Control of oocyte maturation, sperm activation and spawning in two lugworm species: Arenicola marina and A-defodiens

In addition to the morphological differences between Arenicola defodiens (Cadman and Nelson-Smith, 1993) and Arenicola marina (L.) this study demonstrates clear differences in the reproductive biology, timing of reproduction at a population level, and endocrine control of reproduction in females. Fecundity is significantly higher in females of A. marina and the mean diameter of their fully grown oocytes is also significantly larger than in A. defodiens. The timing of reproduction at a population level is also different with A. defodiens spawning approximately 1 to 2 mo later than sympatric A. marina. In vitro and in vivo experiments have established fundamental differences as well as similarities in the hormonal control of reproduction of both sexes between the 2 species. Male A. defodiens can be induced to spawn by the injection of 8,11,14-eicosatrienoic acid into the coelomic cavity, putatively shown to be the natural sperm maturation factor and spawning hormone in A. marina. In females, injection of female prostomial homogenate from either species into the coelomic cavity induces oocyte maturation and subsequent spawning in both species. However, oocytes of A. marina, whilst maturing in the presence of CMF (Coelomic Maturation Factor) in vitro, do not mature in the presence of prostomial homogenate of either species, whereas A. defodiens oocytes do. In A. marina, oocyte maturation and subsequent spawning is under the control of 2 hormones: (1) a substance from the prostomium, Prostomial Maturation Hormone (PMH), which induces the production of (2) CMF which acts on the oocyte. In A. defodiens, we show that only PMH is required for oocyte maturation and spawning. The in vitro induction of oocyte maturation in A. marina, by a variety of chemicals and treatments that have already been shown to induce maturation in A. defodiens and species from other phyla, was investigated. None of the chemicals and treatments tested induces maturation in A. marina or A. defodiens oocytes.