Maturation, Spawning and Development in Siphonaria Pectinata Linnaeus (Gastropoda: Pulmonata) at Gibraltar

A comparative study of some aspects of the reproductive biologyof Siphonaria pectinata was carried out at Gibraltar. Maturationoccurred at 5-6 mm shell length corresponding to an age of 6-12months. At the more sheltered Atlantic site spawning was evidentfrom March to June 1992 with peak spawning occurring in May-June1992. The patterns of spawning activity for the following twoyears were very similar. Egg ribbons were very scarce at themore exposed Mediterranean site and were found in considerablyless quantities than at the Atlantic site. Individuals at bothsites contained mature eggs in their gonads at the onset, andthen throughout the duration of the spawning season, but exhibitedspent gonads by October. The spawn of S. pectinata consistedof small oval ribbons filled with numerous egg-shaped capsulesspaced irregularly in a jelly-like matrix. Spawn was depositedmainly away from the home scar in shallow depressions, cracksand crevices and between barnacles and mussels. S. pectinataexhibited planktonic development. The fertilised eggs took between14 and 21 days to develop at ambient temperature (14-19°),and hatched as free-swimming planktotrophic veligers. The timingof spawning activity and the placement of egg masses in protectivemicrohabitats on the shore are discussed in terms of adaptationsto reduce desiccation stress, predation and possible food shortages.The mode of development in S. pectinata is placed in contextwith current theories regarding siphonariid ancestry and evolution. (Received 6 January 1998; accepted 25 June 1998)     

ASYNCHRONOUS REPRODUCTIVE ACTIVITY IN THE BROADCAST SPAWNER CELLANA CAPENSIS (GMELIN, 1791) (GASTROPODA: PATELLIDAE)

Short-term fluctuations in the reproductive condition of thelimpet Cellana capensis are described. Gravimetric and histologicalanalyses of gonadal development were carried out on samplescollected at 4 day intervals over a 3 month period from theMkambati Nature Reserve, Transkei. The results indicate a distinctlack of reproductive synchrony within the population, whichapplied not only to gametogenic development per se but alsoto spawning activity. Some of the spawning events identifiedduring the study period were more marked than others, thesemay reflect a greater degree of synchronization in activity.Results presented suggest that C. capensis is probably a ‘partial’rather than a ‘complete’ spawner. The implicationsof asynchronous spawning activity for the reproductive successof broadcast spawners are also discussed. (Received 6 December 1988; accepted 15 February 1989)     

THE ECOLOGY OF THE HONG KONG LIMPETS CELLANA GRATA (GOULD 1859) AND PATELLOIDA PYGMAEA (DUNKER 1860): REPRODUCTIVE BIOLOGY

Cellana grata is large, relatively long lived (3 years), withone winter breeding season each year which can be correlatedwith major seasonal climatic and hydro-logical events, e.g.,winter reduction in temperature and higher seas. C. grata ischaracterised by a relatively low value of mean annual reproductiveeffort (males: 23%; females: 18%). Patelloida pygmaea is small,short lived (1 year), with one spring breeding season each yearand devotes a large proportion of metabolic energy for reproduction.P. pygmaea showed a higher value of mean annual reproductiveeffort (males: 46%; females: 31%) than C. grata. Mature gonads of Cellana grata first appeared in June and itreached a peak maturity (100%) in September, remaining so untilDecember, i.e., the maturation of the gonads coincided withincreasing water temperatures, with spawning associated witha decrease in water temperature. Gonadal development by Patelloidapygmaea began in either July or August and reached a peak inDecember, remaining so until a major peak in spawning took placebetween April and May, i.e., gonad maturation coincided witha decline in water temperature, with spawning following thesubsequent increase. Limpet gonadal cycles are likely gearedto temperature and food supply. Spawning occurred between Novemberand December, when wave heights are typically 1 m higher thanin summer. (Received 1 December 1992; accepted 25 June 1993)     

A Quantitative Study of Environmental Factors Influencing the Seasonal Onset of Reproductive Behaviour in the South American Apple-snail Pomacea canaliculata (Gastropoda: Ampullariidae)

Two laboratory experiments were carried out on sets of winter(inactive) pairs of Pomacea canaliculata (Lamarck), one to studythe influence of water temperature (either 18°C or 25°C,corresponding to late winter and summer temperatures in Mendoza, respectively)and day length (either 10 h light/day or 14 h light/day, correspondingto the shortest and the longest day of the year in Mendoza,respectively), and the other to determine the effects of foodavailability (ad libitum feeding vs. restriction to 25% of thead libitum requirements) on the frequency of copulation andspawning, on spawn measurements (number and volume of eggs,and spawn volume), and on an index of the reproductive effort.Animals in all experimental groups were observed during 4 weeks,after seven days of acclimation to the experimental aquaria(under low water temperature and short photoperiod). Low watertemperatures induced a lesser and later activation of copulationand spawning than that induced by warm temperatures. Day lengthwas without effect on both behaviours. Both the frequency ofspawning and the reproductive effort index decreased under restrictedfeeding, without altering the spawn measurements. The latencyperiods for both copulatory and spawning behaviours were similarin both ad libitum and restrictedly fed groups. We concludethat water temperature may be the critical factor that causesthe seasonal onset of copulatory and spawning behaviour in theseapple-snails. However, food availability may also be a determiningfactor, mainly to trigger spawning activity. These results suggestthat the factors that control the seasonal onset of the sexualactivities in Pomacea canaliculata are similar to those thatcontrol the seasonal arrest, thereby establishing the annualpattern of reproduction in this species. (Received 26 January 1998; accepted 23 July 1998)     

Description of Rhynchoteuthion larvae of Illex argentinus from the summer spawning subpopulation

The Rhynchoteuthion larvae of Illex argentinus resulting fromsummer spawning in North Patagonic shelf waters, its distributionand abundance, are described in this paper. The material wascollected in the Argentine Sea (35–55°S) by meansof plankton nets. The research cruises were made by the R/VShinkai Maru and the R/V Walther Herwig during the period April1978 to April 1979. The most important spawning ground of thesummer spawning subpopulation is found in continental-shelfwaters (between 43 and 46°S) during the period December-February.This area was established on the basis of both ripe (December)and spent females (February). The larvae which were caught duringthe same period, especially in March, confirmed the spawningarea of this demographic unit. The larvae showed the lengthof the mantle (ML) to be from 1.2 to 6.5 mm. Tentacles weresplitting in specimens from 5.0 to 6.5 mm ML (transition stage).When 7.0 mm ML or more, all specimens were juveniles and hadtheir tentacles completely separated. Larvae were characterizedas type C, following the proposal of Sato (1973) and Sato andSawada (1974) in the Bulletin of the Shizuoka Prefectural FisheriesExperimental Station.     

A COMPARATIVE STUDY OF LASAEA AUSTRALIS, VULSELLA SPONGIARUM, PINNA BICOLOR AND DONACILLA CUNEATA (MOLLUSCA; BIVALVIA) FROM PRINCESS ROYAL HARBOUR, WESTERN AUSTRALIA

Monthly samples of L. australis, V. spongiartum, P. bicolorand D. cuneata were collected over a period of 12 months fromPrincess Royal Harbour, Western Australia. Preliminary informationon densities and biomass is given. Gonad histology points toseasonal reproductive cycles with autumn spawning in P. bicolorand D. cuneata and irregular spawning in V. spongiantm and L.australis. However, L. australis did show two peaks of larvalbrooding in the study period. Length-frequency data are discussedin the light of the proposed reproductive patterns for the fourspecies. Allometric relationships between length and both heightand width for all species are described and their value to eachspecies assessed. Populations of L. australis from differenthabitats show significant differences in shell shape. (Received 27 June 1983;     

Modeling spawning strategy for sex change under social control in haremic angelfishes

In haremic angelfishes where protogynous (female to male) sexchange is favored, females have been reported to adopt severaltactics for earlier sex change on the basis of a trade-offbetween reproduction and growth, or survivorship. A recentfield study on Centropyge ferrugatus revealed that femalesreduce spawning frequency in competition with similar-sized neighbors for social dominance. To evaluate the optimal spawningstrategy taken by haremic fishes, we developed an evolutionarilystable strategy model that focuses on their life history andsocial structure based on field data of C. ferrugatus. Theresults of the analysis predict that the spawning frequencywill be low when the mortality rate of females is high comparedwith males, the harem size is large, and there is a moderatedegree of social control. Our model further predicts conditionsunder which females completely stop spawning, as if they havebecome bachelors. Thus, the regulated spawning frequency maybe taken as a strategy to optimize the reproductive successof an individual in response to the available choices for sexchange, social control, and environmental conditions. Socialcontrol would also play an important role in sex change inmany other haremic species.     

Environmental and physiological controls on shell microgrowth pattern of Ruditapes philippinarum (Bivalvia: Veneridae) from Japan

The reproductive cycle and shell microgrowth patterns of thevenerid bivalve Ruditapes philippinarum from Matsukawa-ura,a small inlet facing the Pacific Ocean, northeastern Japan wereexamined. Histological examination of the gonads revealed thatspawning in this species occurred twice in 2005, once betweenlate June and early August and the other between late Septemberand early October. Comparison of the shell microgrowth patternswith the developmental stages of the gonad in each individualrevealed that in spawning individuals (mature and spawning stages),the mean lunar-day growth rates were significantly smaller thanthose in individuals which were not in spawning condition (spent,recovery and growing stages). In non-spawning individuals, themean lunar-day growth rates were positively correlated withseawater temperature up to 20°C. However, in spawning individuals,no correlation was observed between shell growth and seawatertemperatures >16°C. These facts suggest that physiologicalstress during reproduction has a negative influence on shellgrowth and results in spawning breaks. The present study indicatethat spawning breaks can be used to identify the timing of sexualmaturity and to count the number of spawning events occurringper year in extant and fossil bivalves.     

Coupling of nauplii release in barnacles with phytoplankton blooms: a parallel strategy to that of spawning in urchins and mussels

We examined the coupling between the release of nauplii in Semibalanusbalanoides and phytoplankton blooms, and compared it with themechanism synchronizing spawning with phytoplankton abundancein green sea urchins (Strongylocentrotus droebachiensis) andblue mussels (Mytilus edulis). Close contact with phytoplanktoncells is required to stimulate the release of nauplii in Semibalanus,whereas spawning in urchins and mussels is triggered by an extracellularmetabolite of phytoplankton. The response is concentration dependentand positively correlated with the frequency of moulting Themoulting rate in Semibalanus is reported to be directly correlatedwith food intake and thus larval release should be proportionalto feeding activity. The release of Semibalanus nauplii is morestrongly stimulated by the diatom Skeletonema costatum thanby Phaeodactylum tricornutum, whereas the highest response isobtained in treatments with nauplii of Artemia salina. We suggestthat these differences are related to size of the planktonicparticles (Artemia nauplii < Skeletonema < Phaeodactylum)Exposure to air, as occurs in the intertidal zone, does notinfluence significantly larval release Larval release in otherCrustacea may similarly be coupled to phytoplankton abundance.     

NATURAL SETTLEMENT AND EARLY GROWTH OF SPAT OF THE QUEEN SCALLOP CHLAMYS OPERCULARIS (L.), WITH REFERENCE TO THE FORMATION OF THE FIRST GROWTH RING

The settlement and early growth of spat of Chlamys opercularis(L.) on benthic epifauna has been studied. Intensity of spatsettlement may not always correspond to intensity of spawningand the minor summer spawning may be of greater importance thanthe more intensive autumn spawning. The growth rates of spatwere estimated from analysis of size frequency data and thenature of the first growth ring has been studied with referenceto the bimodality in size range and the relationship with thetwo peaks of settlement.     

REPRODUCTIVE CYCLES OF CERASTODERMA GLAUCUM(BRUGUIERE) AND C. EDULE (L.) WITH SPECIAL REFERENCE TO THE EFFECTS OF THE 1981-82 SEVERE WINTER

Gonadal changes in two species of Cerastoderma occurring indiscrete populations in South Wales were monitored by stereologicalanalysis during the breeding seasons of 1981 and 1982. Fecundityand spawning efficiencies were determined quantitatively. Therelationship between reproductive activity and changes in meatcondition are discussed. Both species are opportunistic breeders. Their normal patternsof reproduction are similar, consisting of minimum activityin winter and peak activity during spring/early summer. Thetwo species were affected differently by the severe winter of1981–82—C. glau-cum exhibited a single, ‘epidemic’spawning and resumed gametogenesis after a 4-month resting period.C. edule adopted a ‘polycyclic’ pattern withouta resting period. Both of these unusual reproductive strategies,augmented by reduced predation resulted in heavy spatfalls. (Received 20 March 1985; revised 20 March 1985;     

Environmental and Endocrine Influences on Reproduction of Fundulus heteroclitus

Reproduction in Fundulus heteroclitus is adapted to the temperateclimate and the tidal environment of the coastal marshes whichare its primary habitat. Egg deposition and spawning are closelylinked to the tidal cycle. Concentration of spawning on springtides gives the fish access to sites in the high intertidalzone. Eggs are deposited near the high water mark, usually insand in New England populations and in Spartina alternifloraor empty Geukensia demissa shells in Middle Atlantic and southernpopulations. Aerial incubation of eggs appears to be essentialfor their survival in the salt marsh. Loss of eggs due to lackof fertilization, mortality during development and predationwas always less than 30 percent in our observations. Hatchingoccurs only when the eggs are inundated, usually on spring tides.An endogenous semilunar gonadal cycle appears to be involvedin control of spawning, but an effective environmental synchronizerhas not been found. Cyclic changes in estradiol-17ßaccompany the gonadal cycle, while spawning behavior is stimulatedby neurohypophyseal hormones. Both temperature and photoperiodhave been implicated in the control of seasonal reproductionin F. heteroclitus. Early workers focused on males and concludedthat increasing temperature was the stimulus that initiatedgonadal recrudescence in spring. These experiments were notrigorous tests of the effects of photoperiod. We have shownthat in females both warm temperatures and long photoperiodsare involved. In female F. heteroclitus, as in most mammalsand birds, it is the timing rather than the duration of thelight exposure which determines its effectiveness in stimulatinggonadal maturation. Maintenance of gonadal maturity in femaleF. heteroclitus depends on long photoperiods, but the ovarymay become refractory and regress even when stimulatory photoperiodsare sustained in the laboratory. Ovarian maturity can be stimulatedwith gonadotropin injection in refractory animals, indicatingthat the brain-pituitary axis is the site of refractoriness.The pathway by which light influences ovarian maturity may involvean encephalic photoreceptor, since neither the eyes nor thepineal gland is necessary.     

POPULATION STUDIES OF CORBULA GIBBA (OLIVI), BIVALVIA, CORBULIDAE, IN THE NORTHERN ADRIATIC SEA

Populations of Corbula gibba (Olivi) were studied in the northernAdriatic Sea during routine biocenological investigations from1968 to 1978. Statistical analysis, size frequency distributionand the observations of spawning and recruitment indicate astable population structure with good survival. The appearanceof C. gibba in various types of bottom indicates that this speciesis widely distributed even in polluted areas. (Received 20 November 1979;     

Male sperm expenditure under sperm competition risk and intensity in quacking frogs

In the frog Crinia georgiana, reproductive behavior comprisesa "guarding tactic," in which males defend spawn sites and attractfemales by calling, and a "sneak tactic," in which males joinspawning pairs. The aims of the present study were to (1) relateejaculate expenditure by "guarding" and "sneak" males to theirprobability of mating with other males present (sperm-competitionrisk), and (2) determine if males adjust their ejaculate expenditureaccording to the number of males involved in a spawning (sperm-competitionintensity). Theory predicts that because sneak males alwaysmate with other males present, they will experience a highersperm-competition risk and should release larger ejaculatesrelative to that of guarding males. However, as the proportionof sneaks in a population increases so does the risk of spermcompetition to guarders, so expenditure by each tactic shouldmove toward equality. Given that the incidence of sneak behavioris high in C. georgiana, guarders and sneaks were expected toexperience similar risks of sperm competition and show similarinvestment in spermatogenesis. Comparison of testes size andejaculate size showed no difference between tactics. Modelsof sperm-competition intensity predict that males should increasetheir ejaculate size when spawning in the presence of one othermale but decrease their ejaculate size when spawning in thepresence of multiple males. Here, males maintained a constantsperm number irrespective of whether a mating involved one,two, or three males. This result suggests that male C. georgianado not facultatively adjust ejaculate investment in responseto fluctuating intensities of sperm competition.     

Vertical migration and diel activity patterns of hydromedusae: studies in a large tank

Vertical distributions and swimming behaviors of 7 species ofhydromedusae (Aequorea victoria, Bougainvillia principis, Gonionemusvertens, Mitrocoma cellularia, Phialidium gregarium, Polyorchispenicillatus, and Stomotoca atra) were observed over 24-h periodsin a 2 m high, 1500 1 transparent tank. In this tank, most speciesperformed well-marked diel vertical migrations that were mediatedby swimming. Manipulation of the light regime showed the didswimming behaviors to be light-dependent rather than intrinsic,even in species that do not possess recognized photoreceptors.Correlations between vertical migration and spawning times forseveral species of medusae suggest that in cases when verticalmigration reduces the distances between individuals (e.g., inmass movements to the surface) just prior to spawning, enhancedfertilization success may result from such movements. ¹Present address: Friday Harbor Laboratories, Friday Harbor,WA 98250, USA.     

Current Studies on Urotensins

Recent studies on urotensins I and II and experiments on urophysialfunction are described. Chemical and pharmacological studies showed that: (i) The isoelectricpoints of urotensins I and II are pI 5.5 ± 0.05 and 5.9± 0.05, respectively; (ii) two active peaks of urotensinI are obtained by gel chromatography of HCl-extracted urophyseson Bio-Gel P⁶, one corresponding to a substance of mol wt 4000,the other, mol wt 2000; (iii) the rat-hypotensive activity ofurotensin I affects peripheral blood vessels at an undeterminedreceptor site(s) and is not mediated by cholinergic, adrenergic,or histaminergic receptors or the corresponding transmittersubstances; and (iv) urotensins I and II increase blood pressureand urine flow in the American eel (Anguilla rostrata). Urophysial content of urotensin II in the white sucker (Catostomuscommersoni) was high during about 3 months preceding spawningand was considerably lower during the remainder of the year.Pituitary content of isotocin is significantly higher in malesuckers after spawning as compared with the content before spawning.The reverse was found on urophysial content of urotensin IIin the male fish.     

La reproduction de Temora stylifera: ses implications anatomiques en relation avec le facteur 'nutrition'

The culture of copepods under different feeding regimes hasallowed us to determine the effects of food availability onegg laying. In Temora stylifera spawning appears to be modifiedby the food resources of the adult. Conditions encountered duringdevelopment have little effect on spawning. The life span offemales is reduced by high food availability. In such casesthe sex organs are hypertrophied, the oviducts being distendedby the large oocytes. The ovary is little affected by changesin food availability, while the size of the oviducts variesin relation to feeding. The size of the genital system is reducedin older females. Variations in food concentration induce variationsof several days in the time required for egg laying. A rapidmaturation of the oocytes, combined with nutrition and the availabilityof food permits Temora stylifera to optimize egg laying.     

Embryonic, early larval development time, hatching mechanism and interbrood period of the sac-spawning euphausiid Nyctiphanes simplex Hansen

Females of the sac-spawning euphausiid Nyctiphanes simplex Hansenwere incubated under shipboard laboratory conditions to observethe embryonic and larval development time and hatching mechanism.Females ready to spawn have a pale pink ovary that extends fromthe back of the stomach to the first abdominal segment, fillingmost of the haemocoel. This species usually behaves as a totalspawner (produces one batch of oöcytes per cycle of theovary) leaving an ‘empty’ space in the cephalothoraxwhere the spent ovary is located. After spawning, the youngoöcytes mature and turn pale pink. The eggs do not havea measurable perivitelline space (PVS) in any of the embryonicstages (6.6 x magnification). The embryos hatch as nauplius(80–91 h after spawning, 16°C ± 1°C). Theyfurther develop into pseudometanauplii (PMN, 90–105 hafter spawning) and metanauplii (MN, 92–140 h after spawning)inside the ovigerous sac. The nauplius breaks the thin and fragilechorion by increasing the volume of the body and by using thefirst and second antennae. We call this an ‘expansion’hatching mechanism, the fifth distinct hatching mechanism observedso far among euphausiids. N. simplex larvae escape from theovigerous sac late in the MN stage (5 days after spawning),just a few hours before molting into calyptopis 1 (C1) (0.5–4h). This delayed release extends protection by the female, likelydecreasing the risk of predation or early cannibalism. Additionally,this may save energy by not swimming independently increasingthe time of not return if the calyptopis does not find favorablefeeding conditions. Females are not ready to spawn again untilat least two days after the previous batch of embryos leavesthe ovigerous sac. The interbrood period (IBP) observed rangedbetween 7 and 15 days at 16–18°C. This IBP is aboutone-fourth to half than was previously assumed for this speciessuggesting a significant underestimation of the fecundity ofthis species. N. simplex hatching success usually was 100%,except for a few females with all of their embryos dying duringembryonic development. Other females either molted before releasingthe embryos, or the oöcytes were spawned unfertilized (0%hatching success), particularly during winter conditions. Efficienthatching and late free-swimming strategy may partially explainwhy this species is the most abundant neritic euphausiid inthe southern part of the California Current System (CCS) andin the Gulf of California.     

Vertical distributions, diel and ontogenetic vertical migrations and net avoidance of leptocephali of Anguilla and other common species in the Sargasso Sea

Day- and night-time vertical distributions and their ontogeneticchanges in Anguilla leptocephali and other common species ofleptocephali were determined and compared during five cruisesin the Sargasso Sea using an opening - closing 2-m ring netto sample discrete depth strata between 0 m and 350 m deep.No difference in vertical distribution was ever found betweenAnguilla rostrata (American eel) and A. anguilla (European eel).Anguilla leptocephali <5 mm long did not exhibit a diel verticalmigration, as they were distributed between 50 m and 300 m bothby day and by night. The vertical distribution of these smalllepto-cephali is probably roughly representative of the depthdistribution of adult spawning. Anguilla     

THE REPRODUCTIVE CYCLES OF THREE TROCHID GASTROPODS FROM THE TRANSKEI COAST, SOUTHERN AFRICA

Changes in gonadal histology were used to determine the reproductivecycles of three trochid gastropods commonly found along theTranskei coast. They were dioecious, the sexes being evenlydistributed both in terms of numbers and size. Despite someasynchrony, Monodonta australis had a distinct reproductivecycle with a short inactive period during the winter, gonadaldevelopment coincided with increasing sea temperatures and spawningtook place from late summer to autumn. Both Oxystele tabularisand O. variegata exhibited asynchronous intermittent spawningthroughout the study period. However, intensified spawning activityby O. tabularis was noted between April and September. The reproductivecycles and mechanisms of these trochids are compared with thoseelsewhere. (Received 20 January 1986;