Collagen gene construction and evolution

Summary Collagen genes appear to have been assembled by the tandem repetition of homologous primary (9 base pair), secondary (54 base pair), and tertiary (702 base pair) modules. In vertebrate interstitial collagen genes many of the secondary modules are separated by introns, but in invertebrate collagen genes the non-coding sequences lie near the ends of supposed tertiary modules and are therefore about 702 (54×13) base pairs apart. The genes for vertebrate interstitial collagens (types I–III) seem to have been constructed by the tandem repetition of five tertiary modules, three of which were subsequently shortened by internal deletions. This shortening of the gene resulted in the non-integral relationship between the period of the fibrils and the length of the molecules of vertebrate collagens, and was therefore responsible for the mechanical properties of the completed product. Comparisons of the amino acid sequences of various collagens indicate that the main types of collagen evolved about 800–900 million years ago, a date that agrees well with the fossil record of primitive Metazoa.     

Spatial and temporal factors associated with nest survival of Gray Flycatchers in managed ponderosa pine forests

Gray Flycatchers (Empidonax wrightii) breed in a variety of habitats in the arid and semi‐arid regions of the western United States, but little is known about their breeding biology, especially in the northern portion of their range where they nest in ponderosa pine (Pinus ponderosa) forests. From May to July 2014 and 2015, we conducted surveys for singing male Gray Flycatchers along the eastern slope of the Cascade Range in Washington, U.S.A, monitored flycatcher nests, and quantified nest‐site vegetation. We used a logistic‐exposure model fit within a Bayesian framework to model the daily survival probability of flycatcher nests. During the 2 yr of our study, we monitored 141 nests, with 93% in ponderosa pines. Mean clutch size was 3.6 eggs and the mean number of young fledged per nest was 3.2. Predation accounted for 90% of failed nests. We found a positive association between daily nest survival and both nest height and distance of nest substrates from the nearest tree. Flycatchers that locate their nests higher above the ground and further from adjacent trees may be choosing the safest alternative because higher nests may be less exposed to terrestrial predators and nests in trees that are farther from other trees may be less exposed to arboreal predators such as jays (Corvidae) that may forage in patches with connected canopies. Nests in trees farther from other trees may also allow earlier detection of approaching predators and thus aid in nest defense.     

Uncertainty associated with river health assessment in a varying environment: The case of a predictive fish-based index in France

Sensitive biological measures of river ecosystem quality are needed to assess, maintain or restore ecological conditions of water bodies. Since our understanding of these complex systems is imperfect, decision-making requires recognizing uncertainty. In this study, a new predictive multi-metric index based on fish functional traits was developed to assess French rivers. Information on fish assemblage structure, local environment and human-induced disturbances of 1654 French river sites was compiled. A Bayesian framework was used to predict theoretical metric values in absence of human pressure and to estimate the uncertainty associated with these predictions. The uncertainty associated with the index score gives the confidence associated with the evaluation of site ecological conditions.Among the 228 potential metrics tested, only 11 were retained for the index computation. The final index is independent from natural variability and sensitive to human-induced disturbances. In particular, it is affected by the accumulation of different degradations and specific degradations including hydrological perturbations. Predictive uncertainty is globally lower for IPR+ than for underlying metrics.This new methodology seems appropriate to develop bio-indication tools accounting for uncertainty related to reference condition definition and could be extended to other biological groups and areas. Our results support the use of multi-metric indexes to assess rivers and strengthen the idea that examination of uncertainty could contribute greatly to the improvement of the assessment power of bio-indicators.     

Estimation of Tissue Construction Cost from Heat of Combustion and Organic Nitrogen Content

Abstract. We present a method for estimating the construction costs of plant tissues from measurements of heat of combustion, ash content, and organic nitrogen content. The method predicts glucose equivalents, the amount of glucose required to provide carbon skeletons and reductant to synthesize a quantity of organic product. Glucose equivalents have previously been calculated from the elemental composition of tissue. We define construction cost as the amount of glucose required to provide carbon skeletons, reductant and ATP for synthesizing the organic compounds in a tissue via standard biochemical pathways. The fraction of the total construction cost of a compound or tissue (excluding costs of transporting compounds) that is reflected in its glucose equivalents is the biosynthetic efficiency ( E _B). This quantity varies between 0.84 and 0.95 for tissues with a wide range of compositions. Using the new method, total construction cost can be estimated to ± 6% of the value obtained from biochemical pathway analysis.
Construction costs of leaves of three chaparral species were estimated using the proposed method and compared to previously published values, derived using different methods. Agreement among methods was generally good. Differences were probably due to a combination of inaccuracy in the estimated biosynthetic efficiency and technical difficulties with biochemical analysis, one of the older methods of determining construction cost.     

Analysis of the H+/sugar symport in yeast under conditions of depolarized plasma membrane

H⁺/sugar symport in the obligatory aerobic yeastRhodotorula glutinis was analyzed under conditions where the plasma membrane was selectively depolarized by the lipophilic cation tetraphenylphosphonium (TPP⁺). Control experiments showed that this treatment did not impair the transmembrane pH, the cell energy charge, and the function of plasma membrane H⁺-ATPase. The kinetic data were fitted to elementary functions derived from a model constructed on the basis of some simplifying premises for ordered (either C + H⁺ + S or C + S + H⁺) and random reaction mechanisms. In addition, the comparison of the kinetic parameters in fully energized and depolarized cells provided information about the free carrier charge. It was concluded that the binding sequence of formation of the ternary carrier/H⁺/substrate complex follows a random mechanism and that the carrier bears a negative charge.     

Diversity in the immune system: “Preconceived ideas” or ideas preconceived?

Two concepts of the evolution and regulation of expression of the combining site repertoire of the immune system, are compared. One view is based on the Associative Recognition Theory as formulated by the author and the other is based on the Idiotype Network Idea as conceived by Jerne. The two concepts are analyzed from the point of view of their logic, internal consistency and factual support.     

流域开发生态建设发展战略

以往研究流域开发战略问题,多从流域内资源的开发利用方面考虑,而衡量其方案的优劣也多以经济效益的大小为准绳。现在,环境污染与生态危机已威胁着人类的生存与发展,因此在研究流域战略问题时,必须开拓思路,     

The relationship between the relative growth rate and nitrogen economy of alpine and lowland Poa species

This study investigates the nitrogen economy of six altitudinally contrasting Poa species which differ in their relative growth rate (R). Two alpine (Poa fawcettiae and P. costiniana), one sub-alpine (P. alpina)and three temperate lowland species (P. pratensis, P. campressa and P. trivialis) were grown hydroponically under identical conditions in a growth room. The low R exhibited by the alpine species was associated with lower plant organic nitrogen concentration (n_p) and lower nitrogen productivity (Π_p, amount of biomass accumulation per mol organic nitrogen and time). The differences in Π_p between the alpine and lowland species did not appear to be due to differences in the carbon concentration or the proportion of total plant organic nitrogen allocated to the leaves, stems or roots. Variations in Π_P were also not due to variations in photosynthetic nitrogen use efficiency (Ψ_N, the rate of photosynthesis per unit organic leaf nitrogen) or shoot or root respiration rates per unit organic nitrogen (Λ_SH and Λ_R, respectively) per se. Rather, the lower Λ_p in the alpine species was probably due to a combination of small variations in several of the parameters (e.g. slightly lower Ψ_N, slightly higher Λ_SH and Λ_R, and slightly higher proportions of total plant organic nitrogen allocated to the roots). The alpine species exhibited lower organic acid and mineral concentrations. However, no differences in whole-plant construction costs (grams of glucose needed to synthesize one gram of biomass) were observed between She alpine and lowland Poa species. The lack of sub-stantial differences in Ψ_N between the alpine and lowland species contrasts with the large differences in Ψ_N between slow- and fast-growing lowland species that have been reported in the literature. The reasons for the unusually high Ψ_N values exhibited by the alpine Poa species are discussed.     

小鼠卵母细胞减数分裂染色体的制备

PreparationofMeioticKarytypeofMouseOocyteLiChaojunYanLeipingZhangXiranChenYifeng(BiologyDepartmentofNanjingNormalUniversity,Nanjing210097)哺乳动物的卵母细胞的减数分裂过程中存在两次自发的停滞现象,第一次是在第一次减数分裂前期的双线期,这一静止期持续很长时间,一直到动物性成熟后卵母细胞进入发有周刎,在保住腺激素的作用下,卵母细胞的第一次减数分裂才重新启动．完成第一次减数分裂后．又停滞在第二次减数分裂的中期,在椅子或化学因素刺激的作用下,完成第二次减数分裂[4]．因此,对哺乳动物的卵母细胞在一…     

Dynamics of energy and nutrient concentration and construction cost in a native and two alien C4 grasses from two neotropical savannas

In Venezuela, the alien grasses Melinis minutiflora Beauv. and Hyparrhenia rufa (Nees.) Stapf tend to displace the native savanna plant community dominated by Trachypogon plumosus (Humb. and Bonpl.) Nees. This occurs in either relatively wetter and fertile highland savannas or in drier and less fertile lowland savannas. Although the native and aliens are perennial C₄ grasses, higher net assimilation leaf biomass per plant and germination rate of the latter are some causes for their higher growth rates and for their competitive success. The objective of this study is to compare seasonal tissue energy, N, P and K concentrations and the calculated construction costs (CC) between the native grass and either one of the alien grasses from lowland and highland savannas. We predict that, in order to out-compete native plants, alien grasses should be more efficient in resource use as evidenced by lower tissue energy and nutrient concentrations and CC.Tissue energy and nutrient concentration were measured throughout the year and compared between M. minutiflora and the co-occurring local population of T. plumosus in a highland savanna and between H. rufa and its neighbor local population of T. plumosus in a lowland savanna. CC was calculated from energy, N and ash concentrations considering ammonium as the sole N source. Differences between co-occurring species, T. plumosus populations, seasons, and organs were analyzed with ANOVA.Highland and lowland grasses differed in concentration and allocation of energy and nutrients whereas the differences between alien and native grasses were specific for each pair considered. Highland grasses had higher energy, N, P and CC than lowland grasses. These variables were always lowest in the culms. In the more stressed lowland site, tissue energy and nutrient concentrations decreased significantly during the dry season except in the roots of both grasses which had the highest energy and nutrients concentrations during the drought. This seasonal response was more marked in the local lowland population of T. plumosus in which maximum CC alternated seasonally between leaves and roots. Energy and nutrient concentrations and CC were the lowest in H. rufa. In the lowland savannas, the higher efficiency of resource use in the invader grass contributes to its higher competitive success through increased growth rate. In the highlands, overall tissue energy concentration and CC, but not N nor P concentration, were lower in the fast growing M. minutiflora but seasonal differences were lacking. The higher leaf CC in T. plumosus can be attributed to the higher proportion of sclerenchyma tissue which is more expensive to construct. Considering CC, both fast growing alien grasses are more efficient in resource use than the co-occurring native grass. However, the role of CC explaining the competitive success of the former, through higher growth rates, is more evident in the more stressful environment of the lowland savanna.