Reproductive Peak Research Articles

Is bigger better? The relationship between size and reproduction in female Asian elephants.

The limited availability of resources is predicted to impose trade-offs between growth, reproduction and self-maintenance in animals. However, although some studies have shown that early reproduction suppresses growth, reproduction positively correlates with size in others. We use detailed records from a large population of semi-captive elephants in Myanmar to assess the relationships between size (height and weight), reproduction and survival in female Asian elephants, a species characterized by slow, costly life history. Although female height gain during the growth period overlapped little with reproductive onset in the population, there was large variation in age at first reproduction and only 81% of final weight had been reached by peak age of reproduction at the population level (19years). Those females beginning reproduction early tended to be taller and lighter later in life, although these trends were not significant. We found that taller females were more likely to have reproduced by a given age, but such effects diminished with age, suggesting there may be a size threshold to reproduction which is especially important in young females. Because size was not linked with female survival during reproductive ages, the diminishing effect of height on reproduction with age is unlikely to be due to biased survival of larger females. We conclude that although reproduction may not always impose significant costs on growth, height may be a limiting factor to reproduction in young female Asian elephants, which could have important implications considering their birth rates are low and peak reproduction is young - 19years in this population.

Reproductive and recruitment dynamics of clionaid sponges on oyster reefs in North Carolina

AbstractBoring sponges belonging to the family Clionaidae have become a destructive nuisance to eastern oyster (Crassostrea virginica) aquaculture and restoration efforts in the southeastern USA. Clionaid sponges colonize the inner layers of oyster shells and remove carbonate material, compromising the quality and marketability of the oyster; however, relatively little is known about reproduction and recruitment of these sponges. Using histological techniques, reproductive activity of clionaid sponges was monitored at two sites (Cedar Island and Masonboro Sound) in coastal North Carolina. Sponge recruitment to limestone tiles (5×5 cm), oyster shells, and clam shells was monitored in 2013 and 2014; recruitment to the limestone tiles was statistically higher than recruitment to clam or oyster shells. Overall, seasonal patterns in reproduction and recruitment of clionaid sponges were generally similar at the two sites. Three species of clionaid sponge were found during field sampling (Cliona celata, C. lobata, and C. truitti), and reproductive activity (eggs and spermatocysts) of these species was observed from April to November, with peak reproduction occurring from June to September for C. lobata and from August to September for C. celata. Recruitment peaked in late summer/early fall. Additionally, the relationship between environmental conditions (temperature, salinity, dissolved oxygen, pH, and chlorophyll a) and clionaid recruitment was explored using a regression model. At Cedar Island, the best‐fit model included salinity and dissolved oxygen, while the best‐fit model at Masonboro Sound included temperature, pH, and salinity. The data from this study show that the primary reproduction and recruitment pulses occur in the fall for local clionaids, and thus mitigation strategies should be applied in the late fall or winter to minimize infestations.

Reproductive cycles in tropical intertidal gastropods are timed around tidal amplitude cycles.

Reproduction in iteroparous marine organisms is often timed with abiotic cycles and may follow lunar, tidal amplitude, or daily cycles. Among intertidal marine invertebrates, decapods are well known to time larval release to coincide with large amplitude nighttime tides, which minimizes the risk of predation. Such bimonthly cycles have been reported for few other intertidal invertebrates. We documented the reproduction of 6 gastropod species from Panama to determine whether they demonstrate reproductive cycles, whether these cycles follow a 2‐week cycle, and whether cycles are timed so that larval release occurs during large amplitude tides. Two of the species (Crepidula cf. marginalis and Nerita scabricosta) showed nonuniform reproduction, but without clear peaks in timing relative to tidal or lunar cycles. The other 4 species show clear peaks in reproduction occurring every 2 weeks. In 3 of these species (Cerithideopsis carlifornica var. valida, Littoraria variegata, and Natica chemnitzi), hatching occurred within 4 days of the maximum amplitude tides. Siphonaria palmata exhibit strong cycles, but reproduction occurred during the neap tides. Strong differences in the intensity of reproduction of Cerithideopsis carlifornica, and in particular, Littoraria variegata, between the larger and smaller spring tides of a lunar month indicate that these species time reproduction with the tidal amplitude cycle rather than the lunar cycle. For those species that reproduce during both the wet and dry seasons, we found that reproductive timing did not differ between seasons despite strong differences in temperature and precipitation. Overall, we found that most (4/6) species have strong reproductive cycles synchronized with the tidal amplitude cycle and that seasonal differences in abiotic factors do not alter these cycles.

Reproductive biology of Philodryas patagoniensis (Snakes: Dipsadidae) in south Brazil: Female reproductive cycle

AbstractIn this study, we describe the female reproductive cycle of Philodryas patagoniensis in south Brazil, which was described through morpho‐anatomical and histological analyses. The peak of secondary vitellogenesis occurred during winter–spring (July–December), ovulation in spring (October–December), mating and fertilization in spring–summer (October–February), oviposition in spring–autumn (October–May) and births from late spring to autumn (December–July). The diameter of vitellogenic follicles/eggs was larger in winter–spring than in other seasons. The diameter of the shell glands was also larger in winter–spring. In spite of the clear reproductive peak, gonads only showed reduced activity in the autumn. Therefore, at the individual level, females have a discontinuous cyclical reproduction; in the populational level, the reproductive cycle is seasonal semisynchronous. We support the hypothesis that P. patagoniensis have the ability to produce multiple clutches with long‐term stored sperm. Sexual dimorphism in body size was evident, and females are significantly larger and heavier than males. Larger females were able to produce follicles and eggs in larger amount and size. The maternal body size was positively related to the reproductive effort and fecundity. To conclude, we deliberated about the proximal and distal causes that influence the reproductive traits and patterns of P. patagoniensis.

Ciclo reproductor e índices de condición usados en Melongena corona (Mollusca: Gastropoda)

Melongena corona bispinosa was studied in Yucatan, Mexico (21°16' N, 89° 49' W) for a year. Males have reproductive peaks in February and December, and a post-copulation peak in June. Female peaks are in March and May, plus oviposition peaks in April and January. Males and females differ in the mean gonadosomic index (F= 13.79, p<0.05) but not in the dry tissue/shell weight (F= 0.0902, p<0.05), dry tissue and total weight (F= 0.2466, p<0.05) and dry tissue weighl/internal shell volume (F= 1.0565, p<0.05).

Geographical and temporal variation in environmental conditions affects nestling growth but not immune function in a year-round breeding equatorial lark

BackgroundVariation in growth and immune function within and among populations is often associated with specific environmental conditions. We compared growth and immune function in nestlings of year-round breeding equatorial Red-capped Lark Calandrella cinerea from South Kinangop, North Kinangop and Kedong (Kenya), three locations that are geographically close but climatically distinct. In addition, we studied growth and immune function of lark nestlings as a function of year-round variation in breeding intensity and rain within one location. We monitored mass, wing, and tarsus at hatching (day 1) and at 4, 7, and 10 days post-hatch, and we quantified four indices of immune function (haptoglobin, agglutination, lysis and nitric oxide) using blood samples collected on day 10.ResultsNestling body mass and size at hatching, which presumably reflect the resources that females allocated to their eggs, were lowest in the most arid location, Kedong. Contrary to our predictions, nestlings in Kedong grew faster than nestlings in the two other cooler and wetter locations of South and North Kinangop. During periods of peak reproduction within Kedong, nestlings were heavier at hatching, but they did not grow faster over the first 10 days post-hatch. In contrast, rainfall, which did not relate to timing of breeding, had no effect on hatching mass, but more rain did coincide with faster growth post-hatch. Finally, we found no significant differences in nestling immune function, neither among locations nor with the year-round variation within Kedong.ConclusionBased on these results, we hypothesize that female body condition determines nestling mass and size at hatching, but other independent environmental conditions subsequently shape nestling growth. Overall, our results suggest that environmental conditions related to food availability for nestlings are relatively unimportant to the timing of breeding in equatorial regions, while these same conditions do have consequences for nestling size and growth.

Effects of rapamycin on life span and on expression of TOR and S6K in Brachionus calyciflorus (Rotifera)

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 26:49-56 (2017) - DOI: https://doi.org/10.3354/ab00673 Effects of rapamycin on life span and on expression of TOR and S6K in Brachionus calyciflorus (Rotifera) Huanhuan Xu, Lulu Liu, Yuqi Su, Ye Liang, Jiaxin Yang* School of Life Sciences, Nanjing Normal University, Nanjing, Jiangsu 210023, PR China *Corresponding author: yangjx@njnu.edu.cn ABSTRACT: The mechanistic target of rapamycin (mTOR) coordinates a complex signal pathway from translation to autophagy that is a key regulator of not only growth and proliferation but also metabolism and aging. mTOR is sensitive to many environmental and endocrine stimuli. We investigated the influence of TOR signaling on aging and reproduction of the rotifer Brachionus calyciflorus using rapamycin as an exogenous inhibitor. We found that 2 and 4 µM rapamycin extended B. calyciflorus life span by 15 and 22%, respectively compared with controls (p < 0.05). The reproductive peak was significantly delayed by rapamycin at 2 and 4 µM (p < 0.01), but the pre- and post-reproduction periods were not significantly different from controls (p > 0.05). Partial cDNAs coding 375 bp for TOR and 951 bp for S6 kinase (S6K) were obtained from B. calyciflorus expressed sequence tags. The identities of the deduced amino acid sequences of B. calyciflorus cDNAs to their human orthologs were 58% for TOR and 68% for S6K. TOR and S6K mRNA expression were up- or down-regulated by different rapamycin concentrations (0.5, 1, 2, 4, 8, and 16 µM) and treatment intervals (control, 12, 24, 36, and 48 h). The results indicated that TOR inhibition acted additively to extend rotifer life span, with up- and down-regulation simultaneously impacting reproduction and gene expression. KEY WORDS: Aging · Life span · mRNA expression levels · Rapamycin · Reproduction · Rotifer Full text in pdf format PreviousNextCite this article as: Xu H, Liu L, Su Y, Liang Y, Yang J (2017) Effects of rapamycin on life span and on expression of TOR and S6K in Brachionus calyciflorus (Rotifera). Aquat Biol 26:49-56. https://doi.org/10.3354/ab00673 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 26. Online publication date: May 15, 2017 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2017 Inter-Research.

Helminth infracommunity of the cane toad Rhinella marina (Anura: Bufonidae) within its native distribution range

During August 2010, a total of 66 cane toad Rhinella marina were collected in Laguna de Coyuca, Guerrero, Mexico and examined for the presence of helminths. Ninety-two percent were parasitized by 1 or more parasite species. A total of 4624 individuals were found, belonging to 8 helminth taxa (1 digenean, 1 cestode and 6 nematodes). Infracommunities harbored by this host species are highly variable (mean Jaccard similarity index 0.31±0.27); mean percent similarity index 0.26±0.32) and depauperate (mean richness 1.91±0.92; mean abundance 64.4±100.34); almost 50% of them were dominated by Rhabdias fuelleborni, a skin-penetrating nematode. Differences related to host gender and size were found, since males registered infracommunities with lower species richness and diversity than females. The reproductive condition of females (collected during the breeding season) might explain the results obtained; during this season, females invest less in resistance to infection in favor of investing resources in reproduction. However, confirmation of this statement can only be made by sampling in the dry season, when the toads do not reach their reproductive peak.

Ovarian development and the reproductive profile of Astyanax altiparanae (Teleostei, Characidae) over one year: Applications in fish farming

Astyanax altiparanae is a Brazilian species of substantial commercial, environmental and scientific importance; however, existing studies on its reproduction do not seem to provide enough details. In light of the increasing use of this species in fish farming and the need for basic studies for the development of new production technologies, we describe the structural and ultrastructural characteristics of the ovaries of A. altiparanae, and characterize the species' reproductive cycle. Females were collected monthly from March 2013 to February 2014, and reproductive management began in October 2013. The ovaries were removed, fixed in Karnovsky's fixative, and prepared for light microscopy, transmission electron microscopy and immunohistochemistry anti-PCNA. These techniques enabled us to characterize the ovaries, the germ cells, and the somatic cells in detail, as well as their changes over time. The reproductive cycle was characterized based on the monthly variation in the gonadosomatic ratio, the proportion of germ cells, and the rate of oogonium proliferation. The macroscopic analysis of the ovaries suggests that the vascularization pattern and color of the ovaries vary according to development. There are new types of analyses that can be applied even in the fish farming industry, such as a comparison between ovaries staining and weight or the frequency distribution of these colors throughout the year. This study also provides details on microscopic characteristics that have never before been reported for species of Astyanax, such as the presence of annulate lamellae in oogonia, the development of the zona pellucida from oocytes in the one-nucleolus step, and the development of the micropylar apparatus in oocytes in the cortical alveolar step. When the reproductive cycle was analyzed, this species was found to have a long period of spawning, with a reproductive peak from October to February and multiple spawning events, confirming the period already described in the literature. Variations in reproductive periods and the ability to reproduce in lentic environments suggest that A. altiparanae has the ability to respond quickly to environmental changes and exhibits high reproductive flexibility. All of these characteristics confirm the great potential of this species in the fish farming industry.

Reproductive biology of the freshwater drum Aplodinotus grunniens in Tabasco, Mexico

Aplodinotus grunniens supports a sustained artisanal shery in the Usumacinta River; however, there are few studies to understand the population dynamics of the species. Relevant aspects of the reproductive biology were documented over an annual cycle, using 593 specimens captured with seine nets. The results indicate that females had a median TL of 32.05 cm, while males had 29.71 cm. The estimated sex ratio was 1.2:1 (males: females). The length-weight relationship showed signi cant difference between sexes, observing an allometric-type growth represented by TW=0.0013(TL)3.5985 with 89.17 % of the data variability explained by the model. Gonadosomatic index (GSI) in females was higher in September (4.29), with males displaying a higher GSI in October (1.02). The highest HSI increase in females was observed in October (1.0). The estimated relative fecundity was 138.74 (± 74.30) oocytes/g of female weight. The macroscopic analysis of gonads indicates that the highest frequency of mature females occurs in June (75 %), while in males it takes place in March and June (35 %). The estimated L 50 for females was 31.89 cm (TL) and 28.78 cm (TL) for males. Though A. grunniens reproduces throughout the year, reproductive peaks coincide with the period when the river level decreases, and shing increases considerably. Hence, preventive measures must be applied in regards to the size of the species at capture and the exploitation volumes of this resource.

Reproductive cycle of seabob shrimp Xiphopenaeus kroyeri (Crustacea, Penaeidea) from the northeast coast of Brazil

The reproductive cycle of Xiphopenaeus kroyeri north-eastern Brazil was described to contribute to the sustainable management of this stock in the region. Specimens were collected monthly from August 2011 to July 2012 using a local vessel of the artisanal fleet. A total of 1201 individuals were analyzed (673 females and 528 males) with a mean carapace length (CL) of 1.88 ± 0.16 cm and total length (TL) of 9.00 ± 1.22 cm. The lowest CL and TL of mature females were 1.33 and 6.5 cm, respectively, and all females above 2.44 cm (CL) and 11.5 cm (TL) were mature. Ovarian maturation was classified into four stages: I (immature), II (maturing), III (mature) and IV (spawned). Individuals of all maturational stages were present throughout the year. Considering the macro and microscopic analysis, it was suggested that this species in north-eastern Brazil has a continuous reproductive cycle, with two seasonal peaks, November/December and February (austral spring and summer). A positive correlation between the percentage of mature females and temperature was observed, and a higher percentage was reported in the warmer months of the year. This suggests that the reproductive peaks can be triggered by water temperature variation throughout the year.

The community of Mata de Limón, central Pacific coast of Costa Rica and the extraction of colonchos Callichirus seilacheri (Bott, 1955) (Decapoda: Axiidea: Callianassidae)

We conducted monthly visits to the coastal community of Mata de Limón (December 2011 to November 2012) in central Pacific of Costa Rica for assessment the extraction of the burrowing shrimp called coloncho Callichirus seilacheri, a species intensely caught as bait for fishing along the Pacific coast of Central America. The outcomes indicate that fishery effort varied between 4 and 14 harvesters day-1 with a high percentage of them from the same community (70-100%). Daily catch varied between 76 and 1120 shrimps and its value was strongly correlated with catches realized for the local harvesters (R2= 0.88). The shrimps density and total abundance in Mata de Limón was estimated in 1.2 ± 0.88 ind m-2 and 49,607 ± 3,638 individuals, respectively. Ovigerous females were exclusively present between May and November, peak in September. According to our outcomes, population of C. seilacheri in Mata de Limón could be in risk of overfishing if the daily catches exceed 800 individuals. The main results of the present study allow recommend the implementation of a total fishing ban during the reproduction peak of C. seilacheri directed to protection and conservation of this local resource for its sustainable harvesting. Also, we suggest the establishment of a management program between the community of Mata de Limón and the Instituto Costarricense de Pesca y Acuicultura (INCOPESCA) in order to optimize and legalize the extraction of this important resource.

Ontogenetic timing as a condition-dependent life history trait: High-condition males develop quickly, peak early, and age fast.

Within-population variation in ageing remains poorly understood. In males, condition-dependent investment in secondary sexual traits may incur costs that limit ability to invest in somatic maintenance. Moreover, males often express morphological and behavioral secondary sexual traits simultaneously, but the relative effects on ageing of investment in these traits remain unclear. We investigated the condition dependence of male life history in the neriid fly Telostylinus angusticollis. Using a fully factorial design, we manipulated male early-life condition by varying nutrient content of the larval diet and, subsequently, manipulated opportunity for adult males to interact with rival males. We found that high-condition males developed more quickly and reached their reproductive peak earlier in life, but also experienced faster reproductive ageing and died sooner than low-condition males. By contrast, interactions with rival males reduced male lifespan but did not affect male reproductive ageing. High-condition in early life is therefore associated with rapid ageing in T. angusticollis males, even in the absence of damaging male-male interactions. Our results show that abundant resources during the juvenile phase are used to expedite growth and development and enhance early-life reproductive performance at the expense of late-life performance and survival, demonstrating a clear link between male condition and ageing.

Seasonal reproductive cycle and variability in plasma testosterone levels in the domestic duck (Anas platyrhynchos)

Morphofunctional gonadal alterations constitute an annual cycle in birds during which four phases can be distinguished in the testes based on histological modifications in the seminiferous epithelium, called quiescence, recrudescence, reproduction and regression. The aim of the present investigation was to conduct a morphometric and morphological study of the seminiferous epithelium on the testis of domestic duck and to evaluate the plasma testosterone levels in order to determine the possible presence of a reproductive cycle in the tropical region. The study was conducted on 60 adult domestic ducks ( Anas platyrhynchos ), where five animals were sacrificed per month and the testes were removed and histologically and morphometrically studied. Blood samples of the five animals were collected monthly in the morning period and the testosterone levels were analyzed. Annual reproductive cycle of the domestic duck presented by four distinct phases, starting with the reproductive phase at the beginning of winter (July) and peak of reproduction in spring (October), accompanied by an increase in tubule seminiferous diameter, epithelium height, weight and testicular volume, followed by a regressive phase at the end of spring (November) and the beginning of summer (December). Testicular quiescence was observed during summer (January and February) and was followed by a phase of spermatogenic recrudescence, which lasted throughout autumn (March to June), corresponding to the longest phase of the cycle. Complete spermiogenesis in terms of spermatozoa maturation and spermiation was observed during the reproductive phase, coinciding with the plasma testosterone peak. At regressive phase an exfoliation of the seminiferous epithelium was observed, accompanied by a great amount of fibrillar collagen. A decrease in tubular seminiferous diameter and epithelium height was observed during testicular quiescence, with predominance of spermatogonia and Sertoli cells and a second plasma testosterone peak was also observed during this phase (January), probably representing the preparation for a gradual return to the spermatogenic process during recrudescence. The latter phase was characterized by gradual recovery of the seminiferous epithelium, accompanied by the increase of spermatogonia, onset of meiosis, and the presence of primary spermatocytes and maturing spermatids. In conclusion the domestic duck presented the testicular cycle divided in four distinct phases in the tropical region with testosterone peaks in the testicular quiescence and reproductive phases.

Does Sarcoptes scabiei synchronize its breeding cycle with that of the Iberian Ibex, Capra pyrenaica?

ABSTRACTWe have analysed five samples from the skin of 368 Iberian ibexes from Sierra Nevada Natural Space (southern Spain) in order to characterize the age structure of the Sarcoptes scabiei metapopulation affecting this host population and, particularly, to search for possible reproductive peaks of the parasite. Monthly mean mite density and number of larvae peaked in November, coinciding with the rutting season of its host, when the size of ibex mixed groups becomes larger. On the other hand, monthly number of nymphs differed significantly, reaching higher values in May (coinciding with the peak of parturitions), August and November. Our results suggest that (i) there is some extent of synchronization between the breeding cycles of both the host and the parasite and (ii) nymphs could play an important role in the mite transmission to offspring. We discuss the potential role of sexual hormones in such increase of larvae and therefore in mite numbers.

Patterns of reproduction in two co-occurring Great Barrier Reef sponges

Reproduction is a key biological process that underpins the persistence and maintenance of populations. However, information on the reproductive biology of Great Barrier Reef (GBR) sponges is depauperate. The present study established the reproductive biology of two co-occurring GBR sponges, namely Ianthella basta (Verongida) and Ircinia sp. (Dictyoceratida). Sponges were haphazardly sampled (monthly) over a period of 1 year. Histological analysis of samples established the sexuality, development, seasonality, gametogenesis and fecundity of the two species, as well as the effects of temperature on reproduction. I. basta is oviparous, whereas Ircinia sp. is viviparous. The mode of sexuality in I. basta could not be determined, because male propagules were not detected, whereas Ircinia sp. is a simultaneous hermaphrodite. Reproduction in I. basta is unique within the verongids and co-occurring oviparous species, with peak reproduction occurring at the minimum annual temperature (23°C) and spawning occurring as the temperature increased above 23.4°C. Reproduction in Ircinia sp. corresponded to patterns reported for other viviparous GBR species, with an increase in reproductive propagules, peak sperm release, fertilisation and spawning occurring at temperatures above 25°C. Fecundity in I. basta and Ircinia sp. is high compared with other sponge species in the region, which may contribute to their apparent abundance on the GBR.

Population and reproductive dynamics of the polychaete Pygospio elegans in a boreal estuary complex

AbstractPygospio elegans is an opportunistic, wide‐spread spionid polychaete that reproduces asexually via fragmentation and can produce benthic and pelagic larvae, hence combining different developmental modes in one species. We documented the density, size distribution, and reproductive activity of P. elegans at four sites in the Danish Isefjord‐Roskilde Fjord estuary complex, where all modes of reproduction were reported. We compared population dynamics of this species to environmental parameters such as salinity, temperature, and sediment characteristics (grain size, sorting, porosity, water content, organic content, C/N). We observed that new cohorts—resulting either from sexual or asexual reproduction—appeared in spring and fall, and old ones disappeared in late summer and winter. Sexual reproduction occurred from September until May, and although their timing was variable, there were two reproductive peaks at three sites. At those sites, we also observed a switch in larval developmental mode. Asexual reproduction peaked in April. While the seasonal dynamics can be related to temperature to a large extent, the differences in population dynamics among sites also correlated with sediment structure and salinity. Populations from sites with coarse and heterogeneous sediment had high levels of sexual reproduction. At the site with lower salinity, intermediate and benthic larvae were present during winter in contrast to pelagic larvae found at the other sites. However, we could not identify one clear environmental factor determining the mode of development. At present, it remains unclear to what degree genetic background contributes to mode of development. Hence, whether the differences in developmental mode are the result of genetically different cohorts will be further investigated.

Evidence of reduced individual heterogeneity in adult survival of long-lived species.

The canalization hypothesis postulates that the rate at which trait variation generates variation in the average individual fitness in a population determines how buffered traits are against environmental and genetic factors. The ranking of a species on the slow-fast continuum - the covariation among life-history traits describing species-specific life cycles along a gradient going from a long life, slow maturity, and low annual reproductive output, to a short life, fast maturity, and high annual reproductive output - strongly correlates with the relative fitness impact of a given amount of variation in adult survival. Under the canalization hypothesis, long-lived species are thus expected to display less individual heterogeneity in survival at the onset of adulthood, when reproductive values peak, than short-lived species. We tested this life-history prediction by analysing long-term time series of individual-based data in nine species of birds and mammals using capture-recapture models. We found that individual heterogeneity in survival was higher in species with short-generation time (< 3 years) than in species with long generation time (> 4 years). Our findings provide the first piece of empirical evidence for the canalization hypothesis at the individual level from the wild.

Reproducción de los róbalos Centropomus undecimalis y C. ensiferus (Perciformes: Centropomidae) en una laguna costera tropical

Snooks C. undecimalis and C. ensiferus are important fishery resources in their distribution area. In Venezuela they are caught by artisanal fisheries along the entire coast. However, studies on their biology that would help establish fishing regulations are scarce. To study reproduction aspects of these species, we analyzed 1 325 individuals of C. undecimalis and 2 025 of C. ensiferus caught by artisanal fishing in the Laguna de Tacarigua in Northern Venezuela, from July 2009 to September 2010. Total length, total weight, sex and stage of gonadal development were recorded. The sex ratio varied throughout the year: there was a significant difference in favor of C. undecimalis males (1.5:1), and C. ensiferus females (1:3.3). Differences were also evident in the sexual proportion at each size group. For both species, males dominated in the lower size ranges while females dominated in the larger size ranges. These results suggested sequential hermaphroditism (protrandry) in both species. Size at sexual maturity (Lm50) for C. undecimalis was ♀= 73.6 and ♂= 59.3 cm, and ♀= 26 and ♂= 21.5 cm for C. ensiferus. C. ensiferus reproduced throughout the year with two periods of higher intensity (August to September and February to April). Although we found very few mature individuals for C. undecimalis, February showed an important reproduction peak. Growth differences were found between males and females of C. undecimalis: positive allometry for females (P= 0.0022*L3.353) and negative allometry for males (P= 0.0108*L2.945). Both males and females of C. ensiferus showed a positive allometric relationship (P= 0.0049*L3.235). Lack of fishing regulations and controls, evidenced in this study by significant volumes of immature individuals in the catches, and the particular reproductive biology of these species, strongly indicates the need to establish regulations to ensure their responsible use. We recommend establishing a closed season during the first quarter of the year and minimum catch sizes for both species.

Population dynamics of Parhyale hawaiensis (Dana, 1853) (Amphipoda: Hyalidae) associated with an intertidal algal belt in southeastern Brazil

Static life tables were used to establish demographic parameters such as size-class structure, abundance trends, sex ratio, net reproductive rate, generation time, and per capita rate of population growth for a population of the amphipod Parahyale hawaiensis (Dana, 1853) (Hyalidae) from the intertidal belt of a red alga Bryocladia trysigera (J. Agardh) F. Schmitz in southeastern Brazil. Collections were taken monthly from December 2012 to November 2013. There were two reproductive peaks, a higher one, May to July, and a second throughout the warmer months, October to January. The continuous reproduction results in the overlapping of generations. A sex ratio biased in favor of females was recorded in all sampling dates, a common pattern in epifaunal species. The estimated net reproductive rate was 1.45 ± 1.01 young per female, the generation time 3.51 ± 1.31 months, and the population growth rate 0.06 ± 0.17 per capita per month. The logistic growth model indicates that an initial population of 10 individuals would reach the carrying capacity for the species in a natural environment in 35 to 40 generations time, a period equivalent to 130 to 150 months. As a result of extinction model application, no possibility of extinction was predicted for the local population. The estimated parameters can be used as endpoints in ecotoxicological tests.