图们江流域林区居民点鸟类群落的研究

居民点鸟类与人类关系极为密切,在居民点生态系统中起着不可忽视的作用,因此对其生态学的研究具有一定意义。杜恒勤(1958、1959)、周昌乔等(1959)、钱国桢(1964)、郑光美(1965、1982),赵正阶(1981)等,对麻雀、家燕、金腰燕等居民点鸟类进行过大量种群生态学研究。居民点鸟类群落研究和数量统计,尚未见有报道。     

Computer-aided three-dimensional reconstructions of the arrangement of primary spermatocytes in human seminiferous tubules

Summary With the use of a digital image-processing method three-dimensional reconstructions of the arrangement of spermatocytes in human seminiferous tubules were performed. With this method it was possible to investigate the cellular distribution in the tubule in nearly any given perspective and projection. In addition, by means of simple mathematical procedures, such as by transformation of Cartesian coordinates into cylindrical coordinates, it was possible to vary the shape of a reconstruction, i.e., to convert the cylindrical image of a tubular portion into a right-angled r--z-representation.The present work not only confirms the existence of a complex helical plan of organization of the human seminiferous epithelium but also provides further aspects of the phenomenon of physiological germ-cell loss and its integration into the kinetics of spermatogenesis.Dedicated to Prof. E.C. Roosen-Runge, Seattle, on the occasion of his 75th birthday     

Dependent competing risks: a stochastic process model

Analyses of human mortality data classified according to cause of death frequently are based on competing risk theory. In particular, the times to death for different causes often are assumed to be independent. In this paper, a competing risk model with a weaker assumption of conditional independence of the times to death, given an assumed stochastic covariate process, is developed and applied to cause specific mortality data from the Framingham Heart Study. The results generated under this conditional independence model are compared with analogous results under the standard marginal independence model. Under the assumption that this conditional independence model is valid, the comparison suggests that the standard model overestimates by 4% the effect on life expectancy at age 30 due to the hypothetical elimination of cancer and by 7% the effect for cardiovascular/cerebrovascular disease. By age 80 the overestimates were 11% for cancer and 16% for heart disease. These results suggest the importance of avoiding the marginal independence assumption when appropriate data are available — especially when focusing on mortality at advanced ages.     

Analysis of the distribution of DNA repair patches in the DNA-nuclear matrix complex from human cells

The distribution of ultraviolet-induced repair patches along DNA loops attached to the nuclear matrix, was investigated by digestion with DNA-degrading enzymes and neutral sucrose gradient centrifugation. When DNA was gradually removed by DNAase 1, pulse label incorporated by ultraviolet-irradiated cells during 10 min in the presence of hydroxyurea or hydroxyurea/arabinosylcytosine showed similar degradation kinetics as prelabelled DNA. No preferential association of pulse label with the nuclear matrix was observed, neither within 30 min nor 13 h after irradiation. When the pulse label was incorporated by replicative synthesis under the same conditions, a preferential association of newly-synthesized DNA with the nuclear matrix was observed. Single-strand specific digestion with nuclease S₁ of nuclear lysates from ultraviolet-irradiated cells, pulse labelled in the presence of hydroxyurea/arabinosylcytosine, caused a release of about 70% of the prelabelled DNA and 90% of the pulse-labelled DNA from the rapidly sedimenting material in sucrose gradients. The results suggest no specific involvement of the nuclear matrix in repair synthesis, a random distribution of repair patches along the DNA loops, and simultaneously multiple incision events per DNA loop.     

Cannibalism and Coprophagy Are Modes of Transmission of Blastocrithidia triatomae (Trypanosomatidae) between Triatomines

Transovarial transmission was not detectable among Blastocrithidia triatomae- infected Triatoma infestans . Rather, B. triatomae was transmitted directiy between triatomines by cannibalism and coprophagy. Cannibalism conditions that excluded coprophagy always resulted in an infection of Dipetalogaster maxima . The efficiency of transmission was not influenced by the blood source—mice or chickens—fed to the infected donor bugs although chicken blood lyses the epimastigotes of the stomach population. Triatoma infestans was infected by coprophagy only if fed, not if unfed. Blastocrithidia triatomae in dry feces was taken up only if the feces were redissolved in fresh feces. Infections also appeared in groups of bugs fed on chickens previously used for feeding infected bugs.     

Effect of Long-Lasting Diabetes Mellitus on Rat and Human Brain Monoamines

Experimental alloxan- or streptozotocin-produced diabetes in rats was accompanied by an increase in the levels of norepinephrine, dopamine, and serotonin, whereas the contents of metabolites, i.e., 5-hydroxyindoleacetic acid and homovanillic acid, in the whole brain gradually decreased with the duration of diabetes. Among the striatum, thalamus, and hypothalamus of alloxan diabetic rats, monoamine alterations were observed only in the hypothalamus; after 1 week an increase of norepinephrine content and after 13 weeks an increase of norepinephrine and dopamine contents were found. Tissues of 11 brain regions of 10 diabetic and 12 control patients post mortem were investigated for monoamine concentrations. Patients were all male, of similar age and interval between death and autopsy. Diabetic patients had an increase in the content of serotonin in the medial and lateral hypothalamus. The content of dopamine increased in the medial hypothalamus, putamen, and medial and lateral pallidus. In diabetic patients, the content of norepinephrine increased in the lateral pallidus and decreased in the nucleus accumbens and claustrum. Thus, it seems that diabetes mellitus in rats, as well as in humans is associated with regionally specific changes in brain monoamines.     

DNA microenvironments and the molecular clock

Summary A few years ago we presented a stationary Markov model of gene evolution according to which only homologous genes from not too divergent species obeying the condition of being stationary may behave as reliable molecular clocks. A compartmentalized model of the nuclear genome in which the genes are distributed in compartments, the isochores, defined by their G+C content has been proposed recently. We have found that only homologous gene pairs that are stationary, and belong to the same isochore, can be used consistently for the determination of phylogeny and base substitution rate. In particular, for the rodent-human couple, only about half of the homologous gene pairs are stationary. Stationary genes evolve at the third silent codon position with the same velocity independent of the genes and base composition. By contrast, nonstationary genes display apparent rate values (pseudovelocities) that are significantly higher. Our results cast doubt upon recent claims of a large acceleration in the rate of molecular evolution in rodents.     

Intra- and interspecies analyses of the carcinoembryonic antigen (CEA) gene family reveal independent evolution in primates and rodents

Summary Various rodent and primate DNAs exhibit a stronger intra- than interspecies cross-hybridization with probes derived from the N-terminal domain exons of human and rat carcinoembryonic antigen (CEA)-like genes. Southern analyses also reveal that the human and rat CEA gene families are of similar complexity. We counted at least 10 different genes per human haploid genome. In the rat, approximately seven to nine different N-terminal domain exons that presumably represent different genes appear to be present. We were able to assign the corresponding genomic restriction endonuclease fragments to already isolated CEA gene family members of both human and rat. Highly similar subgroups, as found within the human CEA gene family, seem to be absent from the rat genome. Hybridization with an intron probe from the human nonspecific cross-reacting antigen (NCA) gene and analysis of DNA sequence data indicate the conservation of noncoding regions among CEA-like genes within primates, implicating that whole gene units may have been duplicated. With the help of a computer program and by calculating the rate of synonymous substitutions, evolutionary trees have been derived. From this, we propose that an independent parallel evolution, leading to different CEA gene families, must have taken place in, at least, the primate and rodent orders.     

Evolution of the power ("squeeze") grip and its morphological correlates in hominids.

The "squeeze" form of power grip is investigated for the purposes of clarifying the hand posture and activities associated with the grip, assessing the potential in chimpanzees for using the grip, and identifying morphological correlates of an effective power grip that may be recognized in fossil hominid species. Our approaches include: (1) the analysis of the human grip, focusing on both the hand posture involved and hand movements associated with use of the grip in hammering; (2) the analysis of similar chimpanzee grips and associated movements; (3) comparative functional analysis of regions in the hand exploited and stressed by the grip and its associated movements in humans; and (4) a review of the literature on the power grip and its morphological correlates. Results of the study indicate that humans use a squeeze form of power grip effectively to wield cylindrical tools forcefully as extensions of the forearm. Several morphological features occur in high frequency among humans which facilitate the grip and are consistent with the large internal and external forces associated with it in hammering and in other tool-using activities. Chimpanzee hand postures resembling this form of human power grip are not fully comparable and lack some of these morphological correlates that facilitate its use. The hand of Australopithecus afarensis does not appear to have been stressed by use of the grip, but there is some evidence for this type of stress in the metacarpals from Sterkfontein Member 4. Hands from Olduvai and Swartkrans do not provide sufficient evidence for assessment of power grip capabilities.