Riparian zones are landscape features adjacent to streams and are widely recognized as important in reducing erosion and filtering
groundwater. Few studies directly investigate rooting dynamics of riparian areas, and little information exists concerning
riparian root densities, biomass, depth profiles, changes through time, or vulnerability to disturbance. This study examined
spatial and temporal patterns in root systems in streamsides influenced by season, hydrologic regime, vegetative composition,
and ice storm disturbance in the eastern Adirondacks, New York. Sequential root cores and in-growth cores were collected from
June 2000 through August 2001 in a riparian area with minimal ice storm damage adjacent to a third-order stream. Data were
used to assess seasonal trends in root biomass and to provide a reference for spatial comparisons. The biomass and surface
area of roots collected in the reference site cores were compared with cores collected at nine additional riparian sites differing
in degree of canopy damage from the January 1998 ice storm. Average root biomass at the reference site was 1330 g/m2, comparable to or greater than values reported for terrestrial and other riparian systems. Root biomass varied seasonally
with a maximum root biomass in August, 2000; this result was not repeated the following year after the water table inundated
much of the rooting zone in mid-June. Root biomass was spatially variable on a range of scales. Although the maximum root
surface area occurred in the upper 10 cm, root biomass peaked at 20–30 cm belowground, unlike observations from most other
root studies where the maximum root biomass has been found in the top 10 cm. Areas severely damaged by the ice storm had significantly
less root biomass and surface area than areas with low damage. This study demonstrates that root biomass in riparian areas
is highly dynamic over time, space, and across disturbance sites. Our findings suggest that the spatial variability in root
densities has direct implications for riparian vulnerability to erosion. 相似文献
Multi-Locus Sequence Typing (MLST) has emerged as a leading molecular typing method owing to its high ability to discriminate
among bacterial isolates, the relative ease with which data acquisition and analysis can be standardized, and the high portability
of the resulting sequence data. While MLST has been successfully applied to the study of the population structure for a number
of different bacterial species, it has also provided compelling evidence for high rates of recombination in some species.
We have analyzed a set of Campylobacter jejuni strains using MLST and Comparative Genomic Hybridization (CGH) on a full-genome microarray in order to determine whether
recombination and high levels of genomic mosaicism adversely affect the inference of strain relationships based on the analysis
of a restricted number of genetic loci. 相似文献
An experiment was performed during the grazing seasons of 1998, 1999 and 2000 to study the influence of the antiparasitic drug ivermectin and the nematophagous fungus Duddingtonia flagrans on cattle dung disintegration. The faeces originated from groups of animals that were part of a separate grazing experiment where different control strategies for nematode parasite infections were investigated. Each group consisted of 10 first-season grazing cattle that were either untreated, treated with the ivermectin sustained-release bolus, or fed chlamydospores of D. flagrans. Faeces were collected monthly on 4 occasions and out of pooled faeces from each group, 4 artificial 1 kg dung pats were prepared and deposited on nylon mesh on an enclosed pasture and protected from birds. The position of the new set of pats was repeated throughout the 3 years of the study. Each year, the dung pats were weighed 4, 6, 8 and 10 weeks after deposition and immediately afterwards replaced to their initial positions.
Results showed that there was no difference in faecal pat disintegration between groups. However, the time-lag between deposition and complete disintegration of the faeces varied significantly between deposition occasions. Dung pats disappeared within 2 weeks (visual observation) when subjected to heavy rainfall early after deposition, whereas an extended dry period coincided with faeces still remaining 12 months after deposition.
The pan-genome of a bacterial species consists of a core and an accessory gene pool. The accessory genome is thought to be
an important source of genetic variability in bacterial populations and is gained through lateral gene transfer, allowing
subpopulations of bacteria to better adapt to specific niches. Low-cost and high-throughput sequencing platforms have created
an exponential increase in genome sequence data and an opportunity to study the pan-genomes of many bacterial species. In
this study, we describe a new online pan-genome sequence analysis program, Panseq. 相似文献
Effective mating between laboratory-reared males and wild females is paramount to the success of vector control strategies aiming to decrease disease transmission via the release of sterile or genetically modified male mosquitoes. However mosquito colonization and laboratory maintenance have the potential to negatively affect male genotypic and phenotypic quality through inbreeding and selection, which in turn can decrease male mating competitiveness in the field. To date, very little is known about the impact of those evolutionary forces on the reproductive biology of mosquito colonies and how they ultimately affect male reproductive fitness.
Methods
Here several male reproductive physiological traits likely to be affected by inbreeding and selection following colonization and laboratory rearing were examined. Sperm length, and accessory gland and testes size were compared in male progeny from field-collected females and laboratory strains of Anopheles gambiae sensu stricto colonized from one to over 25 years ago. These traits were also compared in the parental and sequentially derived, genetically modified strains produced using a two-phase genetic transformation system. Finally, genetic crosses were performed between strains in order to distinguish the effects of inbreeding and selection on reproductive traits.
Results
Sperm length was found to steadily decrease with the age of mosquito colonies but was recovered in refreshed strains and crosses between inbred strains therefore incriminating inbreeding costs. In contrast, testes size progressively increased with colony age, whilst accessory gland size quickly decreased in males from colonies of all ages. The lack of heterosis in response to crossing and strain refreshing in the latter two reproductive traits suggests selection for insectary conditions.
Conclusions
These results show that inbreeding and selection differentially affect reproductive traits in laboratory strains overtime and that heterotic ‘supermales’ could be used to rescue some male reproductive characteristics. Further experiments are needed to establish the exact relationship between sperm length, accessory gland and testes size, and male reproductive success in the laboratory and field settings. 相似文献
Clonal GH4C1 rat pituitary cells are heterogeneous with respect to phorbol dibutyrate receptors (PDBu-R) and protein kinase C (PKC) content. GH cell PDBu-Rs can be separated into two categories based on Ca2(+)-modulation of receptor affinity. Approximately 70% of the cytosolic PDBu-Rs demonstrate Ca2(+)-sensitive receptor affinity and redistribute from the soluble to the particulate fraction in the presence of excess Ca2+. The other 30% of the receptors remain in the cytosol in the presence of excess Ca2+. Their receptor affinity is Ca2(+)-independent. Northern blot hybridization and immunoblot analysis showed that GH4C1 cells express Ca2(+)-independent epsilon-PKC as well as Ca2(+)-dependent alpha- and beta-PKCs. Cell lysis in Ca2+ caused the redistribution of greater than 95% of alpha- and beta-PKC to the particulate fraction, whereas approximately 90% of the epsilon-PKC remained in the cytosol. In contrast, brief treatment of GH cell cultures with PDBu or thyrotropin-releasing hormone caused redistribution of all three isozymes. Prolonged treatment with PDBu down-modulated all three isozymes but at different rates and to different extents. In contrast, prolonged thyrotropin-releasing hormone treatment selectively down-modulated epsilon-PKC. These results demonstrate that GH cells have both Ca2(+)-sensitive and -insensitive PKCs and PDBu-Rs and that both populations are regulated by agonists that control prolactin synthesis and secretion by these cells. 相似文献