Spawning synchrony in Arenicola marina: evidence for sex pheromonal control

Chemical communication systems controlling reproductive behaviour have been shown in a number of marine polychaetes. This study investigated the use of sex pheromones to coordinate spawning behaviour in gravid lugworms (Arenicola marina). Lugworms typically reproduce in the autumn, during low water of spring tides, and often exhibit epidemic spawning. Females release gametes within the burrow whereas males deposit spermatozoa on to the beach surface. The incoming tide dilutes the spermatozoa and transports them to the females'' burrows. Sperm is diluted rapidly and sperm concentrations fall below the minimum required for fertilization within a few minutes. The present investigation establishes the existence of chemical signals synchronizing spawning for the first time in an iteroparous polychaete. The process can be divided into two steps, the induction of gamete release by waterborne chemical cues and burrow irrigation behaviour in females: burrow irrigation representing the means by which spermatozoa are carried to the eggs. In both sexes, the release of gametes can be induced by exposure to sea water into which other individuals had previously spawned. Males also respond to odour compounds from other males. The overall effect of the chemical signals results in synchronized, mass spawning of a population.     

Does seasonal reproduction occur at the optimal time for fertilization in the polychaetes Arenicola marina L. and Nereis virens Sars?

Summary

Many marine invertebrates exhibit highly seasonal and synchronised reproduction, with offspring production often being confined to just two or three days each year. Several models have been proposed to explain the fitness benefits of this reproductive pattern, many of which assume enhanced offspring survival due to temperature constraints placed on fertilization and development at other times of the year. In this investigation the temperature limits and optimum for fertilization were determined for two polychaete species, Arenicola marina and Nereis virens. These two polychaete species are exposed to the same environmental conditions throughout the year, yet breed at very different times. Other seasonal impacts on fertilization, i.e., reduced salinity due to rainfall and the effect of sub-zero temperatures on sperm of A. marina, were also investigated. In both A. marina and N. virens fertilization success was significantly influenced by temperature, with the maximum success recorded at 15–18°C. The ambient seawater temperature at the time of natural spawning for both worms is around 10°C, which means that both species are spawning right at the lower limit for maximum fertilization. Salinity and exposure of A. marina sperm to sub-zero temperatures were also found to influence fertilization success, but only at levels that would not be experienced by these polychaetes under natural conditions at the time of spawning. These results suggest there must be additional selective pressures acting on the fitness of these two polychaetes causing A. marina to breed later than, and N. virens to breed earlier than, the optimum time for fertilization. A. marina apparently waits as late as possible to maximise adult fecundity and survival. N. virens breeds as soon as it can achieve high fertilization to maximise larval and juvenile competitiveness.     

High abundance of small zoobenthos around biogenic structures in tidal sediments of the Wadden Sea

On the tidal flats of the island of Sylt (eastern part of the North Sea) the quantity of micro- and meiofauna associated with shoots of seagrass(Zostera noltii), with infaunal bivalves(Macoma balthica), and with tubes and burrows of polychaetes(Pygospio elegans, Pectinaria koreni, Nereis diversicolor, Nereis virens, Arenicola marina) was found to add up to 5 to 33 % of the overall abundance. These structures, taken together, account for 10 to 50 % of the faunal abundance on an average tidal flat at Sylt. The quantitative effect of biogenic structures at the sediment surface (casts and funnels) is small compared to that of tubes and burrows penetrating the anaerobic subsurface layer. In providing stable oxic microenvironments these elite structures frequently bring together more individuals than occur in the entire reducing sediment below surface. Faunal composition of irrigated dwellings of large infauna is different from that of the oxic surface sediment. The common denominator of all elite structures of the subsurface is an oxic halo. Burrows without such a halo are unattractive. There is no evidence that owners of burrows prey on their smaller inmates.     

A new approach for testing contaminated marine sediments: fertilization success of lugworms following parental exposure

A sediment bioassay is being developed using several marine benthic invertebrates to assess the effects of parental transfer of contaminants to the gametes. In this preliminary study, the emphasis was placed on developing methods for the in vitro fertilization of lugworm, Arenicola marina, oocytes.Lugworms exposed to contaminated sediments in outdoor mesocosms were brought to the laboratory, just before the beginning of the spawning period. The reliability of an in vitro fertilization procedure was tested by varying several parts of the method. Main results are that eggs and embryos may be physically damaged by cleaning over a sieve. However, as no negative effects were observed when leaving eggs and sperm together for 24 h, the sperm need not be washed off until the embryos are preserved for further examination later on.A first, incomplete screening of the effects of contaminated harbour dredged sediments indicated some effect on the reproductive success.     

Nereis succinea nuptial behavior: Does size matter?

Summary

Although Darwin noted that size may affect sexual selection, the effect of size on reproduction is controversial. Mature Nereis succinea, a polychaete that mates in pheromone-mediated twilight nuptial swarms, varies greatly in size, ranging more than 10-fold in body weight from 30 mg to >300 mg. Swim speed of swarming male worms increases with worm size, with the fastest males swimming more than twice the speed of the slowest. The female-produced spawning pheromone, nereithione, stimulates both swimming speed and spawning in males at concentrations of 10^?6 M and above, and lower concentrations cause significant activation of swimming. Individual worms can be stimulated to release sperm up to 40 or more times in a single experimental session. Larger worms release cumulatively more sperm than smaller ones, resulting in significant loss of body mass from repetitive spawning activated by nereithione. Size may enhance mating success of male N. succinea due to encountering more females as a result of faster swimming speed and due to the higher sperm density and number of spawning responses of large animals.     

Fertilization success in marine invertebrates: the influence of gamete age

Gamete age has been postulated to be unimportant to the fertilization ecology of marine invertebrates. However, recent research suggests that, for some species at least, it may have a direct impact upon fertilization success. We present comparative data on the influence of gamete age on fertilization and development success in several marine invertebrates: the polychaetes Arenicola marina and Nereis virens and the asteroid echinoderm Asterias rubens. Oocytes are much longer lived in the polychaetes than in the echinoderm, with A. marina oocytes still capable of fertilizing and developing normally 96 h post-spawning. Developmental abnormalities and failure to reach blastula tend to occur well before the fertilizable life of the oocytes has expired. Sperm are similarly longer lived in the polychaetes; however, fertilizing capacity is markedly reduced following incubation in conspecific egg-conditioned seawater. These results are discussed in terms of the fertilization strategies of the three species. We further suggest that, for A. marina at least, longer-lived sperm and eggs are central to the fertilization strategy of this species.     

Fertilization,post-fertilization development and larval biology of the South African polychaete,Arenicola loveni loveni (Kinberg 1866)

Summary

Larval development in the South African polychaete Arenicola loveni loveni is described, and the effects of seawater temperature on fertilization success, post-fertilization development and early post-settlement survivorship are experimentally determined. Fertilization success was significantly effected by seawater temperature, with maximum fertilization success measured in the range 15–18°C, which is close to the ambient temperature range at the time of natural spawning. Poor fertilization success and abnormal cleavage were observed at the low temperature treatment of 7°C and the high temperature treatment of 23°C. A. loveni loveni exhibits spiral cleavage typical of polychaetes and has a short lecithotrophic swimming trochophore larval stage of 4–5 days. High mortality was noted during the transitional periods from gastrula-trochophore and during the settlement process. Settlement occurs just 4–5 days post-fertilization and the postsettlement stage begins feeding 1 week post-fertilization. Temperatures in the range 16.5–23°C were found to have a significant effect on larval and post-larval survivorship and growth rate increased with temperature within this range. The effects of manipulating spawning date on subsequent offspring survival and development rates were also investigated. Advancing or delaying spawning time caused reduced development rates, and delaying spawning for 3 months was found to significantly reduce offspring survivorship.     

Reproductive behavior of the Atlantic silverside,Menidia menidia (Pisces,Atherinidae)

Synopsis The spawning behavior of the Atlantic silverside,Menidia menidia, was studied at two sites on the North Edisto River estuary in South Carolina. Prespawning schools moved back and forth along the shoreline as the time of high tide approached. Spawning runs took place in the upper intertidal zone at high tide.Spawning fish deposited their eggs on three types of substrates: 1) the lower stems of cordgrass plants,Spartina alterniflora, 2) detrital mats, and 3) exposed cordgrass roots along erosional scraps. Spawning behavior during egg deposition and fertilization was similar for all three substrates. Females released eggs during a rapid fluttering motion of the posterior half of the body. A similar movement accompanied release of sperm by males. Behavior of fish just prior to spawning insured deposition of gametes at locations that provided protection from thermal and drying stress during development. Eggs were deposited at mean intertidal elevations of 1.8 and 1.5 meters above mean low water (MLW) at respective study sites. They were exposed to the atmosphere for approximately ten hours between successive high tides.During spawning runs in which eggs were deposited at the base of cordgrass plants, ambient dissolved oxygen concentrations of the water in the spawning area were sometimes reduced to < 1.0 mg. 1^–1. Spent fish, apparently incurring an oxygen debt while spawning, formed a nonschooling aggregation offshore from the spawning zone.The recurrent use of specific spawning substrates for egg deposition resulted in an uneven distribution of spawning runs along the shoreline at each study site.Contribution No. 409 to the Gulf Breeze Environmental Research Laboratory. Contribution No. 377 to the Belle W. Baruch Institute for Marine Biology and Coastal Research.     

Courtship rate signals fertility in an externally fertilizing fish

Sperm limitation is widespread across many animal species. Several mechanisms of sperm allocation have been proposed, including optimal allocation according to clutch size and equal allocation across females. However, considerably less effort has been directed at investigating the behavioural signals associated with sperm limitation in males, which may include mating rate and the intensity of courtship. We investigated whether multiple successive spawnings affect individual male fertilization success, mating rates and courtship rates in Japanese medaka (Oryzias latipes). Across an average of 17 spawning events per male, fertilization success decreased from 83.7 per cent for the first spawning to 40 per cent for the last spawning while courtship rate decreased from 3.4 to 1.5 min⁻¹. Females appeared to respond to male sperm depletion by reducing clutch size. Our results suggest that male Japanese medaka are sperm-limited, and that courtship rate may be an honest indication of fertilization ability.     

Egg size in relation to fertilization dynamics in free-spawning tropical reef fishes

In marine invertebrates that spawn by simply releasing their gametes into the water (free-spawning), fertilization success likely is often limited by low sperm concentrations, due to dispersion of mates and dispersal of gametes by water movements. Production of large, low density eggs might be advantageous when sperm concentrations consistently are low, because large target size might increase egg/sperm encounters, and more low than high density eggs could be produced per clutch. Although average fertilization success in the labrid Thalassoma bifasciatum is 95% in both group spawns (in which multiple males compete for fertilizations by producing large quantities of sperm) and pair (mono-male) spawns, it is slightly lower in pair spawns, due to low level sperm limitation that arises because pair-spawning males release near the minimum number of sperm necessary for maximum fertilization. I examined whether variation in egg size and content in T. bifasciatum and other free-spawning fishes is related to variation in spawning mode, to assess whether compensatory production of large, low-density eggs might be contributing to high fertilization success in pair spawns. I found no difference between the volume or density of eggs of (1) pair- and group-spawning females of T. bifasciatum, or (2) pair-and group-spawning congeneric species of labrids, scarids, and serranids, or (3) labrids and scarids with vigorous, rapid spawning movements (which could turbulently diffuse gamete clouds) and those with slow movements. Further, egg density does not decline with increasing egg volume among those fishes. Assuming that egg size can affect fertilization success, then sperm limitation seems unlikely to represent a significant problem for pair-spawning T. bifasciatum, probably because mates place their vents close together during gamete release. The situation regarding sperm limitation in other fishes, and effects of environmentally generated water turbulence on it, are less clear. Interspecific variation in the size and content of these fishes' eggs may relate to provisioning of offspring for different larval life-histories.     

Aspects of the reproductive biology of the South African polychaete,Arenicola loveni loveni (Kinberg 1866)

Summary

The annual cycles of gametogenesis, spawning and fertilization biology were investigated in the South African polychaete Arenicola loveni loveni (Kinberg, 1866). Sexes are strictly separate (gonochoric) with a 1:1 ratio and gametogenesis takes place in the coelomic cavity. Reproduction is iteroparous and occurs during a synchronized annual epidemic spawning event during the summer months of February or March, which lasts no longer than 2 weeks at around the time of highest annual seawater temperatures. A slight inter-annual variation in spawning time was observed between 2003 and 2004. Annual fecundity was estimated as 311,200 (± 82,040 standard deviations) oocytes per female per year. Oocytes are arrested at prophase I of the first meiotic division and require a maturation step prior to spawning and subsequent fertilization. Mean spawned oocyte diameter was 141.16 μm ± 0.43 SE. Sperm develop as morulae in the coelomic cavity and also require a maturation step prior to spawning. Spawning can be achieved by injection of prostomial homogenate in both males and females and by injection with 8,11,14- e cosatrienoic acid for males and can be delayed by temperature manipulation. Oocyte maturation and sperm maturation can be induced in vitro by incubating in prostomial homogenate.     

Biology and distribution of the littoral rove beetle Psamathobledius punctatissimus (Le Conte) (Coleoptera: Staphylinidae)

The intertidal macrofauna on a small sheltered marine beach at Pawley's Island, South Carolina, was dominated by insects, primarily Psamathobledius punctatissimus, a small beetle which attained densities of up to 2 260 adults m⁻². Both adult and larval beetles remained buried in the sand when covered by the tide, then emerged to form mole-like surface trails and feed upon diatoms when exposed. Eggs and young larvae were maintained within special maternal burrows, while larger larvae and non-breeding adults occupied their own individual burrows. Both adults and larvae became comatose when in direct contact with water, but recovered after as long as six hours submergence. In the field, burrows retained air during tidal coverage, allowing the beetles to avoid direct contact with sea water. Seaward extension of the population is probably limited by time available for feeding, while longshore distribution is restricted by sand texture and diatom concentration, or by sediment mobility in more exposed locations. Although very locally distributed, P. punctatissimus has achieved considerable success in a habitat poorly exploited by competitors of either marine or terrestrial origin. Contribution No. 434 of the Belle W. Baruch Institute for Marine Biology and Coastal Research Contribution No. 434 of the Belle W. Baruch Institute for Marine Biology and Coastal Research     

PATTERNS OF INTERSPECIFIC INTERACTIONS IN THE ULVA‐DOMINATED INTERTIDAL COMMUNITY IN A SOUTHERN COAST OF KOREA

The reproductive success of marine species with external fertilization depends on environmental conditions during gamete release. There is special interest presently in whether water motion causes sperm limitation under natural conditions. We investigated gamete release of Fucus vesiculosus from an exposed shore to ascertain: 1) when gametes are released during the tidal cycle, 2) when fertilization occurs, and 3) what the natural sperm:egg ratios are. Water samples were collected and concentrated over five minutes every half hour off Pemaquid Point, ME from three replicate sites within each of two locations using a pump‐filter device. Immunofluorescence microscopy revealed that gamete release occurred only on the two calmest spring tides. Sperm became present in the water column at the same time as oogonia (30 min^?1 h prior to high tide [HT]) and reached peak concentration at exactly HT. The sperm:egg ratio was 76:1 on 8 Oct 1999 and 21:1 on 8 Nov 1999 at exactly 30 min prior to HT and dropped sharply after HT. Gametes continued to be collected for several hours after HT but analysis of pronuclear position in aceto‐iron‐hematoxylin stained eggs revealed that all fertilization occurred at approximately HT. We modelled the total number of days when reproduction was possible using these results and wind and wave data from the National Data Buoy Center. Our research provides evidence that gamete release by F. vesiculosus occurs at slack HT on calm days and that sperm are not a limiting factor in fertilization for this species.     

Elevated pCO2 increases sperm limitation and risk of polyspermy in the red sea urchin Strongylocentrotus franciscanus

Anthropogenic carbon dioxide (CO₂) emissions and the resultant acidification of surface ocean waters are predicted to have far‐reaching consequences for biological processes in the marine environment. For example, because changes in pH and pCO₂ can alter sperm performance, ocean acidification may be accompanied by reductions in the success of fertilization in marine broadcast spawners. Several studies have attempted to determine the effects of elevated pCO₂ on marine invertebrate fertilization success, albeit with differing results. These conflicts may stem from the use of inappropriate sperm–egg contact times and, in several cases, the lack of measurements over a range of sperm concentrations extending from sperm‐limited conditions to polyspermy scenarios. In our study, we used biologically realistic sperm–egg contact times and a full range of sperm concentrations to assess the effect of elevated pCO₂ on fertilization in the broadcast spawning sea urchin, Strongylocentrotus franciscanus. Fertilization experiments were carried out in seawater bubbled with CO₂ to 400 (control), 800, and 1800 ppm. Using a fertilization kinetics model, we estimate that elevated pCO₂ levels both increased sperm limitation and reduced the efficiency of fast blocks to polyspermy. Thus, elevated pCO₂ decreased the range of sperm concentrations over which high fertilization success was likely. Given the inherent difficulties in achieving high fertilization success in broadcast spawners, raised pCO₂ levels are likely to exacerbate low fertilization success in low‐density populations or in areas with high water turbulence.     

Activity and feeding of Dotilla fenestrata (Brachyura: Ocypodidae) in a warm,temperate South African estuary

The activity of and consumption of organic material by the sand-bubbler crab Dotilla fenestrata was studied over neap and spring tides on a sheltered sand bank close to the mouth of the warm, temperate Kowie Estuary, South Africa. Crabs emerged from their burrows only after the tide receded, and it was light. Time to emergence therefore varied from about 30 minutes to three hours after exposure, depending on the time of low water in the early morning vs at midday. General activity of the crab population was longer on a spring tide (about five hours) than on a neap tide (about three hours). Maximum densities of active crabs were 140 m^–2 and 41 m^–2 on spring and neap tides, respectively. After emergence, crabs spent 60% to 80% of their time feeding. In the Kowie Estuary, D. fenestrata produced between 7 and 12 pseudofaecal pellets, average weight 0.0358 g per pellet, per minute. These pellets had a significantly lower organic and chlorophyll a content than the substratum, and it was estimated that crabs removed about 25% of the organic content from the sediment.     

Foraging activity of the sand beach isopod Scyphax ornatus Dana

Abstract

The terrestrial isopod Scyphax ornatus lives on exposed sand beaches. Adult isopods spent the daytime in burrows near the high water mark and made nightly foraging excursions over the uncovered middle beach. Hourly records of their night time distribution showed that Scyphax congregated near the water’s edge during the last 4 h of flood tide, where they fed on carrion. Insects (mostly drowned honey bees) were the main food item, but coelenterates, amphipods, crabs, and goose barnacles were also eaten. During ebb and early flood tides Scyphax occurred at low densities over the uncovered middle beach. Analysis of the distribution of large and small food items on the beach showed that by feeding during the flood tide, Scyphax exploited a rich concentration of carrion that accumulated in the swash zone and that was moved slowly up the beach by the incoming tide.     

High fertilization success in a surface-brooding Caribbean gorgonian

Colonies of the Caribbean gorgonian Pseudopterogorgia elisabethae release eggs that are retained on the colony surface where they are fertilized and then develop. In December 2001, spawning on San Salvador Island, Bahamas, occurred over 6 d, with spawning by any one colony limited to 1-3 d. With the exception of the first and last days of the spawning period, fertilization success was high, often greater than 90%. Eggs collected in December 2001 had an overall fertilization success of more than 66%. At one site, the increase in fertilization after the first day of spawning correlated with male spawning, but male gonad index was a poor predictor of fertilization success. The number of male colonies close to a female was not correlated with fertilization success. Surface brooding is an efficient mechanism for "harvesting" sperm released upstream of female colonies. By maintaining their eggs at a single location, surface-brooding species can extend the period over which eggs are likely to encounter sperm. As a result, fertilization success is summed across the temporal variance in sperm availability, and the need for very high densities of sperm, with its concomitant risk of polyspermy, may be reduced.     

A scanning electron microscopical study of sperm development and activation in Arenicola marina L. (Annelida: Polychaeta)

Abstract

The lugworm, Arenicola marina L. has an annual cycle of reproduction with epidemic spawning and external fertilisation. The spermatozoa of Arenicola are unusual in that they are held immotile (as plates of several hundred cells known as morulae) in the coelomic fluid until activated just prior to spawning. Activation of Arenicola sperm is brought about by a sperm maturation factor (SMF) from the prostomium and can be carried out in vitro using an assay technique developed by Bentley (1985). Scanning electron microscopy is used here to examine the changes which occur during in vitro activation. This revealed that the bundles of flagella of inactive sperm become disorganised as flagella beating commences but the flagella at this stage are still bound together at their tips. The sperm heads then become separated from the cytophore and finally the distal binding of the flagella is broken to give free-swimming spermatozoa. Coelomocytes present in the coelomic fluid resorb unspawned gametes prior to the initiation of the next gametogenic phase.     

Quantification of pumping rate of <Emphasis Type="Italic">Chironomus plumosus</Emphasis> larvae in natural burrows

This paper investigates and compares experimentally determined water velocity field above natural macrozoobenthos burrows generated by Chironomus Plumosus larva during their bio-irrigation activity. All experiments were carried out using particle image velocimetry and performed in mesocosms filled with sediment burrowed by larvae, and the water velocity fields near the inlets and outlets of the U-shaped burrows were measured. From water velocity data the average volumetric flow rates between 54.6 and 61.1 mm³/s were calculated. Assuming an average burrow diameter of 2.25 mm, the volumetric flow rates suggest the average flow velocities through burrows during the pumping period between 13.7 and 15.4 mm/s. Two additional interesting phenomena could also be shown by analyzing the flow field generated by the larva. The analysis of the amount of tracers used for visualizations revealed that some of the tracer particles added to the water must have been consumed along their path from the inlet toward the outlet, hinting clearly to the so-called filter-feeding action of C. plumosus. The second phenomenon is due to the form of motion C. plumosus generates. By careful flow visualizations it was found that unlike other organisms such as Urechis caupo that use peristaltic body contractions, C. plumosus worms its body sinusoidally catapulting the fluid far into the overlying water body. This action is of ecological advantage for it avoids generating short oxygen circuits for their respiration and filter feeding.     

Influence of sperm density and contact time on herring egg fertilization

In order to standardize fish egg incubation techniques for bioassay application, fertilization procedures need to be included into the protocols. Nothing is known about the necessary sperm concentrations required to achieve optimal fertilization rates. The tests described here for the herring Clupea harengus L. include trials with 10 different sperm densities and 4 contact times (15, 30, 60 and 120 seconds). The variability of fertilization rates in eggs from different females was also investigated. Fertilization success was mainly influenced by sperm density and less by the actual contact time between unfertilized eggs and sperm containingmedia. Dilution in sperm density to 9.6 × 10⁶ cells ml^-1 or less resulted in reduced fertilization success. There was considerable variability in fertilization rates between females.