Abstract
Hosts manipulated by parasites are profoundly altered organisms exhibiting a broad range of potential modifications. Exploring this multidimensionality is an emerging field. Previous studies have shown that the bird trematode Microphallus papillorobustus induces several behavioural changes in the gammarid Gammarus insensibilis. Knowing that aggregation behaviour and reduced activity levels are strategies that limit predation in other species of amphipods, we explored in this study these behavioural responses for infected and uninfected G. insensibilis in the presence of host and non-host predator olfactory cues (bird faeces and fish mucus). While uninfected individuals reduced their activity level in the presence of predator cues, infected individuals did not change their activity level in presence of aquatic bird faeces. We also studied the gammarid aggregation behaviour. Uninfected gammarids in clean water spent significantly more time in aggregates than did infected individuals. Among the uninfected individuals, the aggregation level tended to increase when bird faeces and fish mucus were added, but the difference was not significant. Among infected individuals, the level of aggregation was significantly increased only with the bird faeces. We discussed our results in the context of the literature on multidimensional manipulations, acknowledging that subtle differences between unparasitized and parasitized gammarids can also be by-products of manipulation on other traits.
Highlights
Altered host phenotypes that enhance the probability of parasite transmission have been well documented over the last few decades
Knowing that aggregation behavior and reduced activity levels are strategies that limit predation in other species of amphipods (Andersson et al, 1986; Krause and Godin, 1994; Wooster, 1998; Dezfuli et al, 2003; Wellnitz et al, 2003), we explored in this study whether M. papillorobustus affects these behavioral responses in G. insensibilis when exposed to either host or nonhost predator olfactory cues in the water
There was a significant decrease in the activity level of uninfected individuals in the presence of predator cues compared to control treatment
Summary
Altered host phenotypes (e.g., behavior, morphology, physiology) that enhance the probability of parasite transmission have been well documented over the last few decades (reviewed by Moore, 2002; Thomas et al, 2005). These phenotypic alterations can vary greatly in their magnitude, from slight shifts in the percentage of time spent in performing a given activity to the production of complex and spectacular behaviors (Poulin and Thomas, 1999; Moore, 2002; Hughes et al, 2012). Multidimensionality in host manipulation has been increasingly addressed (Cézilly and Perrot-Minnot, 2005, 2010; Thomas et al, 2010), little is known regarding its extent and how it evolves, even among the most studied models (Thomas et al, 2010)
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