Abstract
Ants are the hosts of many microorganisms, including pathogens that are incidentally brought inside the nest by foragers. This is particularly true for scavenging species, which collect hazardous food such as dead insects. Foragers limit sanitary risks by not retrieving highly infectious prey releasing entomopathogenic fungal spores. This study investigates whether similar prophylactic strategies are also developed for food associated with weak or delayed risks of fungal contamination. We compared, in Myrmica rubra ant colonies, the retrieval dynamics of dead flies that were (1) conidia-free, (2) covered with a low amount of Metarhizium brunneum entomopathogenic conidia or (3) recently fungus-killed but not yet sporulating. Foragers mostly avoided fungus-killed prey and delayed the retrieval of conidia-covered flies. A second sanitary filter occurred inside the nest through a careful inspection of the retrieved prey. Ultimately, ants mostly consumed conidia-free and conidia-covered flies, but they relocated and discarded all fungus-killed prey outside of the nest. Our study confirms that, as a host of generalist entomopathogenic fungi, Myrmica rubra ants have developed a prophylactic avoidance and a differential management of prey depending on their infectious potential. We discuss the functional value as well as the possible cues underlying pathogen avoidance and prey discrimination in ants.
Highlights
The ecological success of eusocial insects such as ants stems from a high level of cooperation between nestmates
Control flies were retrieved faster than prey that were covered with conidia (HR = 0.70, p = 0.04) or that recently died from fungal infection (HR = 0.09, p < 0.0001)
After three hours of foraging, the number of flies that were retrieved by ants differed significantly between conditions (GLMM: Wald test: W = 29.9, df = 2, p < 0.0001)
Summary
The ecological success of eusocial insects such as ants stems from a high level of cooperation between nestmates. While a few individuals ensure the reproduction, workers are collectively engaged in carrying out different daily tasks such as foraging, nest defence, waste management, nest maintenance and brood care [1]. Cooperation in task performance requires that workers frequently come into contact with each other inside the confined environment of their nest. Coupled with a high level of genetic relatedness between nestmates, such a high rate of interactions increases the risk of disease outbreak resulting from a contamination by hazardous entomopathogens. In the absence of any strategy to counter sanitary threats, the proliferation of a generalist or species-specific pathogen will reduce the activity level of colony members, increase their mortality rate and eventually lead to the collapse of the whole nest population [3,4]
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