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161.
162.
This review examines the evidence that skeletal muscles can sense the status of the peripheral vascular network through group III and IV muscle afferent fibers. The anatomic and neurophysiological basis for such a mechanism is the following: 1) a significant portion of group III and IV afferent fibers have been found in the vicinity and the adventitia of the arterioles and the venules; 2) both of these groups of afferent fibers can respond to mechanical stimuli; 3) a population of group III and IV fibers stimulated during muscle contraction has been found to be inhibited to various degrees by arterial occlusion; and 4) more recently, direct evidence has been obtained showing that a part of the group IV muscle afferent fibers is stimulated by venous occlusion and by injection of vasodilatory agents. The physiological relevance of sensing local distension of the vascular network at venular level in the muscles is clearly different from that of the large veins, since the former can directly monitor the degree of tissue perfusion. The possible involvement of this sensing mechanism in respiratory control is discussed mainly in the light of the ventilatory effects of peripheral vascular occlusions during and after muscular exercise. It is proposed that this regulatory system anticipates the chemical changes that would occur in the arterial blood during increased metabolic load and attempts to minimize them by adjusting the level of ventilation to the level of muscle perfusion, thus matching the magnitudes of the peripheral and pulmonary gas exchange. 相似文献
163.
The effects of dispersal limitation and topographic heterogeneity on beta diversity and phylobetadiversity in a subtropical forest 总被引:1,自引:0,他引:1
Yue Bin Zhigao Wang Zhangming Wang Wanhui Ye Honglin Cao Juyu Lian 《Plant Ecology》2010,209(2):237-256
We assessed the effects of topographic heterogeneity and stem density on species composition between grains of different sizes
(20 × 20, 50 × 50, and 100 × 100 m), based on partial Mantel tests. Similarity in species composition was measured by the
abundance-based Jaccard index (C_J) and by an index that incorporates phylogenetic information into C_J (pC_J). Plants were
divided into five groups, arbor, subarbor, and shrub according to life form and two other groups: species that produce dry
fruits (PDF) and that produce fleshy fruits (PFF). C_J and pC_J between any two grains at each grain size were calculated
separately for these groups and for all species combined. In order to examine what influences C_J and pC_J, we analyzed their
correlations with topographic heterogeneity variables and two dispersal limitation-related variables (stem and topographic
resistance). Our data indicate that at all three grain sizes, C_J and pC_J decrease with increasing distance for all plant
groups. Dispersal limitation and topographic heterogeneity were both important at 20 × 20 and 50 × 50 m grain sizes for C_J
and pC_J of all plant groups; and at 100 × 100 m grain size, topographic heterogeneity dominates over dispersal limitation
for some plant groups. C_J and pC_J of PDFs are less negatively correlated with stem resistance than those of PFFs. We conclude
that both beta diversity and phylobetadiversity are dependent on plant groups and grain sizes. 相似文献
164.
Bruno Lunelli 《Inorganica chimica acta》2007,360(3):1217-1220
A new purification procedure exploiting the simultaneous presence of a solid, liquid, and gas phase in a low surface area system is proposed and discussed. The assumptions of vanishingly low diffusion coefficients in the solid phase and that of the presence of a single “effective impurity” allow to plan the sequence of operations starting from the knowledge of just the melting and boiling points of the substance to be purified and of those of the “effective impurity”. Examples and results are presented. 相似文献
165.
Jeffrey P Mower Pascal Touzet Julie S Gummow Lynda F Delph Jeffrey D Palmer 《BMC evolutionary biology》2007,7(1):135
Background
It has long been known that rates of synonymous substitutions are unusually low in mitochondrial genes of flowering and other land plants. Although two dramatic exceptions to this pattern have recently been reported, it is unclear how often major increases in substitution rates occur during plant mitochondrial evolution and what the overall magnitude of substitution rate variation is across plants. 相似文献166.
Richard P. Duncan 《Biological invasions》2016,18(4):985-996
Both the size of founding populations (propagule size) and environmental suitability are known to influence whether a species newly introduced to a location will establish a self-sustaining population. However, these two factors do not operate independently: it is the interaction between propagule size and environmental suitability that determines the probability an introduced population will establish. Here I use the example of dung beetle introductions to Australia to illustrate the importance of this interaction. I first describe equations that model establishment success jointly as a function of propagule size and environmental suitability. I then show how these equations provide insight into the different outcomes observed in two dung beetle species widely introduced to Australia. In one species, variation in propagule size had relatively little influence on establishment success due to large variation in environmental suitability, leading to an essentially bimodal outcome: sites were either very suitable for establishment and introductions succeeded, or sites were unsuitable and introductions failed regardless of propagule size. For the second species, there was much less variation among locations in environmental suitability, leading to propagule size having a strong influence on establishment success. These examples highlight how the interplay between environmental suitability and founding population size is central to determining the probability an introduced species will establish. 相似文献
167.
168.
Rosa Agudo Ciro Rico Carles Vilà Fernando Hiraldo José Antonio Donázar 《BMC evolutionary biology》2010,10(1):384
Background
Anthropogenic habitat modifications have led to the extinction of many species and have favoured the expansion of others. Nonetheless, the possible role of humans as a diversifying force in vertebrate evolution has rarely been considered, especially for species with long generation times. We examine the influence that humans have had on the colonization and phenotypic and genetic differentiation of an insular population of a long-lived raptor species, the Egyptian vulture (Neophron percnopterus). 相似文献169.
The study was designed to determine whether methionine-enkephalin (M-ENK) was present in the digestive system of the scallop
Chlamys farreri and investigate the effects of M-ENK on the activity of amylase, protease and lipase in the digestive system of C. farreri. The results indicated that M-ENK-like material was present in the epithelium and connective tissue of labial palps, mouth
labia, stomach, intestine, rectum, and hepatopancreas of the scallop C. farreri. Moreover, it was also found that many isolated small cells showing M-ENK-like immunoreactivity were scattered in the epithelial
layer of intestine, and many isolated big epithelial cells showing M-ENK-like immunoreactivity were scattered in tubules of
hepatopancreas of the scallop. The activity levels of amylase and lipase in crystalline style, hepatopancreas and intestine
were enhanced at 1 h after injection of exogenous M-ENK into adductor muscle of the scallops, whereas protease activity levels
were significantly suppressed. Our report constitutes the first characterization of M-ENK in the digestive system of scallop
C. farreri and investigates the effects of M-ENK on the activities of digestive enzymes of mollusk for the first time. The results suggest
an involvement of M-ENK in the functional regulation of the digestive system of C. farreri. 相似文献
170.