A comparative study of the chromosomes in the incipient species of the Drosophila paulistorum complex

Summary Drosophila paulistorum Dobzhansky et Pavan is a complex of six races or incipient species. The races are mostly allopatric, but they are reproductively isolated sufficiently to permit them to exist also sympatrically in some places. The gene arrangements in the chromosomes of the races have been compared by means of examination of the giant chromosomes in the larval salivary glands; 28 strains of all races, and about an equal number of interracial hybrids have been studied.Chromosomal inversion polymorphism has been discovered in all races, even in the Guianan race of which only a single strain is available. Inversion heterozygotes are found in every one of the five chromosomal strands which the species has. Interracial hybrids tend to be heterozygous for more inversions than are present in the strains of the parental races. The Transitional race has however much the same gene arrangements as the widespread Andean — South Brazilian race.With the exception of the Transitional race, and of three other possible exceptions, each race has a collection of its own race-specific inversion polymorphs, not found in the other races. This very striking finding is discussed in connection with the hypothesis which envisages the origin of new species from marginal colonies at the periphery of the geographic distribution area of the ancestral species.The work reported in this article has been carried under Contract No. AT-(30-1)-1151, U.S. Atomic Energy Commission, mostly at the Department of Zoology, Columbia University, New York.     

Ein Beitrag zur Kenntnis des Selektivitätsmechanismus von Pyrazon

Ve snaze identifikovat fyziologické pochody rozhodující o selektivní toxicitě pyrazonu (1-fenyl-4-amino-5-chorpyridazon-6) jsme sledovali jeho vliv na hlavní enzymové systémy ?ídící dýchání ko?en?. Zatímco jsme u ko?en? zeSinapis alba zjistili úplnou inaktivaci dehydrogenázy kyseliny jantarové—u ko?en? cukrovky je stejný enzym stimulován.     

Fluctuations in human serum lipoproteins during the normal menstrual cycle

1. Lipoproteins were measured in sera from 11 young women having a similar environment and diet. Sera were obtained at weekly intervals over a 12-week period. The values of the lipoproteins during periods in the normal ovulatory cycle were compared to assess their relation to reported hormone concentrations in blood. 2. Only the 4–0s_f (HDL₂) (d 1·125 sodium chloride) fraction changed significantly; it increased at ovulation in ten of the 11 subjects and fell as menstruation approached. 3. There was greater variability in most of the low-density rather than the high-density lipoproteins within individuals. The lipoprotein class most characteristic for an individual was the 4–0s_f or HDL₂ fraction.     

Kinetics of ligand binding to a cluster of membrane-associated receptors

The process of ligand binding to a cluster of membrane-associated receptors is examined theoretically. The theoretical model proposed involves the diffusion of ligands from the solution to the disc-like cluster of receptors on the surface of the spherical cell. When the ligand hits the internal part of the disc-like cluster, it begins to move laterally until it leaves the disc through its outer surface or is bound by one of the receptors inside the disc. If the ligand leaves the cluster, it returns to the solution and hits the disc again after a certain period, etc. According to our model the transition from a diffusion-limited to a reaction-limited process of binding is determined by the dimensionless parameter Dt _c/a ², where D is the lateral diffusion coefficient,t _c is the characteristic time of reaction, anda is the radius of the disc-like cluster. The forward rate constantk _f turns out to be a function of . Comparing the results of our calculations ofk _f with some experimental data we found that agreement is achieved at high , i.e. the process of ligand binding by clustered receptors is predominantly reaction-limited.     

Plant communities on anthropogenically disturbed sites on the Chukotka Peninsula,Russia

Abstract. The vegetation of anthropogenically disturbed sites on the Chukotka Peninsula was investigated in 1986 and 1990. 102 sites had been bulldozed free of vegetation and soil between 2 and 20 yr ago and revegetated. Anthropogenic vegetation differs considerably from natural tundra. The total plant cover decreases, lichens are absent, moss composition changes, and graminoids predominate. A floristic classification was developed in order to describe the diversity of anthropogenic communities formed on these sites. Four associations were distinguished, all belonging to the alliance Poion glaucomalacanthae. An additional alliance characterized by Alopecurus alpinus is suggested for colder sites, but it has not yet been described. There is a correspondence of associations to substrate types. The association Phippsietum algidae was found only on loam substrate. The Artemisietum glomeratae and Saxifragetum punctatae are connected with rubble or gravel. The graminoid association Arctagrostietum arundinaceae is generally widespread in disturbed habitats and occurs on a variety of substrate types.     

Epimeletic behavior in a free-ranging female Risso’s dolphin (Grampus griseus)

acta ethologica - Here, we describe the epimeletic behavior of an adult Risso’s dolphin towards a deceased newborn calf of the same species across several days with photographs, acoustic...     

Matrix synthesis of chiral carboxy derivatives: Aldehyde chiral discrimination due to a two-point coordination of Mg2+

To control stereoselectivity in aldol-like reactions with chiral carbohydrate templates, we studied the interaction between completely protected dialdo compounds and magnesium enediolates of arylacetic acids. Diastereomeric mixtures of the highly functionalized acids obtained were esterified to isolate individual methyl uronates. It was found that all the diastereomeric esters exhibit Cotton effects of the same positive sign in the 220–230 nm region and so possess the same S configuration of the aryl chiral center C(6). Chiral center C(5) configurational assignments were performed using IR and ORD spectroscopy. We separated and specified four pairs of diastereomeric methyl uronates. It follows that the precursory acids have the same 5R*, 6S (major isomers) and 5S*, 6S (minor isomers) configurations. A tentative mechanism for complexation and possible models of Mg²⁺ -protected dialdose intermediate complexes has been proposed. We have concluded that a kind of orbital steering is realized, accompanied by some “tuning” of molecular assembly conditioned by two-point coordination between Mg²⁺ and potential cation-binding sites in the substrate molecules. Thus it has been demonstrated that reasonable diastereo-selectivity can be achieved even through the use of small matrix molecules using rather small functional groups, which do not impose any stringent steric requirements. © 1993 Wiley-Liss, Inc.