://doi.org/10.5061/dryad.0zpc86707

Abstract

Ants face unique challenges regarding pathogens, as the sociality which has allowed them to form large and complex colonies also raises the potential for transmission of disease within these colonies. To cope with the threat of pathogens, ants have developed a variety of behavioral and physiological strategies. One of these strategies is self-medication, in which animals use biologically active compounds to combat pathogens in a way which would be harmful in the absence of them. Formica fusca ants are to date the only species of ants proven to successfully self-medicate against an active infection caused by a fungal pathogen by supplementing their diet with food containing hydrogen peroxide. Here, we build on that research by investigating how the prevalence of disease in colonies of F. fusca affects the strength of the self-medication response. We exposed either half of the workers of each colony or all of them to a fungal pathogen and offered them different combinations of diets. We see that workers of F. fusca engage in self-medication behavior even if exposed to a low lethal dose of a pathogen, and that the strength of that response is affected by the prevalence of the disease in the colonies. We also saw that the infection status of the individual foragers did not significantly affect their decision to forage on either control food or medicinal food as uninfected workers were also foraging on hydrogen peroxide food, which opens up the possibility of kin medication in partially infected colonies. Our results further affirm the ability of ants to self-medicate against fungal pathogens, shed new light on plasticity of self-medication and raise new questions to be investigated on the role self-medication has in social immunity.

Methods

The dataset was collected by analyzing pictures of foraging bouts of ant colonies suffering from different levels of pathogen infection (0% workers infected, 50% workers infected, 100% workers infected). Pictures were taken 4 times a day for a total of 6 days, and from the pictures we collected data on how many ants were foraging on either one of the two foods available to them spatially placed either on the left or right.

The foods available varied according to which of the three diet treatments the colonies were subjected to: both foods control food, both foods treated, choice between control and treated food.

Data was also collected on the infection status of the foragers and what type of food they were foraging on, as half of the ants in all colonies were marked to note whether they were infected or non-infected.

Data on the survival of ants in the colonies were also gathered to discern whether any of the combinations of infection treatment an diet were affecting survival of workers in the colonies.

Funding