Sex change and sequential hermaphroditism in Tegillarca granosa (Bivalvia: Arcidae)

This study aimed to confirm sex change in Tegillarca granosa to determine whether this species is a sequential hermaphrodite. Samples of bivalves were divided into two groups, namely, a 1+ year class (14 months) and a 2+ year class (26 months), for analysis. At the beginning of the study, 44.3% of T. granosa were female, and after one year, this increased to 53.9% in the same population. The increase of females in the population was greater in the 1+ year class (12.3%), when compared with the 2+ year class (6.5%). Overall, a sex change ratio of 15.1% (n = 104/688) was recorded for T. granosa. The sex change ratio of the 1+ year class (17.8%) was higher than that of the 2+ year class (12.1%), and displayed the tendency of being higher in the males (21.2%), than the females (6.2%). The results of this study indicate that T. granosa is a sequential hermaphrodite.     

Ultrastructure of the spermatogenesis of the cockle Anadara granosa L. (Bivalvia: Arcidae)

In this paper spermatogenesis and sperm ultrastructure of the cockle Anadara granosa are studied using transmission electron microscopy. The spermatocyte presents electron-dense vesicles and the arising axoneme that begins to form the flagellum. During spermatid differentiation, proacrosomal vesicles appear to migrate towards the presumptive anterior pole of the nucleus; eventually these vesicles become acrosome. The spermatozoon of Anadara granosa is of the primitive type. The acrosome, situated at the apex of the nucleus, is cap-shaped and deeply invaginated at the inner side. The spherical nucleus of the spermatozoon contains dense granular chromatin and shows invagination at the posterior poles. The centriole shows the classic nine triplets of microtubules. The middle piece consists of the centriolar complex surrounded by five giant mitochondria. It is shown that the ultrastructure of spermatozoa and spermiogenesis of Anadara granosa reveals a number of features that are common among bivalves. Received: 29 September 1998 / Received in revised form: 20 May 1999 / Accepted: 14 June 1999     

5个泥蚶群体遗传多样性的RAPD分析

采用随机扩增多态性DNA(RAPD)技术 ,对 5个泥蚶群体的遗传多样性进行了研究。在选择的 2 0个随机引物中共检测到 15 4个扩增片段 ,长度在 30 0bp～ 2 30 0bp之间 ,每个个体扩增条带在 1～ 11条不等。利用Popgen3.2和PHILIP统计软件 ,获得实验数据 ,确立了 5个群体间的亲缘关系。结果表明 :( 1)泥蚶的 5个地理群体分化不明显 ,没有形成不同的地理种群 ;( 2 )聚类分析显示 ,韩国群体与浙江群体亲缘关系最近 ,然后依次为山东群体和福建群体 ;( 3) 5个群体无论是在多态位点比例还是在平均遗传杂合度上都处于较高水平 ,说明泥蚶当前种质资源状况良好 ,遗传多样性水平较高 ,泥蚶养殖有很好的发展前景 ;( 4)与韩国野生群体相比 ,其他 4个泥蚶群体在多态位点比例和遗传平均杂合度上都有不同程度的降低 ,表明人为等因素已经开始影响到泥蚶的种质资源状况。因此 ,为持续发展泥蚶养殖业 ,必须加强保护泥蚶现有的种质资源并制定相应的渔业管理措施。     

重金属Cd2+和Cu2+胁迫下泥蚶消化酶活性的变化

为了探讨重金属Cd²⁺和Cu²⁺胁迫对泥蚶消化酶活性的影响,运用酶学分析的方法,按《渔业水质标准》（GB 11607）规定的Cd²⁺、Cu²⁺最高限量值的1、2、5、10倍设置重金属离子Cd²⁺、Cu²⁺浓度及其组合,研究了在重金属Cd²⁺、Cu²⁺胁迫下,30d内泥蚶3种消化酶活性的变化规律。结果表明：与空白对照组相比,在重金属Cd²⁺、Cu²⁺或其组合的胁迫下,较低浓度组泥蚶的淀粉酶活性实验前期增强（即被诱导）,实验后期减弱（即被抑制）,较高浓度组泥蚶的淀粉酶活性从实验一开始就减弱,并保持在较低水平,毒性比较,同一重金属高浓度 > 低浓度,不同重金属及其组合Cu²⁺ > （Cd²⁺+Cu²⁺）组合 > Cd²⁺;泥蚶脂肪酶的活性实验前期增强,实验后期转为微减弱或减弱,毒性比较,同一重金属高浓度 > 低浓度,不同重金属及其组合（Cd²⁺+Cu²⁺）组合 > Cu²⁺ > Cd²⁺;泥蚶胃蛋白酶的活性实验前期增强,且活性呈现升高-降低-再升高-再降低的变化,实验后期分别表现微增强、微减弱和减弱,毒性比较,同一重金属高浓度 > 低浓度,不同重金属及其组合（Cd²⁺+Cu²⁺）组合 > Cu²⁺ > Cd²⁺。可见：环境中的Cd²⁺和Cu²⁺对泥蚶的消化酶活性起着明显的影响作用。     

浙江乐清湾泥蚶的繁殖习性和生长特性

乐清湾泥蚶雌雄异体,在外形上难以区别,成熟时性腺包被整个内脏团,雌性性腺呈红色或桔黄色,雄性性腺呈乳白色,无性变现象。一般2龄性成熟,但在条件较好的蓄水塘中养殖的泥蚶也有1龄性成熟的现象。自然繁殖期为6月上旬至8月下旬。卵生,体外受精。产卵量大,一颗壳长为2～3em的亲蚶可产卵200—300万颗。乐清湾泥蚶终身生长,但生长速度较慢,且受水温、饵料、潮区、底质和养殖密度等因素影响,一般2年或3年方能达到商品规格。壳长生长前期快,后期慢;体重生长前期慢,后期快。壳长L(mm)与体重W(g)符合W=0．0004L^2.9949(R^2=0．9964)关系。     

Filtration and respiration of the deep living bivalve Acesta excavata (J.C. Fabricius, 1779) (Bivalvia; Limidae)

Here we report the first study of clearance rate and respiration rate of a deep living bivalve, Acesta excavata (J.C. Fabricius, 1779) (Mollusca: Limidae). We found that A. excavata had extreme values both for clearance and respiration rates compared to other bivalves. It has the second largest clearance rate ever reported, 13.36 l h^− 1 g^− 1, and the second lowest value of respiration rate, 0.12 ml O₂ h^− 1 g^− 1. The gill area of 7063 mm² g^− 1 is one of the largest found in bivalves so far. We suggest that these values indicate a physiological adaptation to the low and irregular food supply in the deep sea rather that a specific adaptation to depth.     

福建南北泥蚶种内分化的RAPD分析

采用随机扩增多态性DNA(RAPD)技术,对泥蚶在福建以南(广东汕头和湛江)和福建以北(浙江温岭和韩国)种群(分别合称南方类群和北方类群)做了遗传分化研究。由筛选出的20个随机引物共获得103个清晰可辨的RAPD标记,扩增片段长度在250—2500bp。汕头种群与湛江种群,韩国种群与温岭种群之间的最小遗传距离分别为0．0612和0．0692,而南、北类群间的遗传距离却在0．3261-0．4511。类群间近交系数也大于类群内。NJ和UPGMA法构建的系统树均显示汕头种群、湛江种群首先聚在一起,再与温岭种群和韩国种群聚合,说明两个类群发生了较明显的遗传分化,估计与地理隔离有关。     

pH对不同大小泥蚶清滤率、 滤食率、吸收率的影响

本文以泥蚶（Tegillarca granosa）为实验对象,研究不同大小个体在不同pH（6.5 ~ 9.5）静水水体中的清滤率、滤食率和吸收率。泥蚶共3组,分别为小规格、中规格和大规格,其壳长分别为9.12 mm、22.38 mm、32.35 mm。结果表明,在pH为8.5时,泥蚶清滤率由高到低依次为大规格、中规格、小规格;滤食率由高到低为中规格、大规格、小规格;吸收率由高到低为中规格、小规格、大规格。虽然大规格泥蚶有最高的清滤率,但结合吸收率和滤食率,中规格泥蚶具有更高的摄食和吸收能力。双因素方差分析显示,在清滤率、滤食率和吸收率的实验中,泥蚶受pH快速变化的影响程度均与其规格有关（P < 0.05）。随pH变化,清滤率受影响程度由小到大为小规格（P < 0.05）、中规格（参照）、大规格（P > 0.05）;滤食率受影响程度由小到大为大规格（P > 0.05）、小规格（参照）、中规格（P < 0.05）;吸收率受影响程度由小到大为小规格（P > 0.05）、中规格（参照）、大规格（P < 0.05）。中规格泥蚶的滤食水平受pH变化的影响较大,大规格泥蚶的吸收率受pH变化的影响较大。     

Corbicula fluminea (Bivalvia: Corbiculidae): a possible second molluscan intermediate host of Echinostoma cinetorchis (Trematoda: Echinostomatidae) in Korea.

More than 1,500 clams of Corbicula fluminea, the most favorable food source of freshwater bivalves in Korea, were collected from 5 localities to examine cercarial and metacercarial infection with Echinostoma cinetorchis. Although 3 clams infected with suspicious E. cinetorchis metacercariae out of 200 specimens collected at Kangjin, Chollanam-do were detected, no cercarial and metacercarial infections with E. cinetorchis were observed in field-collected Corbicula specimens. In the susceptibility experiments with laboratory-reared clams, those infected with miracidia of E. cinetorchis did not release their cercariae up to 60 days after infection. To confirm the identity of second intermediate host of E. cinetorchis experimentally, a total of 30 clams were exposed to the cercariae from Segmentina hemisphaerula that had been infected with miracidia of E. cinetorchis. The clams were susceptible to cercariae of E. cinetorchis with an infection rate of 93.3%. Metacercariae from clams taken more than 7 days after cercarial exposure were fed to rats (S/D strain), and adult worms of E. cinetorchis, characterized by 37-38 collar spines on the head crown, were recovered from the ileocecal regions. This is the first report of C. fluminea as a possible second intermediate host of E. cinetorchis.     

Non detection of enterovirus in the bivalve Anadara tuberculosa (Bivalvia:Arcidae) caused by chemical contamination in the Pacific of Costa Rica

Anadara tuberculosa is one of the most abundant mollusks of commercial importance in Costa Rica. Its habitat water is a potential source of fecal and chemical contamination to humans. We wanted to asses enterovirus, mainly poliovirus and hepatitis A virus and chemicals such as sulphates and nitrates in meat and body fluids. Thirteen samples were taken from four sites in Nicoya Gulf, three sites in the Sierpe-Térraba mangrove (Pacific of Costa Rica) and from five fish markets in San José, the capital of Costa Rica. Samples were tested for 1) fecal coliforms (Most Probable Number/100 ml), 2) isolation of enterovirus in cell culture (Hep-2, FrhK-4), 3) cell cytotoxicity in Vero cells and 4) the ability to inactivate 10 ID50% of poliovirus in cell culture. The Most Probable Number/100 ml in surrounding water was higher than the accepted standard for recreational waters, although the number of fecal coliforms in meats and body fluids was lower than in the external water. No cytopathogenic agents were isolated, but we found nitrate and sulphate concentrations that exceeded maxima for human consumption and recreation. The intrinsic cytotoxicity of the samples was at a 1/8 dilution, but some samples were cytotoxic at dilutions of 1/128. Body fluids were more cytotoxic than meats, but a positive correlation between cytotoxicity and chemical contamination was not determined: apparently other pollutants not identified in this study were responsible. Fluid and meat capacity to inactivate 10 ID50% of poliovirus in cell culture was demonstrated. Samples that were toxic for cell cultures also showed a higher percentage of poliovirus inactivation. Monitoring chemical pollution in these waters is highly recommended.     

Feeding behavior and differential absorption of biochemical components by the infaunal bivalve Mulinia edulis and the epibenthic Mytilus chilensis in response to changes in food regimes

We measured changes in the feeding rate and food absorption efficiency of two suspension feeding bivalves, cross-trasplanted between habitats with special emphasis on their capacity for differential absorption of biochemical components from their food supply. Mulinia edulis were moved from the intertidal zone to the subtidal zone, and Mytilus chilensis from the subtidal to the intertidal zone for a period of 7 days, and then compared with animal that had not been transplanted. Experimentally prepared diets similar to those available in the two different environments were offered to the bivalves, and their rates of feeding and differential uptake of biochemical components were determined and statistically compared. The two species did not achieve complete acclimation of their feeding behaviour during the transplant period since the highest ingestion rates for biochemical components occurred under dietary conditions that reflected their habitats of origin. Absorption efficiency showed greater acclimation than the other physiological parameters measured, indicating the capacity of these species to modulate their enzymatic-digestive activity depending on food composition. We conclude that both Mytilus and Mulinia have a certain degree of physiological plasticity in their feeding behaviour and assimilatory balance of biochemical components, being greater in Mytilus. When both species encounter ambient food conditions characteristic of their normal habitats, they show maximum values of food absorption, while under conditions where their typical diets are exchanged (Mytilus in intertidal and Mulinia in subtidal), the energy absorbed declines in each, but in ways very different between the two species. Thus, Mytilus exposed to high concentrations of low quality seston reduced the energy absorbed by 31.7% compared to its normal habitat, while Mulinia exposed to low concentrations of high-quality food reduced their energy absorption by 64%.     

Metatarsal fusion pattern and developmental morphology of the Olduvai Hominid 8 foot: Evidence of adolescence

The morphology of the Olduvai Hominid (OH) 8 foot and the sequence of metatarsal epiphyseal fusion in modern humans and chimpanzees support the hypothesis that OH 8 belonged to an individual of approximately the same relative age as the OH 7 subadult, the holotype of Homo habilis. Modern humans and chimpanzees exhibit a variety of metatarsal epiphyseal fusion patterns, including one identical to that observed in OH 8 in which metatarsal 1 fuses before metatarsals 2-5. More than the metatarsal fusion sequence, however, the principal evidence of the youthful age of OH 8 lies in the morphology of metatarsals 1, 2, and 3. Because both OH 8 and OH 7 come from the same stratum at the FLK NN type site, the most parsimonious explanation of the OH 8 and OH 7 data is that this material belonged to the same individual, as originally proposed by Louis Leakey. The proposition that OH 8 belonged to an adult is unsupported by morphology, including radiographic evidence, and the fusion sequences in human and chimpanzee skeletal material reported here and in the literature.     

Genetics and taxonomy of Chilean smooth-shelled mussels, Mytilus spp. (Bivalvia: Mytilidae)

It has been previously established that native smooth-shelled mussels in southern South America possess close evolutionary affinities with Northern-Hemisphere Mytilus edulis L. 1758 (McDonald et al. (1991) [5]). This result has since been challenged by authors claiming that Chilean mussels should be considered a local subspecies of M. galloprovincialis Lmk. 1819. Moreover, morphological, physiological, ecotoxicological and molecular genetic studies on Chilean smooth-shelled mussels still frequently refer to ‘M. chilensis’ Hupé 1854, even though the previous discovery of alien M. galloprovincialis and considerable heterogeneity in shell morphology among samples collected along the Chilean shores raise concerns that different Mytilus spp. species might have been included under ‘M. chilensis’. Here we reviewed the molecular and morphological data available on smooth-shelled mussels from Chile in an attempt to clarify both their genetic composition and their taxonomic status. Using multivariate analysis on sample × allozyme-frequency matrices, we confirmed the widespread occurrence of the Southern-Hemisphere form of M. edulis along the shores from the North Patagonia region of Chile to the southern tip of the South American continent. The populations sampled in southern central Chile showed some evidence of slight introgression from Southern-Hemisphere M. galloprovincialis. Morphological characterization of a sample from Dichato in southern central Chile was consistent with its previous genetic identification as Mediterranean M. galloprovincialis. The occurrence of Southern-Hemisphere M. galloprovincialis in Punta Arenas at the southern tip of the South American continent was also reported. Southern-Hemisphere M. edulis, including native Chilean smooth-shelled Mytilus, should be assigned subspecific rank and named M. edulis platensis d’Orbigny 1846.     

Presence of a unique male-specific extension of C-terminus to the cytochrome c oxidase subunit II protein coded by the male-transmitted mitochondrial genome of Venustaconcha ellipsiformis (Bivalvia: Unionoidea)

Analyses of unionoidean bivalve male-transmitted (M) mtDNA genomes revealed an approximately 555 bp 3' coding extension to cox2. An antibody was generated against this predicted C-terminus extension to determine if the unique cox2 protein is expressed. Western blot and immunohistochemistry analyses demonstrated that the protein was predominantly expressed in testes. Weak expression was detected in other male tissues but the protein was not detected in female tissues. This is the first report documenting the expression of a cox2 protein with a long C-terminus in animals. Its universal presence in unionoidean bivalve testes suggests a functional significance for the protein.     

Tegumental ultrastructure of adult Gynaecotyla squatarolae (Digenea: Microphallidae)

Gynaecotyla squatarolae (Digenea: Microphallidae) adult flukes were recovered from experimental chicks at day 4-6 post-infection and their tegumental ultrastructure was observed with a scanning electron microscopy. They were pyriform in shape, and their anterior halves were concaved ventrally. The whole body surface was covered with tegumental spines, which were wide and 16-17 digitated between oral and ventral suckers. The density of spines and number of digits decreased posteriorly. The oral sucker was subterminal and the excretory pore was at the posterior end of the worm. Two ventral suckers were similar in appearance and protruded near midline of the worm. The genital atrium was dextral to the small ventral sucker. The dorsal surface was covered with tegumental spines, but the spines were sparser than on the ventral surface. On the middle portion of the dorsal surface, a small opening presumed to be the Laurer's canal was seen. From these findings, it has been confirmed that the adult G. squatarolae has unique characteristics in the surface ultrastructure.     

Morphology and ultrastructure of the earthworm Dendrobaena veneta (Lumbricidae) coelomocytes

Microscope techniques, light microscope (LM), transmission electron microscope (TEM), scanning electron microscope (SEM) were employed to describe and classify coelomocytes of the oligochaete Dendrobaena veneta. Three main cell types were distinguished in the coelomic fluid: eleocytes, amoebocytes and granulocytes. Eleocytes are large, oval cells containing characteristic granules called chloragosomes. Amoebocytes are most numerous coelomocytes and have been divided into two types (I and II). Both amoebocytes of the types I and II often form aggregations of a few to about a dozen cells. Granulocytes are oval cells with spherical nuclei and cytoplasm containing polymorphic, electron dense granules. Contrary to the amoebocytes, the granulocytes do not form aggregations. Morphology and ultrastructure of coelomocytes are presented on micrographs: similarities and differences are compared to coelomocytes of related species.     

Evolution of the tRNA gene family in mitochondrial genomes of five Meretrix clams (Bivalvia,Veneridae)

In contrast to the extreme conservation of nuclear-encoded tRNAs, organization of the mitochondrial (mt) tRNA gene family in invertebrates is highly dynamic and rapidly evolving. While gene duplication and loss, gene isomerism, recruitment, and rearrangements have occurred sporadically in several invertebrate lineages, little is known regarding the pattern of their evolution. Comparisons of invertebrate mt genomes at a generic level can be extremely helpful in investigating evolutionary patterns of variation, as intermediate stages of the process may be identified. Variation of mitochondrial tRNA organization among Meretrix clams provides good materials to investigate mt tRNA evolution. We characterized the complete mt genome of the lyrate Asiatic hard clam Meretrix lyrata, re-annotated tRNAs of four previously sequenced Meretrix clams, and undertook an intensive comparison of tRNA gene families in these clams. Our results 1) provide evidence that the commonly observed duplication of trnM may have occurred independently in different bivalve lineages and, based on the higher degree of trnM gene similarity, may have occurred more recently than expected; 2) suggest that “horizontal” evolution may have played an important role in tRNA gene family evolution based on frequent gene duplications and gene recruitment events; and 3) reveal the first case of isoacceptor “vertical” tRNA gene recruitment (VTGR) and present the first clear evidence that VTGR allows rapid evolution of tRNAs. We identify the trnS^− UCR gene in Meretrix clams, previously considered missing in this lineage, and speculate that trnS^− UCR lacking the D-arm in both M. lyrata and Meretrix lamarckii may represent the ancestral status. Phylogenetic analysis based on 13 concatenate protein-coding genes provided opportunities to detect rapidly evolved tRNA genes via VTGR and gene isomerism processes. This study suggests that evolution of the mt tRNA gene family in bivalves is more complex than previously thought and that comparison of several congeneric species is a useful strategy in investigating evolutionary patterns and dynamics of mt tRNA genes.     

Polymorphic microsatellite DNA markers for the ark shell Scapharca subcrenata (bivalve: Arcidae)

We have isolated and characterized twelve novel polymorphic microsatellite loci from Scapharca subcrenata to analyse the population structure. The number of observed alleles per locus ranged from 3 to 17. Observed heterozygosity (H _O) ranged from 0.321 to 0.929. Cross-species amplification was tested successfully in three other bivalve species. These microsatellite markers will be useful for genetic diversity studies of S. subcrenata and other Lamellibranchia species.