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1.
Else Nøst Hegseth 《Polar Biology》1989,9(8):479-486
Summary Photoadaptation in some marine Arctic diatoms has been studied. Thalassiosira antarctica, Nitzschia delicatissima and Chaetoceros furcellatus were grown at-0.5°C and various irradiances and continuous light. Growth and cellular chlorophyll were followed during transitional phase after the algae had been transferred from one irradiance to another. Adaptation time for cellular chlorophyll was linearly related to the gradient in irradiance, and adaptation to transfer from high to low light was faster than from low to high light. Adaptation time was found to be species dependent, and Arctic diatoms growing at low temperature seemed to adapt as fast as temperate species.Contribution No. 243 from Trondhjem Biological Station 相似文献
2.
MN Kaggwa N Straubinger-Gansberger M Schagerl 《African Journal of Aquatic Science》2018,43(2):123-129
Nine small artificial dams located in different climatic regions of Kenya were studied. The local communities use the stored water for various purposes, such as irrigation, domestic use, watering of livestock and cage fish farming. Such intense use is commonly accompanied by eutrophication, including fast growth of cyanobacteria, which at times produce cyanotoxins threatening human and animal life. We studied the pelagic community, analysed abiotic variables and identified microcystins by means of high performance liquid chromatography and ELISA kits at monthly intervals over a period of one year. Mass spectrometry (MALDI-TOF MS) was used to identify structural variants of microcystins by their protonated masses (M + H). Three dams contained microcystins, with the highly toxic Microcystin-LR being identified as the most prominent substance. Cell content of the toxin varied from 7.2 to 686.7 fg cell?1. Basic limnological variables that indicate the probability of toxin presence were also recorded. Non-parametric Mann–Whitney U-test revealed significant differences in soluble reactive phosphorous, nitrate-N, water depth, total hardness and post-Nauplii stages sampled between toxin-producing and non-toxin-producing dams. Although most of the samples did not contain high amounts of cyanobacteria, the cyanotoxin-problem was evident, suggesting the need for regular cyanotoxin monitoring programs. 相似文献
3.
Jørgensen JB Johansen A Hegseth MN Zou J Robertsen B Collet B Secombes CJ 《Fish & shellfish immunology》2007,23(6):1294-1303
A transgenic cell line for the detection of salmon interferons (IFNs) has been established. It is based on a CHSE-214 cell line containing a reporter construct expressing firefly luciferase under the control of the rainbow trout promoter for the IFN-induced Mx1 gene. This cell line, named CHSE-Mx10, showed IFN-induced luciferase expression after more than 80 passages, confirming the stability of this cell line. Interestingly, the Mx promoter was shown to respond to both salmon IFN-alpha/beta and trout IFN-gamma in a dose-dependent manner, while there was no response to TNF-alpha and IL-1beta. IFN-alpha/beta activity could be measured at a range of 9-150 U/ml, and IFN-gamma showed activity between 10 and 100 ng/ml. The reproducibility of both responses was good. The CHSE-Mx10 reporter system constitutes a versatile tool to study the induction and regulation of IFN signaling in teleost fish. A preliminary study presented herein suggests that both infectious pancreas necrosis virus (IPNV) and salmon pancreas disease virus (SPDV) may block activation of the Mx promoter in CHSE-Mx10 stimulated with IFN-alpha/beta. 相似文献
4.
5.
Thirty five females and 15 males of New Zealand White mature rabbits about 6 months of age, were assigned to 1–5 dietary treatments (7 does+3 bucks for each): uncontaminated control diet, naturally aflatoxin contaminated diet without or with 1,2 and 3% bentonite. Rabbit fed with the aflatoxin-diet had a decreased (P<0.01 or 0.05) physical semen characteristics of bucks and a reproductive performance traits of does. The values of conception rate (%), gestation length (days), litter size (n) and litter weights (g) at birth and viability (%) of litters of doe rabbits, fed with the aflatoxin-diet, recorded, respectively: 64.5; 31.0; 4.4; 275.0 and 57.1 versus 85.6; 30.3; 7.9; 508.0; and 100 for those fed with the uncontaminated diet. Addition of bentonite to the aflatoxin contaminated diet improved in general the physical semen characteristics of buck and reproductive performance traits of doe rabbits. The results of the study demonstrate that adding 1% of Egyptian raw bentonite to the naturally aflatoxin contaminated rabbit diets can provide an effective, cheap and safe practical technique for preventing the aflatoxicosis in mature rabbits. 相似文献
6.
Spatial distribution and life-cycle timing of zooplankton in the marginal ice zone of the Barents Sea during the summer melt season in 1995 总被引:7,自引:0,他引:7
Falk-Petersen S; Pedersen G; Kwasniewski S; Hegseth E; Hop H 《Journal of plankton research》1999,21(7):1249-1264
The marginal ice zone (MIZ) in the northern Barents Sea is ecologically
important because it represents a highly productive area in Arctic water
masses north of the Polar Front. During a multi-disciplinary cruise in
1995, ecological and oceanographic processes were investigated at four
stations located in a north-south transect in the MIZ. This study was
carried out in Arctic water masses north of the Polar Front where ice
conditions varied from dense first-year pack ice to open water. Also, the
phytoplankton development varied along the transect from a pre-bloom
situation at the northern-most station to a post-bloom situation in the
open water. This paper includes a study of the zooplankton community and
population structure of some of the dominant copepod species. Numerically,
the most important mesozooplankton components were the copepods
Calanus glacialis, Pseudocalanus minutus and
Oithona similis. Copepods of Atlantic origin, such as
Calanus finmarchicus and Oithona
atlantica, gave evidence of an advection of Atlantic water
masses into the area. It is concluded that the occurrence of new cohorts of
Arctic copepods coincides with the onset of the phytoplankton bloom in the
MIZ, and, that therefore, the spawning relies on stored energy.
相似文献
7.
The tropane alkaloid (TA) scopolamine is suggested to protect Brugmansia suaveolens (Solanaceae) against herbivorous insects. To test this prediction in a natural environment, scopolamine was induced by methyl jasmonate (MJ) in potted plants which were left 10?days in the field. MJ-treated plants increased their scopolamine concentration in leaves and herbivory decreased. These findings suggest a cause?Ceffect relationship. However, experiments in laboratory showed that scopolamine affect differently the performance of the specialist larvae of the ithomiine butterfly Placidina euryanassa (C. Felder & R. Felder) and the generalist fall armyworm Spodoptera frugiperda (J. E. Smith): the specialist that sequester this TA from B. suaveolens leaves was not negatively affected, but the generalist was. Therefore, scopolamine probably acts only against insects that are not adapted to TAs. Other compounds that are MJ elicited may also play a role in plant resistance against herbivory by generalist and specialist insects, and deserve future investigations. 相似文献
8.
Seasonal dynamics of suspended minerals, organic matter, particulate, and dissolved organic carbon (DOC), chlorophyll, and
their vertical fluxes were studied in a small Arctic fjord (Adventfjorden, Spitsbergen) from November 2006 to October 2007.
The fjord was usually covered with fast ice in winter, but remained open throughout the year since 2005. The open-water winter
period caused increased wave action and resuspension of organic and mineral particles. The lack of sea-ice in spring accelerated
the onset of the productive season. The earlier light signal also caused an earlier appearance of mesozooplanktonic organisms,
accompanied by a significant increase of the DOC pool in the water. In the cold period (winter and spring) 47% of the annual
organic matter settled on the sampling site, a lot coming from the spring diatom bloom in April. Summer melt (July, August)
resulted in turbid and brackish fjord surface water with stratification and increase of both suspended particles and sedimentation,
causing 60% of the annual minerals and 53% of the annual organic matter to settle at the sampling site. Increased dissolved
organic carbon (DOC) through sloppy feeding on the mixo- and heterotrophic protista by the abundant mesozooplankton indicated
intensive secondary production, resulting in a maximum fecal pellets flux of >5 mg C m−2 day−1. A warmer climate with reduced sea-ice cover in fjords will advance the onset of the spring bloom and will also result in
a larger input of turbid melt water in summer, restricting the light availability and enhancing flocculation and thereby sedimentation. 相似文献
9.
Homologies of the adductor mandibulae muscles in Tetraodontiformes as indicated by nerve branching patterns 总被引:4,自引:4,他引:0
Masanori?Nakaem-nakae@cc.kochi-u.ac.jp; KS fishssk@cc.kochi-u.ac.jp" title="MN m-nakae@cc.kochi-u.ac.jp; KS fishssk@cc.kochi-u.ac.jp" itemprop="email" data-track="click" data-track-action="Email author" data-track-label="">Email author Kunio?Sasaki 《Ichthyological Research》2004,51(4):327-336
Homologies of the adductor mandibulae muscles in eight families of Tetraodontiformes were hypothesized from the branching patterns of ramus mandibularis trigeminus. Insertions of the muscles to the upper or lower jaw were weak indicators of homology, migrations of the sites occurring frequently in A1, A2, A2, and A3. In monacanthids, tetraodontids, and diodontids, A1 tended to be split into numerous subsections, whereas in aracanids and ostraciids, A3 was highly developed, comprising three or four subsections. In tetraodontids, A2 was found to be a composite of A1 subsection and A2. The methods of and limits to applying nerve branching patterns to muscle homology are discussed. A new naming system that reflects both muscle homologies and insertions is proposed. 相似文献
10.
Else Nøst Hegseth Egil Sakshaug 《Journal of experimental marine biology and ecology》1983,67(3):199-220
Three species of diatoms, Skeletonema costatum (Grev.) Cleve, Thalassiosira gravida Cleve, and T. pseudonana (Hustedt) Hasle et Heimdal, were grown in in situ dialysis culture in the Trondheimsfjord at depths of 0.5 and 4 m. The rates of growth and the chemical composition of exponentially growing cells were monitored and related to seasonal changes in illumination and temperature. Functions correlating growth rate with temperature were deduced. Growth took place from February to November. During this period temperature ranged from ?1 to 16°C, the average photon flux density (ifI) (per 24 h) from 9 to 570 μE · m?2 · s?1 (0.5 m depth), and the length of the days (I > 1 μE · m?2 · s?1) from 6 to 24 h. Light-limited growth was evident when the product of the average daily light and the chlorophyll/N ratio was < 10; this occurred mostly in early spring and late autumn. Peak densities (> 800 for the Thalassiosira spp. and > 1300–1400 μE · m?2 · s?1 for Skeletonema) seem to inhibit growth. The highest rates recorded were ≈1.6 doubl. · day?1 (July, 15–16°C).The three species exhibit different ecological behaviour. Skeletonema is eurythermal (Q10 = 1.8), whereas Thalassiosira pseudonana favours high temperatures, and T. gravida temperatures < 10°C. Moreover, Skeletonema has generally less chlorophyll and more phosphorus and ATP (≈ 1.4 ×) than the other two species. In Skeletonema, the ATP level seems related to the light-governed growth rate, and independent of temperature. In Thalassiosira no such correlation was found. 相似文献