Authors have raised the possibility of identifying primitive forms of conversational rules in monkeys: temporally ruled vocal interactions, call overlap avoidance, and socially based calling partner preferences. The question as to how these abilities have evolved in the primate lineage remains open to debate, particularly because studies based on apes are scarce and controversial. We studied a captive group of western lowland gorillas and tested the influence of caller characteristics and the type of bond between calling partners on vocal behavior based on the following: age, dominance, spatial proximity, sociopositive contact, and gaze. Four calling patterns that are call type dependent were identified: vocal interaction with and (more frequently) without call overlap, isolated calling, and repeated calling. Adult calls and grunts (contact calls) were predominant during vocal interactions, and the "response" delay was most often around half a second. The frequency of grunt dyadic exchanges was found to be linked to spatial proximity, gaze exchanges, and age proximity between calling partners. The dominance rank of callers determined the rate of contribution to these exchanges. These results show that some apes use rule-governed call exchanges and that these socially guided vocal interactions are more widespread than previously believed. (PsycINFO Database Record

Insect societies have developed sanitary strategies, one of which is the avoidance of infectious food resources as a primary line of defence. Using binary choices, we investigated whether Myrmica rubra ants can identify prey that has been artificially infected with the entomopathogenic fungus, Metarhizium brunneum . We compared the ants' foraging behaviour towards infected prey at three different stages of fungus development : (i) prey covered with fungal conidia, (ii) prey freshly killed by the fungus and (iii) sporulating prey. Most foragers retrieved a corpse covered with a high number of spores but they consistently avoided a sporulating prey and collected less prey that had recently died from fungal infection. Furthermore, ant responses were highly variable, with some individuals retrieving the first prey they encountered while others inspected both available prey before making a decision. Workers were not repelled by the simple presence of fungal conidia but nevertheless, they avoided retrieving cadavers at later stages of fungal infection. We discuss how these different avoidance responses could be related to: differences in the ants’ perceptive abilities; physico-chemical cues characterizing fungus-infected prey or in the existence of physiological or behavioural defences that limit sanitary risks associated with potentially contaminated resources.

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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.