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Transmission risk predicts avoidance of infected conspecifics in Trinidadian guppies

Stephenson, Jessica F., Perkins, Sarah E., Cable, Joanne
The journal of animal ecology 2018 v.87 no.6 pp. 1525-1533
Poecilia, avoidance behavior, fish, host-parasite relationships, hosts, infectious diseases, models, natural selection, parasites, prediction, risk, social behavior, social benefit
Associating with conspecifics afflicted with infectious diseases increases the risk of becoming infected, but engaging in avoidance behaviour incurs the cost of lost social benefits. Across systems, infected individuals vary in the transmission risk they pose, so natural selection should favour risk‐sensitive avoidance behaviour that optimally balances the costs and benefits of sociality. Here, we use the guppy Poecilia reticulata–Gyrodactylus turnbulli host–parasite system to test the prediction that individuals avoid infected conspecifics in proportion to the transmission risk they pose. In dichotomous choice tests, uninfected fish avoided both the chemical and visual cues, presented separately, of infected conspecifics only in the later stages of infection. A transmission experiment indicated that this avoidance behaviour accurately tracked transmission risk (quantified as both the speed at which transmission occurs and the number of parasites transmitting) through the course of infection. Together, these findings reveal that uninfected hosts can use redundant cues across sensory systems to inform dynamic risk‐sensitive avoidance behaviour. This correlation between the transmission risk posed by infected individuals and the avoidance response they elicit has implications for the evolutionary ecology of infectious disease, and its explicit inclusion may improve the ability of epidemic models to predict disease spread.