The manipulation of intermediate host behavior may increase chances of parasite transmission to the definitive host. In freshwater environments of the Neotropical Region, studies on behavioral manipulations by parasites are rare, and the majority of these consider only a single parasite species and/or 1 life stage of a particular parasite species. In Andean Patagonian lakes of Argentina, the amphipod Hyalella patagonica is infected by larvae of the fish nematode Hedruris suttonae and by the bird acanthocephalan Pseudocorynosoma sp. The 3 objectives of the present study were to determine whether H. suttonae and Pseudocorynosoma sp. differ in their effects on behavior of H. patagonica, whether such modification is associated with parasite development, and to assess the associations between behavioral traits. From naturally parasitized amphipods, activity (swimming levels) and phototaxis (light preference) was measured. Only in phototaxis trials did larvae of H. suttonae induce significantly higher levels of photophilia, suggesting that they are manipulative. Scores of activity and phototaxis were positive and significantly related for non-parasitized female amphipods and for amphipods parasitized by larvae of Pseudocorynosoma sp. but were not associated in amphipods parasitized with larvae of H. suttonae (infective and non-infective), suggesting that infection separated the relationship between these variables.

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