Seasonal variations in biochemical constituents during the reproductive cycle of the female dog cockle Glycymeris glycymeris |
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Authors: | C Galap F Leboulenger J-P Grillot |
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Institution: | (1) Laboratory of Marine Invertebrate Physiology, Faculty of Sciences and Techniques, University of Le Havre, 25 rue Philippe Lebon, B.P. 540, F-76058 Le Havre Cedex, France, FR |
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Abstract: | In an attempt to describe the biochemical events associated with the main stages of the annual and reproductive cycles of
the female dog cockle Glycymeris glycymeris L., we studied seasonal variations in the various stages of oocyte development of the ovaries, and the glycogen, total protein
and total lipid content of five body tissues – adductor muscle, foot, tunic coat, visceral mass and mantle. From November
1991 to November 1994, microscopic examination of the ovaries and measurement of the tissue concentrations of glycogen, total
proteins and total lipids in these five body tissues were made monthly on ten female dog cockles originating from the sea
area around Douarnenez (south Brittany, France). Morphological studies revealed that in the population investigated the annual
cycle is characterised by three major periods: a first period of vitellogenesis extending from February/March to April/May
and preceding a spawning in spring; a second period of vitellogenesis extending from May/June to September/October and leading
to either no spawning, a single autumnal spawning event, or to two spawning events in summer and autumn; and a third period
extending from October/November to February/March and characterised by a high level of oocyte lysis. In the muscular body
tissues of the dog cockle, i.e. the adductor muscles, the foot and the tunic coat (the muscular envelope containing the visceral
mass), the concentrations of glycogen, total proteins and total lipids underwent very similar variations during the annual
cycle. During each stage of vitellogenesis, a typical glycogen–protein–lipid sequence was observed in the muscular tissues
that was characterised firstly by a peak of glycogen concentration 2 to 3 mo before spawning, followed by a peak in total
proteins 1 mo before spawning, and finally by a peak in lipid content just before spawning. A similar glycogen–protein–lipid
sequence was also recorded in the first half of the winter period. However, these events were followed by general atresia
affecting all oocytes in the gonad. Maximum energetic value of biochemical constituents in females coincided with peaks in
lipid content in the visceral mass and mantle. These biochemical events occurred principally immediately before and at the
end of oocyte lysis (December/January). A drop in the total energetic value, affecting mainly the visceral mass and the mantle,
was recorded each year during the period January to March, coinciding with the period of shell growth in this species. Our
data clearly indicate that in female G. glycymeris all muscular tissues contribute to the storage of glycogen and proteins, and suggest that glycogen may be the source of energy
triggering vitellogenesis. Biochemical and microscopic observations revealed that oocyte development takes place during the
first half of winter, but that these oocytes undergo atresia in December/January. The metabolites produced from oocyte lysis
could contribute to somatic growth, which occurs in late winter.
Received: 3 March 1997 / Accepted: 23 July 1997 |
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