藏马鸡(Crossoptilon crossoptilon)的繁殖生态研究

藏马鸡是典型高山地牺雉类,见于海拔3,500—3,900米的针叶林带。自4月中至7月底为繁殖期。一“夫”配一“妻”。营巢于海拔3,544—3,790米的岩洞、灌丛中或倒木下。共发现4巢,3巢已被破坏,成功率25％。近年来,由于过渡砍伐森林,天敌的伤害,自身弱点(繁殖率低,成熟期长(3年左右)以及其他因素,藏马鸡的数量日趋减少,正面临绝种的厄运。必须及时地采取有效保护措施。     

DNA sequence patterns in human,mouse, and rabbit immunoglobulin kappa-genes

Summary DNA sequences of the human, mouse, and rabbit immunoglobulin kappa-gene (J-C regions) are compared with respect to various DNA patterns, including dyad symmetry pairings, runs of nucleotides, repeat clusters, and repeats that occur with unusually high frequency. The significant dyad symmetry pairings within each of the sequences emphasize the two control-enhancer elements of the J₅-C intron. Dyad symmetry pairs between the J-C region and a number of kappa variable (V)-gene domains suggest differences in the affinities between the V and J segments. It is the consensus heptamer rather than the consensus nonamer that embodies the longest V-J dyad symmetry combinations. In the rabbit there are long runs and repeat clusters of the sequences that identify regions of high duplication; these regions are absent in the human and mouse sequences. High-frequency oligonucleotides feature the consensus nonamer 5 to the J segments, especially in the mouse sequence.     

Some aspects of the natural history and food selection ofAvahi laniger

Two groups ofAvahi laniger were studied in the Forêt de Analamozoatra near Perinet in the eastern rainforest of Madagascar from August to October 1984. Overlap between the home ranges of neighbouring groups ofA. laniger was minimal. Group size ranged from one to four individuals with a median group size of two. In four out of ten groups a baby was born between August and September.A. laniger were most active after dusk and before dawn. They had an extended resting period around midnight. Their diet consisted mostly of leaves from at least 17 different plant species. They also ate flowers. Fruit eating was recorded twice. Leaves eaten had high contents of protein and sugar but did not contain alkaloids. The concentration of condensed tannins did not differ between food items and non-food items. There was no indication of competition with other prosimians that might explain their nocturnality.     

Softening of lipid bilayers

The softening of wet lipid bilayer membranes during their gel-to-fluid first-order phase transition is studied by computer simulation of a family of two-dimensional microscopic interaction models. The models include a variable number, q, of lipid chain conformational states, where 2q10. Results are presented as functions of q and temperature for a number of bulk properties, such as internal energy, specific heat, and lateral compressibility. A quantitative account is given of the statistics of the lipid clusters which are found to form in the neighborhood of the transition. The occurrence of these clusters is related to the softening and the strong thermal density fluctuations which dominate the specific heat and the lateral compressibility for the high-q models. The cluster distributions and the fluctuations behave in a manner reminiscent of critical phenomena and percolation. The findings of long-lived metastable states and extremely slow relaxational behavior in the transition region are shown to be caused by the presence of intermediate lipid chain conformational states which kinetically stabilize the cluster distribution and the effective phase coexistence. This has as its macroscopic consequence that the first-order transition apperas as a continuous transition, as invariably observed in all experiments on uncharged lecithin bilayer membranes. The results also suggest an explanation of the non-horizontal isotherms of lipid monolayers. Possible implications of lipid bilayer softening and enhanced passive permeability for the functioning of biological membranes are discussed.Abbreviations PC phosphatidvlcholine - DMPC dimyristoyl PC - DPPC dipalmitoyl PC - ac alternating current - DSC differential scanning calorimetry - T _m lipid gel-to-fluid phase transition temperature - TEMPO 2,2,6,6-tetramethylpiperidine-N-oxyl Supported by the Danish Natural Science Research Council and A/S De Danske Spritfabrikkers JubilæumslegatSupported in part by the NSERC of Canada and Le FCAC du Quebec     

Evolution of catalytic proteins

Summary It is believed that all present-day organisms descended from a common cellular ancestor. Such a cell must have evolved from more primitive and simpler precursors, but neither their organization nor the route such evolution took are accessible to the molecular techniques available today. We propose a mechanism, based on functional properties of enzymes and the kinetics of growth, which allows us to reconstruct the general course of early enzyme evolution. A precursor cell containing very few multifunctional enzymes with low catalytic activities is shown to lead inevitably to descendants with a large number of differentiated monofunctional enzymes with high turnover numbers. Mutation and natural selection for faster growth are shown to be the only conditions necessary for such a change to have occurred.     

Feeding and growth of larval herring,Clupea harengus,in relation to density of copepod nauplii

Synopsis Feeding and growth rates of 1–3 wk old herring larvae from four different stocks were compared in laboratory experiments (8°C). For most of the larval groups, feeding rate was saturated at nauplii (Acartia tonsa, nauplii stages 3–5) densities over 301^–1 (5 g d.w. 1^–1). Specific growth rate increased asymptotically with nauplii density, and reached about 6% d^–1 at densities over 120 nauplii 1^–1. The growth rates attained in the laboratory were similar to field measured growth rates of similarly aged herring larvae at comparable food densities. Since food particles were homogenously distributed in the laboratory tanks, patches of dense plankton concentrations are, thus, apparently not necessary for larval growth and survival in the sea. Growth efficiency differed between larval groups, with large sized larvae being the most efficient in transforming ingested matter into growth. The difference probably relates to different sizes rather than to the different geographical origins of the larvae.     

Natural mortality at different population densities of a pine shoot moth,Evetria cristata

A field population of Evetria cristata was studied in 10 plots in 1962 and in 6 plots in 1963. These plots were divided into 2 or 3 groups of different population levels of the shoot moth in respective years. The survival of the insect was then analysed in these different groups of plots. The survival rate of E. cristata from eggs to adults in the first generation was found always higher in the group with low population density, which indicates the existence of some factors that affect the population more severely when the insect is more abundant. Lissonota evetriae and Pediobius sp. seemed to have killed more proportion of the hosts where the shoot moth density was high. However, the total effect of the all natural enemies was not always great in the plots with high density of the moth. The survival of the second generation of the moth in 1963 was observed to be much higher at any population level than in the other generations.     

A maximum likelihood approach to the detection of selection from a phylogeny

Summary A large amount of information is contained within the phylogentic relationships between species. In addition to their branching patterns it is also possible to examine other aspects of the biology of the species. The influence that deleterious selection might have is determined here. The likelihood of different phylogenies in the presence of selection is explored to determine the properties of such a likelihood surface. The calculation of likelihoods for a phylogeny in the presence and absence of selection, permits the application of a likelihood ratio test to search for selection. It is shown that even a single selected site can have a strong effect on the likelihood. The method is illustrated with an example fromDrosophila melanogaster and suggests that delerious selection may be acting on transposable elements.     

Conserved organization of an avian histone gene cluster with inverted duplications of H3 and H4 genes

Summary The organization of histone gene clusters of the duckCairina moschata was studied in the DNA inserts of two recombinant phage that overlap and feature identical histone gene arrangements but differ in sequence details and in the extent of repetition of an AT-rich motif in one of the nontranscribed spacer regions. These few but substantial differences between otherwise nearly identical histone gene groups suggest that we have independently isolated alleles of the same site of the duck genome or that this gene arrangement occurs (with slight variations) more than once per haploid genome. Within the histone gene cluster described, H3 and H4 genes are duplicated (with inverted orientation), whereas one H1 gene is flanked by single H2A and H2B genes. The arrangement of duck histone genes described here is identical to a subsection of the chicken genome but differs from any other published histone gene cluster.