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991.
In recent years population genetics and phylogeographic studies have become increasingly valuable tools for inferring both historical and present-day genetic patterns within marine species. Here, we take a comparative approach to population-level study, analyzing original mitochondrial DNA data from 969 individuals representing 28 chiton (Mollusca: Polyplacophora) species to uncover large-scale genetic patterns along the Pacific coast of North America. The data reveal a distinct latitudinal connectivity gradient among chitons: species that exist at lower latitudes tend to have more isolated populations. This trend appears to be a product of between-species differences; within species, no significant gradient in connectivity is observed. Lower average annual sea surface temperatures are hypothesized to contribute to longer larval duration (and by extension, greater connectivity) among lecithotrophic species, providing a mechanism for the observed positive correlation between gene flow and latitude. Because increased isolation among populations may lead to speciation, a latitudinal trend in gene flow may contribute to the increased species diversity observed at lower latitudes. 相似文献
992.
Hall D Luquez V Garcia VM St Onge KR Jansson S Ingvarsson PK 《Evolution; international journal of organic evolution》2007,61(12):2849-2860
A correct timing of growth cessation and dormancy induction represents a critical ecological and evolutionary trade-off between survival and growth in most forest trees (Rehfeldt et al. 1999; Horvath et al. 2003; Howe et al. 2003). We have studied the deciduous tree European Aspen (Populus tremula) across a latitudinal gradient and compared genetic differentiation in phenology traits with molecular markers. Trees from 12 different areas covering 10 latitudinal degrees were cloned and planted in two common gardens. Several phenology traits showed strong genetic differentiation and clinal variation across the latitudinal gradient, with Q(ST) values generally exceeding 0.5. This is in stark contrast to genetic differentiation at several classes of genetic markers (18 neutral SSRs, 7 SSRs located close to phenology candidate genes and 50 SNPs from five phenology candidate genes) that all showed F(ST) values around 0.015. We thus find strong evidence for adaptive divergence in phenology traits across the latitudinal gradient. However, the strong population structure seen at the quantitative traits is not reflected in underlying candidate genes. This result fit theoretical expectations that suggest that genetic differentiation at candidate loci is better described by F(ST) at neutral loci rather than by Q(ST) at the quantitative traits themselves. 相似文献
993.
Yilmaz B Yasar E Goktepe S Alaca R Yazicioglu K Dal U Mohur H 《Obesity (Silver Spring, Md.)》2007,15(11):2683-2687
Objectives: The purpose of this study was to determine the relationship between autonomic nervous system dysfunction and basal metabolic rate (BMR), and the effect of spasticity on basal metabolic rate. Research Method and Procedures: Twenty men (11 paraplegic and 9 tetraplegic) with American Spinal Injury Association (ASIA)‐A and ‐B grade chronic spinal cord injury (SCI) participated in this study. Total body fat mass and lean tissue mass were measured in all participants using DXA by standard methods. Patients were allocated into 2 groups to determine the effect of autonomic nervous system dysfunction on BMR: Group I (T6 and upper‐level injuries with history of autonomic dysreflexia) and Group II (T7 and lower‐level injuries without history of autonomic dysreflexia). Measurements of BMR were determined by indirect calorimetry under standardized conditions. Results: There were 13 patients in Group I and 7 patients in Group II and the difference between these two in terms of time since injury, BMI, age, weight, lean tissue mass, BMR, and BMR/kg were not significant. Conclusion: We concluded that autonomic nervous system dysfunction does not affect BMR, and it might be ignored in considering energy needs in spinal cord injury. 相似文献
994.
采用LI-6400便携式光合测定系统(Li-Cor Inc., USA)对显脉金花茶光合特性进行研究。结果表明:(1)在夏季,显脉金花茶叶片的Pn日变化呈单峰曲线,最高峰出现在中午11:00。其最大净光合速率(Pmax)为3.81 μmol·m-2·s-1、光饱和点(LSP)为459.9 μmol·m-2·s-1、光补偿点(LCP)为6.9 μmol·m-2·s-1。显脉金花茶的光饱和点和光补偿点都比较低,表明其是一种阴生植物。(2)在控制光照强度和温度的条件下,CO2浓度小于800 μmol·mol-1,Pn几乎呈直线上升,升高CO2浓度可使显脉金花茶的净高合速率增大,提高了叶片对光能的利用率。其叶片CO2饱和点(CSP)大约在1 200 μmol·mol-1左右,CO2的补偿点(Г*)为70.1 μmol·mol-1,最大羧化速率(Vcmax)为17.5 μmol·m-2·s-1,最大电子传递速率(Jmax)为40 μmol·m-2·s-1。 相似文献
995.
According to the instantaneous growth rate (dN/dt) of E. coli CVCC249 growing in batch culture, the entire growth progress was distinguished into four phases: accelerating growth phase,
constant growth phase, decelerating growth phase and declining phase, in each of which obvious variation in physiological
and biochemical properties was detected, including total DNA, total protein, and MTT-dehydrogenase activity, etc., that led
to difference in their antibiotic susceptivity. Antibiotic susceptivity of the population sampled from each phase was tested
by Concentration-killing Curve (CKC) approach following the formula N=N
0/{1+exp[r·(x-BC
50)]}, showing as normal distribution at the individual cell level for an internal population, in which the median bactericidal
concentration BC
50 represents the mean level of susceptivity, while the bactericidal span BC
1−99=(2lnN
0)/r indicates the variation degree of the antibiotic susceptivity. Furthermore, tested by CKC approach, the antibiotic susceptivity
of E. coli CVCC249 population in each physiological phase to gentamicin or enoxacin was various: susceptivity of the population in the
constant growth phase and declining phase all increased compared with that in the accelerating growth phase for gentamicin
but declined for enoxacin. The primary investigations revealed that the physiological phase should be taken into account in
the context of antibiotic susceptivity and research into antimicrobial mechanism. However there are few reports concerned
with this study. Further research using different kinds of antibiotics with synchronized continuous culture of different bacterial
strains is required.
Supported by the Natural Science Foundation of Shandong Province, China (Grant No. Y2005C58), the Natural Key Technology R&D
Program of China (Grant No. 2006BAK02A03-6) and the Youth Scientific Research Foundation of Shandong Academy of Agricultural
Science (2005YQ035) 相似文献
996.
Violeta Mangourova John Ringwood Sarah-Jane Guild Simon Malpas 《Biomedical signal processing and control》2007,2(3):258-266
The control of blood pressure is a complex mixture of neural, hormonal and intrinsic interactions at the level of the heart, kidney and blood vessels. While experimental approaches to understanding these interactions are useful, it remains difficult to conduct experiments to quantify these interactions as the number of parameters increases. Thus, modelling of such physiological systems can offer considerable assistance. Typical mathematical models which describe the ability of the blood vessels to change their diameter (vasoconstriction) assume linearity of operation. However, due to the interaction of multiple vasocontrictive and vasodilative effectors, there is a significant nonlinear response to the influence of neural factors, particularly at higher levels of nerve activity (often seen in subjects with high blood pressure) which leads to low blood flow rates. This paper proposes a number of nonlinear mathematical models for the relationship between neural influences (sympathetic nerve activity (SNA)) and renal blood flow, using a feedback path to model the predominantly nonlinear effect of local vasoactive modulators such as nitric oxide, which oppose the action of SNA. The model structures are motivated by basic physiological principles, while the model parameters are determined using numerical optimisation techniques using open-loop data collected from rabbits. The models were verified by demonstrating correlation between experimental results and model outputs. 相似文献
997.
Seals may delay costly physiological processes (e.g. digestion) that are incompatible with the physiological adjustments to diving until after periods of active foraging. We present unusual profiles of metabolic rate (MR) in grey seals measured during long-term simulation of foraging trips (4-5 days) that provide evidence for this. We measured extremely high MRs (up to almost seven times the baseline levels) and high heart rates during extended surface intervals, where the seals were motionless at the surface. These occurred most often during the night and occurred frequently many hours after the end of feeding bouts. The duration and amount of oxygen consumed above baseline levels during these events was correlated with the amount of food eaten, confirming that these metabolic peaks were related to the processing of food eaten during foraging periods earlier in the day. We suggest that these periods of high MR represent a payback of costs deferred during foraging. 相似文献
998.
Valance D Desprès G Boissy A Mignon-Grasteau S Constantin P Leterrier C 《Genes, Brain & Behavior》2007,6(4):339-346
This study investigated whether genetic selection on a divergent behavioural trait of fearfulness (tonic immobility duration) was related to changes in the nervous control of the heart. Quail selected for either long or short tonic immobility (LTI or STI, respectively) duration was compared with an unselected control line (CTI). The autonomic control of the heart was assessed by heart rate variability analysis and pharmacological blockades. Quail were surgically fitted with a telemetric device. Heart rate before injection did not differ between the three lines. The vagal-sympathetic effect (VSE) at rest differed significantly from 1 in CTI and STI quail, suggesting that parasympathetic activity was dominant. In LTI quail, VSE did not differ from 1, suggesting a balance between parasympathetic and sympathetic activities. The intrinsic heart rate reached after the successive injections of propranolol and atropine did not differ between lines and was higher than the heart rate at rest in STI, which was in line with results of VSE at rest. After atropine injection, the sympathetic activity indicated by the low-frequency power was lower in CTI than in the two selected quail. After propranolol injection, the parasympathetic activity indicated by the root of the mean squares of successive differences and the high-frequency power was higher in STI than in CTI and LTI quail. Selection on tonic immobility duration thus appears to be associated with changes in the sympathovagal control of the heart, which may influence behavioural responses to stressful situations. 相似文献
999.
S. J. Oyler-McCance F. A. Ransler L. K. Berkman T. W. Quinn 《Conservation Genetics》2007,8(6):1339-1353
For management purposes, the range of naturally occurring trumpeter swans (Cygnus buccinator) has been divided into two populations, the Pacific Coast Population (PP) and the Rocky Mountain Population (RMP). Little
is known about the distribution of genetic variation across the species’ range despite increasing pressure to make difficult
management decisions regarding the two populations and flocks within them. To address this issue, we used rapidly evolving
genetic markers (mitochondrial DNA sequence and 17 nuclear microsatellite loci) to elucidate the underlying genetic structure
of the species. Data from both markers revealed a significant difference between the PP and RMP with the Yukon Territory as
a likely area of overlap. Additionally, we found that the two populations have somewhat similar levels of genetic diversity
(PP is slightly higher) suggesting that the PP underwent a population bottleneck similar to a well-documented one in the RMP.
Both genetic structure and diversity results reveal that the Tri-State flock, a suspected unique, non-migratory flock, is
not genetically different from the Canadian flock of the RMP and need not be treated as a unique population from a genetic
standpoint. Finally, trumpeter swans appear to have much lower mitochondrial DNA variability than other waterfowl studied
thus far which may suggest a previous, species-wide bottleneck. 相似文献
1000.
Naohisa Kanda Mutsuo Goto Hidehiro Kato Megan V. McPhee Luis A. Pastene 《Conservation Genetics》2007,8(4):853-864
Bryde’s whales (Balaenoptera brydei) differ from other typical baleen whale species because they are restricted to tropical and warm temperate waters in major
oceans, and frequent trans-equatorial movement has been suggested for the species. We tested this hypothesis by analyzing
genetic variation at 17 microsatellite loci (N = 508) and 299 bp of mitochondrial DNA (mtDNA) control region sequences (N = 472) in individuals obtained from the western North Pacific, South Pacific, and eastern Indian Ocean. Combined use of microsatellite
and mtDNA markers allowed us to distinguish between contemporary gene flow and ancestral polymorphism and to describe sex-specific
philopatry. A high level of genetic diversity was found within the samples. Both nuclear and mtDNA markers displayed similar
population structure, indicating a lack of sex-specific philopatry. Spatial structuring was detected using both frequency-based
population parameters and individual-based Bayesian approaches. Whales in the samples from different oceanic regions came
from genetically distinct populations with evidence of limited gene flow. We observed low mtDNA sequence divergence among
populations and a lack of concordance between geographic and phylogenetic position of mtDNA haplotypes, suggesting recent
separation of populations rather than frequent trans-equatorial and inter-oceanic movement. We conclude that current gene
flow between Bryde’s whale populations is low and that effective management actions should treat them as separate entities
to ensure continued existence of the species. 相似文献