Cohesion Mechanisms Research Articles

Gene trees: A powerful tool for exploring the evolutionary biology of species and speciation

AbstractEvolutionary trees can be constructed from the haplotypes observed with molecular surveys of sequence or restriction site variation. Such gene trees can be constructed regardless of whether or not all of the individual specimens came from one or many species. Hence, these gene trees can straddle the species/population interface, thereby providing a powerful tool for studying the meaning of species and the process of speciation. We illustrate how historical approaches using gene trees can be used to separate the effects of population structure from population history, in order to rigorously test the species status of a group, and to test hypotheses about the process of speciation. A worked example of species status in the Piriqueta caroliniana complex is presented. Species status is evaluated under the cohesion species concept that defines a species as an evolutionary lineage with boundaries arising from the forces that create reproductive communities. Such forces are collectively called cohesion mechanisms and consist of two main subtypes: (i) genetic exchangeability, and (ii) ecological interchangeability. To make this definition operational, populations that behave as separate evolutionary lineages are first identified. A method is reviewed for inferring lineages using explicit statistical criteria from geographic overlays upon gene trees. Once lineages have been identified, the next step is to use the cohesion mechanisms to identify candidate traits that should contribute to genetic exchangeability and/or ecological interchangeability. The cohesion species are then identified by performing overlays upon gene trees in order to identify significant transitions in the candidate traits. Cohesion species are recognized only when statistically significant reproductive/ecological transitions occur that are concordant with the lineages defined earlier. This data‐rich method of recognizing species automatically generates much information about the biogeography, population structure, historical events, and ecology and/or reproductive biology of the group under study. In turn, this information provides much insight into the process of speciation. It also makes the criteria, data, methods of analysis and degree of support for the species inference completely explicit, thereby avoiding confusion, inconsistency and artificial controversies that plague much of the literature on species concepts.

Discourse cohesion in sign and speech

This paper describes the development of discourse cohesion in bilingual children, through an analysis of narrative discourses produced by hearing children of deaf parents(HCDP) in both British Sign Language(BSL) and spoken English. Reference mechanisms in both languages are described in the context of recent work on narrative and discourse organization development in spoken and sign language. Discourse cohesion is achieved in each language through different surface mechanisms, while following a similar underlying organization. The differences in use of referring expressions observed between two children reflect development across both languages in the ability to control and manipulate reference within discourse. Describing acquisition of cohesion mechanisms by bilingual hearing children of deaf families provides a unique opportunity to ask questions about developing two languages with cross-modality differences. An early development of language appropriate narrative devices is reported while apparent differences between languages, in the relative phase of discourse organization development within the same child is suggested. A second question is addressed concerning the impact of bilinguality through an examination of language mixing across modalities.

The budding yeast cohesin gene SCC1/MCD1/RHC21 genetically interacts with PKA, CDK and APC.

Cohesin is a protein that plays a key role in the cohesion and separation of sister chromatids. During the duplication of chromatids, cohesin holds sister chromatids together until the onset of anaphase, and thereby prevents the premature separation of sister chromatids which would otherwise jeopardize the faithful segregation of chromosomes. To investigate the molecular mechanisms of sister chromatid cohesion, we have isolated multicopy suppressors of a temperature-sensitive (ts) mutation in the SCC1/MCD1/RHC21 gene which encodes a component of the cohesin complex in budding yeast. Isolation of multicopy suppressors of rhc21-sk16 and further genetic analyses revealed that several distinct biological pathways are involved in the regulation of SCC1/MCD1/RHC21 function. Firstly, PDE2 and BCY1, each of which inhibits the activity of protein kinase A (PKA), suppressed the temperature sensitivity of the rhc21-sk16 mutant. Secondly, PDE2 suppressed the temperature sensitivity of the cdc16-1 mutant. These results suggest that SCC1/MCD1/RHC21 is negatively regulated by the PKA pathway via the anaphase promoting complex (APC). Thirdly, ZDS1, a multicopy suppressor of cdc28-1N, and its homologue ZDS2 were isolated as multicopy suppressors of rhc21-sk16. Furthermore, the rhc21-sk16 mutant did not grow in the presence of the cdc28-1N mutation. Hence, SCC1/MCD1/RHC21 is positively regulated by the mitotic CDK, CDC28. Finally, SCC1/MCD1/RHC21 was found to interact genetically with CDC20, an activator of APC. Overexpression of CDC20 suppressed the temperature sensitivity of rhc21-sk16, and rhc21-sk16 was shown to be synthetically lethal with cdc20-1. In addition, the growth of the rhc21-sk16 mutant was inhibited by overproduction of the anaphase inhibitor Pds1p, whose degradation is mediated by Cdc20p in APC-dependent proteolysis. The functional relationships between SCC1/MCD1/RHC21 and PKA, CDK or APC are discussed.

Internalization of gap junctions in benign familial pemphigus (Hailey-Hailey disease) and keratosis follicularis (Darier's disease).

Hereditary skin disorders involving acantholysis, such as Hailey-Hailey disease and Darier's disease, have been genetically linked to distinct chromosomal parts which do not code for known structural proteins. Such evidence suggests that the genomic abnormalities underlying these dermatoses may concern functional/regulatory mechanisms of keratinocyte cohesion. Epidermal communication junctions (gap junctions) are responsible for direct coupling of cells and, thus, co-ordinate the behaviour of keratinocytes within the tissue. Consequently, they remain one of the potential, and poorly studied, elements in the pathogenesis of hereditary acantholytic diseases. We have investigated the distribution and fate of gap junctions during non-immune acantholysis, using fine immunolocalization methods at the light and electron microscopic levels. Our results demonstrate normal expression of epidermal gap junction proteins, connexins 26 and 43, in non-lesional skin of Hailey-Hailey and Darier's diseases. The gap junctions were not primarily dismantled during acantholysis, typical of both of the studied dermatoses, but underwent internalization and subsequent cytoplasmic dispersion in the portions of cells which were no longer attached to the rest of the tissue. In Darier's disease, perifollicular acantholysis did not specifically concern epithelium of appendages coexpressing connexin 26 in addition to connexin 43, further indicating that the observed changes in gap junction localization were secondary to the loss of cell-cell contact. We demonstrated that the sequence of changes was identical in both diseases and that the previously described putative differences were apparently related to the degree of acantholysis present in the studied biopsies. The fate of the junctional structures and proteins, documented in the present study, is most probably a form of recycling process also used by normal keratinocytes during organogenesis and tissue differentiation.

Simulations of vibrated fine powders

During the past few decades, several studies have been conducted to understand the behaviour of powders in vibrated beds. This paper introduces a technique of incorporating the agglomeration and deagglomeration phenomena in the simulation of vibrated fine powders. Two-dimensional direct simulations are performed using 300 spheres 2.99 mm in diameter in a trapezoidal container vibrated vertically at an amplitude of 2.5 mm and 20 Hz frequency as preliminary conditions. Under non-cohesive conditions, the results are in agreement with those found in the literature. As a preliminary effort to predict the behaviour of cohesive fine powders under vibrated conditions, agglomeration and deagglomeration processes are modelled as the formation and destruction, respectively, of interparticle bonds during particle collisions. Two parameters used to model agglomeration and deagglomeration are the ease of cohesion and cohesivity of the powder. Dependencies of these parameters on certain physical properties of cohesive powders have been suggested. Simulation results reveal two aggregate populations, one with uniform size aggregates and another population with multi-sized aggregates. The former aggregates were more prevalent in weakly cohesive powders while the latter in highly cohesive powders. Interesting macroscopic bed behaviour such as alternating cycles of agglomeration and deagglomeration were also observed. Further work is needed in which the aerodynamic forces are taken into account and cohesion mechanisms at the particle surface are modelled.

Intensification and Social Complexity in the Interior Lowlands of Papua New Guinea: A Comparison of Bedamuni and Kubo

Kubo and Bedamuni are linguistically, culturally, and technologically related societies of the interior lowlands of Papua New Guinea. They occupy similar environments and have access to essentially the same resources. They differ in population density (Kubo 0.4 people/km2, Bedamuni 7/km2), subsistence orientation (Kubo are hunter-gatherer-like, Bedamuni are farmers who hunt) and intensification of plant food production (Kubo lower, Bedamuni higher). Relative to Kubo, Bedamuni are shown to exhibit increased differentiation within and between production units, greater integration within and between residential units, and heightened forms of evaluation within and between cultural systems. Each of these general characteristics is illustrated by particulars that refer, for example, to role differentiation, rights of access to land and resources, dispute resolution, mechanisms of inter-community cohesion, and exegesis with respect to subsistence practices and cultural identity. In turn, differences between the two societies in terms of these general characteristics sustain an interpretation that Bedamuni is a socially more complex society than Kubo. The awkward notion of complexity is examined; it is understood to comprise two independent dimensions—the “involvement of parts” (which is itself multidimensional) and the “individuation of form.” The latter dimension has received too little attention in discussion and definitions of complexity.

Could asynchrony in activity between the sexes cause intersexual social segregation in ruminants?

In many sexually dimorphic mammal species, the sexes live outside the mating season in separate social groups ('social segregation'). Social segregation occurs in a wide range of environmental conditions, but its cause in unknown. I suggest that social segregation is caused by a lower level of activity synchrony between individuals in mixed-sex groups than in single-sex groups, owing to sex differences in activity rhythm. As a consequence, mixed-sex groups are more likely to break up than single-sex groups, resulting in a predominance of single-sex groups at equilibrium. To test this hypothesis in red deer (Cervus elaphus L.), I developed an index of activity synchronization and showed that deer in mixed-sex groups were significantly less synchronized in their activity than deer in single-sex groups. Thus, low intersexual synchrony in activity can lead to social segregation. However, a lower level of intrasexual (female-female and male-male) activity synchrony within mixed-sex than within single-sex groups implies that additional factors (other than sex differences in foraging rhythm) contribute to the higher degree of instability of mixed-sex groups.

The Effect of Parents' Marital Satisfaction on Young Adults' Adaptation: A Longitudinal Study

Two questions were examined: (a) whether the effects of parents? marital satisfaction on offspring's adaptation are durable and continue to be manifest when offspring grow up, and (b) whether marital satisfaction operates through the mechanisms of family closeness or cohesion. To address these questions a community-based sample of 172 adolescents was studied twice: as teenagers aged 13—18 years, and approximately 6 years later as young adults aged 19—25. At both Time 1 and Time 2 each parent completed a measure of marital satisfaction and their adolescents completed self-ratings of emotional and physical health. At Time 1 adolescents completed three rating scales related to family closeness or cohesion, and at time 2 they rated how close they felt to their mothers and to their fathers. Correlational and regression analyses revealed the following: (a) over a 6-year interval, the marital satisfaction of mothers was somewhat better than that of fathers in predicting the subsequent emotional and physical heal...

Adhesion and cohesion mechanisms of lunar dust on the moon's surface

This review is based on many publications from the US and some from the former Soviet Union. It briefly describes the sources of lunar dust. The problems posed to the past Apollo missions are summarized. The physical properties of lunar soils, such as cohesion, angle of repose, angle of friction, and bearing capacity, as reported by scientists from these two nations, are compared. The composition of lunar soils is described in terms of acidic and basic components. Since lunar soils are mainly silicates, we are the first to point out the importance of the Lewis acid-base interaction to the cohesion and adhesion of lunar dust. The adhesion of lunar dust is similar to that of a xerographic developer. For the adhesion between lunar dust and dissimilar materials, both van der Waals and electrostatic interactions can be the driving force, depending on the size of the dust particles. For particles smaller than 50 μm, van der Waals interaction predominates, while for those larger than 50 μm, electrostatic interac...

Grooming and language as cohesion mechanisms: Choosing the right data

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Primate Calls, Human Language, and Nonverbal Communication [and Comments and Reply

Etude des deux formes de communication utilisee par les humains : le langage et la communication non verbale ; cette derniere forme etant utilisee par les primates pour communiquer. Commentaires, reponse de l'auteur.

Biochemical differentiation in a mutant of Dictyostelium discoideum defective in cyclic AMP chemotaxis and in intercellular cohesion

A temperature-sensitive mutant of Dictyostelium discoideum has been isolated based on its lack of chemotaxis toward cyclic AMP at the restrictive temperature, 27 degrees C. The mutant develops normally at the permissive temperature, 22 degrees C, but fails to aggregate or complete development at the restrictive temperature. The temperature-sensitive phenotype can be bypassed by allowing cultures to grown into late log phase or to starve for 60-90 min at 22 degrees C prior to a shift to 27 degrees C. At 27 degrees C, the mutant overproduces cell surface cyclic AMP receptors of both high and low affinity and is capable of spontaneous oscillations in light scattering in cell suspensions. Despite its complete lack of morphological development, the mutant undergoes extensive biochemical differentiation. At the onset of starvation, it shows increased levels of N-acetylglucosaminidase, it express cyclic AMP receptors at the normal time and, although somewhat slowly, suppresses those receptors as if aggregation had been achieved. Metabolic pulse labellings with [35S]methionine revealed that the mutant at 27 degrees C displays the same changes in the patterns of newly synthesized proteins observed during the vegetative-to-aggregation and the aggregation-to-slug stages of normal development. The only clear difference from wild type was the failure of the culmination-stage isozyme of beta-glucosidase to appear. The mutant is defective in establishment of intercellular cohesion mechanisms, correlated with poor agglutination by concanavalin A, at the restrictive temperature. The properties of the mutant place severe constraints on models regarding the role of chemoreception and intercellular cohesion in regulation of gene expression.

Family adaptation during a pediatric intensive care hospitalization.

The purpose of this study was to investigate characteristics of families, specifically their adaptability, cohesion, and coping mechanisms during a child's intensive care hospitalization. The sample consisted of 30 families with children hospitalized in a pediatric intensive care unit. The Family Adaptability and Cohesion Evaluation Scales (FACES-III) and the Family Crisis-Oriented Personal Evaluation Scales (F-COPES) were used to collect data. Results indicate that the families were, as a whole, healthy in their levels of functioning; their dimensions of adaptability and cohesion were balanced. The families studied utilized a variety of coping mechanisms, and specific characteristics were identified that enabled the families to adjust to the child's intensive care hospitalization.

Will They Still Be Dancing? Integration and Ethnic Transformation among Yugoslav Immigrants in Scandinavia.

Indulged with sociological self-centeredness we have reduced vampires to mechanisms of social cohesion. Hence,we have questioned a culture, seeing vampires as what they are, the dead ones haunting ...

Combined cryo- and thin sectioning (TEM) in the elucidation of mimosoid tetrad/polyad ultrastructure

Cryosections (freeze-sections) of tetrads/polyads and their subsequent examination in the SEM complement traditional methods (LM, SEM, and TEM) by providing both a dynamic three-dimensional overview of polyad morphology and clarifying aperture morphology, internal wall characters and tetrad/polyad cohesion mechanisms. Cryosections of Dinizia tetrads reveal that cohesion is maintained through adhesion/fusion of the apices of clavate elements in localized regions of the subproximal and proximal walls — a feature not discernible using traditional SEM preparations. Cryosections of the globose 20-grained polyads of Parkia species reveal small central grains and triradiate-shaped proximal apertures — features unobservable or misinterpreted using traditional LM, SEM and TEM methods. In Anadenathera polyads, cryosections have clarified the nature and distribution of small gaps present in the lateral and proximal walls of individual grains.

The Evolution of Pollen Tetrads in Onagraceae

In Onagraceae, pollen is shed in mature tetrads in most Epilobieae, many species of Ludwigia (Jussiaeeae), and two closely related species of the large genus Camissonia (Onagreae). Mature tetrads of Camissonia cardiophylla and representative species of Epilobium and Ludwigia were examined with light, scanning, and transmission electron microscopes. Morphological diagnoses of monad units indicated that individual taxa could be readily distinguished. Statistical analyses of tetrads which remained after acetolysis treatment revealed significant differences in the strength of the binding mechanisms. Mechanisms of tetrad cohesion were found to consist of two principal types. Common to all taxa is cohesion of pollen wall surfaces at the aperture margins; this mechanism is well known in many angiosperm groups. With the exception of Camissonia, the remaining taxa also display binding by means of short exine fragments between adjacent pollen units. These fragments, termed bridges and reported here for the first time, are located in the area extending from the aperture margins to near the center of the proximal exine faces. Thin sections reveal that layers of the bridges are identical with those of the exine. Comparisons were made between bridges and viscin threads, both of which occur on the proximal faces of the grains. Viscin threads are present on all pollen grains in Onagraceae and exhibit distinctive morphologies, and bridges were viewed morphogenetically as related to viscin threads but including an endexine layer and occupying a position near the apertures where cohesion of wall surfaces also occurs. In an evolutionary sense, the formation of mature tetrads almost certainly occurred independently in Camissonia and may have done so in Ludwigia and the Epilobieae.

THE EVOLUTION OF POLLEN TETRADS IN ONAGRACEAE.

In Onagraceae, pollen is shed in mature tetrads in most Epilobieae, many species of Ludwigia (Jussiaeeae), and two closely related species of the large genus Camissonia (Onagreae). Mature tetrads of Camissonia cardiophylla and representative species of Epilobium and Ludwigia were examined with light, scanning, and transmission electron microscopes. Morphological diagnoses of monad units indicated that individual taxa could be readily distinguished. Statistical analyses of tetrads which remained after acetolysis treatment revealed significant differences in the strength of the binding mechanisms. Mechanisms of tetrad cohesion were found to consist of two principal types. Common to all taxa is cohesion of pollen wall surfaces at the aperture margins; this mechanism is well known in many angiosperm groups. With the exception of Camissonia, the remaining taxa also display binding by means of short exine fragments between adjacent pollen units. These fragments, termed bridges and reported here for the first time, are located in the area extending from the aperture margins to near the center of the proximal exine faces. Thin sections reveal that layers of the bridges are identical with those of the exine. Comparisons were made between bridges and viscin threads, both of which occur on the proximal faces of the grains. Viscin threads are present on all pollen grains in Onagraceae and exhibit distinctive morphologies, and bridges were viewed morphogenetically as related to viscin threads but including an endexine layer and occupying a position near the apertures where cohesion of wall surfaces also occurs. In an evolutionary sense, the formation of mature tetrads almost certainly occurred independently in Camissonia and may have done so in Ludwigia and the Epilobieae.

Los marcadores argumentativos del discurso: estudio comparado entre el árabe y el español

En esta investigación nos hemos propuesto como objetivo contribuir al estudio comparado entre el árabe y el español de los marcadores del discurso, uno de los mecanismos de cohesión que contribuyen en la creación de la coherencia interna del texto. Es un estudio descriptivo explicativo en que, desde los puntos de vista lingüístico-discursivo y contrastivo, planteamos detectar los puntos de convergencia y de divergencia entre los dos sistemas de los marcadores argumentativos del discurso (los conectores) de la lengua escrita en español y árabe. El procedimiento general del análisis discursivo y contrastivo adoptado consiste en clasificar en categorías los marcadores del discurso objeto de nuestro estudio, identificar las unidades que conforman cada categoría y sus funciones discursivas en árabe y español y finalmente realizar una comparación contrastiva por categorías en el corpus de traducción escogido. Tras presentar las características virtuales de los conectores en la lengua, estudiamos cómo se actualizan en el texto original y cómo se recuperan en el texto meta. Desde la perspectiva textual, se analiza este fenómeno discursivo teniendo en cuenta el contexto de su aparición a nivel textual.