Resting stages in the life cycle of Eudiaptomus graciloides (Lill.) (Copepoda: Calanoida) in Lake Glubokoe |
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Authors: | Pasternak A; Arashkevich E |
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Institution: | P.P.Shirshov Institute of Oceanology RAS, 36 Nakhimov av., Moscow 117851, Russia |
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Abstract: | Seasonal changes in the abundance, age composition, vertical distribution,
lipid and protein body content, development rates in the older copepodids
(CIV and CV) and reproduction characteristics were studied in
Eudiaptomus graciloides in the mesotrophic Lake
Glubokoe (Moscow) region). Two periods of reproduction were observed:
spring and late summer/autumn. The older copepodids, having accumulated
lipid reserves during phytoplankton bloom, descended into the meta- and
hypolimnion at the beginning of the summer. These copepods did not feed,
but instead consumed their lipid reserves. A considerable delay in
development (up to 40-60 days) of CIVs and CVs was found. The descended
CIVs and CVs incubated under ambient temperature developed 4-5 times slower
than their surface counterparts, while temperature dependence could only
account for a 2-fold slow down. The descended copepods are believed to form
a summer resting stock. In October, females began to produce resting eggs.
The period of switching from subitaneous to resting egg production was very
brief, not longer than 2-3 weeks. The percentage of subitaneous eggs
produced in mid-October tended to increase when females were exposed to an
increased photoperiod. At the beginning of February, latent eggs kept in a
cooling container in the darkness started hatching. This process could be
speeded up under natural photoperiod and increased temperature. The
over-wintering population consisted largely of adults. Thus,
E.graciloides includes three types of diapause in the
life cycle: resting eggs, summer resting stage at CIV-CV, and overwintering
adults.
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