Growth,survivorship, life-span,and sex change in the hermaphroditic shrimp<Emphasis Type="Italic"> Lysmata wurdemanni</Emphasis> (Decapoda: Caridea: Hippolytidae)

Lysmata wurdemanni (Gibbes) is a protandric simultaneous hermaphrodite. All individuals first mature as a male-phase individual (MP) and then later change to a female-phase individual (FP) that spawns and broods embryos but can also mate as a male. A Gulf of Mexico population was sampled monthly for 1 year and bimonthly the next. Estimates of basic population parameters were obtained from cohort analysis to reveal possible factors explaining the unusual sexual biology of L. wurdemanni as well as the broad variation in the size (age) of change from MP to FP. Growth rates of individuals from cohorts varied from 4–7 mm carapace length year ^-1. Growth of small MPs in the laboratory was somewhat faster but concordant with growth rates estimated from field samples. The period from recruitment to >50% sex change in cohorts varied from 3 months to 1 year. In the laboratory, the size and interval to sex change was similar to that of the most rapidly changing cohort observed. Survivorship of cohorts was high until later in life; life-span was estimated to be 12–18 months. Rates of sex change were highest from late winter through spring, in time for the spring–summer breeding season. The size and age of sex change in cohorts were related to the season of recruitment. MPs recruited from late winter to mid-spring rapidly changed to FPs at a relatively small size. A majority of MPs recruited in the summer and autumn did not change to FPs until the following late winter to spring, and they did so at a larger size. Rates of sex change were not correlated with the sexual composition of the population. We conclude that seasonal factors related to female breeding greatly influence sex change in L. wurdemanni. We found no evidence to support demographically influenced and socially mediated environmental sex determination, which has been suggested for L. wurdemanni and other sex-changing caridean shrimps.     

Surface glycoproteins are not the contact pheromones in the Lysmata shrimp

Behavioral evidence suggests that some male caridean shrimp, such as those of Lysmata species, identify conspecific females via contact pheromones that coat the cuticle surface of the females. In this study, we attempted to determine whether the contact pheromones in three Lysmata species, Lysmata ankeri, Lysmata boggessi, and Lysmata wurdemanni, are glycoproteins as hypothesized previously in a diverse group of aquatic invertebrates. Twenty lectins were screened and lectin-binding experiments indicated that lectin treatment did not affect mate recognition in the shrimps. The behavior of the male-phase (MP) shrimp in the three treatments (non-lectin-treated MP and lectin-treated euhermaphrodite-phase (EP) shrimp, lectin-treated MP and lectin-treated EP shrimp, and lectin-treated MP and non-lectin-treated EP shrimp) and in the control was not different in responding to lectin-treated and control EP shrimp. All the MP shrimp copulated with lectin-treated and control EP shrimp successfully. All the MP shrimp copulated with ethylenediamine tetraacetate-treated EP shrimp (with glycoproteins removed from their cuticle surface) immediately after they detected the EP shrimp. The results suggest that glycoproteins are not likely to be the contact sex pheromones in the three Lysmata shrimp species.     

Comparative mating success of smaller male-phase and larger male-role euhermaphrodite-phase shrimp, <Emphasis Type="Italic">Lysmata wurdemanni</Emphasis> (Caridea: Hippolytidae)

The protandric simultaneous hermaphrodite shrimp Lysmata wurdemanni (Gibbes 1850) has a pure searching mating system, i.e., males are continually searching for receptive females and copulation is brief. To examine whether size-based advantage in male–male competition occurs and whether the mating ability of male-phase (M) shrimp equals that of euhermaphrodite-phase shrimp serving as males (Em), mating performance, including mating frequency and precopulatory behavior, of M and Em shrimp was compared using two M:Em ratios. Two experiments were carried out from March 2004 to August 2004 at Florida Institute of Technology’s Vero Beach Marine Laboratory using laboratory-cultured shrimp that originated from Port Aransas, TX, USA. In the two experiments, one parturial euhermaphrodite-phase shrimp acting as a female (Ef) was maintained with one M and two Em shrimp (one with and one without an egg mass), and two M and two Em shrimp, respectively. The M shrimp used were always smaller than the Em shrimp. Experiment 1 showed that there was no significant difference in mating ability between Em with and without egg mass. In both experiments, the M shrimp gained mating partners more frequently than the Em shrimp did. In the experiment with two M and two Em shrimp, mating frequencies of the small M and large M shrimp were similar. Precopulatory behaviors of the M shrimp were more active than those of the Em shrimp. Mating between the small M and larger Ef shrimp was sometimes successful even when the size difference was 20.0 mm total length (TL). Mating between a larger M shrimp and smaller Ef shrimp sometimes failed when the size difference was only 13.0 mm TL. Mating frequency of M shrimp over that of Em shrimp with Ef shrimp increased significantly with increasing density and operational sex ratio. The advantage of M over Em shrimp in obtaining mating partners is probably a result of sexual selection and adaptation, and may partially explain the observed delayed sex change in some L. wurdemanni, i.e., some male-phase shrimp grow very large and never become hermaphrodites.     

Hermaphroditism in brown shrimp: lessons from field data and modelling

This study was undertaken to further clarify whether the brown shrimp, Crangon crangon (Linnaeus 1758), is a gonochorist, a facultative or an obligate hermaphrodite. Juvenile shrimps were sampled from intertidal habitats along the German Wadden Sea coast with a push net and from a power plant water inlet to quantify the share of primary females. Length-based sex ratios were determined for about 27,000 individuals using external characteristics. Observed sex ratios were mainly female-biased, and also large males occurred regularly in the catch. This indicates that sex at hatch is not male as would be characteristic for an obligate protandric hermaphrodite and that not all male shrimps change sex. A cohort-based computer simulation, including sex-specific growth rates, mortality and seasonally varying recruitment, generated sex ratios comparable to the field. The observed decline in the proportion of males with increasing size can be explained solely by faster growth of females without involving hermaphroditism. Based on temperature-dependent growth and moult rates as well as length-specific numbers of eggs per female, the potential egg production of primary and secondary females was modelled, yielding contributions of secondary females of <1%. Sex change in C. crangon has previously been observed and may be interpreted as an evolutionary relict of this species having evolved in a habitat characterized by lower population densities, lower predation levels and increased longevity compared to today’s living conditions in North Sea coastal waters.     

Simultaneous hermaphroditism in the marine shrimp Lysmata wurdemanni (Caridea: Hippolytidae): an undescribed sexual system in the decapod Crustacea

Simultaneous hermaphroditism with outcrossing, a previously unconfirmed sexual system in decapod crustaceans, is documented in the shrimp Lysmata wurdemanni (Gibbes), using time-lapse video observations on mating in pairs of “female-phase” (FP) individuals. Copulations between FPs resulted in successful spawning and development of embryos. However, female-phase hermaphrodites maintained in isolation were unable to self-fertilize spawned eggs. All smaller individuals possessed characters typical of caridean males, including male gonopores, appendices masculinae, ejaculatory ducts, and cincinnuli on the first pleopods. However, the gonad of these male-phase (MP) individuals was an ovotestis with an undeveloped ovarian portion. FPs, which spawn eggs and incubate embryos, also had male gonopores and an ovotestis terminating in ejaculatory ducts containing sperm. In FPs, male pleopod characters were absent or reduced, and a female incubatory character, expanded pleopod flanges, showed a greater relative size. Smaller size classes of the population were composed only of MPs while larger size classes consisted of both MPs and FPs. “Transitionals,” individuals with MP characters but an ovotestis containing vitellogenic oocytes, were rare and overlapped completely in size with FP and larger MP individuals. It is suggested that not all MPs transform into FP hermaphrodites. Social interactions may mediate MP change into FP hermaphrodites in L. wurdemanni. The social system of L. wurdemanni and other Lysmata spp. may determine the exact form of the sexual system in these species. Received: 26 October 1997 / Accepted: 21 April 1998     

Experimental test of socially mediated sex change in a protandric simultaneous hermaphrodite,the marine shrimp<Emphasis Type="Italic"> Lysmata wurdemanni</Emphasis> (Caridea: Hippolytidae)

In Lysmata wurdemanni, individuals begin benthic life in a male phase (MP) but later change to a female phase (FP) with female external morphology, but with both male and female reproductive capacity (protandric simultaneous hermaphroditism). Previous studies have demonstrated that the size (timing) of sex change varies considerably in natural populations. We experimentally tested for social mediation of sex change by rearing male-phase individuals (MPs) in both large and small social groups with different sexual and size composition. In the large group experiment, speed of sex change was inversely related to the abundance of female-phase individuals (FPs) in the group (sex-ratio induction). Increased allocation to female function (more rapid change to FP) may occur when male mating opportunities are lower because the simultaneous-hermaphrodite FP can immediately reproduce as a female while maintaining male mating capacity. When FPs are abundant, delayed sex change might be adaptive because the costs of female reproduction are considerable. An MP may gain reproductively by increased growth before changing to FP at a larger size (fewer but much larger broods). Size-ratio induction of sex change by small MPs was suggested but not confirmed. Experimental results from small groups (1–2 individuals) were qualitatively similar but not as conclusive as those from large groups. The number and complexity of social interactions in large groups may be necessary to stimulate labile sex change in this species. In L. wurdemanni, sex change may be influenced not only by abiotic factors related to breeding [Bauer (2002) Biol Bull 203:347–357] but also by social factors in certain demographic situations.Communicated by K. Lindström     

Reproduction in a simultaneous hermaphroditic shrimp, Lysmata wurdemanni: any two will do?

The caridean shrimp Lysmata wurdemanni (Gibbes) displays protandric simultaneous hermaphroditism with out-crossing, but not all males become simultaneous hermaphrodites (euhermaphrodites). In this laboratory study, we attempted to determine why some shrimp remain males. In our experiment, we grew L. wurdemanni from post-larvae to adults in several group sizes and observed their reproductive function. We found that all shrimp reared in isolation become euhermaphrodites. When cultured in a group, the proportion of shrimp remaining male decreased with increasing group size. Except for those that mated within a day, inter-molt euhermaphrodite-phase shrimp (with or without embryos) and inter-molt male-phase shrimp fertilized eggs successfully. On the other hand, euhermaphrodite shrimp can only mate as females and have their eggs fertilized during a narrow post-molt window (less than 12 h.) in each molt cycle (10 days). The fertilization rate of male-euhermaphrodite pairs was similar to that of euhermaphrodite-euhermaphrodite pairs. There are at least two non-exclusive explanations for the persistence of male shrimp in a group. In certain group compositions, an individual may gain more reproductive fitness as a large male with multiple mate partners than as a small female with low clutch size. Alternatively, the presence of male-phase individuals, with variable molt-cycle duration (5-8 days), may be necessary to ensure mating. This study is the first direct experimental demonstration of social control of sex change in the decapod crustaceans.     

Reproduction in a simultaneous hermaphroditic shrimp, Lysmata wurdemanni: any two will do?

The caridean shrimp Lysmata wurdemanni (Gibbes) displays protandric simultaneous hermaphroditism with out-crossing, but not all males become simultaneous hermaphrodites (euhermaphrodites). In this laboratory study, we attempted to determine why some shrimp remain males. In our experiment, we grew L. wurdemanni from postlarvae to adults in several group sizes and observed their reproductive function. We found that all shrimp reared in isolation become euhermaphrodites. When cultured in a group, the proportion of shrimp remaining male decreased with increasing group size. Except for those that mated within a day, inter-molt euhermaphrodite-phase shrimp (with or without embryos) and inter-molt male-phase shrimp fertilized eggs successfully. On the other hand, euhermaphrodite shrimp can only mate as females and have their eggs fertilized during a narrow post-molt window (less than 12 h) in each molt cycle (10 days). The fertilization rate of male-euhermaphrodite pairs was similar to that of euhermaphrodite-euhermaphrodite pairs. There are at least two non-exclusive explanations for the persistence of male shrimp in a group. In certain group compositions, an individual may gain more reproductive fitness as a large male with multiple mating partners than as a small female with low clutch size. Alternatively, the presence of male-phase individuals, with variable molt-cycle duration (5-8 days), may be necessary to ensure mating. This study is the first direct experimental demonstration of social control of sex change in the decapod crustaceans.     

Characterization of a sex pheromone in a simultaneous hermaphroditic shrimp, Lysmata wurdemanni

Olfactory chemical cues have been described to play important roles in the control of mate recognition in many decapod crustaceans. However, we still know very little about the chemical characteristics of the cues that coordinate pre-copulative behaviour. In this study, we partially characterized a waterborne sex pheromone of a marine shrimp, Lysmata wurdemanni. Female moulting water was collected and ultrafiltered using 1,000 and 500-Da membranes, respectively, and analysed using HPLC with a Lichrosphere™ RP18 (C18) column. The sex pheromone is likely to be a molecule between 500 and 1,000 Da in size because behavioural bioassays showed that males responded to the supernatant of 500-Da and to the 1,000-Da filtrate, but did not respond to the supernatant of 1,000-Da or to the 500-Da filtrate. There was only one dominant peak (2.86 min) detectable in HPLC chromatograms of the supernatant of the 500-Da filtration. This peak showed a UV absorbance maximum at 274 nm, similar to the recently identified shore crab sex pheromone Uridine-di-phosphate (UDP). Behavioural bioassays confirmed that this peak is a bioactive component of a potential pheromone bouquet, but is different from UDP, which showed no bioactivity in Lysmata wurdemanni. Our results lay the foundation for future studies to purify and eventually identify this sex pheromone.     

Maternal characteristics and the production and recruitment of sons in the eastern kingbird (<Emphasis Type="BoldItalic">Tyrannus tyrannus</Emphasis>)

Sex allocation theory predicts that if variance in reproductive success differs between the sexes, females who are able to produce high-quality young should bias offspring sex ratio towards the sex with the higher potential reproductive success. We tested the hypothesis that high-quality (i.e., heavy) female eastern kingbirds (Tyrannus tyrannus) that bred early in the breeding season would produce male-biased clutches. A significant opportunity for sexual selection also exists in this socially monogamous but cryptically polygamous species, and we predicted that successful extra-pair (EP) sires would be associated with an excess of male offspring. Although population brood sex ratio did not differ from parity, it increased significantly with female body mass and declined with female breeding date, but was independent of the morphology and display (song) behavior (correlates of reproductive success) of social males and EP sires. Male offspring were significantly heavier than female offspring at fledging. Moreover, the probability that male offspring were resighted in subsequent years declined with breeding date, and was greater in replacement clutches, but lower when clutch size was large. Probability of resighting female offspring varied annually, but was independent of all other variables. Given that variance in reproductive success of male kingbirds is much greater than that of females, and that male offspring are more expensive to produce and have a higher probability of recruitment if fledged early in the season, our results support predictions of sex allocation theory: high-quality (heavy) females breeding when conditions were optimal for male recruitment produced an excess of sons.     

Mortality estimates from repeated visual censuses of a parrotfish (Sparisoma viride) population: demographic implications

Repeated visual censuses of different categories (juveniles, females, territorial and group males) of the stoplight parrotfish (Sparisoma viride, a protogynous hermaphrodite) over a 3-year period indicated a relatively stable size and structure of the adult population. This allowed estimates of size-specific mortality, sex change, and territory acquisition probabilities from previously reported growth rates. Comparison of the predicted number of survivors, sex changers, and territory take overs with field observations indicates that our estimates are quite reliable. However, rather large differences in mortality are obtained for the largest three size classes (>25 cm), which may be due to reduced accuracy of length estimates of large fish. A pooled mortality for these classes is therefore suggested as a more realistic estimate. The life-history implications of our findings are investigated by comparing the predicted survival and future reproductive success of fish that change sex at different sizes. Ten percent of the adults reach an age of ca. 17 years, once a length of 20 cm is attained, as predicted from the pooled estimates. Calculations based on these estimates indicate that the predicted reproductive output of a 15-year-old fish (2500 matings) is the same for early (i.e. at 20 cm) and late (>30 cm) sex changers and for an average fish subject to the estimated daily sex change and territory acquisition probabilities. These findings suggest that S. viride individuals are able to flexibly adjust the timing of sex change in an adaptive way to unpredictable local conditions. However, independent mortality estimates are needed to corroborate our present findings. Received: 2 January 1997 / Accepted: 27 January 1997     

A stochastic simulation model of brown shrimp (Penaeus aztecus ives) growth,movement, and survival in Galveston Bay,Texas

A stochastic simulation model of brown shrimp (Penaeus aztecus Ives) population dynamics in Galveston Bay, Texas, is described, validated, and used to evaluate the effects of management alternatives and changing environmental conditions on shrimp dynamics. The model is composed of submodels representing: (1) recruitment, (2) growth, (3) natural mortality, (4) fishing mortality, and (5) emigration of brown shrimp. The model predicts significant changes in total annual harvest from the food shrimp, bait, and recreational fisheries resulting from (1) closure of the bay system to all fishing except during the spring and fall open seasons, (2) two-week postponement of the opening and closing of the open seasons for the food shrimp fishery, (3) a 2.5°C increase and (4) a 2.5°C decrease in mean water temperature, (5) an 80% increase and (6) an 80% decrease in fishing effort. No significant change in the total annual harvest is predicted when the food shrimp fishing season is extended from May 15 through December 15. Sensitivity analysis suggests that field experimentation designed specifically to test the hypothesis of a 60-day time lag between brown shrimp recruitment into the bays and exposure to the fishery should receive high priority. Simulation results are discussed within a management framework.     

Seasonal abundance,distribution and growth of postlarval and juvenile grass shrimp (Palaemonetes pugio) in a Georgia,USA, salt marsh

Postlarval and juvenile grass shrimp (Palaemonetes pugio Holthuis) ≦15 mm total length (TL) were abundant at low tide in shallow aquatic microhabitats (i.e. puddles and films of residual tidal water) in the intertidal zone of a salt marsh on Sapelo Island, Georgia, USA from 1982 to 1984. The highest concentrations of young P. pugio occurred at 190 to 200 cm above mean low water, ∼10 to 20 cm below mean high water. The intertidal distributions of young grass shrimp expanded and contracted with changes in tidal amplitude. Postlarval grass shrimp (6 to 8 mm TL) continuously recruited into the intertidal marsh population from May until October, but densities varied in a regular pattern with peaks in abundance occurring at ∼2-week intervals, corresponding to spring tide periods in the lunartidal cycle. Although present nearly year-round in the intertidal marsh, juveniles (9 to 15 mm TL) were most abundant from August to October. Apparent growth rates of individuals up to 15 mm TL averaged 0.268±0.026 (mean±95% C.I.) mm d^-1 from May to October and 0.070±0.032 mm d^-1 in November and December. Unlike larger aquatic organisms, which can forage in the emergent marsh only when it is flooded by the tide, juvenile grass shrimp have constant access to intertidal resources. Although potentially important predators in this system, the role of young P. pugio in the trophic organization of salt marsh benthic invertebrate assemblages has yet to be examined. Contribution No. 576 of the University of Georgia Marine Institute     

Bi-directional sex change in a coral-dwelling goby

Bi-directional sex change has recently been reported among obligate coral-dwelling gobies of the genus Gobiodon. However, neither the functional role of this pattern of sex change nor the frequency of sex change in either direction in natural populations is known. We investigated the social structure and pattern of sex change of Gobiodon histrio at Lizard Island on the Great Barrier Reef. The social structure of G. histrio within coral colonies usually consisted of a single juvenile or a heterosexual adult pair. The size of adult social groups was not constrained by coral colony size. In contrast to expectations for pair-forming species, G.␣histrio was primarily a protogynous hermaphrodite. All immature G. histrio were females and sex change from female to male occurred readily when two mature females were placed in a coral colony. In addition, male G. histrio were able to change back to females when two mature males were placed in a coral. Sex change from female to male, however, occurred with over twice the frequency of sex change from male to female. Where two males were placed in a coral colony, heterosexual pairs were most frequently re-established by immigration of females from outside the treatment population. This pattern might be predicted if sex change from male to female is more expensive than sex change from female to male for G. histrio. Where sex change is expensive, movement may be favoured over sex change, particularly where coral densities are high and movement among corals incurs little mortality risk. Received: 10 November 1997 / Accepted after revision: 16 May 1998     

Body color change and serum steroid hormone levels throughout the process of sex change in the adult wrasse, <Emphasis Type="Italic">Pseudolabrus sieboldi</Emphasis>

Gonadal sex steroid hormones are the principal factors that directly control the gonadal and morphological alterations during sex change in hermaphrodite fish; however, the physiological mechanism of action by which these hormones govern body coloration is poorly understood. The protogynous wrasse Pseudolabrus sieboldi is a good model for understanding the physiological mechanisms of gonadal and body color change during sex change in hermaphrodite fish. To obtain information on the relationship between sex steroids and body color change during the process of gonadal sex change, we analyzed body color, gonadal histology, and serum levels of sex steroids. Body color was analyzed using a quantitative analytical method based on the hue value. Compared to other body parts of the fish, the anal fin changed color the most, becoming increasingly redder in association with gonadal changes that converted ovaries to testes. Levels of serum 11-ketotestosterone (11KT) increased as the gonadal sex change proceeded, whereas no significant change was observed in estradiol-17β (E2) levels. Moreover, we found a significant correlation between the hue value of the anal fin and serum 11KT levels, but not E2 levels. These results suggest that androgen, but not estrogen, plays a principle role in the changes in both gonadal morphology and body color in the transformation from female to male in this species. To our knowledge, this is the first quantitative demonstration of the relationship between body color and serum steroid levels during sex change in fish.     

Do protandric pandalid shrimp have environmental sex determination?

Based on demographic analysis of four different temporally enclosed demes of Pandalus borealis in Gullmarsfjorden on the Swedish west coast and published information, I discuss the notion of environmental sex determination in protandric pandalid shrimps as suggested by sex allocation theory. Demographic results showed that age structure and mortality rates varied substantially between four studied periods without noticeable effects on the age of sex change in the fjord populations. The majority of shrimps changed sex at an approximate age of 3 years and became females at an age of 3 to 4 years, however, low proportions (4 to 7%) of 2nd year females (transitional at ca. 1 year) and 3rd year females (5 to 12%) (transitional at ca. 2 years) were present each year. Low proportions of primary females were also found in two of the temporally enclosed demes, in 1985 (9%) and in 1987 (5%). These results do not indicate that yearly variations in age structure, mortality, or frequency of older breeders in the breeding population affect the age of sex change in temporally enclosed fjord demes of this protandric species. An alternative to assuming that the protandric mode of reproduction in pandalid shrimp is combined with environmental sex determination is suggested. Received: 24 September 1996 / Accepted: 6 November 1996     

Aesthetascs in Lysmata spp. shrimp: sexual dimorphism and relationship with social environments

Aesthetascs are the olfactory receptor organs responsible for mate recognition in many decapod crustacean species. The number of aesthetascs varies greatly among species in different environments, but the functional significance of this variation is poorly understood. This study examined the relationship between social environment and the number of aesthetascs in six species of caridean shrimp in the genus Lysmata. Generally, the number of aesthetascs was greater in group-living species (L. boggessi and L. wurdemanni) than in low-density (L. ankeri and L. pederseni) and pair-living species (L. amboinensis and L. debelius). Aesthetascs are innervated by olfactory receptor neurons (ORNs). The total number of ORNs is related to the sensitivity of olfactory odor detection, and it was higher in group-living species than in pair-living species. Sexual dimorphism in the number of aesthetascs was present in L. boggessi, L. wurdemanni, and L. ankeri but not in L. pederseni and L. amboinensis.     

Amino and fatty acid dynamics of<Emphasis Type="Italic"> Lysmata seticaudata</Emphasis> (Decapoda: Hippolytidae) embryos during early and late reproductive season

The present study investigates amino and fatty acid dynamics of embryos of different-sized simultaneous hermaphrodite shrimp (SH) (Lysmata seticaudata) during early (ERS) and late reproductive seasons (LRS). A significant relative decrease in total amino acids and essential amino acids (EAA) was recorded (P<0.05) during the development of embryos produced by shrimp collected during ERS and LRS. The content of non-essential amino acids (NEAA) showed a smaller variation, without a marked decrease. During the last embryonic stage, the major EAAs of embryos were, in decreasing magnitude, lysine and arginine, while the major NEAAs were glutamic acid and valine. A substantial decrease in lipid content (P<0.05) was observed, and the quantitatively more important fatty acids were the saturates 16:0 and 18:0, the monounsaturates 18:1n-9 and 18:1n-7 and the polyunsaturates 20:4n-6 (arachidonic acid, ARA), 20:5n-3 (eicosapentaenoic acid, EPA) and 22:6n-3 (docosahexaenoic acid, DHA). Monounsaturates were used at a higher rate, and embryos produced by SH shrimp displayed similar consumption rates of saturated and polyunsaturated fatty acids. Considering individual fatty acids, no clear utilization pattern between different-sized SH shrimp in ERS and LRS was recorded. The inexistence of consistent differences between amino and fatty acid utilization during embryogenesis among different-sized SH shrimp in ERS and LRS emphasizes the variability affecting offspring in decapod crustaceans.Communicated by S.A. Poulet, Roscoff     

Bioaccumulation and toxic effects of copper on growth and oxygen consumption by the postlarvae of Penaeus indicus

The aim of this study was to assess the toxic impact of copper on postlarvae (PL) of the penaeid shrimp Penaeus indicus. Tolerance, growth, oxygen consumption and metal accumulation were investigated in these PL on exposure to copper. Tolerance studies were conducted for 96 h to assess the tolerance limits of P. indicus PL exposed to different concentrations of copper using static renewal bioassay tests. Using the Probit method, the regression equation was calculated as Y=0.4899+2.3562 X, with a correlation coefficient of 0.9707. The 96 h LC₅₀ was 0.8204 ppm. The effect of sublethal (one-fifth of 96 h LC₅₀) copper on PL for short- and long-term exposures revealed a significant (p<0.05) decrease in the rate of oxygen consumption, metabolic rate, mean length, wet and dry weight of the exposed PL over their respective controls which can be attributed to a gradual and time-dependent accumulation of the metal, as noticed in the exposed PL through accumulation studies. Overall, the data suggest that on chronic exposure even sublethal concentrations of copper can reduce the metabolic rate and growth in P. indicus PL. This is perhaps the first attempt to use the wild P. indicus PL as a bioindicator of copper toxicity.     

Population dynamics, sex ratio and size at sex change in a protandric simultaneous hermaphrodite, the spiny shrimp Exhippolysmata oplophoroides

One of the main goals of sex allocation theory is understanding sex ratio evolution. However, theoretical studies predicting sex ratios in species with unusual sexual systems, such as protandric simultaneous (PS) hermaphroditism, are rare. In PS hermaphrodites, juveniles first develop into functional males that mature into simultaneous hermaphrodites later in life. Here, we report on the sex ratio (males/males + hermaphrodites) in the PS hermaphroditic shrimp Exhippolysmata oplophoroides. A 2-year study demonstrated that hermaphrodites dominated the population in two different bays. This skewed sex ratio may be explained by limited encounter rates among conspecifics. In agreement with this idea, the density of shrimps was extremely low (≤1 shrimp km⁻²) at the two study sites. Size at sex phase change and sex ratios remained relatively stable through time at the two bays. The stability of these parameters might be explained by the rather steady population structure of this species during the study period. A review of sex ratios in PS hermaphroditic shrimps (Lysmata and Exhippolysmata) revealed considerable variation; some species have male- and others hermaphrodite-skewed sex ratios. The conditions explaining inter- and intra-specific sex ratio variation in protandric simultaneous hermaphroditic species remain to be addressed.