共查询到20条相似文献,搜索用时 15 毫秒
1.
Mohammad K. Khalesi H. H. Beeftink R. H. Wijffels 《Marine biotechnology (New York, N.Y.)》2009,11(4):488-494
The branching zooxanthellate soft coral Sinularia flexibillis releases antimicrobial and toxic compounds with potential pharmaceutical importance. As photosynthesis by the symbiotic algae
is vital to the host, the light-dependency of the coral, including its specific growth rate (μ day−1) and the physiological response to a range of light intensities (10–1,000 μmol quanta m−2 s−1) was studied for 12 weeks. Although a range of irradiances from 100 to 400 μmol quanta m−2 s−1 was favorable for S. flexibilis, based on chlorophyll content, a light intensity around 100 μmol quanta m−2 s−1 was found to be optimal. The contents of both zooxanthellae and chlorophyll a were highest at 100 μmol quanta m−2 s−1. The specific budding rate showed almost the same pattern as the specific growth rate. The concentration of the terpene flexibilide,
produced by this species, increased at high light intensities (200–600 μmol quanta m−2 s−1). 相似文献
2.
Han Gil Choi Ki Hoon Lee Hyun Il Yoo Pil Jun Kang Young Sik Kim Ki Wan Nam 《Journal of applied phycology》2008,20(5):729-735
The effects of temperature, irradiance, and daylength on Sargassum horneri growth were examined at the germling and adult stages to discern their physiological differences. Temperature–irradiance
(10, 15, 20, 25, 30°C × 20, 40, 80 μmol photons m−2s−1) and daylength (8, 12, 16, 24 h) experiments were carried out. The germlings and blades of S. horneri grew over a wide range of temperatures (10–25°C), irradiances (20–80 μmol photons m−2s−1), and daylengths (8–24 h). At the optimal growth conditions, the relative growth rates (RGR) of the germlings were 21% day−1 (25°C, 20 μmol photons m−2s−1) and 13% day−1 (8 h daylength). In contrast, the RGRs of the blade weights were 4% day−1 (15°C, 20 μmol photons m−2s−1) and 5% day−1 (12 h daylength). Negative growth rates were found at 20 μmol photons m−2s−1 of 20°C and 25°C treatments after 12 days. This phenomenon coincides with the necrosis of S. horneri blades in field populations. In conclusion, we found physiological differences between S. horneri germlings and adults with respect to daylength and temperature optima. The growth of S. horneri germlings could be enhanced at 25°C, 20 μmol photons m−2s−1, and 8 h daylength for construction of Sargassum beds and restoration of barren areas. 相似文献
3.
M. M. Ribeiro C. Plomion R. Petit G. G. Vendramin A. E. Szmidt 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2001,102(1):97-103
Genetic variation in 12 Pinus pinaster (maritime pine) populations spanning most of the distribution range of the species in Portugal was evaluated using six polymorphic
chloroplast microsatellite (cpSSR) loci. Thirty-two haplotypes were found. There were indications of very weak differentiation
among populations (Weir’s θcoefficient, 0.023), and the R
ST value, derived from the stepwise mutation model (SMM), was not significantly different from zero. The pattern, in which similarities
in allele size, in base pairs, do not contribute to the genetic structure, may be due to the recent mixing of genetic material
from different stands through plantations. Overall, a high level of haplotypic variation within populations was detected.
Using the SMM estimator (mean genetic distance of individuals within populations, D
2
sh
–––) we divided the populations into two groups, with above and below average values. The first group contained 5 populations,
mainly from the central part of the country, which possess, in general, high levels of haplotypic diversity. Among them, 2
populations were divergent from the others based on the pair-wise Nei’s distance. The results indicate that there is no discernible
geographic genetic pattern for the Portuguese populations of P. pinaster investigated. The history of expansion of the species range in Portugal during the twentieth century (mainly due to human
activity) and extensive gene flow among populations associated with the expansion could explain this finding.
Received: 15 February 2000 / Accepted: 14 April 2000 相似文献
4.
Pakkasmaa S Penttinen OP Piironen J 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2006,176(5):387-391
The metabolic rate (specific heat output) of individual eyed-stage eggs of Arctic charr Salvelinus alpinus (Linnaeus, 1758) originating from different families was measured with direct microcalorimetry. Metabolic rates varied between 2.3–7.9 μW ind−1 and 0.06–0.22 μW mg−1. Absolute heat output was unrelated to egg size, but size-scaled or specific heat output was negatively correlated with egg size, measured as diameter, dry mass or fresh mass. Metabolic rates varied significantly between families, suggesting that genetic and/or maternal effects affect embryonic metabolism in Arctic charr. Heat output increased almost linearly from 3.4 to 16.7 μW ind−1 (0.09–0.67 μW mg−1) during the embryonic development. Although the metabolic rate varied between the families and egg metabolic rate increased during development, there was an unexpected disconnect between metabolic rate and hatching time. 相似文献
5.
In January 2004 the microplankton community from the coastal waters of Terre Adélie and Georges V Land (139°E–145°E) was studied.
Results showed a diatom-dominated bloom with chlorophyll a levels averaging 0.64 μg l−1 at 5 m depth (range 0.21–1.57 μg l−1). Three geographic assemblages of diatoms were identified, based on principal diatom taxa abundances. The stratified waters
near the Mertz Glacier presented highest phytoplankton biomasses (0.28–1.57 μg Chl a l−1 at 5 m) and diatom abundances (6,507–70,274 cells l−1 at 5 m), but low diversity, dominated by Fragilariopsis spp. Lower biomasses (0.38–0.94 μg Chl a l−1 at 5 m) and abundances (394–9,058 cells l−1 at 5 m) were observed in the mixed waters around the Astrolabe Glacier with a diverse diatom community characterised by larger
species Corethron pennatum and Rhizosolenia spp. Finally an intermediate zone between them over the shallower shelf waters of the Adélie Bank represented by Chaetoceros criophilus, where biomasses (0.21–0.35 μg Chl a l−1 at 5 m) and abundances (1,190–5,431 cells l−1 at 5 m) were lowest, coinciding with the presence of abundant herbivorous zooplankton. 相似文献
6.
Genetic diversity is often considered important for species that inhabit highly disturbed environments to allow for adaptation.
Many variables affect levels of genetic variation; however, the two most influential variables are population size and type
of reproduction. When analyzed separately, both small population size and asexual reproduction can lead to reductions in genetic
variation, although the exact nature of which can be contrasting. Genetic variables such as allelic richness, heterozygosity,
inbreeding coefficient, and population differentiation have opposite predictions depending upon the trait (rarity or clonality)
examined. The goal of this study was to quantify genetic variation and population differentiation in a species that resides
in a highly stochastic environment and is both rare and highly clonal, Spiraea virginiana, and to determine if one trait is more influential genetically than the other. From populations sampled throughout the natural
range of S. virginiana, we used microsatellite loci to estimate overall genetic variation. We also calculated clonal structure within populations,
which included genotypic richness, evenness, and diversity. Gene flow was investigated by quantifying the relationship between
genetic and geographic distances, and population differentiation (θ) among populations. Observed heterozygosity, genotypic richness, and inbreeding coefficients were found to be representative
of high clonal reproduction (averaging 0.505, 0.1, and –0.356, respectively) and the number of alleles within populations
was low (range = 2.0–3.6), being more indicative of rarity. Population differentiation (θ) among populations was high (average = 0.302) and there was no relationship between genetic and geographic distances. By
examining a species that exhibits two traits that both can lead to reduced genetic variation, we may find an enhanced urgency
for conservation. Accurate demographic counts of clonal species are rarely, if ever, possible and genetic exploration for
every species is not feasible. Therefore, the conclusions in this study can be potentially extrapolated to other riparian,
clonal shrubs that share similar biology as S. virginiana. 相似文献
7.
Commiphora wightii is a medicinally important endangered species endemic to the Thar Desert of Rajasthan, India and adjoining areas of Pakistan.
The populations of this species are declining sharply because of its extensive use as a natural herb. Random amplified polymorphic
DNA analysis was conducted to find the genetic variation among 7 populations of C. wightii. Of the 100 random primers screened, 44 primers yielded 220 loci. Statistical analysis indicated low genetic diversity (H
pop = 0.0958; I = 0.1498; mean polymorphic loci = 14.28%), and high genetic differentiation among the populations (G
ST = 0.3990; AMOVA Φ
ST of 0.3390; Bayesian θ
(II) = 0.3002). The low genetic diversity may be due to geographic isolation and restricted gene flow (N
m = 0.7533) between the fragmented populations. Unsustainable utilization of the plant has fragmented the population continuum
which served the purpose of genetic exchange between populations. Mantel’s test was performed which revealed a highly significant
positive correlation between genetic and geographic distance (r
2 = 0.614, P = 0.023) among the populations studied. Low variation can also be attributed to poor seed setting and the slow growth pattern
of the species, which is also an apomict. In UPGMA dendrogram the Commiphora wightii samples were divided into two major and one minor cluster. These findings can serve as a guide to preserving the genetic
resources of this medicinal plant species. 相似文献
8.
Production rates, abundance, chlorophyll a (Chl a) concentrations and pigment composition were measured for three size classes (<2 μm, 2–11 μm and >11 μm) of phytoplankton
from May to December 2000 in deep, mesotrophic, alpine lake Mondsee in Austria. The study focuses on differences among phytoplankton
size fractions characterised by their surface area to volume ratio ([mm2 l−1: mm3l−1]), pigment distribution patterns and photosynthetic rates. Particular attention was paid to autotrophic picophytoplankton
(APP, fraction <2 μm) since this size fraction differed significantly from the two larger size fractions. Among the three
fractions, APP showed the highest surface area to volume ratios and a high persistence in the pattern of lipophilic pigments
between temporarily and spatially successive samples (about 80% similarity of pigment composition between samples over seasons
and depths). The epilimnetic abundance of APP varied seasonally with an annual maximum of 180 × 103 cells ml−1 in June (at 4–9 m). The minimum (October at 12 m) was more than an order of magnitude lower (4.9 × 103 ml−1). APP peaked during autumn and contributed between 24% and 42% to the total area-integrated Chl a (10–23 mg m−2) and between 16% and 58% to total area-integrated production (5–64 mg m−2 h−1) throughout seasons. 相似文献
9.
Le Dinh Hung Kanji Hori Huynh Quang Nang Tran Kha Le Thi Hoa 《Journal of applied phycology》2009,21(3):265-272
The three color morphotypes of the red alga Kappaphycus alvarezii (brown, red and green) were cultured in Camranh Bay, Vietnam, using the fixed off-bottom monoline culture method to evaluate
the growth rate, carrageenan yield, 3,6-anhydrogalactose, gel strength and lectin content. The brown morphotype was cultivated
over a 12-month period; the red and green morphotypes were over a 6-month period. At the 60-day culture timepoint, the brown
morphotype showed a higher growth rate (3.5–4.6% day−1) from September to February, and lower growth rate (1.6–2.8% day−1) from March to August. Significant (P < 0.05) differences in growth rate between culture months were found with the brown morphotype. High growth rates for the
red (3.6–4.4% day−1) and green (3.7–4.2% day−1) morphotypes were obtained from September to February. The carrageenan yield, 3,6-anhydrogalactose and gel strength of the
three morphotypes showed little variation, with the highest values obtained in November–December. At the 30-day sampling point,
the brown morphotype had a higher lectin content (167–302 μg g−1 dry alga) from August to March and a lower lectin content (23–104 μg g−1 dry alga) from April to July. High lectin contents were recorded for the red (139–338 μg g−1 dry alga) and green (124–259 μg g−1 dry alga) morphotypes from September to February. This study shows that the different morphotypes of K. alvarezii can be grown in the tropical waters of the Camranh during the northeast monsoon, and part of the southwest monsoon, especially
the brown morphotype, which can be grown during any season. 相似文献
10.
Franciane Pellizzari Eurico C. Oliveira Nair S. Yokoya 《Journal of applied phycology》2008,20(1):75-82
Gayralia K.L. Vinogr. is a monostromatic green alga of commercial importance in the southern Brazil, and its cultivation is being
considered. This paper reports some basic aspects of the biology of this poorly known genus. Two populations of Gayralia spp., from outer and inner sectors of Paranaguá Bay, showed an asexual life history with a distinct pattern of thallus ontogeny.
In one population (Gayralia sp. 1), zooids developed an expanded monostromatic blade directly, while in the other (Gayralia sp. 2) zooids produced an intermediate saccate stage, before giving rise to a monostromatic blade. Thalli of the two species
differ in size and in cell diameter. The effects of temperature (16–30°C), irradiance (50–100 μmol photons m−2 s−1), and salinity (5–40 psu) on the growth of both populations were assessed. Plantlets of Gayralia sp. 1 from in vitro cultures showed a broader tolerance to all salinity and irradiance levels tested, with the highest growth
rate (GR; mean 17% day−1) at 21.5°C and 100 μmol photons m−2 s−1. Plantlets of Gayralia sp. 1 collected during the winter in the field showed higher GR, ranging from 5% day−1 to 7.5% day−1 in salinities from 20 to 40 psu, and 2.0% day−1 and 4.3% day−1 for plantlets collected during the summer. Gayralia sp. 2 from the field showed highest GR at salinity of 15 psu. These results suggest distinct physiological responses of the
two species, in accordance with their distribution: Gayralia sp. 2 is limited to the inner areas of the estuary, while Gayralia sp. 1 grows in outer areas, where salinity values are higher than 20 psu. These data indicate that Gayralia sp. 1 has a higher potential for aquaculture than Gayralia sp. 2 due to its larger thalli, higher GR, and wider tolerance to environmental variations. 相似文献
11.
Anna Pérez-Lezaun Francesc Calafell E. Mateu David Comas Rosalía Ruiz-Pacheco J. Bertranpetit 《Human genetics》1996,99(1):1-7
This study presents an analysis of 20 tetranucleotide microsatellites in 16 worldwide human populations representing the
major geographic groups. Global Fst values for the 20 microsatellites are indicators of their relative validity as tools in
human population genetics. Four different measures of genetic distance (Fst, DSW, δμ
2 and Rst) have been tested and compared with each other. Neighbor-joining trees have been constructed for all the measures
of genetic distance and populations. Measures of genetic distance such as Fst, which does not consider different mutational
relationships among alleles and has a known relationship to differentiation by drift, and to some extent DSW, reflect what is known of human evolution, while mutation-based distances such as Rst and δμ
2 give very different results from those recognized from other sources (genetic or archaeological). When the genetic relationship
between human populations is analyzed through allelic frequencies for microsatellites, the choice of distance may be a key
issue in the picture obtained of genetic relationships between human populations. The results of the present study suggest
that genetic drift played the main role in generating the present distributions of microsatellite alleles and their variation
among human populations; the role of mutation must have been less important owing to the time constraint imposed by the small
timescale in which most human differentiation has occurred. Moreover, the results support the theory of a recent origin of
modern humans, although the existence of strong bottlenecks in the origin of the various human groups seems unlikely.
Received: 20 March 1996 相似文献
12.
We investigated seasonal variation of grazing impact of the pigmented nanoflagellates (PNF) with different sizes upon Synechococcus in the subtropical western Pacific coastal waters using grazing experiments with fluorescently labeled Synechococcus (FLS). For total PNF, conspicuous seasonal variations of ingestion rates on Synechococcus were found, and a functional response was observed. To further investigate the impact of different size groups, we separated
the PNF into four categories (<3, 3–5, 5–10, and >10 μm). Our results indicated that the smallest PNF (<3 μm PNF) did not
ingest FLS and was considered autotrophic. PNF of 3–5 μm in size made up most of the PNF community; however, their ingestion
on Synechococcus was too low (0.1–1.9 Syn PNF−1 h−1) to support their growth, and they had to depend on other prey or photosynthesis to survive. The ingestion rate of the 3–5 μm
group exhibited no significant seasonal variation; by contrast, the ingestion rates of 5–10 and >10 μm PNFs showed significant
seasonal variation. During the warm season, 3–5 μm PNF were responsible for the grazing of 12% of Synechococcus production, 5–10 μm PNF for 48%, and >10 μm PNF for 2%. Taken together, our results demonstrate that the PNF of 3–10 μm consumed
most Synechococcus during the warm season and exhibited a significant functional response to the increase in prey concentration. 相似文献
13.
In winter of 2009/2010, Aphanizomenon flos-aquae bloomed in the ice and snow covered oligo-mesotrophic Lake Stechlin, Germany. The photosynthesis of the natural population was measured at eight temperatures in the range of 2–35°C, at nine different irradiance levels in the range of 0–1,320 μmol m−2 s−1 PAR at each applied temperature. The photoadaptation parameter (I k) and the maximum photosynthetic rate (P max) correlated positively with the temperature between 2 and 30°C, and there was a remarkable drop in both parameters at 35°C. The low I k at low temperatures enabled the active photosynthesis of overwintering populations at low irradiance levels under ice and snow cover. The optimum of the photosynthesis was above 20°C at irradiances above 150 μmol m−2 s−1. At lower irradiance levels (7.5–30 μmol m−2 s−1), the photosynthesis was the most intensive in the temperature range of 2–5°C. The interaction between light and temperature allowed the proliferation of A. flos-aquae in Lake Stechlin resulting in winter water bloom in this oligo-mesotrophic lake. The applied 2°C is the lowest experimental temperature ever in the photosynthesis/growth studies of A. flos-aquae, and the results of the P–I and P–T measurements provide novel information about the tolerance and physiological plasticity of this species. 相似文献
14.
Klaus Martin Meiners S. Papadimitriou D. N. Thomas L. Norman G. S. Dieckmann 《Polar Biology》2009,32(7):1055-1065
Physical, biogeochemical and photosynthetic parameters were measured in sea ice brine and ice core bottom samples in the north-western
Weddell Sea during early spring 2006. Sea ice brines collected from sackholes were characterised by cold temperatures (range
−7.4 to −3.8°C), high salinities (range 61.4–118.0), and partly elevated dissolved oxygen concentrations (range 159–413 μmol kg−1) when compared to surface seawater. Nitrate (range 0.5–76.3 μmol kg−1), dissolved inorganic phosphate (range 0.2–7.0 μmol kg−1) and silicic acid (range 74–285 μmol kg−1) concentrations in sea ice brines were depleted when compared to surface seawater. In contrast, NH4
+ (range 0.3–23.0 μmol kg−1) and dissolved organic carbon (range 140–707 μmol kg−1) were enriched in the sea ice brines. Ice core bottom samples exhibited moderate temperatures and brine salinities, but high
algal biomass (4.9–435.5 μg Chl a l−1 brine) and silicic acid depletion. Pulse amplitude modulated fluorometry was used for the determination of the photosynthetic
parameters F
v/F
m, α, rETRmax and E
k. The maximum quantum yield of photosystem II, F
v/F
m, ranged from 0.101 to 0.500 (average 0.284 ± 0.132) and 0.235 to 0.595 (average 0.368 ± 0.127) in the sea ice internal and
bottom communities, respectively. The fluorometric measurements indicated medium ice algal photosynthetic activity both in
the internal and bottom communities of the sea ice. An observed lack of correlation between biogeochemical and photosynthetic
parameters was most likely due to temporally and spatially decoupled physical and biological processes in the sea ice brine
channel system, and was also influenced by the temporal and spatial resolution of applied sampling techniques. 相似文献
15.
Buatong Jirayu Phongpaichit Souwalak Rukachaisirikul Vatcharin Sakayaroj Jariya 《World journal of microbiology & biotechnology》2011,27(12):3005-3008
The aim of this work was to select endophytic fungi from mangrove plants that produced antimicrobial substances. Minimal inhibitory
concentrations (MIC) and minimal bactericidal concentrations (MBC) or minimal fungicidal concentrations (MFC) of crude extracts
from 150 isolates were determined against potential human pathogens by a colorimetric microdilution method. Ninety-two isolates
(61.3%) produced inhibitory compounds. Most of the extracts (28–32%) inhibited Staphylococcus aureus (MIC/MBC 4–200/64–200 μg ml−1). Only two extracts inhibited Pseudomonas aeruginosa (MIC/MBC 200/>200 μg ml−1). 25.5 and 11.7% inhibited Microsporum gypseum and Cryptococcus neoformans (MIC/MFC 4–200/8–200 μg ml−1 and 8–200/8–200 μg ml−1, respectively), while 7.5% were active against Candida albicans (MIC/MFC 32–200/32–200 μg ml−1). None of the extracts inhibited Escherichia coli. The most active fungal extracts were from six genera, Acremonium, Diaporthe, Hypoxylon, Pestalotiopsis, Phomopsis, and Xylaria as identified using morphological and molecular methods. Phomopsis sp. MA194 (GU592007, GU592018) isolated from Rhizophora apiculata showed the broadest antimicrobial spectrum with low MIC values of 8–32 μg ml−1against Gram-positive bacteria, yeasts and M. gypseum. It was concluded that endophytic fungi from mangrove plants are diverse, many produce compounds with antimicrobial activity
and could be suitable sources of new antimicrobial natural products. 相似文献
16.
The freshwater microalga Chlorella vulgaris was grown heterotrophically in fed-batch 50–600-L fermenters at 36°C, on aerated and mixed nutrient solution with urea as
a nitrogen and glucose as a carbon and energy source. Cell density increased from the initial value 6.25 to 117.18 g DW L−1 in 32 h in the fermenter 50 L at a mean growth rate 3.52 g DW L−1 h−1. The DW increase in the fermenter 200 L was from 7.25 to 94.82 g DW L−1 in 26.5 h at a mean growth rate 3.37 g DW L−1 h−1. Mean specific growth rate μ was about 0.1 h−1 in the both fermenters, if nutrients and oxygen were adequately supplied. The DW increase in the fermenter 600 L was from
0.8 to 81.6 g DW L−1 in 66.5 h at a mean growth rate 1.22 g DW L−1 h−1 and μ = 0.07 h−1. A limitation of the cell growth rate in 600 L fermenter caused by a low dissolved oxygen concentration above cell densities
higher than 10 g DW L−1) occurred. Specific growth rate decreased approximately linearly with increasing glucose concentration (25–80 g glucose L−1) at the beginning of cultivation and decreased with the time of cultivation. The cell yield was 0.55–0.69 g DW (g glucose)−1. The content of proteins, β-carotene, and chlorophylls in the cells steadily increased and starch content decreased, by keeping
aerated and mixed culture another 12 h in fermenter after the cell growth was stopped due to glucose deficiency. 相似文献
17.
Irzykowska L Bocianowski J Waśkiewicz A Weber Z Karolewski Z Goliński P Kostecki M Irzykowski W 《Journal of applied genetics》2012,53(2):237-247
Thirty single-spore isolates of a toxigenic fungus, Fusarium oxysporum, were isolated from asparagus spears and identified by species-specific polymerase chain reaction (PCR) and translation elongation
factor 1-α (TEF) sequence analysis. In the examined sets of F. oxysporum isolates, the DNA sequences of mating type genes (MAT) were identified. The distribution of MAT idiomorph may suggest that MAT1-2 is a predominant mating type in the F. oxysporum population. F. oxysporum is mainly recognised as a producer of moniliformin—the highly toxic secondary metabolite. Moniliformin content was determined
by high-performance liquid chromatography (HPLC) analysis in the range 0.05–1,007.47 μg g−1 (mean 115.93 μg g−1) but, also, fumonisin B1 was detected, in the concentration range 0.01–0.91 μg g−1 (mean 0.19 μg g−1). There was no association between mating types and the mycotoxins biosynthesis level. Additionally, a significant intra-species
genetic diversity was revealed and molecular markers associated with toxins biosynthesis were identified. 相似文献
18.
Paul I. Boon 《Microbial ecology》1991,22(1):27-52
Billabongs, lentic waterbodies common to the floodplain of Australian rivers, differ considerably from the lotic riverine
environment in terms of hydrology, physiochemical characteristics, and biological assemblages present. As little is known
regarding the bacterial ecology of billabong habitats, a comparison was made of the bacterial assemblages in the water column
of seven paired river/billabong sites in the Murray-Darling Basin of southeastern Australia. Billabongs supported larger populations
of bacteria (1–157×109 cells liter−1; 11–10,270 μg C liter−1) than did rivers (1–10×109 cells liter−1; 6–143 μg C liter−1). Phospholipid analyses confirmed that billabongs (14–111 μg phospholipid fatty acid liter−1) had larger bacterial populations than rivers (<12 μg liter−1). Bacterial production, measured with3H-leucine, was also greater in billabongs (0.28–3.05 μg C liter−1 hour−1) than rivers (0.05–0.62 μg C liter−1 hour−1). Production calculated from the frequency of dividing cells confirmed this conclusion, and suggested bacterial production
in some billabongs could exceed 100 μg C liter−1 hour−1. An INT-formazan method indicated that usually <25% of bacterial cells were active in either habitat, but this was probably
an underestimate of the bona fide value. Turnover times of glucose were usually shorter in billabongs, and the cell-specific
activity greater for billabong than river assemblages. The factors most likely to be responsible for the differences between
the bacterial assemblages in rivers and billabongs relate to hydrological regime and the availability of organic carbon substrates. 相似文献
19.
Andrew R. Whiteley Kim Hastings John K. Wenburg Chris A. Frissell Jamie C. Martin Fred W. Allendorf 《Conservation Genetics》2010,11(5):1929-1943
Following glacial recession in southeast Alaska, waterfalls created by isostatic rebound have isolated numerous replicate
populations of coastal cutthroat trout (Oncorhynchus clarkii clarkii) in short coastal streams. These replicate isolated populations offer an unusual opportunity to examine factors associated
with the maintenance of genetic diversity. We used eight microsatellites to examine genetic variation within and differentiation
among 12 population pairs sampled from above and below these natural migration barriers. Geological evidence indicated that
the above-barrier populations have been isolated for 8,000–12,500 years. Genetic differentiation among below-barrier populations
(F
ST = 0.10, 95% C.I. 0.08–0.12) was similar to a previous study of more southern populations of this species. Above-barrier populations
were highly differentiated from adjacent below-barrier populations (mean pairwise F
ST = 0.28; SD 0.18) and multiple lines of evidence were consistent with asymmetric downstream gene flow that varied among streams.
Each above-barrier population had reduced within-population genetic variation when compared to the adjacent below-barrier
population. Within-population genetic diversity was significantly correlated with the amount of available habitat in above-barrier
sites. Increased genetic differentiation of above-barrier populations with lower genetic diversity suggests that genetic drift
has been the primary cause of genetic divergence. Long-term estimates of N
e based on loss of heterozygosity over the time since isolation were large (3,170; range 1,077–7,606) and established an upper
limit for N
e if drift were the only evolutionary process responsible for loss of genetic diversity. However, it is likely that a combination
of mutation, selection, and gene flow have also contributed to the genetic diversity of above-barrier populations. Contemporary
above-barrier N
e estimates were much smaller than long-term N
e estimates, not correlated with within-population genetic diversity, and not consistent with the amount of genetic variation
retained, given the approximate 10,000-year period of isolation. The populations isolated by waterfalls in this study that
occur in larger stream networks have retained substantial genetic variation, which suggests that the amount of habitat in
headwater streams is an important consideration for maintaining the evolutionary potential of isolated populations. 相似文献
20.
Toshiya Katano Shin-ichi Nakano Hiroyuki Ueno Osamu Mitamura Kaori Anbutsu Masayuki Kihira Yasuhiro Satoh Takeshi Satoh Valentin V. Drucker Yuji Tanaka Yuki Akagashi Masahito Sugiyama 《Limnology》2008,9(3):243-250
The abundance and composition of phytoplankton were investigated at six stations along a transect from the Barguzin River
inflow to the central basin of Lake Baikal in August 2002 to clarify the effect of the river inflow on the phytoplankton community
in the lake. The water temperature in the epilimnion was high near the shore at Station 1 (17.3°C), probably due to the higher
temperature of the river water, and gradually decreased offshore at Station 6 (14.5°C). Thermal stratification developed at
Stations 2–6, and a thermocline was observed at a 17–22-m depth at Stations 2–4 and an 8–12-m depth at Stations 5 and 6. The
concentrations of nitrogen and phosphorus nutrients in the epilimnion at all stations were <1.0 μmol N l−1 and <0.16 μmol P l−1, respectively. Relatively high concentrations of nutrients (0.56–7.38 μmol N l−1 and 0.03–0.28 μmol P l−1) were detected in the deeper parts of the euphotic zone. Silicate was not exhausted at all stations (>20 μmol Si l−1). The chlorophyll a (chl. a) concentration was high (>10 μg l−1) near the shore at Station 1 and low (<3 μg l−1) at five other stations. The <2 μm fraction of chl. a in Stations 2–6 ranged between 0.80 and 1.85 μg l−1, and its contribution to total chl. a was high (>60%). In this fraction, picocyanobacteria were abundant at all stations and ranged between 5 × 104 and 5 × 105 cells ml−1. In contrast, chl. a in the >2 μm fraction varied significantly (0.14–11.17 μg l−1), and the highest value was observed at Station 1. In this fraction, the dominant phytoplankton was Aulacoseira and centric diatoms at Station 1 and Cryptomonas, Ankistrodesmus, Asterionella, and Nitzschia at Stations 2–6. The present study demonstrated the dominance of picophytoplankton in the pelagic zone, while higher abundance
of phytoplankton dominated by diatoms was observed in the shallower littoral zone. These larger phytoplankters in the littoral
zone probably depend on nutrients from the Barguzin River. 相似文献