MEPS 280:211-226 (2004)  -  doi:10.3354/meps280211

Ecophysiology of overwintering in the copepod Neocalanus plumchrus: changes in lipid and protein contents over a seasonal cycle

Robert W. Campbell1,3,*, Palmira Boutillier2, John F. Dower1,2

1School of Earth and Ocean Sciences, University of Victoria, PO Box 3055 Stn CSC, Victoria, British Columbia V8W 3P6, Canada
2Department of Biology, University of Victoria, PO Box 3020 Station CSC, Victoria, British Columbia V8W 3N5, Canada
3Present address: Institute for Hydrobiology and Fisheries Science, University of Hamburg, Olbersweg 24, 22767 Hamburg, Germany

ABSTRACT: Changes in lipid and protein content, and the activity of the enzyme glutamate dehydrogenase (GDH) were measured in a relatively isolated population of Neocalanus plumchrus in the Strait of Georgia between December 2001 and March 2003. Lipid contents (primarily wax esters, WE) were highest in overwintering Stage 5 copepodids, and consumption of wax ester stores began approximately 2 mo prior to moulting in situ. The rate of WE use in the in situ population, estimated from changes in WE over time, was 1.5 µg individual-1 d-1, with approximately 28% of total wax ester reserves used prior to moulting. Loss rates in laboratory incubations ranged from 2.7 to 7.8 µg individual-1 d-1, with 36 to 65% of total wax ester reserves being used prior to moulting. Protein declined following the moult to adulthood, and was variable in active, surface-dwelling CV copepodids. Measurements of GDH activity were consistent with protein catabolism for actively growing CV copepodids and adults, but not overwintering individuals, which suggests that protein is not an important metabolic substrate during overwintering. Individuals kept in the laboratory moulted in advance of the in situ moulting period, after a 1 to 2 mo post-capture lag. Individuals collected early in the overwintering period postponed moulting relative to individuals collected closer to the time of the in situ moulting period. This suggests that the timing of moulting in N. plumchrus involves an interaction between an endogenous clock and an unknown cue that stimulates the termination of dormancy and the onset of reproductive development and maturation.

KEY WORDS: Copepod overwintering · Lipid physiology · Protein · Dormancy · Diapause

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