Scaling effects on muscle function in fast and slow muscles of Xenopus laevis

Fibre bundles or whole muscles from Xenopus laevis, ranging in size from 0.5-60g, were studied. Maximum power output of predominantly fast (sartorius) and slow (adductor magnus) muscles was measured at cycle frequencies between 0.5 and 20Hz, using the work loop technique. Power output was highly dependent on cycle frequency, and in 50-60g adults was maximal at 6 Hz for fast fibres (65 Wkg^-1), and 2 Hz for slow fibres (14 Wkg^-1). The cycle frequency for maximum power output was dependent on body mass (M_b), and decreased as a function of M_b^-0.07 in fast fibres, and M_b^-0.23 in slow fibres. The functional significance of these differences is discussed.     

What the hen can tell about her eggs: egg development on the basis of energy budgets

By a simple model involving the state variables size and storage, it is possible to describe a wide variety of observations on the feeding, growth, energy storage and reproduction of animals. The model is based on the assumption that reproduction, growth as well as maintenance depend on the stored energy only and not directly on feeding. If an egg is thought of as a non-feeding animal, the model predicts the respiration ontogeny and growth of the embryo inside the egg. These predictions seem to hold well for published data on the development of eggs of fish and ratite, precocial and altricial birds. The latter two are known to follow different respiration ontogenies, but both are described well, differing only in one (compound) parameter value. The model explains why the incubation times of eggs of different species tend to increase linearly with egg size to the power 1/4, and why kiwis and petrels, which lay relatively large eggs, have to brood them much longer than larger birds with eggs of the same size. Conversely, it explains why the small eggs of the (parasitic) European cuckoo, hatch earlier than the still smaller eggs of their tiny hosts.Furthermore, it has been shown how the maintenance rate constant, which frequently appears in the microbial literature, can be obtained from measurements on the respiration and weight ontogeny in embryos, so linking independent lines of research. Application of the model shows an increase of the maintenance rate constant from bacteria, crustaceans, up to fish and birds, and a decrease from bacteria to green algae, suggesting lines of evolutionary development.     

Allometric relations of teeth and jaws in man

Static adult intraspecific allometry of jaws and teeth was investigated in a sample of 100 Negro crania. The relations between tooth area, postcanine surface, incisor surface, and four viscerocranial measures were examined separately for males and females. Our results indicate a marked lack of morphological integration between P-sets within the orofacial subregion and a similar lack of correspondence between jaw size and tooth size. Allometric analyses indicate that mandibular length scales negatively allometric to maxilloalveolar length and to bigonial width, that canine base area scales positively to upper and lower jaw length, and that all the other teeth scale negatively to jaw length. The postcanine surface area was found to be negatively allometric to the canine base area, which in turn scaled isometrically to incisor surface. Hence, any lengthening of the mandible will tend to be associated with a relative shortening of the maxilla, with relatively larger canines and a relative reduction of the cheek teeth.     

Gradient analysis of reversed treelines and grasslands of the Valles Caldera,New Mexico

Objective: : Treeless meadows and parks are widespread but poorly understood features of the montane vegetation of the western USA. These communities frequently form reversed treelines where grassy valleys occur below forested slopes above. Our purpose was to assess the environmental correlates of such treelines, as well as patterns in the composition and diversity of grasslands and forest margins in the Valles Caldera National Preserve. Location: Valles Caldera National Preserve (35°50′‐36°00’ N, 106°24′‐106°37’ W, 2175–3150 m), Jemez Mountains, New Mexico, USA. Methods: We conducted a gradient analysis based on 200 nested quadrats on transects crossing reversed treelines and spanning the compositional heterogeneity of grasslands. We used cluster analysis and non‐metric multidimensional scaling to assess relationships between compositional variation and environmental variables. Results: We found strong, highly significant relationships of the vegetation to gradients in slope inclination, soil texture, moisture, nutrient availability, and nighttime minimum temperatures. Reversed treelines are most strongly associated with shifts in the thermal regime, exhibit weaker relationships with soil texture and nutrient content, and show no relationship with gravimetric soil moisture. Gradients in aspect, soil moisture, and annual mean temperature are associated with compositional variation within grasslands and forest margins. Conclusions: Lower nightly minimum temperatures and fewer consecutive frost‐free days resulting from cold‐air drainage may prevent tree seedling establishment in valley bottoms via photo‐inhibition, tissue damage, or frost heaving. Fine‐textured soils may also impede tree seedling establishment in valley bottoms. These findings lay the groundwork for experimental and physiological tests of these potential causes of these reversed treelines.     

Mitochondrial dysfunction and metabolic syndrome—looking for environmental factors

The centerpiece of the pathophysiologic mechanism of metabolic syndrome is insulin resistance. Recently, it is becoming evident that mitochondrial dysfunction is closely related to insulin resistance and metabolic syndrome. The underlying mechanism of mitochondrial dysfunction is very complex, which includes genetic factors from both nuclear and mitochondrial genome and numerous environmental factors. Several mitochondrial DNA polymorphisms are associated with the components of metabolic syndrome. Numerous chemicals and drugs may cause mitochondrial dysfunction and insulin resistance. Notably, it was recently reported that serum levels of several mitochondrial toxins, such as persistent organic pollutants are associated with metabolic syndrome, which necessitates further investigation to reveal its precise mechanism. Given that the health impact of metabolic syndrome is tremendous, it is necessary to develop therapeutic modalities to correct mitochondrial dysfunction or at least to halt its aggravation. In this regard, exercise can improve both mitochondrial function and insulin sensitivity, and some pharmaceutical agents were reported to improve mitochondrial function. However, further studies are warranted to find more effective therapeutic strategies to treat mitochondrial dysfunction. By doing so, we can also shed light on the path of research for other diseases related to mitochondrial dysfunction.     

离散广义Logistic模型的混沌控制

利用Lyapunov指数方法,验证了一类离散广义Logistic模型存在混沌现象,并采用混沌控制中OGY方法的基本思想,研究了这类模型的混沌控制问题,得出了消除混沌,保持种群稳定到不动点和2-周期轨道的充分条件．     

Effects of body mass and temperature on routine metabolic rate of juvenile largemouth bronze gudgeon Coreius guichenoti

The effects of body mass (M) and temperature (T) on routine metabolic rate (m(R) ) were assessed in the largemouth bronze gudgeon Coreius guichenoti, from Three Gorges Reservoir, Yangtze River, China. The m(R) increased with increasing M by factors (b-value in the equation m(R) = aM(b) ) of 0·843, 0·800, 0·767, 0·788 and 0·822 at 10, 15, 20, 25 and 30° C, respectively. A significant interaction between M and T on m(R) was observed. The variation in the b-value at different T suggests that the b-values were not consistent with the universal allometric exponent 0·75. After controlling for M, the relationship between the normalized standard metabolic rate (m(S), mg O(2) kg(-1) h(-1)) and T was described by an exponential equation: m(S) = 9·89e((0·093T)) . The results indicate that the effects of M on m(R) depend on T. The increased water temperature induced by dam construction on the Yangtze River may cause a marked increase in energy demand by this species, with potential ecological consequences.     

Fine-structured multi-scaling long-range correlations in completely sequenced genomes—features,origin, and classification

The sequential organization of genomes, i.e. the relations between distant base pairs and regions within sequences, and its connection to the three-dimensional organization of genomes is still a largely unresolved problem. Long-range power-law correlations were found using correlation analysis on almost the entire observable scale of 132 completely sequenced chromosomes of 0.5 × 10⁶ to 3.0 × 10⁷ bp from Archaea, Bacteria, Arabidopsis thaliana, Saccharomyces cerevisiae, Schizosaccharomyces pombe, Drosophila melanogaster, and Homo sapiens. The local correlation coefficients show a species-specific multi-scaling behaviour: close to random correlations on the scale of a few base pairs, a first maximum from 40 to 3,400 bp (for Arabidopsis thaliana and Drosophila melanogaster divided in two submaxima), and often a region of one or more second maxima from 10⁵ to 3 × 10⁵ bp. Within this multi-scaling behaviour, an additional fine-structure is present and attributable to codon usage in all except the human sequences, where it is related to nucleosomal binding. Computer-generated random sequences assuming a block organization of genomes, the codon usage, and nucleosomal binding explain these results. Mutation by sequence reshuffling destroyed all correlations. Thus, the stability of correlations seems to be evolutionarily tightly controlled and connected to the spatial genome organization, especially on large scales. In summary, genomes show a complex sequential organization related closely to their three-dimensional organization. This article has been submitted as a contribution to the festschrift entitled “Uncovering cellular sub-structures by light microscopy” in honor of Professor Cremer’s 65th birthday.     

The link between metabolic rate and body temperature in galliform birds in thermoneutral and heat exposure conditions: The classical and phylogenetically corrected approach

Three galliform species (grey partridges, ring-necked pheasants, and king quail) were involved in body temperature and resting metabolic rate measurements over a broad range of ambient temperatures (20–45 °C). At thermoneutrality, inter-species differences in colonic temperature, as well as in metabolic rate, were observed. During heat exposure, all species reacted by elevating their body temperatures above 44 °C, thereby inducing temporary hyperthermia. Heat-stressing birds resulted in a slightly increased metabolic rate in king quail, but not in partridges and pheasants. Based on data of body temperature and weight specific (per body mass unit) basal metabolic rate among ten species of Galliformes order, classical and phylogenetically corrected analyses of covariation between these two physiological traits were performed. The scaling of body temperature to body mass, revealed a significant exponent of: −0.0062 and −0.0080 for conventional and phylogenetical methods, respectively. In the analyzed species, a strong positive relationship between residuals of body mass values between body temperature and metabolic rate were found. The results obtained may show a plausible evolutionary link between these traits in galliform birds.     

Thresholds in transient dynamics of signal transduction pathways

Transient dynamics of signal transduction pathways play an important role in many biological processes, including cell differentiation, apoptosis, metabolism and DNA damage response. Recent examples of quantitative methods to characterize transient signals include transient metabolic control coefficients and finite time Lyapunov exponents. In our work we compare these quantitative methods to characterize transient phenomena and specifically discuss their predictive power for three examples. We focus on the identification of thresholds that separate different transient dynamic behaviors. Our investigation leads to the following results: The spectrum of the finite-time Lyapunov exponents unambiguously and reliably identifies putative thresholds in transient dynamics. Metabolic control coefficients do not reliably detect all thresholds and suffer from false positives.