Behaviour of fathead minnows infected with a brain-encysting parasite

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Shirakashi, Sho
University of Lethbridge. Faculty of Arts and Science
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Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 1999
A wide variety of parasites are known to cause changes in host behaviour. The altered behaviours range from simple changes in features such as activity and phototaxis, to the creation of behaviours that are new, and often bizarre. In this study, I investigated the effect of a trematode parasite, Ornithodiplostomum ptychocheilus (Strigeidae; Diplostomidae), on the behaviour of its intermediate host, the fathead minnow (Pimephales promelas). The larval stage (metacercaria) of this parasite resides within the central nervous system, specifically the optic lobes. In fish, one of the main functions of the optic lobes is to receive visual stimuli from the retina and then coordinate the optomotor response (OMR). This response is an innate component of rheotaxis that plays an important role in motion detection, navigation and orientation. In an initial experiment, 16 wk-old metacercariae reduced minnow OMR by 42% compared to uninfected controls. However, in a follow-up experiment, it was 2- and 4- wk old metacercariae that caused the greater (39 and 41% respectively) decrease in OMR. Because 2- and 4-wk old metacercariae are not infective to birds (the next host in the life-cylce), alterations in minnow OMR at this time are unlikely to be a parasite adaptive. During this period, reduced OMR is more likely a result of pathology caused by developing larvae within the optic lobes. However, negative effects of infection on OMR performance persisted to 16 wk post-infection indicating the parasite-induced reduction in host performance could be an adaptive strategy to increase parasite transmission. Surprisingly, the magnitude of reduction in minnow OMR was only loosely linked to metacercarieae intensity. Although both low (<5 parasites/fish), and high intensities (>100) led to large decreases in OMR, intermediate intensities had only a small effect. Such non-linearity between intensity and the magnitude of host behavioural changes suggest that the mechanisms leading to altered host behaviours are varied, and complex.
vii, 79 leaves : ill. ; 29 cm.
Parasitology , Fathead minnow -- Parasites , Dissertations, Academic