STUDY ON MIXIS POTENTIAL OF ROTIFER RESTING EGGS（ BRACHIONUS PLICATILIS ） WITH DIFFERENT COLLECTION TIMES AND DIFFERENT PRESERVATION PERIODS

The present study investigated the possible changes in the mixis potential of rotifer resting eggs produced by a single stock of Brachionus plicatilis and collected and preserved annually from 1985 - 1998. Several clones derived from each batch of resting eggs were cultured under the same conditions for 21 days. The percentage of clones appearing resting eggs and the average yield of resting eggs produced from each clone were recorded and statistically analyzed to find the differences between the mixis potential of those resting egg batches. Results showed that different batches of resting eggs had different mictic levels among their descendent clones; but no regular relationship was found between the mixis potential of resting eggs and their collection times/preservation periods. Several internal and external factors that might affect the mixis potential of resting eggs were discussed.     

Effects of sexual reproduction of the inferior competitor Brachionus calyciflorus on its fitness against Brachionus angularis

Sexual reproduction adversely affects the population growth of cyclic parthenogenetic animals. The density-dependent sexual reproduction of a superior competitor could mediate the coexistence. However,the cost of sex may make the inferior competitor more vulnerable. To investigate the effect of sexual reproduction on the inferior competitor,we experimentally paired the competition of one Brachionus angularis clone against three B rachionus calyciflorus clones. One of the B. calyciflorus clones showed a low propensity for sexual reproduction,while the other two showed high propensities. The results show that all B. calyciflorus clones were excluded in the competition for resources at low food level. The increased food level promoted the competition persistence,but the clones did not show a clear pattern. Both the cumulative population density and resting egg production increased with the food level. The cumulative population density decreased with the mixis investment,while the resting egg production increased with the mixis investment. A trade-off between the population growth and sexual reproduction was observed in this research. The results indicate that although higher mixis investment resulted in a lower population density,it would not determinately accelerate the exclusion process of the inferior competitor. On the contrary,higher mixis investment promoted resting egg production before being excluded and thus promised a longterm benefit. In conclusion,our results suggest that mixis investment,to some extent,favored the excluded inferior competitor under fierce competition or some other adverse conditions.     

Sexual reproduction and short-term fitness advantage in the rotifer Brachionus calyciflorus: implications for the coexistence of sympatric clones

Large numbers of rotifer eggs from sediment resting egg banks may hatch simultaneously under appropriate conditions;therefore,natural populations are likely to be multiclonal in a growing season.A recent field investigation showed that subordinate and ephemeral clones were able to establish populations in an environment with several strongly dominant clone populations.However,it was not clear how the subordinate populations maintained their growth under these conditions where the crowding signal would induce high levels of sexual reproduction in the dominant clone populations.In the present study,we conducted a continuous passage to 60 generations for new populations at three different temperatures(15°C,25°C,and 35°C).These populations emerged from resting eggs produced by a clone population.At the first,30th,and 60th generations,the populations were sampled and fitness was assayed using the life-table method.We found a significant short-term fitness advantage for populations newly emerged from resting eggs produced by a clone population of the rotifer Brachionus calyciflorus,followed by a significant decrease in relative fitness with long-term continuous passage.Our results suggested that the early shortterm fitness advantage was important for later-hatched and subordinate clone populations in an environment with multiple sympatric clones.The early short-term fitness might also promote the coexistence of sympatric clones because it could help to offset the cost of early sexual reproduction.     

Reduction of hydrocarbon contamination on viability of <Emphasis Type="Italic">Acartia pacifica</Emphasis> benthic resting eggs

The potential effect of hydrocarbon contamination on the hatching success of benthic resting eggs of Acartia pacifica in Xiamen Bay was investigated experimentally. The number of nauplii emerging from the sediment samples decreased with increasing Fuel Oil #0 concentration. The estimated rate of mortality increased markedly with the increase of Fuel Oil #0 concentration. Successive fuel Oil #0 concentrations from 50 mg/kg to 5000 mg/kg reduced the number of hatched nauplii by 3.8% -100%. The mortality of A. pacifica resting eggs due to Fuel Oil #0 contamination did not significantly increase as time progressed at each concentration level. The LC50 values of resting eggs, changing from 237.12 to 279.59 mg/kg, remained at an almost stable level in two months. The number of A. pacifica nauplii that hatched from the sediment at 10℃ was higher than those from the sediment at 30℃, which indicates that the toxicity of Fuel Oil #0 on A. pacifica resting eggs increases with increasing temperature.     

Offspring of aged mothers of rotifer Brachionus calyciflorus shows lower sexual propensity than their elder siblings under crowded conditions

Maternal effects are one of the most interesting topics in evolutionary ecology as they can affect the rate of evolution and population dynamics by phenotypic manipulation of offspring related to fitness.At present,studies examining the interaction between maternal environment effects and maternal age(birth order)effects are scarce.We designed an experiment to reveal whether environmentally induced maternal manipulation works equally on offspring across birth orders in rotifer Brachionus calyciflorus.In the experiment,newborn amictic mothers(FO)were cultured parallelly in low(LD)and high(HD)population density.Offspring(F_1)of young(YF_0)and old(OF_0)mothers in both LD and HD groups were cultured under a crowded condition and the mixis ratios of both F_1 and F_2 were examined.Results show that F_1 from HD-YF_0 had a significantly higher mixis ratio and those amictic ones produced daughters(F_2)with higher mixis ratio in response to crowding than those from HD-OF_0.In contrast,no such differences among F_1 siblings were found in the LD-F_0 group.Therefore,the effect of maternal age on the sexual propensity of the offspring can be affected independently by the maternal population density.     

方斑东风螺不同批次卵质量的比较

2005年5月~8月在雷州市覃斗镇海威水产种苗基地的室内水池进行方斑东风螺亲螺培育,对亲螺不同批次产出的卵囊、卵、及其幼虫进行比较。结果表明:随着亲螺产卵批次的增加,亲螺产卵囊数、卵囊含卵数、产卵量逐次减少;卵囊长、宽逐次变小,厚逐次增加,形状由葵花子片状的比例大变为棒状的比例大;幼虫浮游期逐次延长;变态期幼虫壳长逐次变小;各批次之间的变态率逐次降低;卵径、孵化率、出囊幼虫大小差异不显著。     

Dormant stages of crustaceans as a mechanism of propagation in the extreme and unpredictable environment in the Crimean hypersaline lakes

A pool of dormant stages of planktonic organisms in saline lakes is a substantial component in the plankton communities;we need to take it into account to understand plankton dynamics.Hypersaline water bodies in Crimea,the largest peninsula in the Black Sea,constitute a very characteristic and peculiar habitat type in the region.We examined the presence of crustacean resting stages in sediments of dried up sites of the Crimean hypersaline lakes.Sediment samples were taken in 9 different lakes.Experiments performed on the hatching of these resting stages showed the presence of Moina salina(Cladocera),parthenogenetic Artemia and Artemia urmiana(Anostraca),Eucypris mareotica( inflata)(Ostracoda),and Cletocamptus retrogressus(Harpacticoida).Comparing the experimental results obtained with clean dried brine shrimp cysts and those kept in sediment samples,it was noted that clean cysts hatched much faster than those from sediments did.Some components in bottom sediments slow down and desynchronize hatching from resting eggs in different groups of crustaceans.The sediments of different lakes inhibited the nauplii output from Artemia and ostracod resting eggs to different degrees.More data are needed before we can discuss the reasons of this inhibition.The nonsynchronous output of active stages from the bottom resting ones may be an adaptation that allows crustacean species to exist in extreme and unpredictably changing environments,avoiding the risk that all may emerge at once under unsuitable conditions.     

Genetic discrimination for three gynogenetic clones of silver carp Hypophthalmichthys molitrix, based on restriction endonuclease analysis of Nd5-Nd6 region of mitochondrial DNA

1 INTRODUCTION Silver carp (Hypophthalmichthys molitrix) is an important species in freshwater fisheries and ranks the first in world fish production (Li, 1993). China has a long history of aquaculture of silver carp that is very difficult for selective breeding because it has a long life cycle. However, development of cytoge-netics and modern molecular genetics built up a strong impact to the research on selective breeding. A rapid, efficient approach for establishment of a pure line of…     

Genetic discrimination for three gynogenetic clones of silver carp Hypophthalmichthys molitrix , based on restriction endonuclease analysis of Nd5-Nd6 region of mitochondrial DNA

Three artificial gynogenetic clones of silver carp were produced for the analysis of restriction enzyme digestion patterns of ND5-ND6 region from mtDNA of the clones. It is revealed that all intraclonal individuals shared completely the same digestion patterns but among interclonal individuals did not. The three clones were mixed and cultured in a pond together for two years, and restriction endonuclease digestion patterns of ND5–ND6 were used as genetic markers to assess the growth performance of each clone. Project supported by the National Natural Science Foundation of China (No. 39830300).     

Triploidy induction with heat shocks toPenaeus chinensis and their effects on gonad development

Heat shocks effectively produced triploids inPenaeus chinensis. Fertilized eggs heat shocked (28–32°C) for 8 to 16 minutes, starting from 8 to 20 minutes after spawning, resulted in triploidy induction rates of 39%–75%. Several triploid populations were cultured to 10 cm. In a triploid population, two kinds of ovaries were observed. Histological examination showed apparent differences between these two kinds of ovaries, whereas among male shrimp, there were no such differences. Contribution No. 3465 from the Institute of Oceanology. Chinese Academy of Sciences. The study was supported by the International Foundation for Science, Asian Fisheries Society and Chinese Climbing Project PDB 6–2, and Chinese National 863 Project (No. 863-819-01-05).     

Temperature effect on the life history of three types of Brachionus calyciflorus females

The effect of temperature on the life history characteristics of amictic females (AF), unfertilized mictic females (UMF) and fertilized mictic females (FMF) inBrachionus calyciflorus was studied with replicated individual cultures at 20°C, 25°C and 30°C, and with algaeScenedesmus obliquus for their food. There were highly significant effects of both temperature and female type, independently and interactively, on the duration of juvenile and post-reproduction periods, and the number of eggs produced by the rotifer per life cycle. Among all the temperature-female type combinations, all the juvenile periods of FMF, and the post-reproduction periods of UMF and FMF at 20°C, were the longest, and the number of eggs produced by an UMF at 30°C was the highest. There were highly significant effects of both temperature and female type on the duration of the reproduction period, but no clear correlation was observed between temperature and female type. The reproduction period of AF was longer than that of UMF and FMF. Only temperature influenced significantly the mean life-span of the three types of female. The duration of juvenile, reproduction and post-reproduction periods as well as the life-span of the three types of females were all reduced very significantly with rise of temperature, but the rates of reduction varied with female type. Among the three types of females, the number of eggs produced per life cycle by an UMF was the highest, and that of a FMF was the lowest. A significant relationship between the number of eggs produced per life cycle and temperature was observed only in the UMF. Projects supported by NSFC (No. 39870158), Natural Science Foundation of Anhui Province (No. 100330: No. 042416) and the Excellent Youth Foundation (No. 04043050).     

The reaction time of organ-forming substance in goldfish EGG and its relationship with mesodermal formation

Fertilized goldfish eggs were dechorionated with a pair of forceps and were cut off along or a little above the equator into animal and vegetative parts at desired stages with a glass needle or ligated into two connected fragments before cleavage with baby hair loop. Some of the ligated eggs were detached by further fastening soon after ligation, and some released later at different stages (2-cell, 16-cell, 128-cell, 512-cell, mid-blastula) to let the organ-forming substance (OFS) enter the blastoderm. The cholinesterase (ChE) in the resulting embryos was assayed. The results are as follows. 1. All the 142 embryos developed from the animal hemispheres cut off or ligated off before cleavage gave rise to hyperblastula in which no ChE activity was observed. 2. All 50 embryos obtained from animal halves isolated at the 8-cell stage produced ChE. 3. Embryos developed from the eggs released before the 512-cell stage formed ChE, but the later the releasing of the hair knots, the smaller the number of ChE-producing embryos. 4. After the 512-cell stage (excluding this stage), neither ChE nor tissue differentiation occurred in the embryos developed from the unfastened eggs though their OFS flow was set free. Since ChE is thought to be a muscle-specific enzyme in the early developmental stage, it is concluded that the OFS in goldfish egg appears to be indispensable for the establishment of the mesoderm. Contribution No. 1507 from the Institute of Oceanology, Academia Sinica     

Construction of a metagenomic DNA library of sponge symbionts and screening of antibacterial metabolites

To study the bioactive metabolites produced by sponge-derived uncultured symbionts, a metagenomic DNA library of the symbionts of sponge Gelliodes gracilis was constructed. The average size of DNA inserts in the library was 20 kb. This library was screened for antibiotic activity using paper disc assaying. Two clones displayed the antibacterial activity against Micrococcus tetragenus. The metabolites of these two clones were analyzed through HPLC. The result showed that their metabolites were quite different from those of the host E. coli DH5α and the host containing vector pHZ132. This study may present a new approach to exploring bioactive metabolites of sponge symbionts.     

罗非鱼开口饵料的初步研究

研究了配合饵料、轮虫、蛋黄、轮虫+人工配合饵料(3～12日龄投喂轮虫,13日龄起投喂配合饵料)等4种开口饵料对奥尼罗非鱼仔鱼生长、发育和存活影响。结果表明,1)投喂不同饵料对奥尼罗非鱼仔鱼生长具有显著影响(P<0.05),轮虫+配合饵料组生长较快,绝对增重率和特定增重率分别为0.011g/d和17.18%d-1;蛋黄组生长最慢,绝对增重率和特定增重率与其他各组差异显著(P<0.05)。2)轮虫+配合饵料与轮虫组的仔鱼成活率较高,分别为90.3%和89.7%,2组差异不显著(P>0.05),且仔鱼发育较好,大部分个体进入稚鱼阶段;蛋黄组成活率最低,只有40.7%,个体发育较为缓慢,与其他各组差异显著(P<0.05)。可见,投喂鲜活的天然饵料(轮虫)+配合饵料是罗非鱼苗种培育的最佳开口饵料。     

Hybrids between olive flounder Paralichthys olivaceus and stone flounder Kareius bicoloratus: karyotype, allozyme and RAPD analyses

The hybrid between olive flounder Paralichthys olivaceus and stone flounder Kareius bicoloratus was produced by artificial insemination of olive flounder eggs with stone flounder Sperm. Sinistral and dextral are two types of hybrid progeny after metamorphosis. Karyotypes of both hybrid flounders are the same as those of the two parental species. Of the 22 loci examined from 12 allozymes,12 confirmed hybridization of the paternal and matemal loci in hybrids and no difference was found in allozyme patterns of sinistral and dextral hybrid fishes. RAPD patterns of these specimens were also studied with 38 primers selected from 104 tested. Among them, the PCR products of 30 primers showed hybridization of the paternal and maternal bands. Genetic variation between hybrids and their parental stocks was analyzed by RAPD using 10 of the above 38 primers. The average heterozygosity and genetic distance were calculated. The results suggested that the filial generation could inherit a little more genetic materials from paternal fish than that from maternal fish.     

High genetic diversity in gametophyte clones of Undaria pinnatifida from Vladivostok, Dalian and Qingdao revealed using microsatellite analysis

Breeding practice for Undaria pinnatifida (Harvey) Suringar requires the screening of a large number of offspring from gametophyte crossings to obtain an elite variety for large-scale cultivation. To better understand the genetic relationships of different gametophyte cultures isolated from different sources, 20 microsatellite loci were screened and 53 gametophyte clone cultures analyzed for U. pinnatifida isolated from wild sporophytes in Vladivostok, Russia and from cultivated sporophytes from Dalian and Qingdao, China. One locus was abandoned because of poor amplification. At the sex-linked locus of Up-AC-2A8, 3 alleles were detected in 25 female gametophyte clones, with sizes ranging from 307 to 316 bp. At other loci, 3 to 7 alleles were detected with an average of 4.5 alleles per locus. The average number of alleles at each locus was 1.3 and 3.7 for Russian and Chinese gametophyte clones, respectively. The average gene diversity for Russian, Chinese, and for the combined total of gametophyte clones was 0.1, 0.4, and 0.5, respectively. Russian gametophyte clones had unique alleles at 7 out of the 19 loci. In cluster analysis, Russian and Chinese gametophyte clones were separated into two different groups according to genetic distance. Overall, high genetic diversity was detected in gametophyte clones isolated from the two countries. These gametophyte cultures were believed to be appropriate parental materials for conducting breeding programs in the future.     

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不同区域地震前重力变化与垂直形变关系的差异性及其可能机制

为了探讨不同区域地震前重力变化及其与地壳垂直形变关系差异性的可能机制，本文首先研究了地震前膨胀体在不同应力状态下四种性质不同的徽裂隙所引起的重力变化及其与垂直位移的关系，给出了相应的一些数值结果。分析了震源体处在不同力学和构造环境下，重力变化可能存在的差异以及唐山地震前重力变化的可能机制。研究结果表明，不同区域地震前重力变化与垂直位移关系的差异的一种可能机制是由于震源体所处的力学和构造环境不同，造成膨胀体内微裂隙破裂方式不同所引起；唐山地震前重力变化则可能是震前在震源区内丛集了大量垂直向张性微裂隙以及深部物质迁移至微裂隙中。     

Hybrids between olive flounder Paralichthys olivaceus and stone flounder Kareius bicoloratus： karyotype, allozyme and RAPD analyses

The hybrid between olive flounder Paralichthys olivaceus and stone flounder Kareius bicoloratus was produced by artificial insemination of olive flounder eggs with stone flounder sperm. Sinistral and dextral are two types of hybrid progeny after metamorphosis. Karyotypes of both hybrid flounders are the same as those of the two parental species. Of the 22 loci examined from 12 allozymes, 12 confirmed hybridization of the paternal and maternal loci in hybrids and no difference was found in allozyme patterns of sinistral and dextral hybrid fishes. RAPD patterns of these specimens were also studied with 38 primers selected from 104 tested. Among them, the PCR products of 30 primers showed hybridization of the paternal and maternal bands. Genetic variation between hybrids and their parental stocks was analyzed by RAPD using 10 of the above 38 primers. The average heterozygosity and genetic distance were calculated. The results suggested that the filial generation could inherit a little more genetic materials from paternal fish than that from maternal fish. Supported by National Natural Science Foundation of China (No. 30571445), National High-Technology Research and Development Program (863 Program, No. 2006AA10A404), and Project from the Ministry of Science and Technology of China (No. 2006DKA30470-017)