Taxanes are defensive metabolites produced by Taxus species (yews) and used in anticancer therapies. Despite their medical interest, patterns of natural diversity in taxane-related genes are unknown. We examined variation at five main genes of Taxus baccata in the Iberian Peninsula, a region where unique yew genetic resources are endangered. We looked at several gene features and applied complementary neutrality tests, including diversity/divergence tests, tests solely based on site frequency spectrum (SFS) and Zeng's compound tests. To account for specific demography, microsatellite data were used to infer historical changes in population size based on an Approximate Bayesian Computation (ABC) approach. Polymorphism-divergence tests pointed to positive selection for genes TBT and TAT and balancing selection for DBAT. In addition, neutrality tests based on SFS found that while a recent reduction in population size may explain most statistics' values, selection may still be in action in genes TBT and DBAT, at least in some populations. Molecular signatures on taxol genes suggest the action of frequent selective waves with different direction or intensity, possibly related to varying adaptive pressures produced by the host-enemy co-evolution on defence-related genes. Such natural selection processes may have produced taxane variants still undiscovered. 相似文献
Catch per unit effort (CPUE), length, weight and maturity data for Clarias gariepinus were collected during monthly gillnet surveys in the upper Okavango Delta between 2001 and 2009 to investigate their relationship with the annual flood-pulse. CPUE, condition factor (K) and the proportion of ripe-running fish (PRR) in the population followed a unimodal annual cycle that could be modelled using water temperature and flood-pulse hydrology. Increased CPUE during declining water levels was most likely a result of feeding migrations and aggregation behaviour. The observed increase in K during low floods in October and November preceded the increase in PRR, which increased mainly with increasing temperature but appeared less dependent on flow. This study provided quantitative evidence that the biology of fish in the Okavango Delta is mainly dependent on the annual flood regime and, therefore, that conservation efforts should be focused on maintaining natural flow patterns in the face of climate change and potential water extraction schemes upstream. 相似文献
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 RST 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, D2sh–––) 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
Fragmented populations at the edges of a species’ distribution can be highly exposed to the loss of genetic variation, unless sufficient gene flow maintains their genetic connectivity. Gene movements leading to successful establishment of external gametes (i.e. effective gene flow) into fragmented populations can solely be assessed by investigating the origin of natural regeneration. This study is focused on studying gene flow patterns in two silver fir stands in Central Apennines, where the species has a highly fragmented distribution. By using nuclear and chloroplast microsatellite markers, we investigated genetic variation, fine-scale spatial genetic structure, effective gene flow rates and large-scale connectivity characterizing both stands. Similar levels of genetic variation and low genetic differentiation between stands (FST = 0.005) and across generations were found, coupled with low inbreeding and weak to absent SGS in the adult cohort (Sp < 0.003). On the other hand, substantial differences between the two stands in terms of gene flow rates were observed. Irrespective of the parentage approach used, higher gene flow rates were found in the stand located at the upper silver fir altitudinal limit, especially for seed-mediated gene flow (0.79 in the upper stand vs. 0.48 in the lower stand). Conversely, the lower stand was characterized by a higher reproductive dominance of local adults. Our findings suggest that, despite similar levels of genetic variation and generally high gene flow rates, different processes may be acting on the two stands, reflecting varying ecological conditions. 相似文献
Tropical trees undergo severe stress through seasonal drought and flooding, and the ability of these species to respond may
be a major factor in their survival in tropical ecosystems, particularly in relation to global climate change. Aquaporins
are involved in the regulation of water flow and have been shown to be involved in drought response; they may therefore play
a major adaptive role in these species. We describe genetic diversity in the PIP sub-family of the widespread gene family
of Aquaporins in five Neotropical tree species covering four botanical families. 相似文献
Wetlands are among the most diverse environments on the planet and are strongly threatened by human activities. Their restoration and/or mitigation of human impacts, therefore, relies on information that can aid to the management of impacted wetlands so that they return to a (semi-) natural state. We investigate in this study the relationship between dormant stages of zooplankton and clay removal in areas subjected to mining. We evaluate whether a gradual increase in topsoil addition from donor natural wetlands to the sediment of mined wetlands influenced the zooplankton community. Eight wetlands were sampled in the Sinos River floodplain, four natural and four mined. In the laboratory, four field sediment samples were incubated for zooplankton hatching in five treatments comprising sediments from: mined wetlands, natural wetlands, and three treatments containing mined sediments added with low (5%), medium (20%) and high (40%) quantities of sediment from natural wetlands. Hatching consisted of 61 individuals distributed across eight zooplankton taxa. Copepod nauplii were the most abundant (31.1%) followed by Epiphanes sp. (29.5%) and Ovalona glabra (16.4%). While natural wetlands provided 42.6% of the hatched zooplankton, mined wetlands had just 6.5%. Zooplankton richness and abundance were higher in natural wetland sediments compared with mined and added sediment wetlands. To some degree, the sediment soil donation from natural to mined wetlands was considered viable. As long as prior studies are performed to test the size and quality of the dormant banks present in the sediment of candidate donor wetlands, sediment from donor wetlands may aid in the establishment of a more diverse community in disturbed systems.
? Premise of the study: To study the genetic structure among three morphotypes of an African rainforest tree species, Santiria trimera, nuclear microsatellite markers were isolated and characterized. ? Methods and Results: Seven polymorphic loci were isolated using a pyrosequencing-based protocol and successfully amplified on three different morphotypes of S. trimera. For six of the seven loci, there is at least one private allele for one of the three morphotypes. The mean effective number of alleles is about four for each of the three morphotypes. ? Conclusions: These microsatellite markers are promising to explore the genetic delimitation among sympatric morphotypes found in Gabonese forests and to study the spatial genetic structure within each gene pool. 相似文献
While most of the clinical benefits of inhaled corticosteroid (ICS) therapy may occur at low doses, results of dose-ranging studies are inconsistent. Although symptom/lung function response to low and high dose ICS medication is comparable, it is uncertain whether low dose ICSs are as effective as high dose in the treatment of inflammation and remodeling.
Methods
22 mild or moderate asthmatic adult subjects (corticosteroid free for > 2 months) participated in a randomized, parallel group study to compare effects of fluticasone propionate (FP) 200 mcg/day and 1000 mcg/day. Alveolar macrophage (AM)-derived cytokines and basement membrane thickness (BMT) were measured at baseline and after 7 weeks treatment while symptoms, spirometry, exhaled nitric oxide (eNO) and airway hyperresponsiveness (AHR) to mannitol at baseline and 6 weeks.
Results
FP improved spirometry, eNO, symptoms and AHR with no difference between low and high dose FP. Both high and low dose FP reduced GM-CSF, TNF-alpha and IL-1ra, with no change in BMT and with no differences between low and high dose FP.
Conclusions
200 μg/day of FP was as effective as 1000 μg/day in improving asthma control, airway inflammation, lung function and AHR in adults in the short term. Future studies should examine potential differential effects between low and high dose combination therapy (ICS/long acting beta agonist) on inflammation and airway remodeling over longer treatment periods. 相似文献