Metallothionein responses in the Asiatic clam (Corbicula fluminea) after exposure to trivalent arsenic

The main objective of this work was to evaluate arsenic effects on metallothionein (MT) induction by exposing a freshwater Asiatic clam (Corbicula fluminea) to different concentrations of this metalloid. The presence of MT-like proteins was detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis and compared with a standard rabbit MT. In addition, the polarographic response showed good correspondence between standard MT and MT-like curves from C. fluminea, allowing MT quantification. The results show that clams exposed to different concentrations of arsenic are able to induce significant levels of MTs. Although variability was found in MT induction, significant differences in MT levels were found after 28 days of exposure in all treatments in comparison with the controls, suggesting that exposure to arsenic induced MT-like proteins in C. fluminea.     

Metallothionein responses in the Asiatic clam (Corbicula fluminea) after exposure to trivalent arsenic

The main objective of this work was to evaluate arsenic effects on metallothionein (MT) induction by exposing a freshwater Asiatic clam (Corbicula fluminea) to different concentrations of this metalloid. The presence of MT-like proteins was detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis and compared with a standard rabbit MT. In addition, the polarographic response showed good correspondence between standard MT and MT-like curves from C. fluminea, allowing MT quantification. The results show that clams exposed to different concentrations of arsenic are able to induce significant levels of MTs. Although variability was found in MT induction, significant differences in MT levels were found after 28 days of exposure in all treatments in comparison with the controls, suggesting that exposure to arsenic induced MT-like proteins in C. fluminea.     

Linking environmental warming to the fitness of the invasive clam Corbicula fluminea

Climate warming is discussed as a factor that can favour the success of invasive species. In the present study, we analysed potential fitness gains of moderate warming (3 °C above field temperature) on the invasive clam Corbicula fluminea during summer and winter. The experiments were conducted under seminatural conditions in a bypass-system of a large river (Rhine, Germany). We showed that warming in late summer results in a significant decrease in the clams' growth rates (body mass and shell length increase) and an increase in mortality rate. The addition of planktonic food dampens the negative effect of warming on the growth rates. This suggests that the reason for the negative growth effect of temperature increase in late summer is a negative energetic balance caused by an enhanced metabolic rate at limited food levels. Warming during early summer revealed contrasting effects with respect of body mass (no warming effect) and shell length (increased shell growth with warming). This differential control of both parameters further enhances the loss of the relative (size-specific) body mass with warming. In contrast, warming in winter had a consistently positive effect on the clams' growth rate as demonstrated in two independent experiments. Furthermore, the reproduction success (as measured by the average number of larvae per clam) during the main breeding period (April) was strongly enhanced by experimental warming during winter, i.e. by eight times during the relatively cold winter 2005/2006 and by 2.6 times during the relatively warm winter 2007/2008. This strong, positive effect of moderate winter warming on the clams' fitness is probably one reason for the recent invasion success of C. fluminea in the northern hemisphere. However, warm summer events might counteract the positive winter warming effect, which could balance out the fitness gains.     

水体腐殖酸影响下河蚬对低浓度镉的蓄积和释放

研究了水体中低浓度镉(1μg?L-1)单独存在以及低浓度镉(1μg?L-1)和腐殖酸(1mg?L-1、10mg?L-1)共存情况下河蚬对低浓度镉的蓄积和释放,以了解实验室条件下水体腐殖酸对河蚬蓄积和释放的影响。在实验室中曝露15d内分别于1d、2d、3d、10d、15d取样,对比实验结果发现两种处理方式均存在镉在河蚬体内存在蓄积的现象,该蓄积效应与其蓄积时间呈显著线性正相关,但在腐殖酸影响下,河蚬对低浓度镉的蓄积减少。释放10d和20d的实验结果发现低浓度镉进入河蚬体内后难以释放。腐殖酸对镉从河蚬体内的释放效应影响极小。     

非生物因子对河蚬重金属富集量的影响

对影响长江口滨岸带河蚬体内重金属富集量的4个主要非生物因子依次进行分析。结果表明,较高温度有助于河蚬对Cu、Zn、Cr、Ni的吸收;盐度对河蚬的重金属累积量影响比较复杂,仅在秋季表现出一定相关性,春季盐度影响不大;河蚬体内Cu含量与沉积物粒径存在显著正相关,Zn与沉积物中有机质含量存在一定正相关,Pb与沉积物中有机质含量存在着负相关;河蚬体内重金属元素两两间的相关性明显,多种元素间的相互作用机理值得进一步探讨。     

Ecological resistance to the invasion of a freshwater clam,Corbicula fluminea: fish predation effects

Summary Fish predation is shown to have a twenty nine fold effect on the abundance of the invasive freshwater clam, Corbicula fluminea, in a Texas reservoir. This predation has prevented the clam from establishing the high densities commonly reported for it elsewhere. The high magnitude of the fish effect is attributed to Corbicula being an invader to this reservoir and not being able to cope well with the mix of resident fish species. In the absence of fish, colonization of the reservoir by Corbicula is spatially patchy. When fish interact with these clams, they remove sufficient numbers of individuals from dense patches to create the appearance of a spatially uniform distribution.     

蓝藻堆积对河蚬N2O释放通量及其肠道细菌群落结构的影响

【背景】底栖动物是湖泊生态环境的重要组成部分,在泥水界面氮迁移转化中扮演着重要的角色,是一个潜在的N_2O释放源,其N_2O释放量与栖息环境有关。蓝藻堆积区通常是湖泊N_2O释放的热点区域,其水质环境不同于无藻区。【目的】为了解蓝藻堆积与无藻堆积时底栖动物河蚬N_2O释放情况。【方法】采用室内微宇宙实验,以河蚬为研究对象,通过气相色谱和现代分子生物学相结合的技术测定蓝藻堆积区域底栖动物N_2O释放特征及其内在微生物学机制。【结果】蓝藻堆积区河蚬N_2O释放通量为447.2pmol/(ind·h),相比无藻区河蚬减少63%左右。河蚬肠道内总细菌及反硝化细菌对蓝藻堆积有不同的响应。454测序结果显示,无藻区河蚬肠道内细菌以变形菌门(β-和δ-变形菌纲)、绿弯菌门和拟杆菌门为主,三者相对丰度为67.3%,而蓝藻堆积区河蚬肠道细菌优势类群为变形菌门(α-和β-变形菌纲),相对丰度达到85.8%。Chao1和Shannon指数表明,蓝藻堆积区河蚬肠道细菌丰富度和多样性低于无藻区河蚬。对河蚬肠道内具有反硝化功能细菌进一步分析发现,蓝藻堆积区河蚬肠道内反硝化菌相对丰度可达到22.6%,是无藻区河蚬的2.3倍,反硝化作用得到增强。【结论】蓝藻堆积导致河蚬肠道内细菌丰富度和多样性降低,反硝化功能菌丰度增加,完全反硝化作用得以强化,导致河蚬N_2O释放通量降低。研究结果有助于揭示富营养化中湖泊底栖动物的环境效应,为湖泊温室气体控制提供理论支撑,具有重要的理论和现实意义。     

巢湖富营养化对河蚬和环棱螺分布及种群密度影响

2001年9月和2002年9月两次对巢湖河蚬和环棱螺的调查表明,在富营养化程度较重的西湖区,河蚬生物量分别为17.87和47.29 g·m^-2;环棱螺生物量分别为45.45和12.56 g·m^-2.而在富营养化程度较轻的东湖区,河蚬的生物量分别为67.86和96.18 g·m^-2;环棱螺的生物量分别为32.00和31.21 g·m^-2.河蚬和环棱螺的种群密度和生物量均随水体富营养化的加剧而下降.近岸带河蚬和环棱螺的密度和生物量明显高于敞水区.河蚬的分布型为核心型,而环棱螺更接近随机性分布.河蚬和环棱螺的种群密度和生物量与水深均无明显相关(P>0.05).环棱螺生物量与总氮TN、硝态氮NO₃-N、总磷TP和溶解性磷PO₄-P浓度呈显著负相关,而河蚬生物量仅与PO₄-P呈负相关.现有河蚬资源量与1981年相比有较大幅度的下降.探讨了其它环境因子对河蚬和环棱螺分布和生长的影响.     

Comparison of oxygen consumption in freshwater mussels (Unionidae) from different habitats during declining dissolved oxygen concentration

The rate of oxygen consumption (OC) of 9 species of freshwater mussels was measured under declining dissolved oxygen (DO) concentrations. The effects of temperature for some species also was investigated. The pattern of the OC vs. DO curve for each species was used in a hyperbolic model to compare abilities to regulate OC under low oxygen conditions. At 24.5 °C, Pyganodon grandis (from lakes), Amblema plicata and Quadrula pustulosa (from mud or sand in large rivers), Elliptio complanata (from pool areas in rivers), and Elliptio fisheriana and Elliptio lanceolata (from bank margins of rivers) were better able to maintain OC under low DO than were Villosa iris and Villosa constricta (which inhabit riffles) and Pleurobema cordatum (found in rivers with moderate flow). Villosa iris was especially sensitive to low oxygen conditions. The ability to maintain normal OC at low DO was improved considerably at 16.5 °C for V. iris, P. grandis and E. complanata. It is concluded that oxygen regulation ability appears to be related to the degree of hypoxia a species normally experiences in its habitat type, and it is enhanced at low temperature. The measurement of OC vs. DO may be a useful technique for estimating DO water quality criteria for endangered species because it is noninvasive.     

Valve closure responses of the Asiatic clam Corbicula fluminea exposed to cadmium and zinc

The valve movement patterns of immobilized Asiatic clams (Corbicula fluminea) were monitored during exposure to constant concentrations of cadmium (0.0, 0.1, 0.2, 0.3, and 0.4 mg 1^–1) or zinc (0.0, 0.1, 0.3, 0.5, and 0.9 mg 1^–1) for 24 h following a 24-h acclimation period. Data indicate that the duration of response was concentration dependent and toxicity related. Durations of periods with valves parted declined as the concentration of heavy metal increased. Behavior was consistent for both mean time to first closure following the initial exposure and mean time per valve parting episode over a 24-h exposure period. Mean time per valve parting episode during the 24-h exposure period ranged from 600 minutes for control trials to 36 and 69 minutes for the highest concentrations of cadmium and zinc tested, respectively. There was no association between durations of periods with valves sealed and solutions of cadmium; however, lengthening durations of periods with valves sealed coincided with exposure of clams to progressively more concentrated zinc solutions. In addition, Asiatic clams demonstrated a greater rate of response (decline in the duration of periods with valves parted) to progressively more concentrated solutions of cadmium than to comparable increases in the concentrations of zinc solutions.     

Heat shock protein response to thermal stress in the Asiatic clam,Corbicula fluminea

A recent approach to evaluate environmenta induced damages has been damages has been suggested, based on the stress response. The approach involves the detection of stress protein induction in organisms to infer about environmental conditions in their surroundings. However, to be an indicator of adverse biological effects in the environment, the elevation of stress proteins should be compared to a response pattern for the experimental species. JuvenileCorbicula fluminea, collection from a control site, were submited to heat-shock stress in the laboratory to obtain the stress response pattern under normal and extreme conditions. Acclimated to 26°C, the specimens were submited to 29, 32, 35 and 38°C, for 96 h. After 1, 2, 4, 8, 24, 48, 72 and 96 h of exposure, clams were removed from each vial and prepared for stress protein analysis. Animals from the control site were frozen in liquid nitrogen at the time of collection, and prepared for stress protein analysis. Hsp60 and 70 were detected by immunoreactivity after separation on 12.5% polyacrylamide gels and transference to nitrocellulose by western blotting, to determine the stress protein concentrations. The result showed that hsp70 increased at 4h from the beginning of the experiment and progressed over the 96 h experimental period in animals exposed to 35°C. However hsp70 levels decreased between 4 h and 24 h for the clams stressed at their lethal temperature of 38°C. Immunoblotting with hsp60 showed similar reactivity. At 38°C there was an increase in the amount of hsp60 at 4h, reaching a maximum eight-fold level at 8h. By 96h, the amount decreased to levels lower than those observed at 4h. At 38°C the level of hsp60 began to decrease at 8 h and continue to decline to 24 h when the clams died. The data support the hypothesis of increasing concentrations of stress protein until the heat shock approaches the thermal limits for the species. The results of this research suggest the usefulness of using the stress response as a diagnostic in environmental toxicology. They confirm that the sps response may serve as a valid biomonitoring tool under chronic, sublethal exposures when it is still possible to prevent effects at organismal or higher organizational levels.     

Introduced bivalves in freshwater ecosystems: the impact of Corbicula on organic matter dynamics in a sandy stream

Previous research on Corbicula fluminea (a well-established, non-native bivalve) has clearly shown that this single species impacts ecosystem processes such as nutrient and dissolved organic carbon cycling in the water column of streams. Surprisingly, little was known about how Corbicula might influence similar processes in streambed sediments. Here, we used both laboratory and field experiments to determine how filter- and pedal-feeding by Corbicula impact organic matter dynamics in the sandy streambed (Goose Creek, Virginia). Corbicula consumed significant quantities of organic material in the streambed when conditions favored pedal-feeding but increased buried organic matter stores when filter-feeding promoted deposition of organic matter (by production of feces and pseudofeces). Corbicula contributed significantly to total benthic community respiration (and thus carbon dioxide production), and used pedal-feeding on benthic organic material to grow at a faster rate than that possible by filter-feeding alone. Corbicula should be an important coupler between benthic and pelagic processes because this bivalve uses organic matter from both the water column and the stream sediments. Given the widespread occurrence of this species, we speculate that the introduction of Corbicula may have had major implications for organic matter dynamics in this and many other streams in the United States. Received: 5 October 1998 / Accepted: 6 February 1999     

长江口滨岸带河蚬的时空分布特征及其指示作用

以长江口滨岸湿地生态系统习见的大型底栖动物河蚬为对象,研究了河蚬种群密度、生物量的时空分布特征,分析了河蚬及环境中悬浮颗粒物和沉积物中的重金属含量.结果表明,不同季节、不同采样点以及相同采样点的不同断面河蚬的分布都有差异.河蚬种群密度、生物量的季节分布趋势是春、秋两季＞夏季;其中,浒浦河蚬的年度平均种群密度与平均生物量最高;河蚬在崇明中潮滩的种群密度、生物量高于低潮滩和高潮滩.研究表明,河蚬对沉积物中的重金属元素Cu、Zn富集能力强,对Pb、Cr的富集能力弱,其中,河蚬体内Pb含量与沉积物中Pb含量呈显著负相关(R=-0.924,P<0.01).     

Detection and phylogenetic analysis of norovirus in Corbicula fluminea in a freshwater river in Japan

To study the molecular epidemiology of noroviruses (NoVs) in bivalves residing in freshwater rivers, we detected, quantified and phylogenetically analyzed the NoV genome in purified concentrates obtained from the gills and digestive diverticula of Corbicula fluminea in a freshwater river in Gunma Prefecture, Japan. We detected the NoV genome in 35 of the 58 C. fluminea samples. Based on our phylogenetic analysis, the NoV genome detected in the samples was classified into 4 genotypes (GI/1, GI/2, GI/3 and GI/4) in genogroup I and 5 genotypes (GII/3, GII/4, GII/5, GII/8 and GII/12) in genogroup II. The phylogenetic tree showed wide genetic diversity among the genogroups. In addition, more than 10(4) copies of the NoV genome were detected in 2 of 35 samples. These results suggest that the freshwater bivalve C. fluminea is a reservoir for NoVs, similar to seawater bivalves such as oysters.     

Cytological evidence of spontaneous androgenesis in the freshwater clam Corbicula leana Prime

 Cytological observations and DNA microfluorometry of the hermaphrodite freshwater triploid clam Corbicula leana revealed unusual androgenetic development as follows: (1) the maternal genome of zygotes was extruded as two polar bodies just after karyokinesis of the first meiosis, (2) only chromosomes derived from one male pronucleus constituted the metaphase of the first cleavage of zygotes, (3) DNA content of 7-day-old veliger larvae was identical to the somatic cells of the parent. This spontaneous androgenetic process in C. leana zygotes is the first case in the phylum Mollusca and may be related to the specialized mode of reproduction; i.e. hermaphroditism and self-fertilization. Received: 22 September 1997/Accepted: 7 December 1997     

The impact of an introduced bivalve (Corbicula fluminea) on the benthos of a sandy stream

1. The effect of an exotic, burrowing bivalve ( Corbicula fluminea ) on the benthic fauna of a sandy-bottomed stream was assessed by field and laboratory experiments. Corbicula differs from other freshwater, non-native bivalves in that it both filter- and pedal-feeds and thus has the potential to influence the streambed community in different ways.
2. In the field, cages were used to vary the abundance of Corbicula in the streambed. Increasing abundance of Corbicula was negatively associated with the abundance of benthic bacteria and flagellates but had no apparent effect on other protists or meiofauna.
3. In the laboratory, we compared the effect of Corbicula on the benthic community when the bivalves were able both to filter- and pedal-feed with that when they were able only to filter-feed. Bivalves restricted to filter-feeding were placed in sediment lacking benthic fauna and organic matter, then the benthos in nearby natural sediment was compared with the community present when Corbicula was able to move freely through the sediment and both to filter- and pedal-feed. Corbicula able to pedal-feed were again associated with a decreased abundance of benthic flagellates and bacteria, as well as diatoms.     

Evidence for cryptic hybridization between different evolutionary lineages of the invasive clam genus Corbicula (Veneroida,Bivalvia)

We studied two Corbicula morphotypes in a syntopic population in the Rhine River in order to reveal their taxonomic, reproductive and phylogenetic relationship, using morphometrics, DAF‐fingerprinting, mitochondrial COI and nuclear ITS1 sequence variation. Morphometric analysis showed that two statistically distinguishable morphotypes with few intermediates were present.Mitochondrial sequence analysis detected two divergent clades. DAF‐fingerprinting revealed three highly distinctive multilocus genotypes. Two of the multilocus genotypes were significantly associated with different morphotypes and mitochondrial lineages. The third genotype B, however, was found in both morphotypes, intermediates and mitochondrial lineages. Conclusive evidence for hybridization came from RFLP analysis of the nuclear ITS1 locus. We interpret the hybrids as F1 hybrids between different evolutionary lineages. Integration of Corbicula sequences from all over the world into Maximum Parsimony analysis suggested a simultaneous radiation resulting in several evolutionary lineages whose species status remained doubtful. An unequivocal taxonomic assignment of the two evolutionary lineages in the Rhine population was therefore not possible.     

Effects of invasive clam (Corbicula fluminea) die‐offs on the structure and functioning of freshwater ecosystems

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All-male asexuality: origin and maintenance of androgenesis in the Asian clam Corbicula

Androgenesis is a rare form of asexual male reproduction found in disparate taxa across the Tree of Life. Phylogenetic analyses of mitochondrial genes suggest that androgenesis has arisen repeatedly in the Asian clam genus Corbicula. Two of these androgenetic species have been introduced to North America. Multiple lines of genetic evidence suggest that although nuclear recombination between these two species is rare, mitochondrial genome capture is a frequent consequence of androgenetic parasitism of heterospecific eggs. Egg parasitism may also rarely result in partial nuclear genome capture between closely related species of Corbicula, which provides a mechanism for the otherwise clonal species to avoid the deleterious effects of asexuality. Egg parasitism among congeners may explain why androgenesis has been maintained in Corbicula after fixation and has not yet led to population extinction. This mechanism also provides an explanation for the apparent multiple origins of androgenesis in Corbicula as seen on the mitochondrial DNA phylogeny. We suggest that a single androgenetic lineage may have repeatedly captured mitochondrial genomes (as well as portions of nuclear genomes) from various sexual species, resulting in several distinct androgenetic species with distantly related mtDNA genomes and divergent morphologies.     

Reproduction and development of the freshwater clam Corbicula australis in southeast Australia

The freshwater clam Corbicula australis is an important component of the macrobiota of the river systems of southeast Australia. Reproduction of two populations of this clam in the Nepean River at Douglas Park and Menangle was investigated to document the gametogenic cycle, larval morphology and to determine when they incubate embryos. C. australis is a simultaneous hermaphrodite and broods its young in the inner demibranchs. The gonads are ovotestes with oogenic and spermatogenic regions in each ascinus. The sperm are biflagellate, a condition unique in the Bivalvia to clonal corbiculids. Gametogenesis was continuous and did not exhibit a seasonal pattern. In contrast, spawning and incubation of embryos was limited to the warmer months of the year. Embryos were present in the gills from October to May. C. australis develops through a modified veliger larva with a vestigially ciliated velum which is not used for swimming or particle capture. The velum is covered by microvilli and it is suggested that the velar epithelium may be specialised for nutrient uptake in the marsupial environment. C. australis produces several clutches each year and the young are released as advanced juveniles with a well-developed foot. Reproductive output differed between the two populations. This was in part due to the larger size of the clams from Menangle and may also reflect the enhanced productivity at this site. The suite of life history traits exhibited by C. australis: hermaphroditism, potential for self-fertilization/androgenesis, brooding progeny to the crawl-away juvenile stage and a high reproductive output, provide for rapid colonization and population growth in this clam which typically inhabits disturbance prone sandy lotic habitats.