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First published online December 10, 2003
Journal of Experimental Biology 207, 325-336 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00759
Ontogeny of osmoregulatory structures and functions in the green crab Carcinus maenas (Crustacea, Decapoda)
1 Biologische Anstalt Helgoland/Stiftung Alfred-Wegener-Institut für
Polarund Meeresforschung, Meeresstation, D-27498 Helgoland, Germany
2 Equipe Adaptation Ecophysiologique et Ontogenèse, UMR 5000 GPIA,
Université Montpellier II, F-34095 Montpellier cedex 05,
France
* Author for correspondence (e-mail: ucieluch{at}awi-bremerhaven.de)
Accepted 16 October 2003
The ontogeny of osmoregulation, the development of branchial transporting
epithelia and the expression of the enzyme Na+/K+-ATPase
were studied in Carcinus maenas (L.) obtained from the North Sea,
Germany. Laboratory-reared zoea larvae, megalopae and young crabs were exposed
to a wide range of salinities, and hemolymph osmolality was measured after 24
h exposure time (72 h in juveniles). Zoea I larvae slightly hyper-regulated in
dilute media (10.2
and 17.0
) and osmoconformed at
>17
. All later zoeal stages (II-IV) osmoconformed in salinities
from 10.2
to 44.3
. The megalopa hyper-regulated at salinities
from 10.2 to 25.5
. Young crabs hyperregulated at salinities from
5.3
to 25.5
, showing an increase in their osmoregulatory
capacity. The development of transporting epithelia and the expression of
Na+/K+-ATPase were investigated by means of transmission
electron microscopy and immunofluorescence microscopy. In the zoea IV, only a
very light fluorescence staining was observed in gill buds. Epithelial cells
were rather undifferentiated, without showing any features of ionocytes. Gills
were present in the megalopa, where Na+/K+-ATPase was
located in basal filaments of the posterior gills. In crab I juveniles and
adults, Na+/K+-ATPase was noted in the three most
posterior pairs of gills, but lacking in anterior gills. Ionocytes could first
be recognized in filaments of megalopal posterior gills, persisting through
subsequent stages at the same location. Thus, the development of the gills and
the expression of Na+/K+-ATPase are closely correlated
with the ontogeny of osmoregulatory abilities. The morphological two-step
metamorphosis of C. maenas can also be regarded as an
osmo-physiological metamorphosis, (i) from the osmoconforming zoeal stages to
the weakly regulating megalopa, and (ii) to the effectively hyper-regulating
juvenile and adult crabs.
Key words: osmoregulation, ontogeny, hemolymph osmolality, immunolocalization, Na+/K+-ATPase, gill, larva, ionocyte, Carcinus maenas
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