Abstract
Trophically transmitted parasites frequently increase their hosts' risk-taking behaviour, to facilitate transmission to the next host. Whether such elevated risk-taking can spill over to uninfected group members is, however, unknown. To investigate this, we confronted groups of 6 three-spined sticklebacks, Gasterosteus aculeatus, containing 0, 2, 4 or 6 experimentally infected individuals with a simulated bird attack and studied their risk-taking behaviour. As a parasite, we used the tapeworm Schistocephalus solidus, which increases the risk-taking of infected sticklebacks, to facilitate transmission to its final host, most often piscivorous birds. Before the attack, infected and uninfected individuals did not differ in their risk-taking. However, after the attack, individuals in groups with only infected members showed lower escape responses and higher risk-taking than individuals from groups with only uninfected members. Importantly, uninfected individuals adjusted their risk-taking behaviour to the number of infected group members, taking more risk with an increasing number of infected group members. Infected individuals, however, did not adjust their risk-taking to the number of uninfected group members. Our results show that behavioural manipulation by parasites does not only affect the infected host, but also uninfected group members, shedding new light on the social dynamics involved in host–parasite interactions.
Highlights
Many parasites manipulate behaviours of their host [1,2,3]
Our results show that behavioural manipulation by parasites does affect the infected host, and uninfected group members, shedding new light on the social dynamics involved in host–parasite interactions
To investigate whether S. solidus-infected sticklebacks influence the risk-taking behaviour of sticklebacks in shoals with different numbers of infected sticklebacks, we looked at the time individuals spend in the ‘dangerous’ zone of the test tank, before and after an artificial bird attack
Summary
Many parasites manipulate behaviours of their host [1,2,3]. parasites with complex life cycles, involving more than one host species, have evolved strategies to manipulate host behaviour to facilitate transmission to the host [3,4,5,6]. When at least five sticklebacks had approached the water surface (i.e. within two body lengths), an artificial bird attack was triggered and a second food stimulus was provided in the floating ring, to stimulate the sticklebacks to re-enter the ‘dangerous’ zone. To analyse the effect of individual infection status and treatment group on the likelihood of remaining in the ‘dangerous’ versus escaping to the ‘safe’ zone after the bird attack, we used a GLMM with the function ‘glmer’ ( package ‘lme4’ [39]) with a binomial distribution. To analyse the effect of individual infection status, treatment group and bird attack on time spent in the ‘dangerous’ zone, we used linear mixed models with the function ‘lmer’ ( package ‘lme4’ [39]).
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