Evol Ecol Res 19: 487-501 (2018)     Full PDF if your library subscribes.

Individual behavioural responses of an intermediate host
to a manipulative acanthocephalan parasite
and the effects of intra-specific parasite competition

Timo Thünken1, Simon Vitt1, Sebastian A. Baldauf1, Tina Jung1 and Joachim G. Frommen2

1Institute for Evolutionary Biology and Ecology, University of Bonn, Bonn, Germany and 2Division of Behavioural Ecology, Institute of Ecology and Evolution, University of Bern, Hinterkappelen, Switzerland

Correspondence: T. Thünken, Institute for Evolutionary Biology and Ecology, University of Bonn, An der Immenburg 1, 53121 Bonn, Germany. email: tthuenken@evolution.uni-bonn.de


Background: Parasites with complex life cycles depend on the ingestion of their intermediate host by the final host. To complete their life cycle successfully, parasites frequently manipulate the behaviour and appearance of the intermediate host. Within host–parasite systems, there is considerable variation in the intermediate host’s behavioural response to infection.

Aim: Identify sources of parasite-induced variation in intermediate hosts’ traits by focusing on intra- and inter-individual variation in behavioural responses to parasitic manipulation, taking infection intensity – and thus parasitic competition – into account.

Organism: The acanthocephalan parasite Polymorphus minutus, which alters the phototactic behaviour and activity of its intermediate host, Gammarus pulex, thereby increasing the probability of being eaten by the final host.

Methods: We repeatedly examined the behaviour of individual G. pulex varying in intensity of infection with P. minutus from uninfected to multiple-infected. We analysed phototactic responses and activity.

Results and conclusions: Individual gammarids differed in phototactic behaviour and in activity patterns, with repeatability ranging from 20% to 50%. Infected gammarids showed greater between-individual variation in phototaxis but not activity than uninfected gammarids. All uninfected gammarids were photophobic, whereas the phototactic behaviour of infected gammarids ranged from photophobia to photophilia. On average, multiple-infected gammarids were similarly photophobic as uninfected ones. Single-infected gammarids were less photophobic than uninfected and multiple-infected conspecifics. This suggests that intra-specific parasitic competition affects the manipulative abilities of parasites. Both groups of infected gammarids were on average less active than uninfected ones, and this effect was mainly driven by some infected individuals. In conclusion, behavioural variation of gammarids was caused both by individual differences in responses to manipulation/infection, and by the reduced manipulative capacities of parasites facing intra-specific competition.

Keywords: behavioural manipulation, Gammarus pulex, individual variation, Polymorphus minutus, repeatability, host–parasite co-evolution.

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