Seasonal adaptations of Daphnia pulicaria swimming behaviour: the effect of water temperature |
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Authors: | Joshua J Ziarek Ai Nihongi Takeyoshi Nagai Marco Uttieri and J Rudi Strickler |
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Institution: | (1) Department of Biochemistry, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA;(2) Great Lakes WATER Institute, University of Wisconsin-Milwaukee, 600 East Greenfield Avenue, Milwaukee, WI 53204, USA;(3) Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Minato-ku Konan 4-5-7, Tokyo 108-8477, Japan;(4) Department of Environmental Sciences, University of Naples “Parthenope”, Centro Direzionale di Napoli-Isola C4, 80143 Naples, Italy; |
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Abstract: | Daphnia swimming behaviour is controlled by a variety of external factors, including light, presence of food and predators. Temperature
represents a key driver in the dynamics of Daphnia populations, as well as on their motion. In this study, we have investigated the behavioural adaptations of adult Daphnia pulicaria to two different temperatures, representative of the mean winter (3°C) and summer (22°C) temperatures to which these organisms
are exposed to in the real environment. Video observations were conducted both in the presence and in the absence of light
to investigate possible day/night modifications in the motion strategy. Analyses of mean speed, velocity power spectral density
and trajectory fractal dimension point out specific adaptations that allow D. pulicaria to successfully adjust to the changing conditions of the environment. Independently of the light conditions, in cold waters
D. pulicaria swim almost vertically with defined motional frequencies, likely to increase the encounter with food items diluted in the
fluid. A similar behaviour is displayed by the animals at summertime temperatures in the presence of light; however, in this
case the vertical swimming is coupled with the absence of peaks in the power spectra and might be exploited to avoid predators.
In contrast, at 22°C in dark conditions D. pulicaria move horizontally with lateral motions to take advantage of possible patches of phytoplankton. This information sheds new
light into the complex and dynamic adaptations of D. pulicaria in response to external stimuli. |
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