Data from: Parasite-infected sticklebacks increase the risk-taking behavior of uninfected group members

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
six 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.