Gloria Martínez

Interactive effects of diet and temperature on reproductive conditioning of Argopecten purpuratus broodstock

Abstract Adult specimens of Argopecten purpuratus, obtained from Culture Centers of Tongoy Bay (Region IV, North of Chile), were conditioned at two temperatures, 16°C and 20°C, and three different diets: a mixture of pure microalgae, microalgae mixed with lipids and microalgae mixed with carbohydrates. Daily food supply was 6% of dry biomass. Three replicate tanks were assayed for each treatment. The progress of gonadal recovery was followed by periodic determination of gonadic index and histological analysis during three months. Gonadal recovery was slower for the animals conditioned at 20°C than for those at 16°C. Recovery was poorest for the animals fed pure microalgae at 20°C. The highest percentages of mature animals, at the end of the experiment, were obtained for the animals conditioned at 16°C and the maximal value was obtained for those fed microalgae–lipids. This diet also rendered the best result for scallops maintained at 20°C. All scallops conditioned at 16°C responded to spawning induction; the poorest response was for individuals conditioned at 20°C and fed pure microalgae. The percentage fertilization of gametes from the different treatment broodstocks did not differ but the percentage of larvae D survival was much higher for those from scallops conditioned at 16°C and fed pure microalgae or microalgae–lipids. These results indicate that temperature affects gametogenesis and that enriched lipid diets may improve the conditioning of bivalve broodstock.

Effect of different temperature regimes on reproductive conditioning in the scallop Argopecten purpuratus

Abstract Adult Argopecten purpuratus were conditioned under four different temperature regimes and their gonadal development and quality of the resulting offspring evaluated. Biochemical composition of muscle and gonad, during laboratory conditioning at the different treatments, was also examined. Spawned-out individuals were obtained from commercial culture centers for experimentation. Test groups of scallops were independently maintained at: (a) 15 °C, (b) 19 °C, (c) 15 °C in the first stage, raised to 19 °C in the second stage, and (d) 19 °C in the first stage decreasing to 15 °C in the second stage. Scallops were maintained in seawater which was changed daily, provided with aeration, and were continuously fed a diet consisting of 50% Isochrysis galbana (var. T-iso) and 50% Chaetoceros gracilis. The daily ration was equivalent to 6% of the dry biomass of the scallops. Animals were maintained under a constant photoperiod of 12-h light and 12-h dark. Progress of gonadal recovery was followed by periodic determination of gonadosomatic index (GSI) and histological analysis. The highest percentage of scallops attaining spawning condition and highest values for GSI was obtained from animals conditioned under the constant 15 °C regime. The group started at 15 °C and raised to 19 °C showed the most variable pattern of maturation. Of the major biochemical components of the adductor muscle, lipids and proteins changed most during conditioning under any of the temperature regimes; changes in carbohydrate levels in this tissue were only detected for scallops maintained at a constant temperature. Changes in protein levels, depending on the time and temperature of conditioning, were detected in the gonad. Based on quality indicators used in this study, including fecundity, egg size, biochemical composition, and “D” larvae survival, the best physiological conditioning for the reproductive process was obtained in scallops, which were conditioned at a constant temperature of 15 °C, and at an initial temperature of 19 °C and then decreased to 15 °C. Results showed an inverse relationship between temperature and conditioning success and the importance of maintaining stable temperatures during the laboratory conditioning process which permitted adequate accumulation and use of nutritional reserves required to produce highly viable larvae.

Prostaglandins and reproduction of the scallop Argopecten purpuratus: II. relationship with gamete release

Levels of prostaglandins E(2) and F(2alpha) were measured in male and female gonadal portions of the functional hermaphroditic scallop Argopecten purpuratus, at the time of spawning. For these measurements, mature scallops were stimulated to initiate their chain of spawning events, and prostaglandins (PGs) were analyzed in samples before stimulation, when animals appeared stimulated to release sperm, during the release of sperm, when animals appeared stimulated to release oocytes, when most of the oocytes had been released, and 24 hr after the end of spawning. The experiment was run twice, once in winter and once in spring. An additional in vitro experiment was carried out to analyze activity of the monoamines dopamine and serotonin on the levels of these prostaglandins. For this, minced tissue of the female portion of the gonad was incubated for different time periods with each of the amines at 10(-5) M. PGs were determined in the tissue samples by radioimmunoanalysis. The results showed that the amounts of the PGs increased significantly in both parts of the gonad during the global process of spawning and decreased when it had been completed. Incubation of minced gonad with the amines affected the time course of PGs variations, i.e., the effect of these compounds depended on the incubation time used. The results support a model for the regulation of spawning which assumes the occurrence of a stimulus which is detected by receptors, processed by nerve cells, and sent to the gonad where intermediation by amines (changing the time course of the process) induces liberation of gametes, in some way modulated by prostaglandins.

Monoamines and the release of gametes by the scallop Argopecten purpuratus

Levels of dopamine (DA), noradrenaline (NA) and serotonin (5-HT) were measured fluorometrically in the ganglia, gonads and adductor muscle of the functionally hermaphroditic scallop Argopecten purpuratus at different times during the induced release of gametes. The levels of these amines were analyzed in samples before stimulation, when animals looked stimulated, during the release of sperm, during the release of oocytes, and 24 hours after the end of spawning. Levels in muscles of the three monoamines changed during spawning and the greatest change was detected in the level of NA. In nervous tissue, the level of 5-HT decreased, whereas those of DA and NA increased significantly with the release of sperm. In both the female and male portions of gonad, levels of DA and NA increased during spawning while those of 5-HT decreased. However, levels of 5-T in the female portion of gonads did not show any changes in a group of scallops that did not release sperm before releasing oocytes. Separate analysis of levels of monoamines in the visceral ganglion from those in the cerebropedal ganglion, showed that, in spawning animals, levels of DA and ANA did not change in cerebropedal ganglia but decreased in the visceral ganglia, whereas levels of 5-HT decreased only n the cerebropedal complex. The results are consistent with the existence of two different mechanisms for the control of the release of sperm ad oocytes by hermaphroditic pectinids.

In vitro effects of monoamines and prostaglandins on meiosis reinitiation and oocyte release in Argopecten purpuratus Lamarck

Summary The effects of serotonin, dopamine, and prostaglandins E2 and F2α (PGE2, PGF2α) on the release of oocytes, as well as reinitiation of meiosis in them, were evaluated for the scallop Argopecten purpuratus. Germinal vesicle breakdown, signalling reinitiation of meiosis in oocytes, occurs just prior to their release to the environment and was seen in histological sections of female gonad and kidney, made at the time when the scallop appeared ready to release the female gametes. Studies of the effects of the amines and prostaglandins were made in vitro with fresh sections of the female gonadal sector using varied concentrations and exposure times. Serotonin (10−6 to 10−4 M) increased the number of oocytes released, and these numbers increased in relation to the time of incubation. Release of oocytes, relative to control, was reduced by dopamine (10−6 to 10−4). The effects of the amines on oocyte release were blocked by pre-incubation with indomethacin, an inhibitor of PG synthesis. PGE2 (10−6M) increased oocyte release; PGF2α (10−6M) did not affect this process. Serotonin and the two prostaglandins increased the rupture rate of germinal vesicles, a process unaffected by the presence of dopamine. The results suggest separate mechanisms for the regulation of the processes of egg release and reinitiation of meiosis in this mollusc.

Abbreviated Dynamic Source Routing: Source Routing with Non-Unique Network Identifiers

Current ad-hoc network protocols are designed for hosts similar to the ones that are used in fixed networks. These protocols are not suitable for some applications of ad-hoc networks, where resources are very scarce. One point is the size of the network addresses, which may be a critical issue, specially with the use of IPv6 in the DSR protocol. This is because this protocol uses source routing, and, therefore, each datagram must carry the addresses of all the machines in its path. In this paper a new protocol named ADSR is proposed to solve this problem. This new protocol is a modified version of DSR based on the use of abbreviated addresses. The abbreviation procedure can lead to two different nodes having the same address, which we will term collision. ADSR allows rather than averts collisions, as analysed in this paper. Some results on the performance of this new protocol are shown. These results have been obtained by simulations implemented on an ns-2 network simulator.

Cyclic AMP and the reproductive process of the scallop Argopecten purpuratus

The level of cyclic AMP was measured in both female and male gonadal portions of the functionally hermaphrodite scallop Argopecten purpuratus. Measurements were done during both processes of spawning and gonadal recovery. To study the spawning process, samples were analyzed, before stimulation, when animals looked stimulated (with enlarged white gonoducts), during the release of sperm, during the release of oocytes, and 24 hours after the end of spawning. Before the stimulus, the cAMP values were higher in the male gonadal portion than in the female portion. After applying the stimulus no change was detected in the female portion until oocytes were released; at this moment a sharp increase in cAMP level was detected. In the male portion of the gonad, the nucleotide level decreased sharply after applying the stimulus and returned to pre-stimulus values when oocytes were released. For the study during the gonadal recovery period, samples were taken on days 2, 6, 10, 14, 18, 22, and 26 after spawning. In both gonadal portions, the levels of cAMP showed an initial decrease, then an increase in the middle of the study period and a sharp decrease when the process of gonad restoration was being completed. Dopamine and serotonin increased the levels of the nucleotide in the female gonadal portion only in the middle of the gonad restoration period. The results suggest that cAMP is involved in the regulation of the different stages of the reproductive process of this scallop by mechanisms that may involve the phosphorylation of different kinds of proteins for each stage. J. Exp. Zool. 278:243–249, 1997.

Extracellular Ca2+ requirement for serotonin-induced release and meiosis reinitiation from prophase in oocytes of the scallop Argopecten purpuratus

Summary The requirement for Ca2+in the external medium for the release and reinitiation of meiosis in the scallop Argopecten purpuratus was examined. In vitro experiments demonstrated that the serotonin-induced release of oocytes is inhibited in a calcium-free medium. Caffeine (10 and 20 mM), a known activator of ryanodine channels, increased oocyte release by gonadal pieces and 50 μM ryanodine inhibited this release and blocked the serotonin-induced effect. The number of oocytes released under control conditions was not affected when ryanodine was used in concentrations in the nanomolar range. Germinal vesicle breakdown, indicative of meiosis reinitiation, was inhibited in gonadal pieces incubated in calcium-free normal or artificial seawater and serotonin does not overcome this inhibition in the same conditions. An increase in fluorescence on adding serotonin (10−5 M, final concentration) was detected under the confocal microscope when oocytes charged with the calcium fluorescent dye Fluo-3 AM were studied. We postulate that there is a rise in cellular calcium in the serotonin-induced spawning process and that the source for the increase is influx from the external medium and release from internal stores. We suggest that this calcium rise plays a role in germinal vesicle breakdown and in the contraction of gonadal smooth muscle.

Role of second messenger IP3 in the reproductive process of Argopecten purpuratus

Summary Levels of IP3 in the female gonadal portion of the functional hermaphrodite scallop Argopecten purpuratus were measured at different times during an induced spawning and at different times of the gonadal recovery period following this process. The IP3 content in the tissue samples was determined by a radioreceptor analysis. The amounts of IP3 remained unchanged during the intermediate stages of spawning and increased when the release of gametes had just been completed. The content of this compound in the gonads decreased as the gonadal maturation proceeded. IP3 does not appear to be significantly involved in the process of gametogenesis but may be involved in the mechanism of spawning. We postulate that IP3 acts as a second messenger that increases the Ca2+ concentration which would be necessary for gamete release or for gonadal recovery.