A review and new analysis of trophic interactions between Prorocentrum minimum and clams, scallops, and oysters

There has been no consensus on whether Prorocentrum minimum is “toxic,” despite sporadic reports suggesting possible shellfish toxicity and laboratory studies showing harmful effects of this dinoflagellate on molluscan shellfish. Shellfish toxicity outbreaks associated with natural blooms of P. minimum have been confounded by co-occurrence of other toxic phytoplankton. Laboratory studies have demonstrated unequivocally that some P. minimum isolates can produce toxins that kill mice on injection, but the bioactive compound or compounds remain unidentified, and accumulation of toxin in grazing mollusks has not been demonstrated. Laboratory experiments testing the responses of grazing mollusks to P. minimum cultures have yielded variable results, ranging from mortality in scallops and oysters to normal growth of oysters. Effects observed in the laboratory include rejection as pseudofeces by clams, poor larval development in oysters, tissue pathologies (sometimes transient) in oysters and scallops, and systemic immune responses in oysters and scallops. Several recent studies have provided evidence that variation in toxicity of P. minimum is dependent on environmental conditions and their effects on the physiology of this dinoflagellate. Accordingly, seemingly conflicting observations from field and laboratory studies may be explained by transient toxin expression in P. minimum.     

南洞庭湖区软体动物物种多样性评估及保护对策

洞庭湖孕育和维持了较高和独特的软体动物多样性。尽管有关该湖软体动物的调查较多, 但多分散于各文献中。本文结合文献调研和现场调查(2013-2018年), 系统评估了南洞庭湖区软体动物物种多样性, 解析驱动群落格局演变的关键因子, 并提出合理的保护对策。共记录2纲5目14科33属87种(腹足纲41种, 双壳纲46种), 其中本调查记录54种, 隶属于2纲5目12科31属, 包括腹足纲22种, 双壳纲32种。评估结果显示处于近危和受威胁等级物种21种, 包括腹足纲4种和双壳纲17种。调查区域软体动物平均密度和生物量分别为173.1 ind./m ²和279.3 g/m ²。优势种为河蚬(Corbicula fluminea)、大沼螺(Parafossarulus eximius)、铜锈环棱螺(Bellamya aeruginosa)、卵河螺(Rivularia ovum)。基于距离的冗余分析(distance-based redundancy analysis, dbRDA)结果显示, 局域环境因子(底质类型、水深、pH、总溶解固体和总磷)制约软体动物的群落变异。另外, 区域内的人类活动(如商业采砂、建坝和沿岸土地利用、过度捕捞和非法电捕等)亦深刻影响软体动物的生存。这些人类干扰已导致软体动物物种多样性显著下降, 可能造成一些特有物种的局域性灭绝。为了恢复和保护软体动物物种多样性和资源, 应采取一系列对策, 包括管控合法的挖沙业和取缔非法挖沙业、禁止过度捕捞和非法电捕、维持水文的自然节律、恢复沿岸自然湖滨带和控制点源和面源污染物排入等。我们呼吁尽快在南洞庭湖区建立软体动物国家级自然保护区, 以保护该湖区(可能是整个洞庭湖)残存的软体动物物种多样性和特有性。     

A new approach to molecular biosurveillance of invasive species using DNA metabarcoding

Non‐indigenous species (NIS) reach every corner of the world, at times wreaking havoc on ecosystems and costing the global economy billions of dollars. A rapid and accurate biosurveillance tool tailored to a particular biogeographic region is needed to detect NIS when they are first introduced into an area as traditional detection methods are expensive and require specialized expertise. Metabarcoding of environmental and community DNA meets those biosurveillance requirements; a novel tool tailored to the Northwest Pacific Ocean is presented here using an approach that could revolutionize early detection of NIS. Eight newly designed genetic markers for multiple gene regions were implemented to meet the stringent taxonomic requirements for the detection of NIS across four major marine phyla. The tool was considered highly successful because it identified 12 known NIS in the study area and a further seven species representing potential new records. Overall community composition detected here was statistically different between substrate types; zooplankton sampling accounted for significantly higher species richness than filtered sea water in most cases, but this was dominated by mollusk and arthropod species. Both substrate types sampled were required to identify the wide taxonomic breadth of known NIS in the study area. Intensive sampling is known to be paramount for the detection of rare species, including new incursions of NIS, thus it is recommended to include diverse DNA sampling protocols based on species’ life‐history characteristics for broad detection capacity. Application of a metabarcoding‐based molecular biosurveillance tool optimized for biogeographic regions enables rapid and accurate early detection across a wide taxonomic range to allow quick implementation of eradication or control efforts and potentially mitigate some of the devastating effects of NIS worldwide.     

Continuous Hydrolysis of Soluble Starch by Free β-Amylase and Pullulanase Using an Ultrafiltration Membrane Reactor

Enzyme hydrolysis of soluble starch by free β-amylase and pullulanase for the production of maltose was done by the simultaneous use of a stirred tank reactor and an ultrafiltration membrane. Higher conversions of starch to maltose were obtained in the permeates than that in a batch reaction. Using the basic mass balance and rate equations, concentrations of maltose, maltotriose, and substrate in the retentates and permeates could be simulated effectively. More than 99.9% of enzyme was found to be rejected by the membrane. The obtained volumetric productivities were several times higher than those reported in other systems. This system was found to have high maltose productivity with a short mean residence time, being easily controlled by transmembrane pressure.     

To eat or not to eat—relationship of lichen herbivory by snails with secondary compounds and field frequency of lichens

Aims The biochemical defense of lichens against herbivores and its relationship to lichen frequency are poorly understood. Therefore, we tested whether chemical compounds in lichens act as feeding defense or rather as stimulus for snail herbivory among lichens and whether experimental feeding by snails is related to lichen frequency in the field.Methods In a no-choice feeding experiment, we fed 24 lichen species to snails of two taxa from the Clausilidae and Enidae families and compared untreated lichens and lichens with compounds removed by acetone rinsing. Then, we related experimental lichen consumption with the frequency of lichen species among 158 forest plots in the field (Schw?bische Alb, Germany), where we had also sampled snail and lichen species.Important findings In five lichen species, snails preferred treated samples over untreated controls, indicating chemical feeding defense, and vice versa in two species, indicating chemical feeding stimulus. Interestingly, compared with less frequent lichen species, snails consumed more of untreated and less of treated samples of more frequent lichen species. Removing one outlier species resulted in the loss of a significant positive relationship when untreated samples were analyzed separately. However, the interaction between treatment and lichen frequency remained significant when excluding single species or including snail genus instead of taxa, indicating that our results were robust and that lumping the species to two taxa was justified. Our results imply lichen-feeding snails to prefer frequent lichens and avoid less frequent ones because of secondary compound recognition. This supports the idea that consumers adapt to the most abundant food source.     

Maternal impact on egg development in Lymnaea stagnalis: a growth factor is produced by the albumen gland in the reproductive tract

Summary

In the freshwater snail Lymnaea stagnalis, perivitellin fluid is the main source of nutrition for developing embryos; it contains predominantly galactogen and proteins. The fluid is produced by the albumen gland, a large exocrine organ in the female reproductive tract. To further define the protein products of this gland and provide more information about the maternal contribution to egg development, albumen glands were extracted and the extracts purified by reversed-phase HPLC. One major HPLC peak fraction exhibited neurotrophic activity when bioassayed on identified Lymnaea neurons in vitro; it has been partially sequenced and has the highest degree of sequence identity with epidermal growth factor (EGF). These results demonstrate that a growth factor with neurotrophic activity is produced by the albumen gland, and is packaged along with the eggs to serve a growth-promoting function in the embryo.     

Molluskan Dorsal–Ventral Patterning Relying on BMP2/4 and Chordin Provides Insights into Spiralian Development and Evolution

Although a conserved mechanism relying on BMP2/4 and Chordin is suggested for animal dorsal–ventral (DV) patterning, this mechanism has not been reported in spiralians, one of the three major clades of bilaterians. Studies on limited spiralian representatives have suggested markedly diverse DV patterning mechanisms, a considerable number of which no longer deploy BMP signaling. Here, we showed that BMP2/4 and Chordin regulate DV patterning in the mollusk Lottia goshimai, which was predicted in spiralians but not previously reported. In the context of the diverse reports in spiralians, it conversely represents a relatively unusual case. We showed that BMP2/4 and Chordin coordinate to mediate signaling from the D-quadrant organizer to induce the DV axis, and Chordin relays the symmetry-breaking information from the organizer. Further investigations on L. goshimai embryos with impaired DV patterning suggested roles of BMP signaling in regulating the behavior of the blastopore and the organization of the nervous system. These findings provide insights into the evolution of animal DV patterning and the unique development mode of spiralians driven by the D-quadrant organizer.     

Seasonal variations of Mediterranean interstitial opisthobranch assemblages

Characteristic seasonal cycles have been found for interstitial Opisthobranchs living in various sandy biotopes of different exposure in the Gulf of Marseilles (Mediterranean coast of France). Abnormal progressive degradation of the environment caused by increased human pollution and a striking decrease of regional wind frequency throughout a seven year period changed these cycles. The sensitivity of these interstitial Opisthobranchs to the degradation of their habitat makes them valuable biological indicators which could be used to identify clean sublittoral sandy bottoms which need to be protected.     

Comparison of quantitative gonad maturation scales in a temperate oyster (Crassostrea gigas) and a sub-tropical oyster (Crassostrea corteziensis)

Quantitative scales to evaluate maturity of female gonads were compared for a temperate oyster, Crassostrea gigas and a tropical oyster, Crassostrea corteziensis grown in the same locality. C. gigas had well-defined maturation and spawning periods and a resting phase in winter; in C. corteziensis mature individuals occurred most of the year and there were several spawning peaks. Of the quantitative scales used here, average oocyte diameter and gonad coverage area, much used for C. gigas, and ovary maturity index, less used, were inadequate to distinguish the reproductive pattern of C. corteziensis, since they both skewed the degree of maturation in vitellogenic stages in favor of C. gigas. Maximum oocyte diameter and maximum cytoplasm area were different among species at vitellogenic stages and also in previtellogenic stages. Nucleus:cytoplasm ratio was significantly different in previtellogenic and spawned stages between C. gigas and C. corteziensis. The Index of gonadal development was skewed in favor of C. gigas in postvitellogenic stage. The only scale that was comparable between species was reproductive potential, but it also was one of the most laborious. Other ordinal scales commonly used, such as a visual external evaluation of the gonad, only classified correctly a quarter of the stages.