Is <Emphasis Type="Italic">Hippolyte williamsi</Emphasis> gonochoric or hermaphroditic? A multi-approach study and a review of sexual systems in <Emphasis Type="Italic">Hippolyte</Emphasis> shrimps

Sexual systems vary considerably among caridean shrimps and while most species are gonochoric, others are described as sequential protandric hermaphrodites or simultaneous hermaphrodites with an early male phase. At present, there is confusion about the sexual system exhibited by several species mostly because those studies attempting to reveal their sexual system draw inferences solely from the distribution of the sexes across size classes. Here we investigated the sexual system of the shrimp Hippolyte williamsi from Chile to determine if the species is protandric or gonochoric with sexual dimorphism (males smaller than females). Morphological identification and size frequency distributions indicated that the population comprised small males, small immature females, and large mature females, which was confirmed by dissections. No transitional individuals were found. Males maintained in the laboratory molted 1–8 times, and many grew up to reach sizes observed in only a small fraction of males in the field. No indication of sex change was recorded. Our results indicate that H. williamsi is a sexually dimorphic gonochoric species and emphasizes the importance of using several kinds of evidence (size measurements, growth experiments, morphological dissections, and histological studies) to reveal the sexual system of Hippolyte species. Whether the observed size dimorphism between males and females in many species of Hippolyte is expression of contrasting sexual and natural selection, and whether divergent sexual fitness functions can contribute to the evolution of hermaphroditism remains to be revealed in future studies.     

Male mating opportunities affect sex allocation in a protrandric-simultaneous hermaphroditic shrimp

Sex allocation theory predicts phenotypic adjustments by individuals in their investments into the male and female reproductive function in response to environmental conditions. I tested for phenotypically plastic shifts in sex allocation in a protandric simultaneous hermaphrodite, in which individuals mature and reproduce as males first, and later in life, as simultaneous hermaphrodites. I predicted that initially maturing males should adjust the timing of maturation as hermaphrodites according to male mating opportunities mediated by population size of hermaphrodites. In a first experiment, males maintained with only one hermaphrodite reduced the time they spent as males in comparison to males maintained with no conspecifics, presumably because total reproductive output is maximized by two individuals being simultaneous hermaphrodites when the mating system is a pair. Conversely, males maintained in groups with two or more hermaphrodites increased the time they spent as males in comparison to single males. This delay in maturation was not an effect of resource depletion with increasing shrimp density because the growth rate of males did not differ among most of the experimental treatments. One hypothesis to explain this social mediation of sex allocation is that the smaller males are more successful in mating as males than are the larger hermaphrodites: it will pay reproductively for males to delay maturation as hermaphrodites in large but not in small groups. In agreement with this notion, a second experiment demonstrated that smaller males were four times more successful than were larger hermaphrodites in inseminating shrimps reproducing as females. The informative cue that males may use to perceive different group sizes deserves further attention.     

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.     

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     

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.     

Effects of density and simulated recruitment and mortality on sex change in a protandric simultaneous hermaphroditic shrimp, Lysmata wurdemanni

Sex change in many hermaphrodite animals has been suggested to be environmentally determined, especially socially. To investigate whether sex change in the protandric simultaneous hermaphrodite shrimp Lysmata wurdemanni (Gibbes 1850) is socially mediated, two experiments were conducted in the laboratory between September 2002 and April 2004 using laboratory-cultured shrimp that originated from Port Aransas, Texas, USA. The size at sex change (from male to simultaneous hermaphrodite) in this shrimp is variable, with the minimum around 2.4 cm in total length (TL). Large shrimp (2.4–4.5 cm TL) still in the male-phase (MP) have been found in the wild and laboratory environments. This study tested the hypothesis that large MP shrimp delay changing to the euhermaphrodite-phase (EP) due to social control. In the first experiment, ten shrimp were raised in large (110-l) and small (20-l) containers to test the effect of habitat size/density on sex change. The percentage of shrimp changing to EP was significantly higher in the large container (low density) than in the small container after 60 and 120 days. But after 570 days sex ratios were the same, 2 MP:8 EP. In the second experiment, group composition was changed over time to simulate population recruitment and mortality. MP shrimp delayed sex change when EP shrimp were present. However, if group structure is stable, some MP shrimp may not change sex during their lifetime. Under certain demographic conditions, such as when postlarvae (PL) were added to (simulating recruitment) or EP shrimp were removed from (simulating mortality) a group, all old MP (from original PL) shrimp changed to EP. The response of old MP shrimp to simulated recruitment is faster than to simulated mortality. The present study confirms that social control affects the size and timing of sex change in L. wurdemanni. However, some MP shrimp never change sex suggesting that genetics might also play a role in the sex ratios of L. wurdemanni populations.     

Mating system of the hermaphroditic coral-reef fish,Serranus baldwini

Summary The lantern bass, Serranus baldwini, is a small hermaphroditic serranid found adjacent to coral reefs throughout the Caribbean. Data from gonad inspection, spawning behavior, and gamete release from individuals all confirm that populations consist of simultaneous hermaphrodites and males. This gender pattern appears to be sequential, with larger males derived from smaller hermaphrodites. The social system is haremic, with the male defending an area containing 1–7 hermaphrodites. The social system and gender pattern are similar to those of the eastern Pacific serranid, Serranus fasciatus. Males obtain disproportionately high mating success by being nearly the sole mates of hermaphrodites within their harems. Hermaphrodites obtain very low levels of mating success through male function. This pattern may result from female choice by hermaphrodites, mate sequestering tactics by males, or both. The serranids that change gender from hermaphrodite to male appear to have a higher environmental potential for polygyny than other simultaneous hermaphrodites in this family. Factors that may maintain male function in hermaphroditic S. baldwini are outlined, but none currently provides clear evidence for why this species has not evolved to protogyny.     

Not all ctenophores are hermaphrodites. Studies on the systematics,distribution, sexuality and development of two species of Ocyropsis

The lobate ctenophores Ocyropsis maculata and O. crystallina are not simultaneous hermaphrodites, based on morphological, histological and experimental evidence. Sex ratios in populations, sex ratios of size classes within populations, and average sizes of males and females support the hypothesis that both species are dioecious, rather than sequential hermaphrodites. We have divided each species into two subspecies, based on morphology and geographic distribution. Preliminary evidence suggests that the subspecies also differ in reproductive behavior. One subspecies, O. crystallina guttata, spawns on a daily cycle in the laboratory, and spawning becomes more synchronous when males and females are placed together. Species of Ocyropsis, all of which are oceanic in distribution, are probably descended from a common ancestor that was a simultaneous hermaphrodite. That this group of oceanic ctenophores evolved dioecy directly contradicts the assertion that there is a selective advantage to hermaphroditism in environments where the probability of finding a mate is reduced.     

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.     

Sex determination inScalpellum scalpellum (Cirripedia: Thoracica: Lepadomorpha), a hermaphroditic goose barnacle with dwarf males

The cyprid larvae ofScalpellum scalpellum (L.), a hermaphroditic goose barnacle with dwarf males, are morphologically alike and no characters distinguish the sexes. To elucidate the controversy over the relative significance of genetic and environmental factors in the sex determination of this species, laboratory experiments were performed involving the introduction of cyprid larvae of different parental origin to different densities of adult hermaphrodites without dwarf males. Cyprids introduced to adult hermaphrodites metamorphosed to either dwarf males or hermaphrodites significantly different from the controls without adult hermaphrodites. The proportion which metamorphosed into dwarf males increased with increasing adult density. Not more than 51% metamorphosis to dwarf males could be obtained, indicating a genetic component in the sex differentiation. It was concluded that all cyprids are potential hermaphrodites, but that about 50% possess the capability of metamorphosing into dwarf males as well, if adult hermaphrodites with free receptacles are available. Consequently, both genetically and environmentally controlled components influence sex determination in this species.     

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.     

Biased primary sex ratio in the bushcricket Poecilimon veluchianus,an insect with sex chromosomes

Offspring sex ratio at hatching was examined in the bushcricket Poecilimon veluchianus. Offspring sex ratios varied significantly between females (Fig. 1). Low mortality prior to sex determination established that this heterogeneity was already present in the primary offspring sex ratio. Sperm age and female age had no influence on offspring sex ratio (Fig. 2). Male age at copulation, however, correlated significantly with offspring sex ratio (Fig. 3). There were two types of males: one type produced predominantly daughters when young and an increasing proportion of sons with age. The other type produced, independent of age, 1:1 offspring sex ratios (Fig. 4). The two types of males seem to occur in approximately equal numbers. Sex ratio variation (1) may adaptively compensate for local sex ratio biases caused by sex-specific motility, or (2) it may be adaptive if there is a sex-differential effect of laying date on offspring fitness. Received: 14 March 1996/Accepted after revision: 24 June 1996     

Gonad morphology, sexual development, and colony composition in the obligate coral-dwelling damselfish Dascyllus aruanus

Gonad morphology and colony composition support the existing supposition that the obligate coral-dwelling damselfish Dascyllus aruanus has a protogynous hermaphroditic sexual pattern. Adults had either an active ovary containing vitellogenic oocytes, an ovotestis, or a spermiated testis and were classified as adult female, hermaphrodite, or adult male, respectively. Among individuals having male function, the testis (or testis portion of the ovotestis) takes the form of an unrestricted spermatogonial lobular testis. Among hermaphrodites having an ovotestis, a small proportion of individuals had a gonad in which both the ovarian and testicular portions were inactive (inactive hermaphrodites), whereas the majority had a predominantly testicular ovotestis that contained spermatozoa (male-active hermaphrodites). The size range of individuals within gonadal classes indicates that all D. aruanus first develop an ovariform gonad. Some individuals then undergo ovarian maturation to become adult females while others develop testicular tissue to form an ovotestis and become male-active hermaphrodites. Subsequently, progressive loss of ovarian tissue results in the development of a secondary testis from an ovotestis with the retention of a residual, afunctional lumen among adult males. The wide size range of individuals having an ovotestis suggests that some hermaphrodites function as adult females before developing testicular tissue while other individuals do not pass through an adult female stage. If this is the case, D. aruanus exhibits a diandric protogynous hermaphroditic sexual pattern. The apparent prolonged retention of an ovotestis with both healthy oocytes and an ovarian-type lumen in a spermiated ovotestis, as well as a functional sex ratio of 1:1 for adult females:adult males plus male-active hermaphrodites also raises the possibility that D. aruanus may be capable of bidirectional sex change during the hermaphroditic stage. Such a capability would be highly adaptive for a species having limited mobility and unpredictable recruitment of new colony members resulting in unpredictable mating opportunities.     

Colony level sex allocation in a polygynous and polydomous ant

The colony-level sex allocation pattern of eusocial Hymenoptera has attracted much attention in recent studies of evolutionary biology. We conducted a theoretical and empirical study on this subject using the dolichoderine ant Technomyrmex albipes. This ant is unusual in having a dispersal polymorphism in both males and females. New colonies are founded by an alate female after mating with one or more alate males in the nuptial flight. In mature colonies, the reproductive role of the foundress queen is taken over by wingless offspring (supplementary reproductives). Mature colonies are extremely polygynous, with many wingless queens reproducing through intea-colonial mating with wingless males (inbreeding), and producing both alate and wingless sexuals. The population sex ratio of wingless sexuals was found to be extremely female-biased, while the population allocation ratio of alates was almost 1:1. This result suggests that there is local mate competition among wingless sexuals. A specific model for this extraordinary life cycle predicted that the asymmetry of regression relatedness (b _f/b _m) will disappear during the first few generations of wingless reproductives after the foundress dies. If colonies begin to produce alates after several wingless generations, this undermines the hypotheses for intercolonial sex ratio variation based on the relatedness asymmetry. We compared the magnitude of variation in sex ratios and other characteristics between two levels (within-colony-inter-nest and between-colony). Although there was considerable within-colony variation in all the examined characteristics, between-colony variances were always larger. This means that allocation is important at the whole-colony level, not that of the nest. There was no apparent correlation between the sex ratio of alates and colony size. Furthermore, partial correlation analysis indicated that neither the number of workers nor investment in alates explained the variation in the sex ratio of alates. The only factor which was significantly correlated with the sex ratio of alates was the sex ratio of wingless sexuals (a positive correlation). We conclude that both the alate and wingless sex ratios may be influenced by a common primary sex ratio at the egg stage, the variance of which may have genetic components. In the wingless sexuals, partial correlation analysis indicated that colony size and the number of workers explained the sex allocation ratio. The number of wingless females was strongly (positively) correlated with the total investment in wingless sexuals, while the number of males showed no such correlation. There is, however, no convincing explanation for the variation in sex allocation ratio of wingless sexuals, because the estimates of investment in wingless males may have a large sampling error. Correspondence to: K. Tsuji     

Extra-pair paternity, offspring mortality and offspring sex ratio in the socially monogamous coal tit (Parus ater)

Females of many socially monogamous bird species commonly engage in extra-pair copulations. Assuming that extra-pair males are more attractive than the females’ social partners and that attractiveness has a heritable component, sex allocation theory predicts facultative overproduction of sons among extra-pair offspring (EPO) as sons benefit more than daughters from inheriting their father’s attractiveness traits. Here, we present a large-scale, three-year study on sex ratio variation in a passerine bird, the coal tit (Parus ater). Molecular sexing in combination with paternity analysis revealed no evidence for a male-bias in EPO sex ratios compared to their within-pair maternal half-siblings. Our main conclusion, therefore, is that facultative sex allocation to EPO is absent in the coal tit, in accordance with findings in several other species. Either there is no net selection for a deviation from random sex ratio variation (e.g. because extra-pair mating may serve goals different from striving for ‘attractiveness genes’) or evolutionary constraints preclude the evolution of precise maternal sex ratio adjustment. It is interesting to note that, however, we found broods without EPO as well as broods without mortality to be relatively female-biased compared to broods with EPO and mortality, respectively. We were unable to identify any environmental or parental variable to co-vary with brood sex ratios. There was no significant repeatability of sex ratios in consecutive broods of individual females that would hint at some idiosyncratic maternal sex ratio adjustment. Further research is needed to resolve the biological significance of the correlation between brood sex ratios and extra-pair paternity and mortality incidence, respectively.     

Male influence on sex allocation in the parasitoid wasp Nasonia vitripennis

Sex allocation is an important reproductive decision for parents. However, it is often assumed that females have substantial control over sex allocation decisions, and this is particularly true in haplodiploid insects, in which females apparently determine sex by deciding whether to fertilise an egg (and produce a diploid daughter) or not (and produce a haploid son). Mechanisms by which males may influence sex allocation are not so straightforward, and their potential influence on sex ratios has been somewhat neglected. Here, we test whether males influence offspring sex ratios in the parasitoid wasp Nasonia vitripennis. We show that some of the variation in observed sex ratios can be attributed to males when comparing the affect of male strain on sex ratio. We did not find among-male variation in sex ratio with a less powerful experiment using males from only one strain or an effect of male mating environment. Our data suggest that males can influence female sex ratios and contribute to the variation around the sex ratios optimal for females. However, the influence is not large, suggesting that females have more influence on sex allocation than do males. We conclude by considering whether male influences on sex ratio represent differences in male reproductive competence or deliberate attempts by males to increase their fitness by influencing daughter production.     

A histological study of reproduction in the serpulids<Emphasis Type="Italic"> Pomatoceros triqueter</Emphasis> and<Emphasis Type="Italic"> Pomatoceros lamarckii</Emphasis> (Annelida: Polychaeta)

The reproductive cycles of the serpulid polychaetes Pomatoceros lamarckii (Quatrefages, 1865, as Vermilia) and P. triqueter (Linnaeus, 1767, as Serpula triquetra) were studied by histological examination during 1999 and 2000 at Bantry Bay, south-west Ireland. Gametogenesis, sex ratios and hermaphroditism were also investigated. The male/female ratio in P. lamarckii was approximately equal, but in P. triqueter it deviated significantly in favour of females. There was no significant variation in the sex ratios throughout the year in either species. Results confirm that the species are protandric hermaphrodites. In P. lamarckii, but not in P. triqueter, sexual dimorphism was exhibited in body size, the females being larger than the males of the same species. In both species, the proportion of females increased with increasing body size. Simultaneous hermaphroditism was recorded in P. lamarckii, but not in P. triqueter. There was no clearly defined annual gametogenic cycle in either species. Both species appear to have an extended reproductive season, with numerous small-scale peaks in reproductive maturity that can vary annually. Spawning was broadly synchronous between sexes. Visual observation alone (i.e. without histology) was insufficient to accurately assess reproductive condition in individuals not in, or close to, a ripe state.     

Sex change in a giant endemic limpet,Patella kermadecensis,from the Kermadec Islands

Sex-ratios of the limpetPatella kermadecensis Pilsbry, collected at three times of the year during 1984 and 1985 at Raoul Island in the Kermadecs group, varied with the size of the limpets. Small limpets were predominantly male, while amongst larger ones about half were female. The presence of hermaphroditism inP. kermadecensis was confirmed by microscopic examination of gonad material from over 50 limpets, which revealed a high percentage of individuals with both male and female gametes in their gonads. It is postulated that protandric sex change occurs in this large limpet, and that this phenomenon is related to a change in habitat from the backs of large shells (limpets less than approximately 50 mm) to bedrock (larger limpets). The pattern of sex change inP. kermadecensis is compared with that in other species of limpet, and it is suggested that a reproductive system consisting of gonochoristic males and sequential hermaphrodites may be particularly advantageous for a large, slow-growing species that has a very restricted geographical range.     

How do dietary diatoms cause the sex reversal of the shrimp <Emphasis Type="Italic">Hippolyte inermis</Emphasis> Leach (Crustacea,Decapoda)

Hippolyte inermis Leach 1915 is a protandric shrimp largely distributed in Posidonia oceanica meadows and other Mediterranean seagrasses. Previous studies demonstrated several physiological peculiarities, such as absence of female gonadic buds in adult males (the new female gonad is produced starting from few undifferentiated cells), the consequent absence of an ovotestis, 2 yearly periods of reproduction with different population structures (a spring outburst producing both males and primary females, and a fall reproduction producing mainly males), and a process of sex reversal influenced by the diatom food ingested. We performed several laboratory analyses to compare the effects of various species of benthic diatoms, in order to test the effect of different diatoms and provide information on the mechanism of action of the ingested compounds. In addition, we performed molecular tests (TUNEL) and TEM observations, to check the hypothesis that the effect of benthic diatoms may be mediated by a process of apoptosis acting on the male gonad. The results obtained allowed for a ranking of a series of benthic diatoms according to their effects on sex reversal, and a confirmation of the striking effect of Cocconeis sp. diatoms, which are able to trigger the appearance of primary females. We also demonstrated the presence of apoptosis both in the male gonad and in the androgenic glands of postlarvae. The effect is species specific, strictly localized to the male gonad and androgenic gland, and limited to a very short period of time, from the 5th to the 12th day of postlarval development.     

Changes in gonadal development,androgenic gland cell structure,and hemolymph vitellogenin levels during male phase and sex change in laboratory-maintained protandric shrimp, <Emphasis Type="Italic">Pandalus hypsinotus</Emphasis> (Crustacea: Caridea: Pandalidae)

Most pandalid shrimps show protandric hermaphroditism, and male sexual differentiation is considered to be controlled by the androgenic gland. In the present study, we examined the histology of gonadal development during the male phase and sex change and the involvement of the androgenic gland in regulating male reproduction in laboratory-maintained Pandalus hypsinotus. Juvenile shrimps developed testicular tissues in the peripheral part of gonads during the age of 16–31 months and produced spermatozoa between 34 and 36 months. After reaching sexual maturity, male shrimps exhibited seasonal testicular development: active production of spermatozoa (February–May), disappearance of spermatozoa (spent, April–June), increase of spermatocytes (May–November), appearance of spermatids and spermatozoa in the gonads (November–February). The androgenic gland cells became larger and the rough endoplasmic reticulum in the cytoplasm developed at male sexual maturity. The cell structure shows that the androgenic gland hormone is a peptide. Furthermore, bilateral eyestalk ablation on immature male shrimps induced hypertrophy of the androgenic gland and acceleration of male sexual maturation. These results indicate the involvement of androgenic gland hormone and some eyestalk factor in regulating male sexual maturation. Over a 1-year laboratory-rearing period, some male shrimps (16.7%) changed sex. In transitional shrimps, testicular tissues in the gonads and androgenic glands degenerated; on the other hand, oocytes started yolk protein accumulation and hemolymph vitellogenin levels became high. These results suggest that androgenic gland degeneration is a trigger for sex change and that the vitellogenin level is a useful marker for sex change.