Planktonic Larval Stage Research Articles

Early development and growth of a selective line of Argopecten irradians concentricus

PDF HTML阅读 XML下载 导出引用 引用提醒 墨西哥湾扇贝选育系早期发育与生长 DOI: 作者: 作者单位: 广西大学 动物科学技术学院, 广西 南宁 530004 作者简介: 封杰(1991-),男,硕士研究生,主要从事海洋贝类遗传育种与繁育研究.E-mail:dzfjdyx@163.com 通讯作者: 中图分类号: S968 基金项目: 广西科学研究与技术开发计划项目（桂科攻14121006-2-5）. Early development and growth of a selective line of Argopecten irradians concentricus Author: Affiliation: College of Animal Science and Technology, Guangxi University, Nanning 530004, China Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在水温28~29℃、盐度24~25条件下，研究墨西哥湾扇贝（）选育系的早期发育及幼虫和稚贝的生长。受精卵经50 min发育至卵裂，经22~24 h发育至D形幼虫，经11 d发育至眼点幼虫并出现足，进入附着变态阶段。选育系的胚胎发育时间和浮游幼虫前期壳长、壳高与对照系比较差异不显著（<0.05）。选育系的附着变态率和存活率与对照系比较均差异显著（<0.05），且优势明显。本研究表明，墨西哥湾扇贝浮游幼虫发育前期缓慢，幼虫后期、稚贝期生长迅速；壳长和壳高的生长速度不同步，幼虫前期壳长生长快于壳高，后期壳高生长快于壳长，并于第28~30天时壳高超过壳长。墨西哥湾扇贝选育系在幼虫和稚贝阶段生长速度明显快于对照系，具有明显的生长优势及生长潜力。 Abstract:Development of embryos, larvae, and juveniles of were observed using an optical microscope, with a digital camera at water temperatures of 28℃ to 29℃ and salinity of 24 to 25. Zygotes began the first cleavage at 50 min post-fertilization, developed to D-shaped larvae between 22 and 24 h, and the larvae developed eye points and feet at day 11 and entered the attachment metamorphosis stage. There was no significant difference in the time of embryo development between the selective and control lines (>0.05). The shell length and shell height were not significantly different at the embryonic and early larval stages between the selective and control lines (>0.05), but there was a significant difference in shell length and shell height at the post-larval and attachment metamorphosis stages between the selective and control lines (<0.05). The metamorphosis and survival rates of the selective line were significantly different from those of the control line (<0.05), and the selective line has obvious advantages. The results show that the growth of the early planktonic larval stage of was slow but at the post-larval and juvenile stages, it was rapid. The growth of shell length and shell height of was not synchronized. The growth speed of shell length exceeded that of shell height at the earlier larval stage, and at the later larval stage, the growth speed of shell height exceeded that of shell length; at 28 to 30 days, shell height exceeded shell length. At the larval and juvenile stages, the growth of the selective line significantly exceeded that of the control line. The selective line has obvious growth advantages and growth potential. 参考文献 相似文献 引证文献

Spatial variation in life history characteristics of waved whelk (Buccinum undatum L.) on the U.S. Mid-Atlantic continental shelf

Abstract Recent expansion of the unmanaged waved whelk (Buccinum undatum) fishery within the United States Mid-Atlantic continental shelf region has prompted investigation into local life history parameters. Limited adult dispersal and lack of a planktonic larval stage has the potential to create spatially distinct populations with respect to size of sexual maturity and size frequency. During the summer of 2015, a comprehensive survey was undertaken to evaluate population structure, sex ratio, relative abundance, and size of sexual maturity for whelk in the Mid-Atlantic. Samples (n = 228) were collected from Georges Bank through the DelMarVa region using a modified scallop dredge at depths ranging from 27.4 to 112 m, with most whelk caught between 40–75 m, and peak abundances at 51–60 m. All whelk collected (n = 3877) were sexed, weighed, measured, and assessed for maturity. Sex ratios were skewed in favor of females in the south and balanced through the rest of the regions. Size of maturity ranged from approximately 56–73 mm and varied among regions and sex. Estimates of size of sexual maturity for B. undatum from other regions of the world were compiled, demonstrating that the size of maturity for this species is highly variable, and current minimum landing size regulations tend to fall below the estimated size of sexual maturity, potentially increasing the risk of recruitment overfishing. Overall, spatial variation in whelk phenotype suggests local adaptation in this species, indicating that regional management would be most appropriate.

Genetic diversification of intertidal gastropoda in an archipelago: the effects of islands, oceanic currents, and ecology

Marine organisms with a planktonic larval stage can passively disperse long distance and are thus expected to have a wider distribution range and lower geographic variation. However, recent molecular phylogenetic studies have revealed that they often display a clear geographic genetic structure or even form a geographically fragmented species complex. These genetic divergences can be facilitated by the presence of dispersal barriers such as oceanic currents and/or by the limitation of suitable habitats. Using comprehensive phylogenetic analyses, we evaluate how such dispersal barriers shape genetic divergence and speciation in the intertidal snail genus Monodonta. Our phylogenetic analysis revealed various patterns of cladogenesis in Monodonta in East Asia. Genetic segregation between the Japanese and Ryukyu Archipelagos are detected in M. labio and M. perplexa perplexa. However, the relationship of geographical border and lineages does not correspond to those two because they show different habitat preference. M. labio distributed in the Japanese mainland is separated by the boundary corresponding to the point from which oceanic currents split into different directions. In contrast, species inhabiting various environments such as M. confusa are not genetically separated in Japan. In the peripheral oceanic Ogasawara Islands, two Monodonta species form each endemic lineage, although these two underwent different colonization processes to the islands. These findings suggest that the genus Monodonta has been genetically diversified around Japan, probably due to its correlations with dispersal ability, oceanic current, and habitat preferences. These factors may be effective causes for diversification of marine gastropods with a planktonic stage.

NMR Profiling of Metabolites in Larval and Juvenile Blue Mussels (Mytilus edulis) under Ambient and Low Salinity Conditions

Blue mussels (Mytilus edulis) are ecologically and economically important marine invertebrates whose populations are at risk from climate change-associated variation in their environment, such as decreased coastal salinity. Blue mussels are osmoconfomers and use components of the metabolome (free amino acids) to help maintain osmotic balance and cellular function during low salinity exposure. However, little is known about the capacity of blue mussels during the planktonic larval stages to regulate metabolites during osmotic stress. Metabolite studies in species such as blue mussels can help improve our understanding of the species’ physiology, as well as their capacity to respond to environmental stress. We used 1D 1H nuclear magnetic resonance (NMR) and 2D total correlation spectroscopy (TOCSY) experiments to describe baseline metabolite pools in larval (veliger and pediveliger stages) and juvenile blue mussels (gill, mantle, and adductor tissues) under ambient conditions and to quantify changes in the abundance of common osmolytes in these stages during low salinity exposure. We found evidence for stage- and tissue-specific differences in the baseline metabolic profiles of blue mussels, which reflect variation in the function and morphology of each larval stage or tissue type of juveniles. These differences impacted the utilization of osmolytes during low salinity exposure, likely stemming from innate physiological variation. This study highlights the importance of foundational metabolomic studies that include multiple tissue types and developmental stages to adequately evaluate organismal responses to stress and better place these findings in a broader physiological context.

Skeletal microstructure of uintacrinoid crinoids and inferences about their mode of life

Uintacrinoids (Uintacrinoidea) are among the most bizarre of all the crinoids. These stratigraphically important Late Cretaceous crinoids are characterized by an atypical large stalkless globular cup without cirriferous centrodorsal and extremely long arms. Owing to this unusual morphology, the mode of life of these crinoids has confused palaeontologists for more than a century. While uintacrinoids have been commonly regarded as pelagic forms, either swimming actively or floating passively by means of a putative buoyancy mechanism, some recent authors have favoured a benthic mode of life. However, evidence supporting a benthic lifestyle hypothesis is still limited. Here we describe the stereom microstructure of Marsupites and Uintacrinus. In Marsupites, thecal plates are typically comprised of coarse to medium, clearly structural, galleried stereom, which alternates with zones of fine and deeply penetrating galleried stereom oriented perpendicular to the plate margins. The latter stereom type corresponds to the external ribbed ornament of the theca, and is indicative of collagenous sutural fibers for binding adjacent plates. In Uintacrinus, thecal plates are almost entirely composed of fine galleried stereom diagnostic for collagenous sutural fibers. In both taxa, a perforate stereom layer, that is known to increase plate strengthening and resistance to abrasion in some Recent echinoderms, is developed most externally, and also produces a characteristic interior growth banding pattern. No skeletal adaptations for maintaining buoyancy, such as skeletal lightening and hollow architecture, that are known to occur in nektonic and pseudoplanktonic crinoids, are observed. Instead, the stereom organization in uintacrinoids closely resembles those observed in Recent benthic crinoids. Our findings thus strongly support a benthic mode of life of uintacrinoids. Their widespread distribution within a short time interval can be best explained by having a very long-term planktonic larval stage as previously hypothesized by some authors.

Persistence, Extinction, and Recolonization of an Epibenthic Gastropod Population on an Intertidal Sandflat: 35-Y Contingent History of a Key Species of the Benthic Community in Metapopulation and Metacommunity Contexts

For marine benthos with planktonic larval stages, demographic metapopulation and empirical metacommunity studies are scarce. Asink nature was shown for a local intertidal sandflat population of the gastropod Umbonium moniliferumin an estuarine to coastal oceanic region in Amakusa, Kyushu, Japan. The gastropod has a 3-day planktonic larval duration (PLD). It inhabited 11 sandflats, which were shared by the ghost shrimp Nihonotrypaea harmandi. The shrimp is a burrow-dwelling bioturbator with a 30-day PLD. On one sandflat (hereafter U0) in Amakusa, the density and distribution of the two species was monitored from 1979 to 2014. All their main local populations were surveyed in 1998. In July 1979, the gastropod and shrimp were distributed on the lower and upper zones of U0 separately, with mean densities of 1,740 and 170 ind/m2. The gastropod population declined to extinction in 1986, associated with the increase in shrimp density to 440 ind/m2 and distribution to the lowest shore. Shrimp sediment destabilization was most likely to inhibit gastropod recruitment. The gastropod population began to recover in 1997 owing to shrimp population shrink. The regional survey results showed that (1) eight local populations (U0–U7 sandflats) of the two species along a 25-km shoreline of Amakusa, presumably, constitute each substantial metapopulation, and (2) their largest populations were at the shoreline opposite ends. These features would be generated by the interaction of speciesspecific larval dispersal traits and shoreline physiography. The threshold shrimp density of 160 ind/m2 precluding gastropod recruitment was detected from U1–U7. In 2001 and 2009, gastropod population density on U0 reached respective peaks comparable to that in 1979. This population fluctuation was due to varying recruit abundance, which corresponded well with the year-to-year change in shrimp population density across that threshold. The recolonization of the U0 gastropod population ought to be made by allochthonous larvae from the U1–U7 populations, especially U6–U7, suggesting a rescue effect in the source—sink relationship. The degree of self-persistency of the U0 gastropod population was estimated by calculating net reproductive rate (R0) based on the parameters about pre-settlement larval return-home and survival rates and post-settlement juvenile and adult survival rates. The availability of data set restricted the estimation to potential R0 for four year-segments, with each 1-y parameter set extrapolated to the gastropod 4-y life span. On U0 in 1979 to 1981, despite with minimum shrimp influences, the gastropod population could still be a demographic sink probably due to a limited larval return-home rate and due to a low post-settlement survival rate of juveniles caused by epibenthic predation or storm for their first 1 y to reach sexual maturity.

Marine ecoregion and Deepwater Horizon oil spill affect recruitment and population structure of a salt marsh snail

AbstractMarine species with planktonic larvae often have high spatial and temporal variation in recruitment that leads to subsequent variation in the ecology of benthic adults. Using a combination of published and unpublished data, we compared the population structure of the salt marsh snail, Littoraria irrorata, between the South Atlantic Bight and the Gulf Coast of the United States to infer geographic differences in recruitment and to test the hypothesis that the Deepwater Horizon oil spill led to widespread recruitment failure of L. irrorata in Louisiana in 2010. Size‐frequency distributions in both ecoregions were bimodal, with troughs in the distributions consistent with a transition from sub‐adults to adults at ~13 mm in shell length as reported in the literature; however, adult snails reached larger sizes in the Gulf Coast. The ratio of sub‐adults to adults was 1.5–2 times greater in the South Atlantic Bight than the Gulf Coast, consistent with higher recruitment rates in the South Atlantic Bight. Higher recruitment rates in the South Atlantic Bight could contribute to higher snail densities and reduced adult growth in this region. The ratio of sub‐adults to adults in Louisiana was lower in 2011 than in previous years, and began to recover in 2012–2014, consistent with widespread recruitment failure in 2010, when large expanses of spilled oil were present in coastal waters. Our results reveal an important difference in the ecology of a key salt marsh invertebrate between the two ecoregions, and also suggest that the Deepwater Horizon oil spill may have caused widespread recruitment failure in this species and perhaps others with similar planktonic larval stages.

Non-equilibrium plasma prevention of Schistosoma japonicum transmission.

Schistosoma japonicum is a widespread human and animal parasite that causes intestinal and hepatosplenic schistosomiasis linked to colon, liver and bladder cancers, and anemia. Estimated 230 million people are currently infected with Schistosoma spp, with 779 million people at risk of contracting the parasite. Infection occurs when a host comes into contact with cercariae, a planktonic larval stage of the parasite, and can be prevented by inactivating the larvae, commonly by chemical treatment. We investigated the use of physical non-equilibrium plasma generated at atmospheric pressure using custom-made dielectric barrier discharge reactor to kill S. japonicum cercariae. Survival rate decreased with treatment time and applied power. Plasmas generated in O2 and air gas discharges were more effective in killing S. japonicum cercariae than that generated in He, which is directly related to the mechanism by which cercariae are inactivated. Reactive oxygen species, such as O atoms, abundant in O2 plasma and NO in air plasma play a major role in killing of S. japonicum cercariae via oxidation mechanisms. Similar level of efficacy is also shown for a gliding arc discharge plasma jet generated in ambient air, a system that may be more appropriate for scale-up and integration into existing water treatment processes.

In Silico Prediction of Neuropeptides/Peptide Hormone Transcripts in the Cheilostome Bryozoan Bugula neritina.

The bryozoan Bugula neritina has a biphasic life cycle that consists of a planktonic larval stage and a sessile juvenile/adult stage. The transition between these two stages is crucial for the development and recruitment of B. neritina. Metamorphosis in B. neritina is mediated by both the nervous system and the release of developmental signals. However, no research has been conducted to investigate the expression of neuropeptides (NP)/peptide hormones in B. neritina larvae. Here, we report a comprehensive study of the NP/peptide hormones in the marine bryozoan B. neritina based on in silico identification methods. We recovered 22 transcripts encompassing 11 NP/peptide hormone precursor transcript sequences. The transcript sequences of the 11 isolated NP precursors were validated by cDNA cloning using gene-specific primers. We also examined the expression of three peptide hormone precursor transcripts (BnFDSIG, BnILP1, BnGPB) in the coronate larvae of B. neritina, demonstrating their distinct expression patterns in the larvae. Overall, our findings serve as an important foundation for subsequent investigations of the peptidergic control of bryozoan larval behavior and settlement.

Lethal and sub-lethal effects of Deepwater Horizon slick oil and dispersant on oyster (Crassostrea virginica) larvae

In April 2010, crude oil was spilled from the Deepwater Horizon (DWH) oil platform for 87 days, coincident with the spawning season and recruitment of the oyster, Crassostrea virginica, in the Gulf of Mexico. Impacts of acute exposures to surface-collected DWH oil (HEWAF), dispersed oil (CEWAF) and dispersant alone (Corexit 9500A®) on planktonic larval stages of C. virginica (veliger, umbo and pediveliger) were tested in the laboratory. Exposures to HEWAF, CEWAF and dispersant were toxic to larvae impairing growth, settlement success and ultimately survival. Larval growth and settlement were reduced at concentrations of tPAH50 ranging from 1.7 to 106 μg L−1 for HEWAF and 1.1–35 μg L−1 for CEWAF, concentrations well within the range of water sampled during the DWH oil spill. Sublethal effects induced by oil and dispersant could have significant ecological implications on oyster populations and on the whole estuarine ecosystem.

Recruitment patterns in an intertidal species with low dispersal ability: the reef-building Dendropoma cristatum (Biondi, 1859) (Mollusca: Gastropoda)

In the Mediterranean, the gastropod Dendropoma cristatum (sin. D. petraeum (Monterosato, 1884)) is the primary builder of the vermetid reef, an intertidal bioconstruction of exceptional ecological importance. Despite awareness of the need for conservation of this key species, the biology of D. cristatum remains poorly understood. The recruitment of D. cristatum deserves particular attention because the absence of a planktonic larval stage limits its dispersal ability. We examined the temporal pattern of recruitment during the breeding season of D. cristatum from June to September in 2013. Specifically, we compared the two portions of the vermetid reef (i.e. the inner edge and the outer edge) at localities with different exposures to wave motion. The number of recruits peaked in July, when it was significantly higher in the outer than in the inner edge. No differences emerged between localities with different wave exposures; however, the width of the reef was significantly related to the exposure index. Although there are still several gaps in our knowledge of the recruitment dynamics of D. cristatum, this study contributes to characterising recruitment rate variation at small spatial and temporal scales.

Incubation Time Required for Hatching, and Ecological Characteristics of the Mode of Life Related with Total Numbers of the Suckers on Each Short Arm of the Hatched Juvenile Larvae of Octopus ocellatus (Cephallopoda: Octopodidae), in Western Korea

The incubation time required for hatching of O. ocellatus were investigated through the processes of egg and embryonic developments by the dissecting microscopic and visual observations. And differences in ecological characteristics of the plankton mode of life or the benthic mode of life according to total numbers of the suckers on each short arm of the hatched juvenile larvae of O. ocellatus were studied by comparisons with other octopodidae species. Compared with the recent a few results reported by other researchers associated with the incubation time required for hatching by female adult mother of O. minor (73-90 days after spawning at 20.9-21.5℃ ranges), in this study, the incubation time required for hatching by female adult mother of O. ocellatus was 56-57 days after spawning at 11.0-20.4℃. Therefore, the incubation time required for hatching by female adult mother varied with Octopodidae species. In this studies, each ovarian egg laid by a female was connected to an egg string attaching to the surface of the wall or bottom of vacunt shell of Rapana venosa. Egg and embryonic developments of this species were studied in the indoor aquaria, in the specific gravity ranging 1.024-1.025. the hatched juvenile of O. ocellatus is 10.3 mm in the mean total length and 4.5 mm in mantle length, and each of its short arms has 18-20 suckers. The just hatched juvenile larvae of O. ocellatus enter the benthic mode of life (benthic larval stage) after hatching. In particular, regarding differences in ecological characteristics of the mode of life according to total numbers of the suckers, O. vulgaris may not need to have many suckers because they enter the planktonic mode of life after hatching, however O. ocellatus may need to have many suckers, because they should adapt to the benthic mode of life. And also the just hatched juvenile larvae of O. minor (bearing many suckers more than O. ocellatus) enter the benthic mode of life (benthic larval stage) after hatching. Therefore, the total number of the suckers on each short arm of the hatched juvenile larvae can be used for determining whether an octopus species has planktonic larval stages or benthic larval stage (benthic mode of life). In particular, The intracohort cannibalism phenomena appeared at the hatched juvenile larval stage because the larval stage of O. ocellatus and O. minor enter into the benthic larval stage in the early stage, unlike entering into the plaktonic larval stage in other Octopus species such as O. vulgaris: at this time, the early hatched larvae fed the late hatched larvae (they are the same species and almost same ages). Therefore, the intracohort cannibalism pheneomena occur in the just hatched juvenile stage of only O. ocellatus and O. minor.

Metabolomic analysis of competent larvae and juvenile veined rapa whelks (Rapana venosa)

Metamorphosis of a planktonic larval stage to a benthic juvenile is an important process in many marine invertebrates including the whelk, Rapana venosa, but understanding of the variety of molecular mechanisms underlying metamorphosis in different invertebrate clades is still poor. The present study examined the metabolic profiles of competent larval and post-larval stages of R. venosa using GC-MS. The whelk egg capsules were collected in Laizhou Bay, Shandong, China, in June 2015, and the larvae and post-larvae were cultured in the laboratory. A total of 263 metabolites were detected, 53 of which had different concentrations in larvae and post-larvae: 29 that were apparently higher following metamorphosis and 24 that were lower. Among the metabolites whose concentrations were higher in post-larvae, quinoline-4-carboxylic acid, the dipeptide cysteinylglycine, and anandamide were the most abundant. The metabolites present in higher concentrations in the competent larvae were a suite of oligosaccharides ( maltotriose, glucose-6-phosphate, cellobiose, and maltose), L-homoserine, adrenosterone, and sarcosine. Although the roles of these and other metabolites in whelk development are not yet completely known, they provide some clues to the changes in energy metabolism and cell signaling that take place during metamorphosis.

Predicting the effectiveness of depth-based technologies to prevent salmon lice infection using a dispersal model

Salmon lice is one of the major parasitic problems affecting wild and farmed salmonid species. The planktonic larval stages of these marine parasites can survive for extended periods without a host and are transported long distances by water masses. Salmon lice larvae have limited swimming capacity, but can influence their horizontal transport by vertical positioning. Here, we adapted a coupled biological-physical model to calculate the distribution of farm-produced salmon lice (Lepeophtheirus salmonis) during winter in the southwest coast of Norway. We tested 4 model simulations to see which best represented empirical data from two sources: (1) observed lice infection levels reported by farms; and (2) experimental data from a vertical exposure experiment where fish were forced to swim at different depths with a lice-barrier technology. Model simulations tested were different development time to the infective stage (35 or 50°-days), with or without the presence of temperature-controlled vertical behaviour of lice early planktonic stages (naupliar stages). The best model fit occurred with a 35°-day development time to the infective stage, and temperature-controlled vertical behaviour. We applied this model to predict the effectiveness of depth-based preventive lice-barrier technologies. Both simulated and experimental data revealed that hindering fish from swimming close to the surface efficiently reduced lice infection. Moreover, while our model simulation predicted that this preventive technology is widely applicable, its effectiveness will depend on environmental conditions. Low salinity surface waters reduce the effectiveness of this technology because salmon lice avoid these conditions, and can encounter the fish as they sink deeper in the water column. Correctly parameterized and validated salmon lice dispersal models can predict the impact of preventive approaches to control this parasite and become an essential tool in lice management strategies.

Composition of decapod larvae in a northeastern Brazilian estuarine inlet over a full tidal cycle

ABSTRACT. Composition changes of decapod larvae in a neotropical estuarine inlet (Catuama inlet, northeast Brazilian coast) were studied in a complete tidal cycle in August 2001. Sampling was performed at three stations at two or three depth levels that were located along a transect across the inlet. The collections were performed in 3 h intervals under a neap tide regime. Samples were taken with a pump and the water was filtered through 300 μm plankton net. 27 planktonic decapod taxa were identified, which included the first larval stages of the coastal and oceanic shrimps Lucifer faxoni and Acetes americanus, besides larvae of the estuarine and coastal decapods Pinnixa spp., Uca spp., Petrolisthes armatus , Upogebia spp. and Alpheidae, which were the most frequent taxa. All of the planktonic larval stages were observed for most of the decapods, suggesting that the probable exportation from the estuary is to the inner adjacent shelf area, instead of the outer oceanic area. Keywords: decapod larvae, meroplankton, tidal changes, neotropical estuary, northeastern Brazil.

Testing hypotheses on the origin and dispersion of Limnoperna fortunei (Bivalvia, Mytilidae) in the Iguassu River (Paraná, Brazil): molecular markers in larvae and adults

The invasive bivalve Limnoperna fortunei (Dunker 1857) was introduced in South America in 1991, with the first occurrence in Brazil in 1998. In the Iguassu River, the species was recorded in 2001; however, it is unknown how it was introduced and spread. Adults and larvae were sampled in Iguassu and Parana Rivers, and the genetic profiles were compared. The species was absent in the upper reaches and only larvae were found, in low densities, in intermediary reaches. The L. fortunei populations from the lower Iguassu River presented no genetic differentiation among themselves, suggesting strong connectivity, and were significantly different from the Parana River populations, most likely because of Iguassu Falls. Furthermore, the results suggest that the Parana River represents the source of propagules to the Iguassu River. Generally, no significant differences were observed between the genetic structure inferred from adults and larvae. Only the population from the Iguassu National Park, a lotic environment, differed from the remaining subpopulations. The characterization of genetic profile using larval stages of L. fortunei populations was satisfactory, and represents an important protocol for studying the population genetics of aquatic species with planktonic larval stages.

Unravelling the effects of gene flow and selection in highly connected populations of the silver-lip pearl oyster (Pinctada maxima)

Many marine organisms often display weak levels of population genetic structuring as a result of both environmental characteristics (e.g., ocean currents) and life history traits (e.g., widely dispersed planktonic larval stages) maintaining high levels of gene flow. This can lead to the assumption that these organisms can be managed as a single stock based on high levels of population connectivity. However, this neglects to account for other micro-evolutionary forces such as selection, which also shape these populations. This study utilizes 1130 genome-wide SNP loci to unravel the effects of gene flow and selection shaping three highly connected populations of the silver-lip pearl oyster (Pinctada maxima) in the ecologically and economically important Indo-Pacific region (Aru, Bali, and West Papua). Twenty-two loci under directional selection were identified amongst the populations, providing further supporting evidence of strong local adaptation (i.e., G×E effects) among populations in this region. Global Fst values for directional outliers (0.348) were up to eight times greater than for neutral markers (0.043). Pairwise Fst comparisons between Aru and Bali revealed the largest directional differences (0.488), while Bali and West Papua had the least (0.062). Unrooted neighbour-joining (NJ) distance trees and genetic diversity indices of directional outliers revealed that individuals from Bali and West Papua had reduced allelic variation (MAFavg=0.144, Ho=0.238 and MAFavg=0.232, Ho=0.369, respectively) compared to Aru (MAFavg=0.292, Ho=0.412). This indicates that directional selection is most likely acting upon genetic variation within the Bali and West Papua populations. NJ distance trees, discriminant analysis of principal components, and Fst analyses of directional outliers revealed two divergent groups (“Bali/West Papua”; “Aru”) that had previously gone unrecognized. This study not only illustrates that relatively strong local adaptive forces are occurring despite high gene flow, but identifies the populations that are most likely experiencing selection. Additionally, this study highlights the need to understand all micro-evolutionary forces acting on populations when resolving stock structure.

The sensitivity of the early benthic juvenile stage of the European lobster Homarus gammarus (L.) to elevated pCO2 and temperature

The early benthic juvenile stage of many marine invertebrates is a key step in the transition from the planktonic larval stages to the benthic adult stage. It is characterised by high mortality, in part, due to sensitivities to abiotic factors. The impacts of elevated pCO2 and temperature on the physiology and life history of these sensitive life stages are, however, poorly understood. Consequently, the aim of the present study was to investigate the vulnerability of survival, growth, metabolic rate, feeding rate, organic content, and carapace mineralisation of the early benthic juvenile stage of the European lobster Homarus gammarus (L.) to predicted levels of elevated pCO2 [ocean acidification (OA) and carbon capture and storage (CCS) scenarios] and elevated temperature [ocean warming (OW)]. Early benthic juvenile H. gammarus exhibited increased mortality under both OA and CCS conditions at both experimental temperatures, and these mortalities were due to moult death syndrome. There were OA-related reductions in metabolism, food acquisition, and carapace mineral content, while CCS-exposed lobsters exhibited severe shell dissolution. We suggest that disruption of metabolic and calcium homoeostasis is associated with, and possible the cause of, the increased incidence of moult-related mortalities in juvenile lobsters. We conclude that early benthic juvenile lobsters are sensitive, in terms of physiology and life history traits, to both OA and CCS, with OW sometimes mitigating and at other times increasing sensitivities.

THE LITTLE BIVALVE Planktomya UNMASKED

The enigmatic bivalve Planktomya henseni has masqueraded as a holoplanktonic animal for nearly a century. Allen and Scheltema (1972) showed that all the evidence pointed to a benthic clam with an unusually long planktonic larval stage. This benthic clam has finally been found in the tropical western Atlantic, and appears to be a member of the Family Sportellidae. Comparison with fossil species in this family shows a trend toward a large prodissoconch and apparently a long planktonic larval stage

Genetic Population Structure of Macridiscus multifarius (Mollusca: Bivalvia) on the Basis of Mitochondrial Markers: Strong Population Structure in a Species with a Short Planktonic Larval Stage.

The clam Macridiscus multifarius with a planktonic larval stage of about 10 days is an ecologically and economically important species in the coastal regions of China. In this study, 3 mt-DNA markers (COI, 12S rRNA, and ND1) were used to investigate the population structure and demography of wild M. multifarius populations in 3 coastal localities of the East China Sea (ZS and ZP populations) and Beibu Gulf in the South China Sea (BH population). Sequences of 685 bp in COI, 350 bp in 12S rRNA, and 496 bp in ND1 were determined. High level and significant F ST values were obtained among the different localities on the basis of either COI (F ST = 0.100–0.444, p < 0.05) or 12S rRNA (F ST = 0.199–0.742, p < 0.05) gene, indicating a high degree of genetic differentiation among the populations. F ST values were significant but weak for the ND1 gene because it is highly conservative. The median-joining network suggested an obvious genetic differentiation between ZS and BH populations, and the finding is consistent with the results of our demographic analyses using the unweighted pair group method with arithmetic mean. Our study unraveled the extant population genetic structure of M. multifarius and explained the strong population structure of a species with a short planktonic larval stage species; this information could be useful for fishery management measures, including artificial breeding and conservation.