The development of the female gamete in the endosymbiont-bearing bivalve Loripes lucinalis

Abstract

The development of the female gonad in Loripes lucinalis (Lamarck) from Brest Harbour (Brittany, France) was examined over a one-year period. Throughout the year, several size classes of eggs were observed, and spawning was seen to occur twice. A major spawning occurred in May leaving the gonad completely empty in June. A minor spawning is also thought to have occurred between the November and December sampling periods. These spawnings do not seem to correlate with the classical environmental factors often associated with gametogenesis and spawning, namely temperature and chlorophyll a levels. The energy for gametogenesis seems to be obtained from the transfer of metabolites to the oocytes via specialized follicle cells. These metabolites are believed to be of heterosynthetic origin. An inverse relationship exists between the thickness of the follicle cell epithelium and the occupancy level of the gametes. During periods of gonadal proliferation, these cells represent the nutritive cells of the gonad, but during periods of non-proliferation they make up a somatic tissue used for metabolite storage until conditions are adequate for gonadal development.