Parasite-induced plasticity in host social behaviour depends on sex and susceptibility

Abstract

Understanding the effects of parasites on host behaviour, of host behaviour on parasite infection, and the reciprocal interactions between these processes is vital to improving our understanding of animal behaviour and disease dynamics. However, behaviour and parasite infection are both highly variable within and between individual hosts, and how this variation affects behaviour-parasite feedbacks is poorly understood. For example, it is unclear how an individual's behaviour before infection might change once it becomes infected, or as the infection progresses, and how these changes depend on the host's parasite susceptibility. Here, using the guppy, Poecilia reticulata, and a directly transmitted ectoparasite, Gyrodactylus turnbulli, I show that parasite-induced behavioural plasticity depends on host sex and susceptibility. Among females, time spent shoaling (sociality), a behaviour that increases parasite transmission, did not depend on infection status (infected/not) or susceptibility. By contrast, male sociality in the absence of infection was negatively correlated with susceptibility, suggesting that the most susceptible males use behaviour to avoid infection. However, in late infection, when parasite transmission is most likely, male sociality and susceptibility became positively correlated, suggesting that susceptible males modify their behaviour upon infection potentially to increase transmission and mating opportunities. I discuss the implications of these patterns for disease dynamics.

Keywords: Poecilia reticulata; behavioural disease ecology; behaviour–parasite feedback; parasite-induced behavioural plasticity; sex-biased parasitism; social behaviour.

Figure 1.

(a) Overhead and (b) side views of the set-up for quantifying sociality. (Online version in colour.)

Figure 2.

The proportion of time guppies spent within one body length of the stimulus shoal tank (sociality) depended on a three-way interaction between infection integral (susceptibility), sex and infection stage. Points are partial residuals from the ‘infected only’ model, back-transformed to the response scale and lines give model fits. Box plots give the median (dark line), interquartile range (box) and values within 1.5× the interquartile range (whiskers) of the sham-infected controls; associated open points give the raw data. (Online version in colour.)