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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 123 (1995), S. 775-780 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mytilus edulis L. heterozygotes with a null allele at the octopine dehydrogenase (Odh) locus or an allele coding for low activity at the glucose phosphate isomerase (Gpi) locus were found to grow significantly faster (p(0.05) than other juvenile mussels in the same laboratory cultures. Odh null homozygotes were not significantly different in growth from mussels with active Odh alleles. No additive effects were seen in individuals which had both the Odh null allele and the allele coding for low GPI activity. These results do not support the contention that null alleles are a significant cause of the observed correlation between multiple-locus heterozygosity and fitness in mussels. The apparent deficiencies of heterozygotes against Hardy-Weinberg expectations observed at the Odh locus in two Netherlands M. edulis populations can be more than accounted for by the null-allele frequency calculated, assuming Hardy-Weinberg equilibrium, from the observed frequency of null homozygotes in these populations.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 106 (1990), S. 227-233 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Laboratory cultures of offspring from single families and a mass mating ofMytilus edulis were reared to the spat stage at different temperatures. Some cultures were reared further to the juvenile stage at the same, or at an altered temperature. Using electrophoresis, frequencies of genotypes at theOdh, Pgm, Gpi, Hex, EsD, Pgk andDia loci were recorded at the spat stage and, again, where possible, in juveniles. Significant deviations from expected genotype frequencies were observed at most loci in at least some cultures, but in no cases were these deviations related to the temperature at which the cultures had been reared. We speculate that these differences may have been due to variations in the density of mussel spat in the cultures. Very extensive and consistentPgm genotype-specific mortalities were evident in one family, and, in another family, consistent deviations were seen at theHex locus. Weaker, but nevertheless significant, deviations from expected genotype frequencies occurred at most other loci and it is concluded that, in most cases, the loci were acting as markers for a locus, or loci, on the same chromosome which had a strong effect on fitness. It is thought unlikely that evidence for similar levels of selection would be found in natural populations because, in wild populations, particular marker-locus genotypes would be associated with a range of genetic backgrounds rather than a single chromosome.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 46 (1978), S. 181-183 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When the Hardy Weinberg ratios of m isoalleles are tested using the χ2 distribution, the correct number of degrees of freedom is 1/2 (m 2-m). The derivation from two definitions of degrees of freedom is given.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 76 (1983), S. 285-289 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Adult Pecten maximus (L.) were dredged off north-east Anglesey, Wales, UK, during 1981. A 2×5 factorial mating was carried out involving self- and cross-fertilisation and the use of stripped spermatozoa. Assessments of yield, normality, and larval size were made at the D larva stage and larval size and mortality were measured after a fortnight's growth of the veligers. Underlying genetic variation was evident at all stages, with egg and sperm generally having a significant interactive effect. Cultures sired with stripped spermatozoa had fewer larvae, with more abnormality, grew slower and suffered higher mortality than most other cultures. Larvae from selfed cultures grew significantly slower than all other larvae. Data from past larval cultures also show that selfed larvae have a reduced growth rate. it is suggested that stripped spermatozoa may interfere with egg and sperm interaction at fertilisation, thus reducing the viability of larvae. On the other hand, the poor growth rate of selfed larvae is probably due to overall reduced heterozygosity compared to outbred larvae.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 71 (1982), S. 97-100 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Veliger larvae of Mytilus edulis (L.) from Menai Straits, North Wales, were maintained for up to 2 mo during 1981 at 5°C and then grown on to metamorphosis at 17°C. Larvae so treated showed similar low mortality and equivalent spat production to control larvae. Growth rate at 17°C was less in treated larvae than in controls, but treated larvae grew a little during the period at low temperature. Larvae of Pecten maximus (L.) from the Irish Sea suffered high mortality at low temperature but larvae surviving 2 wk at 8°C could be grown on to spat at 17°C. The longevity of M. edulis larvae is discussed in relation to the genetic homogeneity of adult populations around the UK.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 15 (1972), S. 350-355 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Development of the scallop Pecten maximus (L.) from egg to metamorphosis takes 33 to 38 days at 16°C. The shelled veliger first appears 2 days after fertilisation, and crawling pediveligers at around 2 days before metamorphosis. The pediveliger can attach temporarily to filamentous objects by means of a byssus thread and, even after metamorphosis, periods of attachment alternate with periods of crawling. The larvae are reared in polythene bins containing 30 l of full salinity sea water (pre-filtered through 0.2μ filters), which is changed every 2 days. Mixtures of algal foods (Isochrysis galbana, Chaetoceros calcitrans, Pyramimonas obovata and Tetraselmis suecica), concentrated by centrifugation, are added at each change from the third day onwards to give a concentration of 50 cells/μl. Larval density is maintained below 10/ml. Antibiotics are added at each change, but very careful sterilisation of all equipment is necessary to guard against the introduction of diseases.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 46 (1995), S. 0 
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Proportion of loci polymorphic (P) and mean heterozygosity per locus (Hexp) were P= 0.130 and Hexp= 0.096 for C. albula from the English Lake District and P= 0.217 and Hexp= 0.046 for C. lavaretus from the English Lake District and Llyn Tegid, Wales in 1991–2. Significant deviation from the Hardy-Weinberg model was observed at the superoxide dismutase (sSOD*) locus in C. albula from Bassenthwaite Lake. This could have been due to chance, to the Wahlund effect or to selection. Genetic distances between the two species were consistent with their taxonomy and genetic differentiation was much greater for the C. lavaretus populations than for the two geographically close C. albula stocks. Llyn Tegid C. lavaretus showed unique alleles at two loci and conservation of fish in this lake is therefore of great importance. Red Tarn C. lavaretus differed most from other Lake District populations probably due to founder effects from early stocking events and/or from selection due to the high altitude of this lake.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effect of the introduction of fry of anadromous sea trout, Salmo trutta L., on the genetic integrity of landlocked brown trout populations was evaluated. Samples were taken from six brown trout populations from streams above impassable waterfalls in the Conwy river system (North Wales, U.K.) in 1989 and 1990. Three of these streams had no known stocking history and three had been stocked with sea trout fry from the lower Conwy system over the last few years. Representatives of these sea trout were collected from two streams in the lower Conwy system and from a hatchery. Allele frequencies at 13 loci, six of which were polymorphic, were determined by starch gel electrophoresis.The stocked populations were intermediate in their allele frequencies between unstocked brown trout and sea trout samples. A principal component analysis suggested significant numbers of hybrids in all of the stocked streams. This shows that some of the introduced sea trout did not migrate down the falls to the sea, but stayed in fresh water and hybridized with the local population. The significance of this finding for the conservation of the genetic resource of brown trout stocks is discussed.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1438-3888
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Summary 1. The scallopPecten maximus (L.) can be conditioned in the laboratory to produce ripe gametes at times other than its normal spawning seasons. 2. The spawning stimulus consists of taking the scallop out of water for a period of approximately 2 h. Spawning occurs within 2 to 4 h of re-immersion in water. 3. More larvae and a higher proportion of normal larvae are produced by eggs incubated at low density levels. 4. The higher sperm concentrations produce fewer larvae and higher percentages of abnormal larvae than the lower concentrations. 5. Eggs incubated at 7 per cm2 bottom area produce very few abnormal larvae but large numbers of normal larvae can be produced more efficiently by incubating at a density level of 700 eggs per cm2 although a higher percentage of abnormal larvae must be tolerated.
    Notes: Kurzfassung Die KammuschelPecten maximus (L.) erzeugt bei 15° C nahezu während des ganzen Jahres reife Keimzellen. Der Reifeprozeß der Geschlechtszellen kann durch Erniedrigung der Temperatur auf 7° bis 8° C arretiert werden. Der Laichvorgang läßt sich dadurch auslösen, indem Kammmuscheln 2 Stunden lang aus dem Wasser entnommen werden. Danach, innerhalb von 2 bis 4 Stunden nach Rückführung in Meerwasser, werden die Keimzellen entleert. Die Spermatozoen, die gewöhnlich zuerst abgegeben werden, müssen entfernt werden, bevor die Eier erscheinen. Bei der Eiablage werden im allgemeinen auch einige Spermatozoen entlassen, so daß es auch zu Selbstbefruchtung kommt. Das prozentuale Verhältnis von Samen- zu Eizellen ist entscheidend für den Anteil abnorm gebildeter Larven, die aus den befruchteten Eiern hervorgehen können. Je mehr Spermatozoen den Eiern zugegeben werden, um so geringer ist der Prozentsatz der entstehenden Larven und desto höher ist der Anteil fehlgebildeter Larven. Die für die Erzeugung abnormer Larven verantwortlichen Faktoren sind nicht bekannt. Da Polyspermie nachgewiesen wurde, ist ein ursächlicher Zusammenhang zu der Verringerung der Larvenzahlen bzw. der Entstehung abnormer Larven nicht auszuschließen. Die Anzahl der Eier pro Volumeneinheit Meerwasser beeinflußt ebenfalls den Prozentsatz sich entwickelnder normaler Larven. Bei geringen Eizahlen entstehen nur wenige abnorm gestaltete Larven. In der Praxis lassen sich die besten Zuchtergebnisse bei einer Konzentration von 700 Eiern pro cm2 Bodenfläche erzielen, wobei eine große Zahl von Larven erzeugt wird, zugleich jedoch ein relativ hoher Prozentsatz Fehlentwicklungen in Kauf genommen werden muß.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Marine biology 84 (1985), S. 301-308 
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The long, drifting threads secreted by young post-larval mussels (Mytilus edulis L.) are simple monofilaments, distinct in form and function from the attachment byssus threads. The diameters of both thread types are in the micron or sub-micron range but, whereas the attachment threads are of restricted length and terminate in an attachment plaque, drifting threads exceed the post-larva in length by more than two orders in magnitude and are without plaques or any other structures. Transmission electron micrographs of drifting threads show no evidence of internal sub-structure. In contrast, attachment threads appear to be made up of filaments. These studies confirm that the drifting threads are highly effective in enhancing the dispersal of young mussels. The terminal sinking velocity of young drifters is typically ca. 1 mm s-1. At this velocity the suspension range above the sea bed, assuming given values of vertical diffusivity, is estimated to be 0.5 to 5 m. Calculations of the fluid drag experienced by post-larvae in the water column show that the theoretical viscous drag force on the thread is sufficient to account for the reduced sinking rate of drifters. The calculated contribution of the thread to the total drag is approximately one order of magnitude greater than that of the post-larval body. A rapid thread-deployment strategy, shown by post-larvae which are brought into suspension, may prolong each drifting excursion and thus further enhance dispersal in turbulent marine environments.
    Type of Medium: Electronic Resource
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