Physiological traits associated with a reproductive-resting stage in Coullana canadensis (Copepoda: Harpacticoida) |
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Authors: | D J Lonsdale R P Hassett F C Dobbs J Yen |
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Institution: | (1) Marine Sciences Research Center, State University of New York at Stony Brook, Stony Brook, New York 11794-5000, USA, US |
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Abstract: | We investigated physiological traits associated with a reproductive-resting stage in adult female harpacticoid copepods,
Coullana canadensis (Willey). Our hypothesis was this stage represents a life-history strategy that could increase fitness by improving winter
survivorship and future reproductive success in spring. To test if physiological rates are suppressed in this stage, we compared
gut-cell morphology, nitrogen excretion rates, enzyme activities, and phytoplankton grazing rates of reproductive-resting
and reproductive females reared in the laboratory under high food conditions. Copepods came from laboratory cultures originating
from individuals collected in Maine and Maryland, USA in 1990. Reproductive-resting females had lower physiological rates,
and the surface area of gut-cells was reduced compared to reproductive females. Distinct morphological differences in the
distribution of lipids between reproductive and reproductive-resting females were observed under light and electron microscopy,
the latter having a diffuse accumulation of lipid in the area normally occupied by the ovaries. Differences in lipid composition
were also found. Reproductive copepods had a significantly higher ratio (%) of polar lipids to total lipid, and a lower proportion
of triacylglycerols compared to reproductive-resting copepods. These laboratory findings are consistent with the hypothesis
that the reproductive-resting stage in C. canadensis is an adaptive response to increase winter survival.
Received: 29 May 1996 / Accepted: 3 December 1997 |
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