Hatching mechanism and accelerated hatching of the eggs of a sac-spawning euphausiid Nematoscelis difficilis

Observation of the sac-spawning euphausiid Nematoscelis difficilisHansen during shipboard laboratory incubations showed that itsembryos usually hatch as pseudometanauplius (PMN) or metanauplius(MN). The eggs, which have a minute perivitelline space, arespherical at spawning and become elliptical after the nauplius1 develops. When ready to hatch, the PMN or MN embryos extendand contract their first and second antennae in a swimming movement,breaking the chorion into almost equal halves joined by onesmall section in the anterior part of the chorion. The mandiblesplay a secondary role in cutting the chorion. Then the embryopushes itself backwards with the first and second antennae toescape from the chorion. This is known as ‘push-off’hatching. The embryos always hatch progressively from the distalend towards the proximal end of the ovigerous sac. The timebetween hatching of the first and last embryo may reflect thetime the females require to lay a clutch of eggs (<2.1 h).Development time to the PMN stage at 10°C was     

Hatching mechanism and delayed hatching of the eggs of three broadcast spawning euphausiid species under laboratory conditions

Three different egg hatching mechanisms were observed underlaboratory conditions in Euphausia pacifica Hansen, Thysanoessaspinifera Holmes and Thysanoessa inspinata Nemoto: backward,forward and flipping. Like all broadcast spawning euphausiids,these species usually hatch as nauplius 1 (N1). Some hours beforehatching the vitelline membrane breaks and the embryo is freelysuspended within the chorion; later the embryo takes on a slightlyoval shape. When ready to hatch, the N1 pushes against the chorionwith the posterior part of the abdomen producing a protuberance.No spine or egg tooth is present to break the chorion. The pressurebreaks the chorion, and the nauplius pushes itself backwardswith the first and second antennae and mandible to slide fromthe chorion. After about three quarters of the body is outside,the nauplius brings all the appendages together to move backwardswithout becoming stuck in the chorion. This is the backwardhatching mechanism. The vitelline membrane remains within theegg after the nauplius leaves the chorion. Hatching takes 5–20s, and most of the eggs in a clutch hatch during <2 h. Severaleggs of E. pacifica hatched as meta-nauplii (MN) (>200 hafter spawning) or as calyptopis 1 (C1) stage (>232 h), ratherthan as N1. Delayed hatching of embryos also was observed inT. spinifera as nauplius 2 (N2) (>120 h) or as MN stage (>180h), and in T. inspinata as N2 (106 h) after spawning. Eggs withlarvae in stages of development beyond N1 have not been observedfrom preserved zooplankton samples. However, eggs spawned inthe field and incubated in the laboratory also had extendeddevelopment and late hatching but with low frequency (<0.06%).It is proposed that, if the backward hatching mechanism fails,alternate hatching mechanisms can be used by the euphausiid.There is high flexibility in their hatching modes. The N2 andMN break the chorion with the first and second antennae, hatchingforwards, and the C1 breaks it with the telson spines and byflipping of the abdomen, resembling the decapod hatching mechanism.Delayed hatching using the forward and flipping mechanisms wereassociated with low hatching success in comparison with thebackward hatching mechanism.     

Spatial distribution of Euphausia pacifica (Euphausiacea: Crustacea) in the Yellow Sea

Euphausia pacifica were collected in the Yellow Sea in summer(August, 1997) and winter (February, 1998), and their distributionwas investigated in terms of the developmental stages in relationto environmental factors (temperature, salinity and chlorophylla). In summer, the water column was highly stratified with athermocline between 10–30 m depth, whereas the water columnwas well mixed in winter. Seasonal variation in temperaturewas large, ranging between 6.3 and 28.8°C in summer and3.9 and 12.2°C in winter. Chlorophyll a concentration changedlittle seasonally but a high concentration was observed in coastalareas. Salinity in the two seasons varied little spatio-temporally.In the studied area and sampling period, E.pacifica was themost dominant euphausiid species (99.7 and 99.8% in summer andwinter, respectively), and comprised adults and juveniles (74.6%in summer and 41.9% in winter), furcilia (17.5 and 44.9%) andcalyptopis (7.9 and 13.1%). The spatial distribution of theE.pacifica population varied seasonally depending on developmentalstage and appeared to be related primarily to the seawater temperatureand secondly to the chlorophyll a concentration, but not tosalinity. In summer, adults were abundant in areas below 10°C,and furcilia and calyptopis above 9°C. In winter, adultswere confined to areas between 7 and 10°C, and furciliaand calyptopis, to areas between 6 and 8°C. Furcilia andcalyptopis were concentrated in the vicinity, or at the centerof chlorophyll a-rich water masses, whereas adults seemed toavoid those water masses.     

SPAWNING SEASON AND EGG PRODUCTION IN FORTH ESTUARY RETUSA OBTUSA (MONTAGU) (GASTROPODA: OPISTHOBRANCHIA)

Retusa obtusa held individually in the laboratory carried largeoocytes in the gonad but did not spawn in December-late January.In late Jan-early Feb, however, the first few individuals producedbatches of 8–17 eggs and, by early February, most individualswere producing means of 2–4 eggs d^–1 and maximain late Feb of <7.9 d^–1. Spawning declined to low levelsin few individuals in late March. By early April, spawning hadvirtually ceased prior to the drastic loss of adults in thepopulation by May. Larger R. obtusa generally produced more eggs than smaller onesand the few specimens shorter than 3.8 mm produced markedlyfewer than those of 3.8–5.0 mm shell length. Twenty of the 34 R. obtusa held in the main breeding period(4 sets started 29 Jan-3 Mar) spawned in 3 or more successiveweeks whereas only 6 of them failed to spawn in 2 consecutiveweeks, so indicating that several successive batches of eggsare commonly produced. Yet in virtually all individuals (exceptat the start of breeding) more eggs were produced in the firstweek of captivity than subsequently. These first-week valuesimply total production by individuals in the spawning seasonof some 112-305 eggs comprising about 2.8-7.6 mg dry weightor, by the Forth estuary population, of 26880-73200 eggs m^–2comprising 0.67-1.83 g dry weight m^–2. (Received 19 August 1988; accepted 30 September 1988)     

The reproductive biology of Cyclops vicinus

Investigations of the reproductive biology of Cyclops vicinusrevealed that mated females oscillate between gravid and nongravidreproductive conditions. The gravid condition can be dividedin two recognizable phases: gravid/nonovigerous and gravid/ovigerous,the former phase being shortest. The maturation of new oocytestakes place when the old egg sacs are still being carried; thisensures a rapid clutch succession. Females which remain unmated,extrude few eggs, in no case complete egg sacs, and remain gravidthus conserving oocytes. Females which mate only once, showa similar reproductive pattern (clutch size and clutch succession)to those which remain combined with males, and thus have theopportunity to remate, but tend to produce fewer clutches. Malesare able to fertilize 3–4 females day^–1. Matingcapacity of males is possibly limited by the time needed tofill a new spermatophore. Short-term starvation (5 days) lengthenedclutch-to-clutch periods and diminished clutch size. When thestarvation period started in the gravid/ovigerous phase, a normalclutch was extruded but no new oocytes matured during starvation,indicating that the energy for egg maturations is provided inthe first part of the reproductive cycle.     

The diel migrations and vertical distributions of zooplankton and micronekton in the Northwestern Mediterranean Sea. 1. Euphausiids, mysids, decapods and fishes

Vertical distributions and diel migrations of the main speciesof micronekton, four euphausiids, one mysid, one decapod andthree fishes, were described in detail in the 0–1000 mwater column on a fixed station in the Northwestern MediterraneanSea. The euphausiids Euphausia krohni and Thysanopoda aequalis,the decapod Gennadas elegans and, to a lesser extent, the fishArgyropelecus hemigymnus were shown to perform clear diel verticalmigrations. Results of horizontal hauls at a given depth aroundsunrise and sunset showed a marked diurnal symmetry of the migratorycycles, particularly for E.krohni, T.aequalis and G.elegans.The behaviour of the euphausiid Nematoscelis megalops was morecomplex: it presented a repetitive bimodal day distributionand only part of its population migrated. As very weak or non-migratorswe found the euphausiid Stylocheiron longicorne and the bathypelagicmysid Eucopia unguiculata, for which migration concerned onlysome of the older individuals. The fishes Cyclothone braueriand Cyclothone pygmaea appeared to be non-migrants. As depthincreased, C.braueri was replaced by C.pygmaea, with maximumconcentrations at 350–550 and 550–700 m depth, respectively.     

Some observations on moulting, growth and maturation of krill (Thysanoessa inermis) from the Barents Sea

The moulting interval of the euphausiid Thysanoessa inermisfrom the Barents Sea was found to be temperature dependent withinthe range of 1.5–8.0°C. Each moult accounted for a2.1% loss of dry body wt, equivalent to a 1.2–1.3% lossof body carbon or nitrogen. During 5 months of observation bothbody length and secondary sexual characters (thelycum and petasma)of specimens varied greatly, including positive and negativegrowth periods and progression and regression of maturity stages.Characteristics of eggs spawned by one female are described.     

Larval release in the crab Rhithropanopeus harrisii (Gould): chemical cues from hatching eggs

Decapod crustaceans have rhythmic larval release patterns. Inthe case of Rhithropanopeus harrisii substances associated withhatching eggs induce ovigerous crabs to exhibit stereotypiclarval release behavior involving vigorous abdomen pumping.In this study, the pumping response of ovigerous crabs was usedto investigate the chemistry of the substances (pumping factor)that evoke larval release behavior. Pumping was induced by polarsubstances released into sea water upon egg hatching. Pumpingfactor was concentrated and desalted by adsorption chromatographywith Amberlite XAD-7 resin. Size fractionation by cascade pressuredialysis indicated that most of the active material had a mol.wt. <500 daltons. Biological activity was destroyed by incubationof pumping factor with a non-specific protease. Amino acid analysisof hydrolyzed factor indicated that arginine comprised –50%of the amino acids. Pumping responses were elicited experimentallyby abnormally high concentrations of mixtures of the two majoramino acids (arginine and glycine) in the hydrolysate. Theseresults suggest that pumping factor is a heterogeneous groupof small peptides each containing arginine.     

Growth, reproduction and feeding behavior of the planktonic shrimp, Lucifer faxoni Borradaile, off the Texas coast

The planktonic shrimp, Lucifer faxoni, lives to an age of 30–40days off the Texas coast. In the laboratory, the shrimp took28.9 and 18.9 days to reach sexual maturity at 22 and 30°Crespectively. Oviposition was observed at night between 20.00and 23.00. Females attach eggs to the 3rd pereiopods and broodthem until the nauplii emerge. Multiple broods are produced,giving a maximal lifetime fecundity of >140 eggs per female.In addition, females may also be able to synchronize the timeof their hatching to occur at night, perhaps to further reducemortality due to predation and cannibalism. A rapid turnoverof generations, each with a short adult lifespan, sequentialspawnings, and protection of eggs until hatching, characterizesthe life strategy of this small shrimp. Adult L.faxoni are carnivorous.However, their feeding appendages do not exclude the possibilityof omnivory. The maximal, dry-weight-based, specific ingestionrate was 0.7 day^–1. Feeding activity was not affectedby either time of day or light regime.     

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)     

Egg capsules, eggs and embryos of the southwestern Atlantic gastropod Coronium coronatum (Gastropoda: Muricidae)

The egg capsules, eggs and embryos of the muricid gastropodCoronium coronatum are described for the first time. Capsulesare sessile, bulliform, semi-circular, with a plug in the dorsalcenter. Sutures split the capsule into two asymmetrical halves.Recently laid capsules showed the presence of 3639 (n = 2) uncleavednurse eggs with a diameter of 180–210 µm (mean= 197.4 ± 8.9). The number of early embryos was 9–11.The size of the embryos was 320 x 320 to 820–880 µm.Nine pre-hatching embryos of 3.94 mm (n = 8, SD = 0.32)were found inside the older capsule. SEM illustrations of embryosand radulae are provided. Comparison of shell and radula ofembryos with the protoconch and radulae of adults of C. coronatumrevealed that the capsule belongs to this species. (Received 18 March 2006; accepted 10 October 2006)     

Reproductive biology of the sea anemone shrimp Periclimenes rathbunae (Caridea,Palaemonidae, Pontoniinae), from the Caribbean coast of Costa Rica

Caridean shrimps are a highly diverse group and many species form symbiotic relationships with different marine invertebrates. Periclimenes rathbunae is a brightly colored shrimp that lives predominantly in association with sea anemones. Information about the reproductive ecology of the species is scarce. Therefore, we collected 70 ovigerous females inhabiting the sun sea anemone Stichodactyla helianthus in coral reefs from the southern Caribbean coast of Costa Rica. Females produced on average 289 ± 120 embryos. The volume of recently-produced embryos was on average 0.038 mm³, and embryo volume increased by 192% during the incubation period. The average embryo mortality during embryogenesis was 24%. The reproductive output was 0.24 ± 0.094, considerably higher than in many other pontoniine shrimps. Females carrying embryos close to hatching showed fully developed ovaries, suggesting consecutive spawning. We assume that the sheltered habitat, living on sea anemones, allows Periclimenes rathbunae to allocate more energy in embryo production than most other free-living caridean shrimps. This is the first record of Periclimenes rathbunae for Costa Rica.     

Food type induces different reproductive responses in the copepod Centropages typicus

Egg production and hatching success were determined for individualCentropages typicus fed two diatoms (Thalassiosira rotula andPhaeodactylum tricomutum) and two dinoflagellates (Prorocen-trumminimum and Gonyaulaxpolyedrd). Both reproductive responseswere strongly affected by food type. Females incubated withoutmales produced eggs with all diets, but fecundity was twiceas high with the larger T. rotula and G.polyedra cells. In contrast,hatching success was 2–3 times higher with the dinoflagellatediets. The presence of males did not enhance egg productionrates. Males also did not improve hatching success when thediet consisted of the diatom T.rotula. However, egg viabilitywas higher for couples fed the dinoflagellate G.polyedra, indicatingthat egg viability was possibly being controlled by both rematingand food type. Egg viability was artificially lowered by exposingnewly spawned eggs to high concentrations (10⁴–10⁹ pgC) of extracts from T.rotula, whereas the development of eggsproceeded normally at all concentrations of extracts from P.minimum.Blockage of egg development was not due to anoxia, but to thepresence of intracellular, deleterious chemical compounds indiatoms, suggesting that bottom-up prey control mechanisms underlieseasonal fluctuations in C.typicus populations at sea.     

Allis shad adopts an efficient spawning tactic to optimise offspring survival

The potential effects of global warming on the allis shad population were tested by combining a time series of spawning acts with expected thermal survival rates for embryos and larvae until 14 days post hatching. The yearly mean survival of spawn for each reproductive season was calculated and an index of reproductive efficiency based on this survival rate was proposed. The randomness of the spawning tactics was evaluated by shuffling the spawn acts time series. This approach was applied to the Gironde-Garonne-Dordogne (south-west France) population, which recently collapsed. The yearly mean thermal survival of spawn is slightly variable at approximately 55% over 2003–2012 despite fluctuating temperatures. An especially low survival (35%) was recorded for the last season (2013). For eight of the 11 reproductive seasons, the index of reproductive efficiency was high (> 80%) and largely above indices obtained by a random spawning tactic. Therefore shad are able to adopt an efficient spawning tactic to anticipate favourable thermal conditions for survival of their offspring. However, thermal behavioural rules still need to be expanded to understand the failures in their reproduction efficiency.     

Description of the developmental stages in Acartia bifilosa Giesbrecht (Copepoda: Calanoida)

The developmental stages and increase in length of Acartia bifilosa,a dominant planktonic copepod in Kyeonggi Bay, Yellow Sea, Korea,were investigated in a laboratory. Adults laid eggs at a rateof 2.5 eggs day^–1 female^–1 and up to 97% of eggshatched. The eggs were 92 µm in diameter and larger thanthe eggs of other Acartia species. The body segmentation wasrecognizable at the fifth nauplius stage and sex distinctionwas possible at the fourth copepodite stage. Thesix naupliusstages took -7.5 days and the five copepodite stages -8.5 days.Sexually mature males and females appeared at the 16th day,and by the 20th day the adults laid eggs that hatched and grewsuccessfully into the nauplius stages. The detailed morphologicalcharacteristics of each developmental stage are presented anddiscussed in relation to A.dausi.     

Non-copulatory spawning and female participation during early egg care in a marine sculpinHemilepidotus gilberti

The reproductive behavior of a marine sculpin,Hemilepidotus gilberti, was observed in the aquarium. The behavioral sequence comprised fight for terriotory, courtship and fight for females, spawning and caring for the egg mass. Females very slowly deposited eggs enclosed with viscous ovarian fluid onto the substrate. Almost all the eggs contained in the ovary were released in a single spawning, its completion requiring 21–22 min. Territorial males emitted of spawning. Sneaking by neighboring males followed subsequently. This was the first observation of non-copulatory spawning among marine sculpins. Females cared for the eggs for severl days after spawning, and then male alone care continued until hatching (47–49 days after spawning). Participation by females in egg caring is likely to be caused by their spawning only once during the spawning season and the consequent lack of urgency for post-spawning feeding.     

The presence of a common embryonic blastema for ovarian and testicular parenchymal (follicular,interstitial and tubular) cells in cattle,Bos taurus

Summary The early embryonic gonadal development in the cattle is characterized by the appearance of an alkaline phosphatase positive blastema. Its derivatives in gonads of both sexes, follicular cells in the female and interstitial cells in the male, also show positive alkaline phosphatase reaction. Primordial germ cells are equally alkaline phosphatase positive, but loose this activity when they later transform to oögonia and oöcytes, or to spermatogonia respectively. Using the enzyme activity as label to trace these constituents in the developmental steps of the bovine gonads, the following results were obtained.Differentiation processes leading to the appearance of the sex cords take place in situ within the gonadal blastema which occupies the main central part of the gonadal fold. It is essentially a segregation process of the follicular cell cords or of the interstitial cells and the tubular primordia from the undifferentiated common anlage.The so-called germinal epithelium is not involved in the differentiation of sex cords. Its participation — if any — in the gonadal development is restricted to a very short and rather early period. Secondary sex cords (Pflügers cords) do not occur. In the cattle there is no reason to assume a cortico-medullary antagonism in the sex determined gonadal development.It can be assumed that the follicular cells in the ovary and the interstitial cells in the testis are homologous. This applies possibly also to the tubular cells of the testis. Homology should be admitted also for the rete structures, which remain small and undeveloped in the ovary while in the male they show considerable development.In the ovary the follicular cell cords differentiating within the central blastema match in a junctional zone with the peripheral layer of oögonia. These are taken up by the most peripheral branches of the follicular cell cords, thus transforming to ovigerous cords. During the downward movement within these cords the germ cells transform to oöcytes which for their part proceed through first meiotic prophase and reach the dictyotene stage. The maturation of the germ cells seems to be controlled by the follicular cells and may even temporarily get out of control until an adequate number of follicular cells is found in vicinity of individual oöcytes to form primordial follicles.The alkaline phosphatase reaction reveals the presence of numerous persisting remnants of follicular cell cords in the developing and even adult ovary.It is suggested that the findings in the cattle gonads can be applied also to other mammals, mainly to those with longer gestation periods like man.Contribution No 58-66, Department of Biology, City of Hope Medical Center. This work was supported in part by a grant (CA 05138) from the National Cancer Institute, U.S. Public Health Service. The project was undertaken during a five-month visit to Dr. Ohno's laboratory by the senior author whose expenses were covered by the Deutsche Forschungsgemeinschaft.     

Embryo and early larval stages of the Humboldt Current krill Euphausia mucronata (Crustacea: Euphausiacea)

The Humboldt Current krill, Euphausia mucronata (Crustacea: Euphausiacea), is an endemic and keystone species in the food web of this highly productive eastern border current ecosystem. The morphology and ontogeny of E. mucronata is known from calyptopis I to the adult phase, but the embryonic and early‐life stages (nauplius and metanauplius) of this broadcast spawning species are unknown. We describe the morphology and development time of these life stages to complete the knowledge of its life cycle. Embryos were obtained from purple‐gonad gravid females collected off Dichato, central Chile, during November 2012. Eight gravid females (mean=16 mm total length) were incubated in seawater at 12°C under laboratory conditions. The average development time from single‐cell embryos to the metanauplius stage was 2.2 d and hatching occurred between 20 and 25 h. The average growth rate was 0.35 mm d^?1 from the late limb bud to the metanauplius stage (range=0.21–0.48 mm d^?1). Embryos of E. mucronata had a mean chorion diameter of 0.460 mm, embryo diameter of 0.343 mm, and perivitelline space of 0.056 mm. Our biological information reported here constitutes a baseline for future ecological studies on distribution and temporal variability of spawning activity and reproductive strategies of E. mucronata in the highly variable and productive Humboldt Current ecosystem.     

Bioluminescence of sound-scattering layers in the Gulf of Maine

Submersible-based investigations of bioluminescence were conductedin sound-scattering layers (SSLs) in the Gulf of Maine, usingintensified video and dual-beam acoustic methods. Stimulatedbioluminescence in the SSLs was high (3–41 µW sr^–1m^–3 while spontaneous bioluminescence was not detected.The average intensity of individual bioluminescent sources inthe SSLs was 30–200 times greater than the intensity oflight emitters outside the SSLs. The two brightest sources ofbioluminescence were identified as the euphausiid, Meganyctiphanesnorvegica and the cydippid ctenophore, Euplokamis sp. Meganyctiphanesnorvegica formed a SSL within 50 m of the bottom during theday and migrated to the uppermost 30 m of the water column atnight, forming a near-surface SSL. Euplokamis sp., which producedexceptionally intense and long-lasting bioluminescent secretions,occurred within the near-bottom SSL in concentrations up to7 m^–3. Our findings indicate that traditional methodsof identifying the primary light emitters in a region, basedon light measurements from net- or pump-captured organisms,may have underestimated the significant in situ bioluminescencepotential of euphausiids and gelatinous zooplankton. ³ Present address: NOAA/NURP/R-OR2, Silver Spring, MD 20910,USA     

Courtship displays and coloration as indicators of safety rather than of male quality : the safety assurance hyposthesis

Male courtship displays and bright coloration are usually assumedto provide information to females about some aspect of themale's value as a mate. However, in some species, courtshipmay serve another function—namely, indicating the currentpredation risk at the mating site and assuring the female thatit is safe to mate there at this time. We developed this safetyassurance hypothesis (SAH) and tested its predictions in thebluehead wrasse (Thalassoma bifasciatum), a Caribbean reef fish. Females in this species come to males' territories to spawn,and males court each arriving female. Males with larger whiteflank patches court less intensely than less bright males.We show that such males are probably more visible to predatorsand thus need not court so intensely to provide the same degreeof safety assurance to a female. When model lizardfish predatorsare presented at spawning sites, males habituate to them quickly,but newly arriving females who see the predator are expectedto demand more assurance of site safety. Accordingly, and consistentwith the SAH, males court females more intensely (longer averagecourtship bout length) under such circumstances, but maleswith bright flank patches do not increase their courtship asmuch as duller males do. Despite this relatively low intensityof courtship, the spawning rate of bright males does not declinerelative to that of duller males in the presence of a predator,suggesting that bright coloration conveys a differential benefit.Females of species like the bluehead wrasse, who spawn repeatedlyover the course of their life, are expected to be more concernedwith their own risk of mortality during each spawning boutthan with the quality of a particular male. It is in such speciesthat we expect the SAH to be most applicable.