The spawning ofArenicola marina(L.) III. Maturation and shedding of the Ova

Abstract

SUMMARYExperiments are described in which attempts were made to fertilize eggs of the lugworm taken from the coelom. These were unsuccessful except when the eggs were taken from spent or partially spent worms or from worms kept in the laboratory until they were about to spawn. It was concluded from this that maturation of the eggs precedes spawning but only by a matter of hours. That maturation begins in the body cavity was confirmed by histological examination of eggs from partially spent worms and criteria are given for the recognition of immature and mature eggs. Lack of success in previous attempts to fertilize coelomic eggs from non-spawning worms may be because females which are just about to spawn are not obtained by the normal methods of collection. It is suggested that this is due to a change in the behaviour of the worms associated with retention of eggs in the burrow after oviposition. With regard to the stimulation of spawning in female worms, it has been shown that maturation immediately precedes the onset of shedding. This, together with the fact that if eggs undergoing maturation are injected into a nonspawning worm they are shed automatically suggests that the primary stimulus for the onset of shedding is, simply, one which will induce maturation of the eggs.Observations made during the above experiment together with the fact that worms can be induced to shed a few unripe eggs by injection of tissue extracts suggest, however, that spawning is not entirely passive and dependent on maturation. The lipid fraction of tissue extracts stimulates the active uptake of eggs from the coelom but it fails to induce maturation of the eggs and hence the free spawning produced in male worms. While the release of lipid into the body cavity may have some effect on the spawning of female worms (under natural conditions) similar to that previously suggested for males, it cannot provide the primary internal stimulus for spawning.

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

“…The injection of fernale Arenicola marina prostomial homogenate into the coelomic cavity of female A. marina is now a reliable endocrine technique to induce spawning of ripe females (Howie 1961, Pacey & Bentley 1992a, Watson & Bentley 1997, 1998b. The results shown in Fig.…”

“…For Arenicola manna 79% of the oocytes at least in females, is different. Vitellogenesis in A. mamatured in coelomic fluid with CMF activity, while nna begins in mid-June and results in the production of 100% of A. defodiens' oocytes matured when incufully-grown (approximately 175 pm diameter) but imbated in female A. defodiens prostomial homogenate mature oocytes (Howie 1961). In contrast oocytes of A. at a concentration of 0.5 prostomia ml-'.…”

“…In males, the fatty acid 8,11,14-eicosatrienoic acid has been putatively identified as the Sperm Maturation Factor (SMF) and spawning hormone found in the prostomium (Bentley 1985, Bentley et al 1990, Pacey & Bentley 1992a, b, Bentley & Hardege 1996. In females, oocyte maturation involves the progression from late prophase of the first meiosis to metaphase following germinal vesicle breakdown (GVBD) (Howie 1961). Oocyte maturation and subsequent spawning are induced by a hormone from the prostomium (Howie 1961, 1963, 1966, Pacey & Bentley 1992a.…”

“…In females, oocyte maturation involves the progression from late prophase of the first meiosis to metaphase following germinal vesicle breakdown (GVBD) (Howie 1961). Oocyte maturation and subsequent spawning are induced by a hormone from the prostomium (Howie 1961, 1963, 1966, Pacey & Bentley 1992a. Recent work has shown that oocyte maturation and subsequent spawning requires 2 steps: production of the substance from the prostomium, termed the Prostomium Maturation Hormone (PMH), which induces the production of a second substance, the Coelomic Maturation Factor (CMF), which is detectable in the coelomic fluid prior to spawning (Watson & Bentley 1997, 1998a.…”

The activation of gamete migration, maturation and spawning inPectinaria gouldii

“…In many polychaetes, particularly the Nereidae, the onset of gametogenesis results from the withdrawal of a single, inhibitory neurosecretory hormone which decreases as oocyte development continues [ 3,4]. In the lugworm, Arenicola marina, maturation of the oocytes immediately precedes spawning, and the nephromixia will only accept and shed ripe gametes [ 5]. Further experiments by Howie indicated that oocyte maturation, then spawning, were stimulated by a maturation hormone [6,7].…”