Oocyte Size Research Articles

Simultaneous Germinal Vesicle Migration and Oil Droplet Coalescence Predict Final Oocyte Maturation in the Leopard Grouper

AbstractThe size of oocytes during germinal vesicle migration (GVM) and germinal vesicle breakdown (GVBD) was revised for the Leopard Grouper Mycteroperca rosacea. Histology of ovaries, plasma levels of estradiol‐17ß (E2), and testosterone (T) were analyzed in Leopard Grouper at 0, 12, 16, and 24 h after a priming dose of 1,000 IU/kg body weight of human chorionic gonadotropin (hCG) and were compared with control females injected with saline solution. Histological observations were verified in hormonally induced females by observing in vivo intraovarian biopsies after using the same priming dose and a second resolving dose of 500 UI/kg body weight of hCG 16 or 24 h later, which served to analyze spawning performance. Histological and in vivo intraovarian biopsies showed that in full‐yolk oocytes (~455 μm diameter) GVM and GVBD were concomitant with coalescence of a single oil droplet 16 and 24 h after the first injection. The oil droplet became a morphological marker as well as a predicting indicator of the competence and synchronization of maximum vitellogenic oocytes and the effectiveness to respond to hormonal therapy. In the experimental fish group E2 and T reached peaks at the same time, which were significantly higher than those in the controls. Mean fecundity was 168,000 eggs/kg, mean fertilization was 88%, and mean viability was 71% (114,000 eggs/kg), all of which were within the range of other cultivated groupers. These results can be used to improve the induction of final maturation in the Leopard Grouper in captivity and may be used in other species of Mycteroperca that show the same marker.

Reproduction of Megapitaria squalida (Bivalvia: Veneridae) in the Southeast Gulf of California, Mexico

Bivalves reproductive cycle varies according to the particular environmental conditions where they are found, and these reproductive details represent basic information for their capture, management and conservation strategies. With this objective, the reproductive cycle of the clam Megapitaria squalida, inhabiting the Southeast of the Gulf of California (Altata Bay, Sinaloa, Mexico), was studied using histology and changes in the number and size of oocytes, from June 2013 to June 2014. Histological analysis of the gonads showed spawning activity throughout the year, with two peaks. The first was registered in October and it was accompanied by the highest decrease of weight; the second was in February with the highest percentage of spawning population; besides, a resting period was observed in December. The sex-ratio (female:male) of the clam population was 1.08:1 (χ2 = 5.72, d.f. = 1, P < 0.05). Mean oocyte size and number were different (P < 0.05) among all sampling months and fluctuated from 34.6 ± 5.8 µm in June 2014, to 41.9 ± 6.8 µm in February 2014, and from 443.8 ± 424.5 in February 2014, to 1 214.4 ± 267.6 counted in April, respectively. With these results we suggest a protection season from October to November, when the most intense release of gametes occur in this population.

Whole flaxseed, raw soybeans, and calcium salts of fatty acids supplementation for transition cows: follicle development and embryo quality

The objective of this study was to evaluate the effects of diets rich in omega-3 and -6 fatty acids (FA) during the transition period and early lactation on size and number of follicles, oocyte and embryo quality, and blood metabolites of Holstein cows. Forty-two cows were assigned to the diets: control (CON, with no fat sources and dietary ether extract content of 28.8 and 24.8 g/kg during the pre- and post-partum periods, respectively); whole flaxseed (WF, diet rich in omega-3 FA), 60 and 80 g/kg of WF during the pre and post-partum periods, respectively; whole raw soybeans (WS, diet rich in omega-6 FA), 120 and 160 g/kg of WS during the pre and post-partum periods; and calcium salts of unsaturated fatty acids (CSFA, diet rich in omega-6 FA), 24 and 32 g/kg of CSFA during the pre and post-partum periods. Diets were supplied from 35 d of the expected calving date until 84 days in milk (DIM). The ovaries of cows were examined from 14 to 84 DIM. Ovum pick-ups were performed on days 35 ± 7 and 65 ± 7 of lactation. Diets rich in omega-3 and -6 FA had greater follicle number than the CON. No differences were detected among diets rich in omega-3 and omega-6 FA on number and size of follicles and corpus luteum area. Cows had similar oocyte quality regardless of diet supplied. Although FA supplementation had no effect on embryo quality (number of cleaved and viable embryos), diets rich in omega-6 FA had lower viable embryos compared with WF. Supplementation with diets rich in omega-3 and -6 FA resulted in greater blood cholesterol concentration in early lactation cows. Fat supplementation increased the number of small and total follicles of early lactating cows. However, diets rich in omega-3 or -6 FA had no effect on oocyte quality. Cows fed WS during the transition period had the least viable embryos, and consequently cows fed diets rich in omega-6 FA had lower viable embryos than those fed WF.

Ovarian development in Argentinean shortfin squid Illex argentinus: group-synchrony for corroboration of intermittent spawning strategy

Modern living cephalopod species have evolved a wide phenotypic diversity and flexibility of reproductive strategies, which is closely linked to the pattern of oogenesis and oocytes ovulation of species. Although it has been suggested that Argentinean shortfin squid Illex argentinus lay eggs intermittently, there is still little evidence for the mode of oocyte production and development. In this study, the ovarian development of I. argentinus was investigated by using histological analysis of ovaries, and six distinct histological stages of ovarian development were found among the ovaries. For each histological stage of the ovary, the frequency distribution of both number and occupied areas by each oogenesis stage was unimodal, and that gradually progressed along with ovarian development. The oocyte size distribution in ovaries before reaching vitellogenic stage was unimodal, bimodal in vitellogenic ovaries, and polymodal in ripe and partially spent ovaries. This evidence indicates that I. argentinus undergoes group-synchronous ovarian development, with a single dominant oocyte stock being produced to develop in several batches for a multiple-batch group-synchronous ovulation and confirms the intermittent spawning strategy of this species.

Interactive Effects of Endogenous and Exogenous Nutrition on Larval Development for Crown-Of-Thorns Starfish

Outbreaks of crown-of-thorns starfish are often attributed to step-changes in larval survivorship following anomalous increases in nutrients and food availability. However, larval growth and development is also influenced by the nutritional condition of spawning females, such that maternal provisioning may offset limitations imposed by limited access to exogenous sources of nutrients during the formative stages of larval development. This study examined the individual, additive, and interactive effects of endogenous (maternal diet: Acropora, Porites, mixed, and starved) and exogenous (larval diet: high concentration at 104 cells·mL−1, low concentration at 103 algal cells·mL−1, and starved) nutrition on the survival, growth, morphology, and development of larvae of the crown-of-thorns starfish. Female starfish on Acropora and mixed diet produced bigger oocytes compared to Porites-fed and starved treatments. Using oocyte size as a proxy for maternal provisioning, endogenous reserves in the oocyte had a strong influence on initial larval survival and development. This suggests that maternal reserves can delay the onset of obligate exogenous food acquisition and allow larvae to endure prolonged periods of poor environmental nutritive conditions or starvation. The influence of exogenous nutrition became more prominent in later stages, whereby none of the starved larvae reached the mid-to-late brachiolaria stage 16 days after the onset of the ability to feed. There was no significant difference in the survival, development, and competency of larvae between high and low food treatments. Under low algal food conditions, larvae compensate by increasing the length of ciliated feeding bands in relation to the maximum length and width, which improve food capture and feeding efficiency. However, the effects of endogenous nutrition persisted in the later developmental stages, as larvae from starved females were unable to develop larger feeding structures in response to food-limiting conditions. Phenotypic plasticity influenced by endogenous provisions and in response to exogenous food availability may be an important strategy in boosting the reproductive success of crown-of-thorns starfish, leading to population outbreaks.

On the Dolly Varden’s Salvelinus malma (Salmonidae) biology in Kamchatkan spawning rivers of the volcanic areas

Anadromous and stream resident Dolly Varden S. malma were compared in the contaminated and reference rivers across Kamchatka region. Anadromous Dolly Varden’s fry from the polluted and clean rivers were correspondently different by reduced growth rate and narrow length variability. It was observed that juveniles prefer to migrate from the polluted river sections; only seldom fry reaches the smoltification stage at the contaminated sites. The volcanogenic environmental pollution causes paedomorphosis and accelerated sexual maturation in the landlocked brook-dwelling populations. Either the growth rate or the length variability within the age groups were not reduced during the maturation period in the landlocked groups comparing with fish from reference streams. However the weakened individuals with an extremely low body weight were observed among the landlocked fish during maturing. Gonadosomatic index and relative fecundity were comparable for fish from polluted and clean rivers, though relatively high fecundity for the first group was attained by the oocytes size decreasing. Skin cover was damaged; Clark’s condition index and muscle fatness were reduced while liver size was enlarged in either landlocked or anadromous fishes from the polluted water-courses.

Fecundity regulation strategy of the blue jack mackerel, Trachurus picturatus (Bowdich, 1825), off Madeira Island (NE Atlantic)

This contribution intends to verify the type of fecundity regulation of the blue jack mackerel. For this purpose, the oocyte development process was analysed. A total of 158 ovaries were sampled between January 2009 and April 2010 from purse-seiners operating in the Madeira Island waters, NE Atlantic Ocean. Histological analysis and visual image analysis system were used to study the four main criteria applied for fecundity type determination: (1) presence of a hiatus between pre-vitellogenic and vitellogenic oocytes; (2) number of standing stock of advanced vitellogenic oocytes over the spawning season; (3) mean size of standing stock of advanced vitellogenic oocytes over the spawning season; and (4) the incidence of atresia over the spawning season. The analysis of the oocytes size frequency distribution showed that no distinct hiatus could be observed between pre-vitellogenic and vitellogenic oocytes during the spawning season. Considering the whole spawning period but the last month that was poorly sampled, the number of standing stock of advanced vitellogenic oocytes showed no decrease trend along the spawning season, the mean diameter of cortical alveoli oocytes and of the advanced stock of vitellogenic oocytes did not increase over the spawning season and the relative intensity of atresia was always high throughout this period. These findings suggest the blue jack mackerel displays an indeterminate fecundity.

Estimating fecundity using image analysis in Cervimunida johni and Pleuroncodes monodon

Fecundity is directly related to the reproductive potential in all exploited marine species. The gravimetric method has been widely used for the estimation of fecundity in the commercially valuable squat lobsters Cervimunida johni and Pleuroncodes monodon due to its simplicity and precision. However, the procedure is time-consuming because it requires counting of all eggs from the subsample. The fecundity of some fish species has been successfully estimated using the autodiametric method, which consists of the conversion of oocyte size into oocyte density per weight of the ovary. The purpose of this study was to apply and assess an automated image analysis and the autodiametric method for the estimation of fecundity in C. johni and P. monodon. A total of 204 ovigerous females of C. johni and 176 of P. monodon were collected from a fishing survey in August 2015. The results showed that the “counting error” was lower than 12% in the particles analyzed in both squat lobster species. In addition, the “measurement error” generated an average particle exclusion of 16% and 42% for the measurement of egg size in C. johni and P. monodon females, respectively. During the processing time to analyze the mass of eggs from a female in laboratory, the autodiametric method proved to be faster and more efficient because it lasted on average 61% and 73% less than the gravimetric method in C. johni and P. monodon, respectively. The potential fit between the volume-based mean egg diameter (DV) and egg density (g−1 egg mass) was significant for both species. The relationship between female size and fecundity was significant for both squat lobster species. Furthermore, the analysis of covariance indicated that the coefficients were not significantly different between both methods. We discussed the autodiametric procedure and the precision of fecundity estimates for both squat lobster species.

Gametogenesis and Spawning of the Ribbed Mussel (Geukensia demissa) near the Northern Limit of its Range (Maritime Canada)

Ribbed mussels (Geukensia demissa) help form the basis of highly productive salt marshes along the Atlantic coast of North America, in southern New England, and further south. Little is known about their ecology and reproductive biology at more northern latitudes (Maritime Canada; >43o N). As a step in determining the sustainability of ribbed mussel populations near the northern limit of their range (Northumberland Strait, Gulf of St. Lawrence, Canada), gametogenesis and spawning were monitored over 3 years (May–August 2012, June–November 2014, and April–October 2015) at four sites spanning ~100 km of coastline. These sites are typically ice-covered from mid-December to March or April. The onset of gametogenesis was later, the reproductive stages on any given date were more varied, and the reproductive season was shorter than for southern populations of ribbed mussels. Oocyte density and size did not vary among sites, indicating similar site-level processes, but did vary among years. Oocyte density and size varied greatly among mussels at a given site, and within a single gonad. This highlights the importance of individual variability, perhaps related to mussel location within a marsh, and the effects of nutrients and temperature on gonads. Accounting for the individual-level variability, reproductive output was estimated at ~105 oocytes per ripe female mussel, which is within the fecundity estimates for other marine bivalve broadcast spawners.

Ovarian Maturation Stages of Wild and Captive Mud Crab, Scylla olivacea Fed with Two Diets

This study was aimed to determine the ovarian maturation stages of wild and captive orange mud crab, Scylla olivacea fed with different diets via gonadosomatic status, oocyte diameter and histological examinations. Captive crabs were fed with blood cockle, Anadara granosa, or fish, Decapterus spp. Through the histological examinations, ovarian maturation stages of wild and captive S. olivacea was classified into four stages: Immature (Stage 1), Early maturing (Stage 2), Pre-maturing (Stage 3) and Fully matured (Stage 4). Gonadosomatic Index of wild and captive crabs remained low during immature and 2 but increased significantly (p<0.05) in pre-maturing and 4 ovaries. Oocytes size were significantly different (p<0.05) in all ovarian maturation stages of wild and captive crabs. Follicle cells surround the oocyte of immature ovary and small yolk globules start to appear in early maturing ovary with large nucleus size. Oocyte size increased significantly (p<0.05) and yolk globule obviously appeared in pre-maturing ovary. Large and fused yolk globules appeared in the oocytes of fully matured ovary with nucleus was barely visible. The present study revealed that, ovarian maturation stages of S. olivacea are closely related to its morphological appearance and cellular development.

Reproductive traits of the freshwater oyster Etheria elliptica (Bivalvia: Etheriidae) in the Pendjari River, Benin: implications for conservation

The African freshwater oyster Etheria elliptica, which is of great economic importance throughout the continent, is facing overharvesting in many fisheries in West Africa. Its reproductive traits (sex ratio, size at sexual maturity, oocyte diameter and fecundity) were studied at four stations located along the Pendjari River, northern Benin, in April 2013. Histological techniques were implemented to identify sex and gonad development stages. Oocyte sizes were measured based on the histological images and mean oocyte diameter was 38 µm. Fecundity, estimated by counting the developing eggs, averaged 106 724 eggs and increased significantly with shell size. The average sex ratio was approximately 1:1. Hermaphrodites were rare. Males reached sexual maturity at 57.6 mm dorsoventral height, earlier than females at 64.7 mm. The majority of the oyster specimens were in ripe-spawning stages, indicating that reproductive activities partly took place towards the end of the dry season. Both mature and immature individuals were subjected to harvesting at all the investigated fishing sites. The mean size of exploited oysters was 60.6 mm, lower than the size of females at maturity. Management strategies must enforce the minimum size of 65 mm required for harvesting, particularly in open access sites where juveniles are mostly harvested.

Gastrulation in Cnidaria: The key to an understanding of phylogeny or the chaos of secondary modifications?

The data revealed by comparative embryology of basal (diploblastic) metazoans are traditionally considered a valuable potential source of information on the origin and early evolution of the animal kingdom and its major clades. Special attention is paid to the fundamental morphogenetic process of gastrulation, during which the cells of the early embryo differentiate into germ layers and the primary body plan is formed. Comparative analysis of gastrulation in different cnidarian taxa reveals a high level of intergroup, intragroup, and individual variation. With few exceptions, there is no robust correlation between the gastrulation type and the taxon. Current data do not support the idea that the morphogenetic processes underlying cnidarian gastrulation can be divided into several distinct types. Rather, there is a continuum of equifinal ontogenetic trajectories. In cnidarians, the mode of gastrulation apparently depends less on the macroevolutionary history of the species than on various evolutionary plastic features, such as the oocyte size, amount of yolk, number of cells at the blastula (or morula) stage, presence of phototrophic symbionts, or larval ecology. Thus, in cnidarians, the morphogenetic basis of gastrulation contains only a very weak phylogenetic signal and can have only limited application in phylogenetic reconstructions. On the other hand, comparative studies of the ontogeny of basal metazoans shed light on the general rules of the evolution of morphogenetic processes, which is crucial for an understanding of the early history of the animal kingdom.

Dietary saccharides and sweet tastants have differential effects on colonization of Drosophila oocytes by Wolbachia endosymbionts.

ABSTRACTWolbachia bacteria are widespread, maternally transmitted endosymbionts of insects. Maintenance of sufficient Wolbachia titer in maternal germline cells is required for transmission efficacy. The mechanisms that regulate Wolbachia titer are not well understood; however, dietary sucrose was reported to elevate oocyte Wolbachia titer in Drosophila melanogaster whereas dietary yeast decreased oocyte titer. To further investigate how oocyte Wolbachia titer is controlled, this study analyzed the response of wMel Wolbachia to diets enriched in an array of natural sugars and other sweet tastants. Confocal imaging of D. melanogaster oocytes showed that food enriched in dietary galactose, lactose, maltose and trehalose elevated Wolbachia titer. However, oocyte Wolbachia titers were unaffected by exposure to the sweet tastants lactulose, erythritol, xylitol, aspartame and saccharin as compared to the control. Oocyte size was generally non-responsive to the nutrient-altered diets. Ovary size, however, was consistently smaller in response to all sugar- and sweetener-enriched diets. Furthermore, most dietary sugars administered in tandem with dietary yeast conferred complete rescue of oocyte titer suppression by yeast. All diets dually enriched in yeast and sugar also rescued yeast-associated ovary volume changes. This indicates oocyte colonization by Wolbachia to be a nutritionally sensitive process regulated by multiple mechanistic inputs.

Oocyte Quality Control: Causes, Mechanisms, and Consequences.

Oocyte quality and number are key determinants of reproductive life span and success. These variables are shaped in part by the elimination of oocytes that experience problems during the early stages of meiosis. Meiotic prophase-I marks an extended period of genome vulnerability in which epigenetic reprogramming unleashes retroelements and hundreds of DNA double-strand breaks (DSBs) are inflicted to initiate the programmed recombination required for accurate chromosome segregation at the first meiotic division. Expression of LINE-1 retroelements perturbs several aspects of meiotic prophase and is associated with oocyte death during the early stages of meiotic prophase I. Defects in chromosome synapsis and recombination also trigger oocyte loss, but typically at a later stage, as cells transition into quiescence and form primordial follicles. Interrelated pathways that signal defects in DSB repair and chromosome synapsis mediate this late oocyte attrition. Here, I review our current understanding of early and late oocyte attrition based on studies in mouse and describe how these processes appear to be both distinct and overlapping and how they help balance the quality and size of oocyte reserves to maximize fecundity.

Quantitative determination of ovarian development in penaeid prawns (Decapoda: Penaeidae)

We developed histological methods to increase precision in measuring oocyte size and, for the first time, quantify changes in oocyte composition during ovarian development in penaeids. Wild-caught female Metapenaeus dalli Racek, 1957 from the Swan-Canning Estuary, Perth, Western Australia were used as a model species to compare the novel method to traditional techniques. Morphological analysis showed that ovarian development in M. dalli occurs in five stages: immature, early maturing, late maturing, mature, and post spawning, which is consistent with other penaeids. Analysis of key morphometric parameters of length and Gonad Somatic Index (GSI) showed that GSI provided the strongest discriminators of ovarian development. Oogenesis was similar to qualitative descriptions of other penaeid prawns and most-closely related to previous descriptions of Metapenaeus affinis Milne Edwards, 1837. Comparisons between the novel perimeter tracing and traditional single linear methods for measuring oocyte dimensions showed that greater precision was achieved by tracing. This resulted in a 17-40% reduction in the confidence limits of the means for all cell types measured. A novel histological technique of examining oocyte composition was also developed. This technique allowed for the relationship between stages of ovarian development and proportion by volume of oocyte types to be determined. The difference in the proportions of cell types between each stage of ovarian development was found to be statistically significant, except between immature and post spawning females. The novel methods developed in this study provide new opportunities in the study of ovarian development in penaeids and possibly in other species.

Analysis of the reproductive cycle of female wild marble trout Salmo marmoratus in a prealpine brook of the Soča River basin (Northeast Italy)

The reproductive cycle of female wild marble trout Salmo marmoratus was studied in a prealpine watercourse (Northeast Italy). Gonadosomatic index, oocyte growth and plasma levels of 17β-oestradiol and testosterone were bimonthly measured during one year to obtain a detailed dataset and to gain useful tools for the identification of the reproductive stage without impact for the species. Monitored features showed significant variations during the study period: gonadosomatic index and oocyte size increased slightly but significantly during the first part of the cycle (from February to June), while steroid levels remained quite constant; for all parameters, major increases were highlighted between August and the spawning season (which occurred from the middle of November to the middle of December). Ranges and trends observed for gonadosomatic index (from 0.87 ± 0.41% to 10.91 ± 3.37%) and oocyte diameter (from 0.692 ± 0.031 mm to 4.624 ± 0.208 mm) were generally in agreement with literature regarding salmonids, while plasma levels of 17β-oestradiol (from 0.214 ± 0.015 ng ml−1 to 78.090 ± 23.882 ng ml−1) and testosterone (from 0.327 ± 0.086 ng ml−1 to 71.800 ± 29.406 ng ml−1) showed wider ranges. A strong non-linear relationship was found between oocyte size and 17β-oestradiol plasma concentration (r2 = 0.890) and especially between oocyte size and testosterone plasma concentration (r2 = 0.947). This last relationship could likely be used to obtain information relative to the gonadal development, especially in the case of an endangered species like Salmo marmoratus, which needs non-invasive tools for management.

Serine threonine kinase receptor associated protein regulates early follicle development in the mouse ovary.

The molecular mechanisms involved in regulating the development of small, gonadotrophin-independent follicles are poorly understood; however, many studies have highlighted an essential role for TGFB ligands. Canonical TGFB signalling is dependent upon intracellular SMAD proteins that regulate transcription. STRAP has been identified in other tissues as an inhibitor of the TGFB-SMAD signalling pathway. Therefore, in this study we aimed to determine the expression and role of STRAP in the context of early follicle development. Using qPCR, Strap, Smad3 and Smad7 revealed similar expression profiles in immature ovaries from mice aged 4-16 days containing different populations of early growing follicles. STRAP and SMAD2/3 proteins co-localised in granulosa cells of small follicles using immunofluorescence. Using an established culture model, neonatal mouse ovary fragments with a high density of small non-growing follicles were used to examine the effects of Strap knockdown using siRNA and STRAP protein inhibition by immuno-neutralisation. Both interventions caused a reduction in the proportion of small, non-growing follicles and an increase in the proportion and size of growing follicles in comparison to untreated controls, suggesting inhibition of STRAP facilitates follicle activation. Recombinant STRAP protein had no effect on small, non-growing follicles, but increased the mean oocyte size of growing follicles in the neonatal ovary model and also promoted the growth of isolated preantral follicles in vitro Overall findings indicate STRAP is expressed in the mouse ovary and is capable of regulating development of small follicles in a stage-dependent manner.

Sexual reproduction in the Caribbean coral genus Isophyllia (Scleractinia: Mussidae).

The sexual pattern, reproductive mode, and timing of reproduction of Isophyllia sinuosa and Isophyllia rigida, two Caribbean Mussids, were assessed by histological analysis of specimens collected monthly during 2000–2001. Both species are simultaneous hermaphroditic brooders characterized by a single annual gametogenetic cycle. Spermatocytes and oocytes of different stages were found to develop within the same mesentery indicating sequential maturation for extended planulation. Oogenesis took place during May through April in I. sinuosa and from August through June in I. rigida. Oocytes began development 7–8 months prior to spermaries but both sexes matured simultaneously. Zooxanthellate planulae were observed in I. sinuosa during April and in I. rigida from June through September. Higher polyp and mesenterial fecundity were found in I. rigida compared to I. sinuosa. Larger oocyte sizes were found in I. sinuosa than in I. rigida, however larger planula sizes were found in I. rigida. Hermaphroditism is the exclusive sexual pattern within the Mussidae while brooding has been documented within the related genera Mussa, Scolymia and Mycetophyllia. This study represents the first description of the sexual characteristics of I. rigida and provides an updated description of I. sinuosa.

In vitro growth and maturation of isolated caprine preantral follicles: Influence of insulin and FSH concentration, culture dish, coculture, and oocyte size on meiotic resumption

The aims of this study were: (1) to evaluate the effect of different insulin concentrations, alone or in combination with either a fixed FSH concentration or increasing FSH concentrations on the in vitro culture of isolated caprine preantral follicles and (2) to analyze the efficiency of two IVM media and maturation culture systems (with or without coculture with in vivo grown oocytes) on the meiosis resumption. Secondary follicles were cultured for 18 days in a basic medium supplemented with low- or high-insulin concentration alone or with a fixed FSH concentration or with increasing FSH concentrations. Oocytes grown in vivo or in vitro were matured alone or cocultured. The high-insulin concentration associated with fixed FSH treatment had higher meiotic resumption rate (P < 0.05) and was the only treatment capable of producing oocytes in metaphase II. The rates of germinal vesicle, germinal vesicle breakdown, metaphase I, metaphase II (MII), meiotic resumption, and oocyte diameter were similar between the maturation media. In conclusion, a basic medium supplemented with 10-μg/mL insulin and 100-μg/mL FSH throughout the culture period improved meiotic resumption rate and produced MII oocytes from caprine preantral follicles cultured in vitro. The MII rate was similar between in vivo and in vitro grown oocytes ≥110 μm.

Reproductive Seasonality of the Antarctic Sea Pen Malacobelemnon daytoni (Octocorallia, Pennatulacea, Kophobelemnidae).

The pennatulid Malacobelemnon daytoni is one of the dominant species in Potter Cove, Antarctica. Its abundance and range of distribution have increased in recent years probably related to climate change mediated alterations of environmental factors. This work is the second part of a study dealing on the reproductive ecology of Malacobelemnon daytoni, and aims to assess its reproductive seasonality over a two-year period. Sampling was carried out every month during 2009–2010 and samples were examined by histological analysis. Gametogenesis exhibited a seasonal pattern evidenced by the maturity stage index (MSI) and the number of mature oocytes and cysts throughout the year. Immature oocytes and spermatocytes were present year-round, but maturation was seasonal and it seems that more than one spawning per year was possible. These spawnings could be more linked with suspended particulate matter (SPM) (probably available via resuspension events) than with primary production pulses. This idea reinforces the hypothesis that winter time is not so stressful, in energy terms, in Potter Cove, which seems to depend on energy sources other than local phytoplankton production. There was not a strong inter-annual variability between the reproductive characteristics analyzed in 2009 and 2010; the only variable different was the size of oocytes (higher in 2009), suggesting different energy availability in each year, related with a higher concentration of SPM in 2009 (although it was not significant). Malacobelemnon daytoni could be the first reported Antarctic suspension feeder species that presents a reproductive cycle with more than a spawning event per year. This strategy would help to explain the success of this species in the Potter Cove ecosystem and in high ice-impacted areas.