Reproductive traits and relative gonad expenditure of the sexes of the free spawning Chiton articulatus (Mollusca: Polyplacophora)

ABSTRACT

Reproductive studies of an intertidal free-spawning population of Chiton articulatus (Mollusca: Polyplacophora) from Puerto Angel, Oaxaca, Mexico were undertaken during 2011. We used gonad histology and gonadal indices to assess the relative gonad expenditure of the sexes (RGES) and other reproductive traits, accounting for individual and seasonal variation within this population. At this location, C. articulatus is gonochoric, without sexual dimorphism, except internally by gonad colour (testis is ‘salmon’ coloured and ovary olive green). Annual and monthly sex ratios (m/f) do not differ significantly from 1:1. Highest population-level gonadosomatic index (GSI) corresponded to maximum (peak) ripe stage (i.e. maximum gonad investment), with a first peak in May with a high value (8.4 ± 0.5) and a second peak during August-September with a lower value (4.7 ± 0.3). GSI fluctuated throughout year implying that gonad expenditure may be seasonally constrained, but with overall synchrony between sexes of ripe and spawning stages. July to December was the main reproductive season with some facultative spawning occurring off-season. Ripe and spawning RGES did not differ between sexes, suggesting that either sperm competition is intense and/or that sperm limitation is high. Early spawning individuals may quickly replenish their gametes for a second phase of gamete release later.

Abbreviations: RGES: relative gonad expenditure of the sexes; GSI: gonadosomatic index; GDS: gonad developmental stages; MiMI: microscopic maturity index; SST: sea-surface temperature.     

Latitudinal variation in monthly-scale reproductive synchrony among Acropora coral assemblages in the Indo-Pacific

Early research into coral reproductive biology suggested that spawning synchrony was driven by variations in the amplitude of environmental variables that are correlated with latitude, with synchrony predicted to break down at lower latitudes. More recent research has revealed that synchronous spawning, both within and among species, is a feature of all speciose coral assemblages, including equatorial reefs. Nonetheless, considerable variation in reproductive synchrony exists among locations and the hypothesis that the extent of spawning synchrony is correlated with latitude has not been formally tested on a large scale. Here, we use data from 90 sites throughout the Indo-Pacific and a quantitative index of reproductive synchrony applied at a monthly scale to demonstrate that, despite considerable spatial and temporal variation, there is no correlation between latitude and reproductive synchrony. Considering the critical role that successful reproduction plays in the persistence and recovery of coral reefs, research is urgently needed to understand the drivers underpinning variation in reproductive synchrony.

     

Ultrastructure of sperm and male reproductive system in Lineus viridis (Heteronemertea, Nemertea)

Nemerteans possess serially arranged gonads that lie between the midgut pouches. In both sexes the gonads are lined with an epithelium. During maturity, they gain contact to the exterior by a ciliated duct, which is generally assumed to be a derivative of the gonad. Gonad lining and sperm ultrastructure are little known in heteronemerteans, a group of nemerteans belonging to the Anopla, one of the two large nemertean subgroups. Reproduction biology in heteronemertean Lineus viridis allows predicting a modified sperm type, so-called introsperm for this taxon. Nothing is known on the fate of the testes at the end of the reproductive period of this perennial species. In order to test the predictions and to broaden the data base, males of L. viridis were collected at different times of the year. Histological and ultrastructural data show that the gonad wall is lined with different aciliated endothelial cells and germ cells, while the gonoduct is formed by densely ciliated cells. The testes are completely filled with sperm cells during maturity; there is no hint at ongoing spermiogenesis at this time. The sperm consists of head, midpiece and tail. Externally, head and midpiece cannot be discriminated. The acrosome is cup-shaped and lies anterior to the nucleus which contains 6–8 lateral ridges. Three long mitochondria mark the midpiece. They line the posterior section of the nucleus and extend up to the level of the ciliary basal structures. The sperm morphology corroborates the predictions derived from the mode of reproduction. At the end of the reproductive period the male gonads change cellular composition, while the gonoduct degenerates. Provided that both sexes show the same growth rate, male offspring acquire sexual maturity earlier than female offspring, since L. viridis males are always smaller than the females. In contrast to the males, females keep their gonads and gonoducts during most time of the year. Since large males were never found within the studied population, these data indicate that L. viridis might be a consecutive hermaphrodite.     

The multiple spawning pattern of weakfish in the Chesapeake Bay and Middle Atlantic Bight

Weakfish Cynoscion regalis were collected from commercial fisheries in the Chesapeake Bay and the Middle Atlantic Bight (n=4380) during 1989–1992 and their reproductive biology assessed using the gonadosomatic index, macroscopic gonad stages, oocyte diameter distributions, microscopic whole oocyte analysis and histology. Sex ratios were approximately 3:1, females to males, in 1990–1992. Most fish (90%) attained sexual maturity by age 1 and at a small size. Estimated mean length at first maturity was: 164mm total length (TL) for males, and 170 mm TL for females. Weakfish spawn within the Chesapeake Bay, as far north as the Virginia/ Maryland border. Although spawning occurred during May–August and gonad development and initiation of spawning was synchronous, cessation of spawning was asynchronous. There was no indication that older fish exhibited a more extended spawning season than younger fish. Weakfish are multiple spawners with indeterminate fecundity. Oocyte development is asynchronous with oocytes of all stages being present in developed ovaries. Because of the complex and dynamic weakfish ovarian cycle, typical methods of assessing reproduction, such as the GSI and macroscopic gonad stages, are inadequate for this species if not used in conjunction with more detailed methods such as histology.     

An analysis of the reproductive pattern in the sea star Astropecten irregularis (Pennant) from the Bristol Channel

Summary

The reproductive cycle in Astropecten irregularis is described, making use of a range of statistical techniques detailed previously. Analysis of gonad weights proved more satisfactory than the use of gonad indices, as the latter are not independent of animal size. When examining the course of oogenesis, standardised residuals in an (R × C) contingency table are much easier to interpret than size/frequency polygons.

The species has an annual cycle with spawning in June or July, but the gonads are small even when the animals are gravid, and the annual cycle in gonad weights is more marked in males. Proliferation of oogonia may apparently occur at any time of year, and the ripe ovary contains many small, previtellogenic oocytes. There is an annual cycle of small magnitude in the size of the pyloric caecum, with a peak in December.     

Seasonal changes of progesterone and testosterone concentrations throughout gonad maturation stages of the Mexican octopus,Octopus maya (Octopodidae: Octopus)

Variations in progesterone (P₄) and testosterone (T) levels in the gonad of Octopus maya from Sisal in Yucatan State, Mexico, were investigated by radioimmunoassays and in relation to four gonad maturation stages (GMS) and to the reproductive cycle, as represented by two maturity indices (microscopic ‘MiMI’ and macroscopic ‘MaMI’). According to the GMS and the maturity indices, the reproductive season of O. maya from Yucatan occurred from February to June. In females, P₄ and T displayed the same pattern, with a tendency to increase at the same time, although on average, P₄ had seven-fold higher concentrations than T. In contrast, P₄ and T in male gonads displayed a different pattern, where T concentrations were relatively stable throughout all of the study months. In the female gonad P₄ was lowest (close to 0 pg?g^–1) during both developing (GMS-I) and maturing (GMS-II) stages, and increased (189?±?53?pg?g^–1) approaching the mature stage (GMS-III) to a maximum value of 611?pg?g^–1. Concentrations of T in the male gonad were lowest (106?±?9?pg?g^–1) during the maturing stage (GMS-II) and increased up to the mature stage (GMS-III), reaching a maximum of 440?pg?g^–1. Pearson's correlation (r) between hormones and maturity indices showed strong relationships for females (around 0.4 and ?0.7; p?<?0.05), but there were negligible or weak relationships for males (0.2 and ?0.1; p?>?0.05). Hormone correlations in females were inverse with MaMI and direct with MiMI. Our major findings showed that gonadal P₄ levels were elevated during GMS-III and GMS-IV (i.e. periods of vitellogenic oocytes), where the characteristic aspect is an ovary with very high oocyte diameters, with the primary follicle cells deeply infolded in the ooplasm for yolk synthesis. These results suggested a synchrony between P₄ and the process of folliculogenesis, and in turn, vitellogenesis.     

Reproductive cycle of the sea cucumber Holothuria (Platyperona) sanctori (Holothuroidea: Echinodermata) in the southwestern Mediterranean Sea: interpopulation variability

This study is a first contribution on the reproductive biology of Holothuria (Platyperona) sanctori from the Algerian coastline in the southwestern Mediterranean. Sampling was conducted at two sites in central Algeria, one (Ain Taggourait, w. Tipasa) where there is little anthropogenic influence and another (Tamentefoust, w. Alger) where there are two major sources of pollution from Oued el Harrach and Oued el Hamiz effluents which contain particulate organic matter. Significant differences in sea cucumber reproduction were observed between the two sites. This could be due to the difference in organic matter noted in the sediment of the two study sites. However, temporal similarities of the gonad index (GI) and the sexual maturity stages suggest that the reproductive cycle of H. (P.) sanctori is annual with the main spawning event taking place from June to October. Spawning is of high intensity in the Bay of Bou Ismail (Ain Taggourait) and spread out over time in the Bay of Algiers (Tamentefoust), reflecting an environment sufficiently rich in food to insure reproduction. We also show that gonad maturation of males and females was synchronized. Temperature is the most likely factor influencing the reproductive cycle and spawning. At the study sites, H. (P.) sanctori had a winter sexual resting phase, followed by maturation during spring, before spawning in summer. However, there was a slight lag to the start of spawning at the two study sites.     

Histological and morphological aspects of reproduction in the sandbar shark Carcharhinus plumbeus in the U.S. south‐eastern Atlantic Ocean and Gulf of Mexico

The reproduction of the sandbar shark Carcharhinus plumbeus in the U.S. south‐eastern Atlantic Ocean including the Gulf of Mexico was examined using a combination of histological and morphological characteristics of C. plumbeus collected through fishery‐dependent and ‐independent sampling programmes (n = 1,567). Indices of maturity were constructed using measurements of gonads, reproductive tracts and claspers, and sandbar sharks exhibited 50% maturity sizes of 140 and 148 cm fork length for males and females respectively. Gonado‐somatic indices and variation in reproductive tract condition were used to determine seasonal trends in reproduction of mature C. plumbeus. Sandbar sharks have discrete seasonal reproductive cycles in which males produce sperm from January to May with a peak in May and females develop eggs from January to May with ovulation occurring in June. Females were shown to exhibit a >2 year reproductive cycle. Embryonic development was assessed through measurements of masses and lengths of uterine contents. Gestation was 12 months, from July to the following June, with parturition in late June. This research highlights a difference from previously reported data on the periodicity of female reproduction in C. plumbeus in the U.S. south‐eastern Atlantic Ocean and Gulf of Mexico, which may have major effects on future C. plumbeus stock management.     

Reproductive cycle of the European clam Ruditapes decussatus from Óbidos Lagoon,Leiria, Portugal

ABSTRACT

In Portugal, the European clam (Ruditapes decussatus) is an important commercial resource. Óbidos Lagoon is a strong candidate as a cultivation area to increase European clam exploitation. However, the reproductive biology of this population has not been described. In this work, the reproductive cycle of R. decussatus was characterized by determining gonadal development stages, gonad index, condition index, and biochemical composition. The relationship between reproduction and environmental parameters (sea surface temperature, chlorophyll a, and particulate organic matter) was assessed. Ruditapes decussatus had an annual reproductive cycle. The gametogenic cycle started in late winter, and the ripe stage in spring was followed by spawning that began at the end of spring/early summer and extended until early autumn. The subsequent period of sexual rest occurred during the winter. Condition index showed seasonal variations related to food availability (chlorophyll a). The European clams in Óbidos Lagoon recovered rapidly after their reproductive period, most likely owing to the availability of food. This study will help to improve sustainable management of this wild stock and is important for future aquaculture development of this species.     

Growth and sexual strategies in the fishThalassoma duperrey (Labridae), a protogynous hermaphrodite

Synopsis Adults of the fishThalassoma duperrey, a protogynous hermaphrodite, were collected and growth observed in captivity to study the relationship between growth and reproduction among primary males, females, and secondary males. Sexual maturity is reached at about 60 mm standard length, probably less than 1 year after fertilization. Gonosomatic index in both males and females peaks at about 120 mm, nearly 2 years later. Shortly thereafter females typically change sex, and both primary and secondary males undergo color change. At the same time gonosomatic index falls abruptly and remains low in large fish. The above changes appear to reflect differences in reproductive effort over a lifetime and are interpreted as the optimum strategy given the social and mating system of this fish. Unless they cannot acquire enough food to develop large gonads, small individuals put a much greater proportion of energy into growth than reproduction apparently to minimize the period of low fitness. Intermediate-sized males and females generally invest heavily in gametes, though some retain small gonads. Large individuals (both primary and secondary males) greatly reduce their investment in gametes, probably trading the energy required to maintain reproductive territories for it. This kind of gonad ontogeny involving gonad regression, as inT. duperrey and other labrid fishes, is unique among vertebrates.     

A maturity index for holothurians exhibiting asynchronous development of gonad tubules

The gonad morphology of the sea cucumber Isostichopus badionotus, collected during the months of May to November 1996 in Morrocoy Bay on the northwestern Venezuelan coast, was analyzed. The gonadal cycle was characterized by five stages of development: post-spawning, recovery, growth, advanced growth and maturity. Maturation did not proceed at the same pace in all gonad tubules of any one animal. Due to this asynchronous gonad development an Individual Weighted Maturity Index (IWMI) was devised to determine reproductive state. It was calculated from the proportion of the different tubule stages observed in each specimen. The maximum value attainable is 5 if all tubules are in the mature stage. Towards the months of July and August, most, but not all, of the ovarian and testicular tubules had reached maturity as indicated by IWMI values of 4.32 and 4, respectively. IWMI represents a quantitative estimation of gonad maturation in holothurians exhibiting asynchronous development as it revealed the maturation pattern underlying gonadal chronological development.     

State of the reproductive system of populations of species of the genus Glycyrrhiza L. (Fabaceae)

Reproductive features of the valuable medicinal herbs Glycyrrhiza glabra L., G. uralensis Fisch., and G. korshinskyi Grig. were investigated; an assessment was made of the state of the reproductive systems of populations located under introduction conditions in the Central Urals and in the zone contact of the species ranges in the southern cis-Urals. The states of the male and female reproductive systems, seed productivity elements, pollination features, and the viability of seeds produced by different pollination treatments were studied. For the three Glycyrrhiza species, the seed productivity indices were found to decrease considerably starting from the early stages of development of the female reproductive system and continuing to seed maturity. A quantitative analysis of seed productivity elements taking into account the flowering duration of the species showed that the seed production system of the species is very efficient; even in the introduced populations located north of the range, it is able to produce viable seeds in years with favorable growing conditions. Qualitative and quantitative indices of the reproductive system were used to characterize samples from the zone of contact between the ranges. Embryological analysis confirmed the possibility of interspecific hybridization and the prevalence of hybrid forms among the samples. A broad distribution of interspecific hybridization in Glycyrrhiza in various parts of the ranges is assumed. Glycyrrhiza species are characterized by seed and vegetative reproduction. Vegetative reproduction is limited in space but efficiently ensures reproduction of individuals and formation of vegetative clones. Seed reproduction is characterized by indices such as amphimictic seed formation, strict entomophily, and interspecific compatibility. Seed reproduction is a factor that controls the possibility of wide propagation of the genetic material in space and, hence, the formation of mixed and hybrid populations leading to a higher intraspecific and interspecific diversity of the genus.     

Reproduction of the spiny puffer, Diodon holocanthus (Pisces: Diodontidae) in the continental shelf of Mexican Central Pacific

Diodon holocanthus is an important economic and ecological species of the demersal fish community, caught as bycatch from local shrimp fishery. The reproductive biology of this long-spine porcupinefish has not yet been described, and reproductive season, the sex ratio, length distribution, length at first gonad maturity, and the gonad macro and microscopic features are described. A total of 400 organisms, ranging from 5.0 to 40.3 cm (average 18.4 cm) total length, were caught from the continental shelf of the Central Mexican Pacific, from December 1995 and December 1998. Sex ratio was 1:0.86 females to males (n = 253). The length at which 50% of the individuals showed maturing gonads was 19.7 cm for females and 20.1 cm for males. Length of the smallest organism with ripe gonads was 12.2 cm for females and 13 cm for males. Four gonadal maturation stages were found in both sexes, and five oocyte development phases were identified. The oocyte development pattern is of asynchronous type, which means the species can reproduce several times a year. Testicle development is lobular type, as in most teleost fishes. Monthly mean values of the gonad-somatic index suggest the reproduction activity peaks in June, and September-December.     

Reproductive strategy of the Patagonian catfish Hatcheria macraei

This study describes the reproductive strategy of the stream‐dwelling catfish Hatcheria macraei in the Pichileufu River, Argentina. Gonad maturity phases, classified on the basis of histological analysis, stages of gamete development and the frequency distribution of oocyte size, were correlated with macroscopic features of the gonads. Hatcheria macraei has a cystovarian ovary, asynchronous oocyte development and lobular testes. Five oocyte and four spermatogenic stages were identified and related to macroscopic gonad characteristics, making it possible to divide gonad development into five phases for females and males. Mature oocyte diameter ranged from 922 to 1935 µm. Absolute fecundity in mature females varied from 115 to 480 oocytes. Hatcheria macraei has multiple spawning during a protracted reproductive season that extends from December to April. This, together with its small size, is characteristic of an opportunistic reproductive strategy, commonly found in species that inhabit adverse and unpredictable environments, such as the low‐order rivers of Patagonia.     

Aspects of reproductive biology of wild-caught polar cod (<Emphasis Type="Italic">Boreogadus saida</Emphasis>) from Svalbard waters

Polar cod (Boreogadus saida) is considered a key species in the Arctic marine ecosystems. Yet detailed or even basic knowledge regarding its biology and adaptations, especially during the polar night, is in many cases poor. Data are presently unavailable in Western literature on the gonad development of polar cod and its reproductive biology in wild specimens. Accordingly, gonad development of wild-caught polar cod from fjords of the Svalbard archipelago was studied across seasons (April, August, September, November and January). Histological analyses of polar cod showed strong indication of a group-synchronous oocyte development with determinate fecundity and iteroparity. Females started gonadal development prior to April and had not yet reached the final stage of maturation in January. Testes matured more rapidly, with males ready to spawn in January. Furthermore, our data show that polar cod were able to reach sexual maturity at age 1+. Based on our data and previous reports, we hypothesise that polar cod is a total spawner.     

An evaluation of certain indices of eutrophy and maturity in lakes

Summary Data from five Colorado lakes were utilized to test the usefulness of net primary productivity, seston, chlorophyll a and Secchi disc transparency as indices of eutrophy. The four indices were in essential agreement as to the relative degree of eutrophication in each of the five lakes. The concept of maturity is also considered by ranking the Colorado lakes according to several maturity indices: phytoplankton diversity, zooplankton diversity, Margalef's pigment ratio, P/B ratio, and assimilation number. The relative maturity of the lakes shifts considerably, according to which maturity index one utilizes. Specific correlations between maturity indices (e.g., a positive correlation between plankton diversity and pigment ratio) as suggested by Margalef, did not occur in these five lakes. The data from the Colorado lakes suggest that maturity may not be a meaningful concept or, that if it is, it has not been adequately characterized.Contribution No. 55, Limnology Laboratory, University of Colorado, Boulder. This research was supported, in part, by Penrose Fund Grant No. 5284 from the American Philosophical Society and by NSF Grant GY 5306.     

Onset of maturity in male southern rock lobsters Jasus edwardsii in Tasmania,Australia

Summary

The reproductive contribution of male southern rock lobsters Jasus edwardsii has recently become of interest for managing this fishery as changes to the length of seasonal closures have shifted fishing effort towards males. To assess size at onset of maturity, a total of 387 male southern rock lobsters Jasus edwardsii were collected using baited traps from four of the eight fishery regions around the Tasmanian coast during July and August 2000. Sizes at onset of maturity in these samples were estimated by examining the vasa deferentia for evidence of the commencement of spermatid production. In addition, the total combined weight of the vasa deferentia and testis was compared with body size (as a gonad somatic index, GSI). Estimates of size at onset of maturity from the two methods were similar, although estimates from GSI appeared to have broader confidence limits. Although these physiological indices of maturity do not necessarily translate to functional maturity, they indicate that maturity is well below that of the legal minimum size of 110 mm carapace length used for managing the fishery (all estimates by either method for length at 50% sample maturity ≤70 mm carapace length). Production of sperm by males occurs below the size at onset of maturity of females from the same region and spatial patterns in maturity estimated by onset of spermatid production were similar to those of females.     

Mytilus galloprovincialis (Mollusca: Bivalvia) in a warm-temperate South African estuarine embayment

The distribution, population structure, condition and gonad indices, and the attachment strengths of the invasive Mediterranean mussel Mytilus galloprovincialis are described from the Knysna Estuary, South Africa. Mussels were found in the rocky intertidal at the mouth of the estuary and on all man-made hard substrata as far as 12?km from the mouth in 2013. However, mussel beds were found only in the lower reach of the estuary, where mussel densities were as high as 120 per 0.01?m². When compared to mussels from the embayment regions of the estuary, those at the estuary mouth, where wave action was high, were generally smaller, had significantly lower condition and gonad indices, and greater attachment strength. This suggests that mussels within the sheltered regions of the estuary invest more energy in growth and reproduction, and that this is one reason for their success as an invasive species in the Knysna estuarine embayment.