Abstract
The present study investigated the effect of temperature on male and female swimming activity of the calanoid copepod Temora longicornis, sampled during winter (February) and summer (August) in the English Channel coastal ecosystem. Video recordings were conducted at 3 temperatures representative of those to which these organisms are normally exposed (13, 16 and 20 degrees C) and one extreme-event temperature (24 degrees C). Examinations of instantaneous velocity and symbolic analysis (i.e. dynamics of swimming states discretized from time series of instantaneous velocity) showed that T. longicornis changed its behaviour when confronted with environmental temperature variations. Swimming speed increased as temperature increased. In warmer water, this copepod displayed higher swimming activity, break periods were less frequent, and the frequency of jumps increased. This phenomenon was amplified when the environmental temperature was increased to 24 degrees C. These observations revealed a considerable tolerance to high temperatures and an ability to adjust to environmental temperature changes. The 'summer population' was less active in the low temperature range, but the swimming speed reached a higher value at higher temperatures than that shown by the 'winter population'. The results of the present study highlighted changes in the individual behaviour of this copepod in response to changing seasonal conditions in the form of swimming activity, and thus its ability to maintain biological processes throughout the year, even in a restrictive environment.
Highlights
Temperature affects all biological processes, from molecular to population scale, especially in poikilothermic marine invertebrates (Pörtner & Farrell 2008), e.g. copepods (Kinne 1970, Mangum et al 1972)
The present study investigated the effect of temperature on male and female swimming activity of the calanoid copepod Temora longicornis, sampled during winter (February) and summer (August) in the English Channel coastal ecosystem
Examinations of instantaneous velocity and symbolic analysis showed that T. longicornis changed its behaviour when confronted with environmental temperature variations
Summary
Temperature affects all biological processes, from molecular to population scale, especially in poikilothermic marine invertebrates (Pörtner & Farrell 2008), e.g. copepods (Kinne 1970, Mangum et al 1972). The physical properties of cellular components, as well as biochemical reaction kinetics, are highly sensitive to temperature (Brown et al 2004 and references therein), which appears as a key forcing in any life cycle trait These traits include respiration (Gauld & Raymont 1953, Ikeda et al 2001), generation time and stage-specific mortality (HalsbandLenk et al 2002, Devreker et al 2005) and the reproduction of and predation for poikilothermic organisms (Devreker et al 2005, Holste et al 2009). In the marine pelagic ecosystem, copepods are subjected to highly variable and restricted conditions in a 3-dimensional diluted and patchy environment Their ability to maintain constant life processes, i.e. maximize encounter rate with potential partners or prey and minimize predation risk, in spite of changing environmental conditions, is crucial for their fitness.
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