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JPR Advance Access published online on February 27, 2004
Journal of Plankton Research, doi:10.1093/plankt/fbh056
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Received December 28, 2002;
accepted February 20, 2004

Article

Respiratory electron transport system (ETS) activity as an estimator of the thermal tolerance of two Daphnia hybrids

Tatjana Simcic 1* and Anton Brancelj 1

1 National Institute of Biology, Vecna pot 111, SI-1000 Ljubljana, Slovenia

* To whom correspondence should be addressed. E-mail: tatjana.simcic{at}nib.si.


  Abstract

The influence of temperature on respiratory electron transport system (ETS) activity was measuredin one clone of Daphnia hyalina x galeata and one of D. cucullata x galeata, isolated from LakeBled (Slovenia). The ETS activity of ovigerous females acclimated to 7, 20, and 25 °C, was measured at 5, 10, 15, 20, 25, and 30 °C. Population growth experiments showed that D. cucullata x galeata grew better at high rather than low temperatures. D. hyalina x galeata, however, grew moresuccessfully at low temperatures than D. cucullata x galeata . The highest Q10 of ETS activity of D.cucullata x galeata at the lowest temperature range of 5-15 °C indicated the absence of enzymesthat could function sufficiently well at low temperatures. ETS activity of warm-acclimated hybrid D. hyalina x galeata reached a maximum at an incubation temperature of 20 °C, while D. cucullata x galeata had maximal ETS activity at 25 °C. Thus D. cucullata x galeata has a more efficient enzyme system than D. hyalina x galeata at the higher temperature. Higher Arrhenius activation energy (Ea) for D. cucullata x galeata than for D. hyalina x galeata indicates that enzymes from D.cucullata x galeata are more temperature sensitive than those from D. hyalina x galeata. Inconclusion, the ETS of D. cucullata x galeata is adapted to higher temperature and narrower temperature fluctuations than that of D. hyalina x galeata.


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