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  • Springer  (41)
  • Institute of Physics  (18)
  • American Chemical Society (ACS)  (4)
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  • 1
    ISSN: 1439-0361
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Zusammenfassung Die Schlußfolgerungen, dieStegmann (J. Orn. 109, 1968, p. 441–445) für die verwandtschaftliche Stellung der Flughühner auf Grund seiner eigenen Untersuchungen und an Hand anderer Quellen zieht, werden kommentiert. Es wird gezeigt, daß einige dieser Schlußfolgerungen nur auf morphologischen Merkmalen beruhen und mit den zu anderen Resultaten gelangten ethologischen und physiologischen Untersuchungsergebnissen nicht zu vereinbaren sind. Außerdem erscheint es unwahrscheinlich, daß die Flughühner, deren Ursprung von bodenlebenden Nestflüchtern unbestritten ist, auf dem „Umweg“ über die baum- und felsbewohnenden nesthockenden Tauben erst sekundär wieder zu bodenbewohnenden Nestflüchtern geworden sind. Es gibt kein einziges Flughuhn-Merkmal, das diese Hypothese stützen könnte.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Minds and machines 10 (2000), S. 79-109 
    ISSN: 1572-8641
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Philosophy
    Notes: Abstract In the debate between simple inference heuristics and complex decision mechanisms, we take a position squarely in the middle. A decision making process that extends to both naturalistic and novel settings should extend beyond the confines of this debate; both simple heuristics and complex mechanisms are cognitive skills adapted to and appropriate for some circumstances but not for others. Rather than ask `Which skill is better?' it is often more important to ask `When is a skill justified?' The selection and application of an appropriate cognitive skill for a particular problem has both costs and benefits, and therefore requires the resolution of a tradeoff. In revisiting satisficing, we observe that the essence of satisficing is tradeoff. Unlike heuristics, which derive their justification from empirical phenomena, and unlike optimal solutions, which derive their justification by an evaluation of alternatives, satisficing decision-making derives its justification by an evaluation of consequences. We formulate and present a satisficing decision paradigm that has its motivation in Herbert Simon's work on bounded rationality. We characterize satisficing using a cost–benefit tradeoff, and generate a decision rule applicable to both designing intelligent machines as well as describing human behavior.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 44 (1997), S. 321 -326 
    ISSN: 1432-1432
    Keywords: Key words: Chironomus — Satellite DNA — Tandem-repetitive DNA — Molecular Evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The subspecies Chironomus thummi thummi and C. t. piger display dramatic differences in the copy number and chromosomal localization of a tandemly repeated DNA family (Cla elements). In order to analyze the evolutionary dynamics of this repeat family, we studied the organization of Cla elements in the related outgroup species C. luridus. We find three different patterns of Cla element organization in C. luridus, showing that Cla elements may be either strictly tandem-repetitive or be an integral part of two higher-order tandem repeats (i.e., Hinf[lur] elements, Sal[lur] elements). All three types of Cla-related repeats are localized in the centromeres of C. luridus chromosomes. This suggests that the dispersed chromosomal localization of Cla elements in C. t. thummi may be the result of an amplification and transposition during evolution of this subspecies.
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  • 4
    ISSN: 1432-1432
    Keywords: Insect globin genes ; Molecular evolution ; Alleles ; In situ hybridization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We isolated genomic clones containing sequences encoding globins I and IA from a Chironomus thummi thummi genomic library. Three clones contain globin IA (ctt-1A) genes, while one contains a globin I (ctt-1) gene. The coding regions of the four genes are identical except for the single base substitution accounting for the globin I/IA polymorphism. The noncoding DNA flanking the coding region is more than 98% similar, confirming a previous hypothesis that the globin ctt-1 and ctt-1A genes are alleles. Hemoglobins I and IA are monomeric in the insect hemolymph. Earlier in situ hybridization studies suggested that monomeric and dimeric globin genes are clustered at different chromosomal loci. In situ hybridization of ctt-1 DNA to polytene salivary gland chromosomes places the ctt-1 gene on the same band as genes for the dimeric globins IIβ and VIIB, forcing revision of the earlier hypothesis that genes for monomeric and dimeric globin genes are at different loci. The evolution of the ctt-1 and ctt-1A alleles and of the two globin gene loci are discussed.
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  • 5
    ISSN: 1432-1432
    Keywords: Key words: Globin — Hemoglobin — Molecular evolution — Multigene family — Gene conversion — Chironomus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. We have studied the evolutionary dynamics of a cluster of insect globin genes by comparing the organization and sequence of the gene group in two distantly related species, Chironomus pallidivittatus and C. t. thummi. Although the general architecture of the globin gene cluster has been conserved, we have found an additional, previously undescribed gene (named Cpa F) in C. pallidivittatus which shows signs of accelerated sequence evolution at nonsynonymous codon positions. This new gene is clearly functional, as demonstrated by Northern analysis. Comparison of paralogous and orthologous genes reveals patterns of intraspecific sequence homogenization. The head-to-head-oriented globin 3 and 4 gene pairs in C. t. thummi and the gb 4 gene pair in C. pallidivittatus have been efficiently homogenized, probably by gene conversion, in their promoter and coding regions. Inverted transcriptional orientation seems to favor efficient conversion. The orthologous genes from C. t. thummi and C. pallidivittatus reveal different levels of sequence conservation, ranging from 85.3 to 94.7% amino acid identity. Surprisingly, globin gene E, for which up to now no corresponding protein has been detected in the larval hemolymph of C. t. thummi, shows the highest degree of interspecies sequence conservation. This points to an essential, as yet unknown function of this globin. The usefulness of globin gene comparisons for dating speciation events in Chironomus is discussed.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Development genes and evolution 184 (1978), S. 115-134 
    ISSN: 1432-041X
    Keywords: Cell interactions ; Fish chromatophores ; Xiphophorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Die Entwicklung von Chromatophoren in regenerierender Haut von Fischen der GattungXiphophorus wurde als Modell zur Untersuchung von Zellinteraktionen benutzt. Der Ablauf der Chromatophorenentwicklung nach Induktion durch Entfernen der Haut wird beschrieben unter besonderer Berücksichtigung der Melanophorendifferenzierung. Zwischen Makro- und Mikromelanophoren, die in der Haut der Xiphophorini vorkommen, existieren folgende Wechselwirkungen: 1. die Makromelanophoren inhibieren die Differenzierung von Melanocyten und Mikromelanophoren 2. die Makromelanophoren induzieren den Abbau von vollentwickelten Mikromelanophoren in ihrer Nachbarschaft. Diese Makro-Mikromelanophoren-Wechselwirkungen, sind außerordentlich zelltyp-spezifisch. Sie sind unabhängig vom Fischgenotyp in der Haut verschiedener Fischarten der GattungXiphophorus wirksam. Sie sind auch dann nachweisbar, wenn Makromelanophoren der einen Fischart in die Haut einer anderen Fischart implantiert werden. Die Rolle der Zellinteraktionen für die Pigmentmusterbildung wird diskutiert.
    Notes: Summary Regeneration-induced development of chromatophores in the skin of fish was used to study cell interactions affecting cell differentiation and cell destruction. The typical differentiation process of chromatophores in the regenerating fish skin is described with special interest in the differentiation of macro- and micromelanophores. Between micro- and macromelanophores two types of cell interactions were found: 1. The macromelanophores inhibit the differentiation of melanocytes and micromelanophores 2. the macromelanophores induce the destruction of micromelanophores in their vicinity. These cell interactions are very specific to cell type, that means they are strictly limited to macro- and micromelanophores. On the other hand, the effectiveness of these cell interactions isnot limited to one genotype or one species of Xiphophorine fish. The inhibiting and the destruction-inducing influence of macromelanophores upon micromelanophores is shown for three different species of Xiphophorine fish. The role of cell interaction in chromatophore development is discussed.
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  • 7
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The ribosomal DNAs from Ch. thummi piger and Ch. th. thummi were cloned and analysed by a variety of restriction endonucleases. Comparison of rDNA clones from the two subspecies revealed a considerable length difference: the length of the analysed rDNA cistrons is approximately 9.0 kb for Ch. th. piger and approximately 14.5 kb for Ch. th. thummi. The nearly 5 kb additional DNA in Ch. th. thummi is clearly located within the non-transcribed spacer region, and consists of AT-rich, reptitive DNA elements. These elements with a basic repeat length of approximately 120 bp, are arranged tandemly in stretches of up to about 50 identical copies, which are characterized by a cleavage site for ClaI restriction endonuclease. They are found only in the Ch. th. thummi rDNA clones and not in the Ch. th. piger clones. Southern hybridizations between cloned ribosomal DNA and “centromeric” highly repetitive DNA have shown that the ribosomal repetitive Cla-elements are closely related to a highly repetitive DNA sequence family, which is present in various chromosomal sites particularly the centromeres. Sequence analysis has revealed more than 90% homology between the ribosomal Cla-elements and the “centromeric” Cla-elements. — Since it is clear from cytological investigations that Ch. th. piger with the small rDNA repeating unit is the phylogenetically older subspecies, we postulate a transposition of Cla-elements into the nucleolar DNA during the evolution of Ch. th. thummi.
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  • 8
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The repetition frequency of a highly repetitive DNA sequence has been measured in the genomes of Ch. thummi thummi and Ch. th. piger. This sequence is known to be involved in the evolutionary duplication of defined chromosomal segments leading to a significant increase in the genome size of Ch. th. thummi. Reassociation of this highly repetitive DNA sequence which has a repeat length of 120 base-pairs, with total Ch. th. thummi and Ch. th. piger DNA has shown that the repetition frequency in the Ch. th. thummi DNA is 5.5 fold higher than in Ch. th. piger. In both genomes a 120 base-pair sequence is present as tandemly repeated sequence as shown by Southern analysis.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Environmental management 17 (1993), S. 613-619 
    ISSN: 1432-1009
    Keywords: Chesapeake Bay ; Habitat requirements ; Scaling ; Waterbirds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Many living resources in the Chesapeake Bay estuary have deteriorated over the past 50 years. As a result, many governmental committees, task forces, and management plans have been established. Most of the recommendations for implementing a bay cleanup focus on reducing sediments and nutrient flow into the watershed. We emphasize that habitat requirements other than water quality are necessary for the recovery of much of the bay's avian wildlife, and we use a waterbird example as illustration. Some of these needs are: (1) protection of fast-eroding islands, or creation of new ones by dredge deposition to improve nesting habitat for American black ducks(Anas rubripes), great blue herons(Ardea herodias), and other associated wading birds; (2) conservation of remaining brackish marshes, especially near riparian areas, for feeding black ducks, wading birds, and wood ducks(Aix sponsa); (3) establishment of sanctuaries in open-water, littoral zones to protect feeding and/or roosting areas for diving ducks such as canvasbacks(Aythya valisineria) and redheads(Aythya americana), and for bald eagles(Haliaeetus leucocephalus); and (4) limitation of disturbance by boaters around nesting islands and open-water feeding areas. Land (or water) protection measures for waterbirds need to include units at several different spatial scales, ranging from “points” (e.g., a colony site) to large-area resources (e.g., a marsh or tributary for feeding). Planning to conserve large areas of both land and water can be achieved following a biosphere reserve model. Existing interagency committees in the Chesapeake Bay Program could be more effective in developing such a model for wildlife and fisheries resources.
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  • 10
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The dominant male sex determiner in chromosome III of the midge Chironomus thummi thummi is closely linked to a large cluster of tandem-repetitive DNA elements, the Cla elements, which are otherwise highly repetitive and distributed over more than 200 sites on all chromosomes. Chromosome III displays a hemizygous cluster of Cla elements in males but not in females. The chromosomal location of this hemizygous Cla element cluster is in the region of the male determiner M as localized by cytogenetic analysis. With Cla elements as hybridization probe, it was possible to clone a large part of the sex determining region. Molecular analysis of the DNA of males and females in this region displayed a number of differences between the two sexes. One striking difference is an unusual transposable element associated with the male sex determining region. The sex determining region also contains several other tandem-repetitive DNA elements in addition to the Cla elements. They are interspersed with single copy DNA. The accumulation of repetitive elements in the sex determining region is interpreted as the result of a lack of recombination between the male/female heteromorphic region, although recombination in the other sections of chromosome III occurs.
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