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1.
Leigh C. LattaIV Debra L. Fisk Roland A. Knapp Michael E. Pfrender 《Conservation Genetics》2010,11(5):1737-1745
Dramatic changes in environmental conditions or community composition may impose severe selective pressures on resident populations.
These changes in the selective regime can lead to demographic bottlenecks or local extinction. The consequence of demographic
contraction is often a reduction of standing genetic variation. Since the level of adaptive genetic variation in populations
plays an important role in persistence and adaptive response, understanding genetic resilience and the time course for re-establishment
of genetic diversity following demographic perturbations is a critical component of assessing the consequences of changing
environments. The introduction of nonnative fish into historically fishless lakes is a particularly dramatic environmental
change frequently contributing to demographic bottlenecks and local extinction of native populations. We examine the quantitative-
and molecular-genetic recovery of two alpine populations of the zooplankton Daphnia melanica from the Sierra Nevada, California, USA. These populations were extirpated by introduced salmonids and subsequently re-established
following the experimental removal of nonnative fish. We obtained data for nuclear and mitochondrial markers and conducted
a common-garden experiment to assess the levels of molecular- and quantitative-genetic variation following experimental fish
removal. Reestablished D. melanica populations attained levels of nuclear genetic diversity only slightly lower than surrounding fishless populations in the
first year following fish removal and substantial mitochondrial and quantitative-genetic diversity within 8 years. This high
level of genetic resilience was likely facilitated by multiple sources of genetic variation, including immigration from neighboring
populations and hatching from a local reservoir of diapausing eggs. Our results highlight the genetic resilience of taxa with
reservoirs of genetic variation in seed or egg banks. 相似文献
2.
Recent research suggests that planktonic organisms in resting stages can perceive predators chemically and delay hatching to evade predation. Using a co-occurring predator–prey pair (Gambusia holbrooki Girard and Daphnia curvirostris Eylmann) from a Mediterranean floodplain wetland, this study tested for such predator-avoidance behaviour of Daphnia. Results show that hatching patterns of Daphnia were not reduced by the presence of different biomass levels of Gambusia. This could be due to the fact that the density of Gambusia in the wetland is high from late spring to late autumn, suggesting that delayed hatchlings would face increased mortality through consumptive predation. 相似文献
3.
In natural host populations, parasitism is considered to be omnipresent and to play an important role in shaping host life
history and population dynamics. Here, we study parasitism in natural populations of the zooplankton host Daphnia magna investigating their individual and population level effects during a 2-year field study. Our results revealed a rich and
highly prevalent community of parasites, with eight endoparasite species (four microsporidia, one amoeba, two bacteria and
one nematode) and six epibionts (belonging to five different taxa: Chlorophyta, Bacillariophyceae, Ciliata, Fungi and Rotifera).
Several of the endoparasites were associated with a severe overall fecundity reduction of the hosts, while such effects were
not seen for epibionts. In particular, infections by Pasteuria ramosa, White Fat Cell Disease and Flabelliforma magnivora were strongly associated with a reduction in overall D. magna fecundity. Across the sampling period, average population fecundity of D. magna was negatively associated with overall infection intensity and total endoparasite richness. Population density of D. magna was negatively correlated to overall endoparasite prevalence and positively correlated with epibiont richness. Finally, the
reduction in host fecundity caused by different parasite species was negatively correlated to both parasite prevalence and
the length of the time period during which the parasite persisted in the host population. Consistent with epidemiological
models, these results indicate that parasite mediated host damages influence the population dynamics of both hosts and parasites. 相似文献
4.
Two repeated DNA sequences isolated from a partial genomic DNA library of Helianthus annuus, p HaS13 and p HaS211, were shown to represent portions of the int gene of a Ty3 /gypsy retroelement and of the RNase-Hgene of a Ty1 /copia retroelement, respectively. Southern blotting patterns obtained by hybridizing the two probes to BglII- or DraI-digested genomic DNA from different Helianthus species showed p HaS13 and p HaS211 were parts of dispersed repeats at least 8 and 7 kb in length, respectively, that were conserved in all species studied. Comparable hybridization patterns were obtained in all species with p HaS13. By contrast, the patterns obtained by hybridizing p HaS211 clearly differentiated annual species from perennials. The frequencies of p HaS13- and p HaS211-related sequences in different species were 4.3x10(4)-1.3x10(5) copies and 9.9x10(2)-8.1x10(3) copies per picogram of DNA, respectively. The frequency of p HaS13-related sequences varied widely within annual species, while no significant difference was observed among perennial species. Conversely, the frequency variation of p HaS211-related sequences was as large within annual species as within perennials. Sequences of both families were found to be dispersed along the length of all chromosomes in all species studied. However, Ty3 /gypsy-like sequences were localized preferentially at the centromeric regions, whereas Ty1/ copia-like sequences were less represented or absent around the centromeres and plentiful at the chromosome ends. These findings suggest that the two sequence families played a role in Helianthusgenome evolution and species divergence, evolved independently in the same genomic backgrounds and in annual or perennial species, and acquired different possible functions in the host genomes. 相似文献
5.
Esteban Balseiro Beatriz Modenutti Claudia Queimaliños Mariana Reissig 《Aquatic Ecology》2007,41(4):599-609
Food quality in terms of carbon (C):phosphorus (P) ratio can constrain the success of highly demanding P herbivores as Daphnia. North Andean Patagonian lakes are ultraoligotrophic with low nutrient concentrations and well-developed euphotic zones.
We investigated the distribution of the large Daphnia commutata in relation with food quality (sestonic C:P ratio) and predation risk in these lakes. The predation risk was estimated based
on the fish species present and their relative eye diameter and transparency of the lake. The C:P ratios in the lakes were
high, varying from 350 to >1,200. The lakes with D. commutata had significantly lower C:P ratio than those without these daphnids. On the other hand, those lakes where Daphnia is present have the lower predation risk than those were Daphnia is absent. In addition, we carried out growth experiments with neonates and natural seston of three lakes with different
C:P ratio. The growth rates were inversely related with C:P of the food. Food quality and predation risk together determined
the success or failure of large Daphnia populations in these Andean clear ultraoligotrophic lakes. 相似文献
6.
A hypothesis on change in prey size selectivity in relation to illumination level was tested on the basis of data on weight
and size composition of the content of the digestive tract of larvae of perch Perca fluviatilis and on zooplankton in the layer 0–6 m (Wallersee Lake, Austria). Larvae foraging in the twilight-night period had almost
two times more food in the intestine than those foraging in the daytime. The size composition of perch larvae and concentration
and size composition of zooplankton hardly differed in the daytime and twilight-night samples. For the first time, it is shown
on field material that more intensive feeding of larvae at twilight is related to selection of significantly larger prey than
in daytime feeding. In the day-time, the larvae consumed more prey but their maximum size did not exceed 0.6 of the diameter
of mouth opening of the fish; at twilight it was over 0.8. In case of feeding on so large prey, not only the weight of the
consumed feed increases but the time used for capture and swallowing also considerably increases. The larvae which in the
period of investigation did not yet form schools, which perform the principal defensive function, were especially vulnerable
for predators feeding on relatively large prey. The decrease of the part of small-sized prey at twilight is not related to
their lesser availability due to a low illumination. It is assumed that feeding on energetically more valuable but less available
prey is shifted to the period of low illumination when the larvae are less exposed to predation risk. The obtained results
are discussed from positions of the triotroph concept (Manteifel’, 1961). 相似文献
7.
Noel H. Holmgren 《Brittonia》2018,70(1):115-139
A revision of Penstemon sect. Saccanthera subsect. Serrulati includes a new species (P. salmonensis), a new variety (P. triphyllus var. infernalis), and the elevation of a subspecies to species (P. curtiflorus), bringing the total number of species to eight, which are keyed and described, complete with nomenclature and type citations. 相似文献
8.
A genetic transformation system has been developed for callus cells of Crataegus
aronia using Agrobacterium
tumefaciens. Callus culture was established from internodal stem segments incubated on Murashige and Skoog (MS) medium supplemented with
5 mg l−1 Indole-3-butyric acid (IBA) and 0.5 mg l−1 6-benzyladenine (BA). In order to optimize the callus culture system with respect to callus growth and coloration, different
types and concentrations of plant growth regulators were tested. Results indicated that the best average fresh weight of red
colored callus was obtained on MS medium supplemented with 2 mg l−1 2,4-dichlorophenoxyacetic acid (2,4-D) and 1.5 mg l−1 kinetin (Kin) (callus maintenance medium). Callus cells were co-cultivated with Agrobacterium harboring the binary plasmid pCAMBIA1302 carrying the mgfp5 and hygromycin phosphotransferase (hptII) genes conferring green fluorescent protein (GFP) activity and hygromycin resistance, respectively. Putative transgenic calli
were obtained 4 weeks after incubation of the co-cultivated explants onto maintenance medium supplemented with 50 mg l−1 hygromycin. Molecular analysis confirmed the integration of the transgenes in transformed callus. To our knowledge, this
is the first time to report an Agrobacterium-mediated transformation system in Crataegus
aronia. 相似文献
9.
D. C. Peñalva-Arana Kenneth Forshay Pieter T. J. Johnson J. R. Strickler Stanley I. Dodson 《Hydrobiologia》2011,668(1):147-154
Zooplankters are hosts to numerous endo- and ectoparasites, some of which have dramatic impacts on their hosts. Epizootics
on zooplankton are probably more widespread in lake systems than it is currently known, and few studies have explored the
direct and indirect importance of parasitism in aquatic food webs. In addition, our understanding of the sublethal effects
of parasitic infections on host organisms and populations is limited. We used a novel electro-chemical based technique to
measure in the outflow of the feeding current changes in the beat rate of the thoracic appendages in female Daphnia pulicaria. We observed simultaneously the heart rates and compared chytrid infected animals with uninfected gravid and non-gravid ones.
We found in uninfected animals a thoracic beat rate of 3.81 ± 018 Hz and a heart rate of 4.67 ± 0.42 Hz. Gravid daphnids had
a 14% lower thoracic beat rate (3.27 ± 0.30 Hz) than non-gravid females while the heart rate did not significantly differ
(4.48 ± 0.28 Hz). In contrast, infected animals showed a 22% lower thoracic beat rate (2.96 ± 0.47 Hz) and a 36% lower heart
rate (2.98 ± 0.5 Hz) when compared with uninfected non-gravid females. We discuss the ways Daphnia are affected by Polycaryum leave infections on the individual and population level. 相似文献
10.
Studying Pneumocystis has proven to be a challenge from the perspective of propagating a significant amount of the pathogen in a facile manner.
The study of several fungal pathogens has been aided by the use of invertebrate model hosts. Our efforts to infect the invertebrate
larvae Galleria
mellonella with Pneumocystis proved futile since P. murina neither caused disease nor was able to proliferate within G. mellonella. It did, however, show that the pathogen could be rapidly cleared from the host. 相似文献
11.
Notocactus scopa cv. Soonjung was subjected to in planta Agrobacterium tumefaciens-mediated transformation with vacuum infiltration, pin-pricking, and a combination of the two methods. The pin-pricking combined with vacuum infiltration (20-30 cmHg for 15 min) resulted in a transformation efficiency of 67-100%, and the expression of the uidA and nptII genes was detected in transformed cactus. The established in planta transformation technique generated a transgenic cactus with higher transformation efficiency, shortened selection process, and stable gene expression via asexual reproduction. All of the results showed that the in planta transformation method utilized in the current study provided an efficient and time-saving procedure for the delivery of genes into the cactus genome, and that this technique can be applied to other asexually reproducing succulent plant species. 相似文献
12.
Background
wFleaBase is a database with the necessary infrastructure to curate, archive and share genetic, molecular and functional genomic data and protocols for an emerging model organism, the microcrustacean Daphnia. Commonly known as the water-flea, Daphnia's ecological merit is unequaled among metazoans, largely because of its sentinel role within freshwater ecosystems and over 200 years of biological investigations. By consequence, the Daphnia Genomics Consortium (DGC) has launched an interdisciplinary research program to create the resources needed to study genes that affect ecological and evolutionary success in natural environments. 相似文献13.
A complex study on the adaptation of cn and vn mutants and the allozymes of alcoholdehydrogenase (ADH) was carried out in initially pure lines, and their panmixia populations during exchange of the mutant genotype with that of wild-type flies (C-S) and D) through saturating crossings. The relative adaptation of the genotypes was estimated by their effect on reproductive efficiency in the experimentally obtained population. Fecundity, lifespan, and the resistance of the studied genotypes to hyperthermia were investigated individually. It was shown that the high level of adaptation of the cn mutants and the low level of adaptation of the vg mutants was correlated with the presence of different ADH allozymes. In the studied population, the F-allozyme of ADH accompanied the vg mutation, while the S-allozyme of the enzyme was detected in cn mutants. Saturating crossings of C-S(Adh S)×vg(Adh F) and D(Adh F) × cn(Adh S), along with the parallel determination of the allele composition of the Adh locus, demonstrated that the complete substitution of the F-allozyme of ADH in the vg mutants by the S-allozyme in D flies, as well as the substitution of the S-allozyme of ADH in the cn mutants by the F-allozyme in D flies was realized only after the 15th–20th backcrosses. These results favor the coadaptation of cn and vg marker genes with alleles of the Adh locus and indicate the important role of the latter in the adaptation of genotypes. In the studied population, selection acted primarily against the vg mutants, which were inferior to the cn mutants, and heterozygote genotypes in indices of the main adaptation components. 相似文献
14.
The maT clade of transposons is a group of transposable elements intermediate in sequence and predicted protein structure to mariner and Tc transposons, with a distribution thus far limited to a few invertebrate species. We present evidence, based on searches of publicly available databases, that the nematode Caenorhabditis briggsae has several maT-like transposons, which we have designated as CbmaT elements, dispersed throughout its genome. We also describe two additional transposon sequences that probably share their evolutionary history with the CbmaT transposons. One resembles a fold back variant of a CbmaT element, with long (380-bp) inverted terminal repeats (ITRs) that show a high degree (71%) of identity to CbmaT1. The other, which shares only the 26-bp ITR sequences with one of the CbmaT variants, is present in eight nearly identical copies, but does not have a transposase gene and may therefore be cross mobilised by a CbmaT transposase. Using PCR-based mobility assays, we show that CbmaT1 transposons are capable of excising from the C. briggsae genome. CbmaT1 excised approximately 500 times less frequently than Tcb1 in the reference strain AF16, but both CbmaT1 and Tcb1 excised at extremely high frequencies in the HK105 strain. The HK105 strain also exhibited a high frequency of spontaneous induction of unc-22 mutants, suggesting that it may be a mutator strain of C. briggsae. 相似文献
15.
Karolina Vrandecic Drazenka Jurkovic Luca Riccioni Jasenka Cosic Tomislav Duvnjak 《Mycopathologia》2010,170(1):51-60
Sunflower (Helianthus annuus) stem canker caused by Diaporthe helianthi is one of the most important sunflower diseases in Croatia. Until recently, sunflower was the only known host for D. helianthi. In our research carried out in the area of Eastern Croatia, isolates of Diaporthe/Phomospis were collected from Xanthium italicum, X. strumarium and Arctium lappa. Using morphological, cultural and molecular ITS rDNA data, isolates from these weeds were identified as D. helianthi. The following isolates were used in the pathogenicity test: one isolate originated from sunflower (Su5/04), three from X. italicum (Xa2, Xa3 and Xa5), two from X. strumarium (Xa9 and Xa12), one from Xanthium sp. (Xa13) and one from A. lappa (Ar3). According to the results, it was determined that isolate Xa5 (originated from X. italicum) was the most pathogenic to sunflower stems. The average length of the lesion was 11.3 cm. The lowest level of pathogenicity
was found in Xa9 (isolated from X. strumarium). The length of the lesion was 0.1 cm. 相似文献
16.
17.
In the presence of size-selective fish daphnids were shown to exhibit two alternative inducible defence strategies: They may
either escape predation by active migration or adopt a life history strategy, e.g., reproduce earlier and at a smaller size.
Depending on the type of habitat, migration may either be vertically (in deep stratified lakes) or horizontally (in shallow
lakes with macrophytes) oriented. Concerning behavioural defence strategies, daphnids living in medium-deep, weakly stratified
water bodies with a poorly developed littoral face a dilemma, since the littoral provides no shelter and the availability
of a deep-water refuge is unpredictable. We studied the population dynamics, life history changes (size at maturity) and daytime
vertical distribution of Daphnia galeata in a weakly stratified reservoir in relation to predation by juvenile fish during 6 years. While temperature gradients were
usually small, oxygen concentrations suggest that a low-oxygen refuge for daphnids was available in every year to some extent.
Our results indicate that, depending on predation intensity and stratification patterns, daphnids exhibit both, behavioural
and life history defences. In years with a high biomass of young-of-the-year (YOY) perch Daphnia abundance declined rapidly at the end of the clear water stage while at the same time the vertical distribution at daytime
shifted to deep strata providing a low-oxygen refuge and the size at maturity decreased. However, while the life history response
in some years lasted throughout most of the summer period, a shift in daytime vertical distribution was exhibited for much
shorter periods. Both traits were much less expressed in years with low YOY fish densities and no negative correlation between
them could be verified. We suggest that under high predation pressure in this relatively shallow reservoir no strictly alternative
(either behavioural or life history) strategies exist, but that daphnids make use of the full range of possible anti-predator
defences available, at least during short periods when predation is most intense.
Guest editor: Piet Spaak
Cladocera: Proceedings of the 7th International Symposium on Cladocera 相似文献
18.
New combinations are proposed in anticipation of the Polygonaceae treatment in the forthcoming volume of Intermountain Flora:
Polygonum kelloggii var. esotericum, P. kelloggii var. watsonii
,
Rumex densiflorus var. pycnanthus
,
R. salicifolius var. utahensis, and R. occidentalis var. tomentellus. Typifications are proposed to facilitate ongoing studies in Polygonaceae and to maintain current usage. 相似文献
19.
Zhengfang Zhang Yanming Sheng Keyi Jiang Zhao Wang Yuguo Zheng Qing Zhu 《Biotechnology letters》2010,32(4):513-516
A newly isolated Bacillus megaterium with epoxide hydrolase activity resolved racemic glycidyl (o, m, p)-methylphenyl ethers to give enantiopure epoxides in 84–99% enantiomeric excess and with 21–73 enantiomeric ratios. The (S)-enantiomer was obtained from rac-glycidyl (o or m)-methylphenyl ether while the (R)-epoxides was obtained from glycidyl p-methylphenyl ether. The observations are explained at the level by enzyme-substrate docking studies. 相似文献
20.
The microtubule-binding protein tau has been investigated for its contribution to various neurodegenerative disorders. However,
the findings from transgenic studies, using the same tau transgene, vary widely among different laboratories. Here, we have investigated the potential mechanisms underlying tauopathies
by comparing Drosophila (d-tau) and human (h-tau) tau in a Drosophila model. Overexpression of a single copy of either tau isoform in the retina results in a similar rough eye phenotype. However, co-expression of Par-1 with d-tau leads to lethality, whereas co-expression of Par-1 with h-tau has little effect on the rough eye phenotype. We have found analogous results by comparing larval proteomes. Through genetic
screening and proteomic analysis, we have identified some important potential modifiers and tau-associated proteins. These
results suggest that the two tau genes differ significantly. This comparison between species-specific isoforms may help to clarify whether the homologous
tau genes are conserved.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
This study was supported by the National Science Foundation of China (30270341; 30630028), the Multidisciplinary Program (Brain
and Mind) of the Chinese Academy of Sciences, the Major State Basic Research Program (“973 program”; G2000077800; G2006CB806600;
2006CB911003), the Precedent Project of Important Intersectional Disciplines in the Knowledge Innovation Engineering of the
Chinese Academy of Sciences (KJCX1-09-03). 相似文献