1,101 research outputs found
Cordagalma tottoni Margulis 1993
No full textCordagalma tottoni Margulis, 1993. Diagnosis. Small, typically heart-shaped nectophores. Pedicular canal, on reaching nectosac, gives rise to only upper and lower radial canals. Lateral canals arise from the upper canal. Remarks. The original description of Cordagalma tottoni was based on fragments of a single specimen collected, using a Juday net in the 100 –0m depth zone, by the Research Vessel Vozrozhedenia on 18 th December 1986 at 35 °S 139 °W, in the middle of the South Pacific Ocean. The material was said to consist of a stem, with pneumatophore and various buds, three nectophores, two gastrozooids, and several siphosomal fragments. The type specimen has been re-examined by the present author. A problem with Margulis' (1993) description of the nectophores is that she had orientated them upside-down, such that she considered the conical lower part of the nectophore to be anterior. This apart, the only real distinguishing feature of the nectophores, the largest of which measured 3.5 mm in height and 2.5 mm in width, was that the pedicular canal, on reaching the nectosac, gave rise to only the upper and lower radial canals (Figure 12). The lateral radial canals then arose from the upper (ventral according to Margulis) canal. This, with some difficulty, was confirmed by the present author and, thus, is in contrast to the arrangement in all other Cordagalma species herein described where all the radial canals arise together from the pedicular canal. It is far from certain that the siphosomal zooids described by Margulis (1993) actually belong to the same specimen as the detached nectophores. Some of the palpons were said to have palpacles (Figure 12) while others did not. This suggests their presence and subsequent loss, which would be in marked contrast to the arrangement in other Cordagalma species, but is in accord with that found for Cardianecta parchelion gen. nov., sp. nov. described below. However, the re-examination showed that the palpons, which were attached at their bases, appeared not to possess palpacles. The loose gastrozooids had the proximal part of the tentacles attached, which bore, presumably, young tentilla with long pedicles and oval cnidobands, with a beak-shaped tip. There was said to be a single row of larger nematocysts on either side of the cnidoband, enclosing numerous smaller ones. No further details could be added. These are quite unlike the tentilla of C. ordinatum that Margulis (1993, Figure 2 E) figured but, again, those of Cardianecta parchelion gen. nov., sp. nov. are very different. The bracts of C. tottoni also were markedly different in having a transverse ridge demarcating a triangular distal facet on the upper side, and with a bracteal canal that was said to end below the middle of a strip of nematocysts running proximally from the distal tip of the bract. Finally, Margulis described the gonophores as being immature but, on re-examination, the sex of some could be determined and they all appeared to be female. It is, however, doubtful that this observation has any significance. Thus, until a complete specimen of Cordagalma tottoni is collected it is impossible to know if the siphosomal zooids described by Margulis (1993) actually belong with the nectophores. Nonetheless, the fact, since confirmed by the present author, that the lateral radial canals on the nectosac arise from the upper canal is a distinguishing feature setting this species apart from all other Cordagalma species. Distribution. Known only from a single specimen collected in superficial waters in the central South Pacific Ocean (c, 35 ° S 139 ° W). Etymology. Named for Arthur Knyvett Totton whose Synopsis of the Siphonophora, published in 1965, remains the most important work on siphonophores published to date.Published as part of P. R. Pugh, 2016, A synopsis of the Family Cordagalmatidae fam. nov. (Cnidaria, Siphonophora, Physonectae), pp. 1-64 in Zootaxa 4095 (1) on pages 16-17, DOI: 10.11646/zootaxa.4095.1.1, http://zenodo.org/record/26138
Lynn Margulis, architect of the endosymbiotic theory
No full textInternational audienceLynn Margulis is known as the scientist who advanced the endosymbiotic theory in the late 60’s (Sagan, 1967) and brought it from its rejection to its acceptance by the scientific community in the 80’s. Nevertheless, Margulis’ contribution was neither new, nor decisive in terms of conclusive experiments. The hypothesis of an endosymbiotic origin of chloroplast was first proposed in the late 19th century. In the 60’s, Margulis professor's Hans Ris showed convincingly that plastids contain their own genetic material and revived the endosymbiotic hypothesis (Ris & Plaut, 1962). Similar hypotheses about mitochondria were made in the early 20th century and their DNA was then discovered in the same period than plastidial DNA. The passionate 70’s debate opposing symbiotic origin supporters and opponents remained unresolved until the development of a new field of biology to which Margulis addressed much criticism: molecular phylogeny. Moreover, the aspects of the theory she was the only scientist to defend (the symbiotic origin of the microtubule system) were not confirmed after 50 years of research. One could wonder which role Margulis played in reaching the consensus.I will argue that the original contribution of Margulis lies in her efforts to contextualize the mitochondrial and plastidial nature in a complete and coherent scenario of the evolution of life on Earth, and to combine all biological disciplines (and beyond): cell biology, biochemistry, genetics, symbiosis studies, systematics, paleontology. Thanks to her, this event of life history became a cross-disciplinary subject in debate at an international level. It allowed to review scattered and sometimes seemingly contradictory data. It stimulated research into this topic, whose results contributed in turn to support the theory. Margulis started a fruitful research program. References:Ris, H., Plaut, W. 1962. Ultrastructure of DNA-containing areas in the chloroplast of Chlamydomonas. The Journal of Cell Biology 13(3): 383‐391.Sagan, L. 1967. On the origin of mitosing cells. Journal of theoretical biology 14(3): 225‐274
Lynn Margulis, architect of the endosymbiotic theory
No full textInternational audienceLynn Margulis is known as the scientist who advanced the endosymbiotic theory in the late 60’s (Sagan, 1967) and brought it from its rejection to its acceptance by the scientific community in the 80’s. Nevertheless, Margulis’ contribution was neither new, nor decisive in terms of conclusive experiments. The hypothesis of an endosymbiotic origin of chloroplast was first proposed in the late 19th century. In the 60’s, Margulis professor's Hans Ris showed convincingly that plastids contain their own genetic material and revived the endosymbiotic hypothesis (Ris & Plaut, 1962). Similar hypotheses about mitochondria were made in the early 20th century and their DNA was then discovered in the same period than plastidial DNA. The passionate 70’s debate opposing symbiotic origin supporters and opponents remained unresolved until the development of a new field of biology to which Margulis addressed much criticism: molecular phylogeny. Moreover, the aspects of the theory she was the only scientist to defend (the symbiotic origin of the microtubule system) were not confirmed after 50 years of research. One could wonder which role Margulis played in reaching the consensus.I will argue that the original contribution of Margulis lies in her efforts to contextualize the mitochondrial and plastidial nature in a complete and coherent scenario of the evolution of life on Earth, and to combine all biological disciplines (and beyond): cell biology, biochemistry, genetics, symbiosis studies, systematics, paleontology. Thanks to her, this event of life history became a cross-disciplinary subject in debate at an international level. It allowed to review scattered and sometimes seemingly contradictory data. It stimulated research into this topic, whose results contributed in turn to support the theory. Margulis started a fruitful research program. References:Ris, H., Plaut, W. 1962. Ultrastructure of DNA-containing areas in the chloroplast of Chlamydomonas. The Journal of Cell Biology 13(3): 383‐391.Sagan, L. 1967. On the origin of mitosing cells. Journal of theoretical biology 14(3): 225‐274
Lynn Margulis, architect of the endosymbiotic theory
No full textInternational audienceLynn Margulis is known as the scientist who advanced the endosymbiotic theory in the late 60’s (Sagan, 1967) and brought it from its rejection to its acceptance by the scientific community in the 80’s. Nevertheless, Margulis’ contribution was neither new, nor decisive in terms of conclusive experiments. The hypothesis of an endosymbiotic origin of chloroplast was first proposed in the late 19th century. In the 60’s, Margulis professor's Hans Ris showed convincingly that plastids contain their own genetic material and revived the endosymbiotic hypothesis (Ris & Plaut, 1962). Similar hypotheses about mitochondria were made in the early 20th century and their DNA was then discovered in the same period than plastidial DNA. The passionate 70’s debate opposing symbiotic origin supporters and opponents remained unresolved until the development of a new field of biology to which Margulis addressed much criticism: molecular phylogeny. Moreover, the aspects of the theory she was the only scientist to defend (the symbiotic origin of the microtubule system) were not confirmed after 50 years of research. One could wonder which role Margulis played in reaching the consensus.I will argue that the original contribution of Margulis lies in her efforts to contextualize the mitochondrial and plastidial nature in a complete and coherent scenario of the evolution of life on Earth, and to combine all biological disciplines (and beyond): cell biology, biochemistry, genetics, symbiosis studies, systematics, paleontology. Thanks to her, this event of life history became a cross-disciplinary subject in debate at an international level. It allowed to review scattered and sometimes seemingly contradictory data. It stimulated research into this topic, whose results contributed in turn to support the theory. Margulis started a fruitful research program. References:Ris, H., Plaut, W. 1962. Ultrastructure of DNA-containing areas in the chloroplast of Chlamydomonas. The Journal of Cell Biology 13(3): 383‐391.Sagan, L. 1967. On the origin of mitosing cells. Journal of theoretical biology 14(3): 225‐274
Lynn Margulis, architect of the endosymbiotic theory
No full textInternational audienceLynn Margulis is known as the scientist who advanced the endosymbiotic theory in the late 60’s (Sagan, 1967) and brought it from its rejection to its acceptance by the scientific community in the 80’s. Nevertheless, Margulis’ contribution was neither new, nor decisive in terms of conclusive experiments. The hypothesis of an endosymbiotic origin of chloroplast was first proposed in the late 19th century. In the 60’s, Margulis professor's Hans Ris showed convincingly that plastids contain their own genetic material and revived the endosymbiotic hypothesis (Ris & Plaut, 1962). Similar hypotheses about mitochondria were made in the early 20th century and their DNA was then discovered in the same period than plastidial DNA. The passionate 70’s debate opposing symbiotic origin supporters and opponents remained unresolved until the development of a new field of biology to which Margulis addressed much criticism: molecular phylogeny. Moreover, the aspects of the theory she was the only scientist to defend (the symbiotic origin of the microtubule system) were not confirmed after 50 years of research. One could wonder which role Margulis played in reaching the consensus.I will argue that the original contribution of Margulis lies in her efforts to contextualize the mitochondrial and plastidial nature in a complete and coherent scenario of the evolution of life on Earth, and to combine all biological disciplines (and beyond): cell biology, biochemistry, genetics, symbiosis studies, systematics, paleontology. Thanks to her, this event of life history became a cross-disciplinary subject in debate at an international level. It allowed to review scattered and sometimes seemingly contradictory data. It stimulated research into this topic, whose results contributed in turn to support the theory. Margulis started a fruitful research program. References:Ris, H., Plaut, W. 1962. Ultrastructure of DNA-containing areas in the chloroplast of Chlamydomonas. The Journal of Cell Biology 13(3): 383‐391.Sagan, L. 1967. On the origin of mitosing cells. Journal of theoretical biology 14(3): 225‐274
Lynn Margulis : discurs llegit a la cerimònia d'investidura celebrada a la sala d'actes del Rectorat el dia 6 de juny de 2007
No full textLa professora Lynn Margulis es va doctorar al Departament de Genètica a la Universitat de Califòrnia, Berkeley (1960-63). Durant els anys seixanta va demostrar una extraordinària capacitat de síntesi al reunir centenars d'experiments i hipòtesis disperses per formular d'una manera coherent la teoria de l' endosimbiosi, per explicar l'origen de la cèl·lula eucariòtica. En la dècada dels anys setanta va viatjar incansablement per defensar l'esmentada teoria, actualment acceptada i que constitueix una de les bases més importants de la moderna biologia cel·lular.Especialment interessant ha estat la intensa col·laboració científica que ha mantingut amb el professor James E. Lovelock, autor de la hipòtesi Gaia, i que considera la Terra com un supraorganisme capaç d'autoregular-se. Aquesta col·laboració la va portar a interessar-se per altres temes com l'Ecologia global o l'evolució dels primers microorganismes. La seva tasca científica ha quedat reflectida en els seus llibres i en un gran nombre de publicacions amb importants contribucions a la biologia cel·lular i a l'evolució microbiana. Pel que fa a la tasca docent, ha estat professora en les universitats de Boston i Masschussets Amherst, a més de professora visitant d'universitats de tot el món. Lynn Margulis ha rebut nombrosos premis i distincions al llarg de la seva carrera i forma part de diversos comitès científics internacionals . És membre de la Acadèmia Nacional de Ciències dels EUA des de 1983 i de l'Acadèmia Russa de Ciències Naturals. Actualment, Lynn Margulis és professora distingida del Departament de Geociències de la Universitat de Massachussets Amherst.Nomenament 01/02/2007. A proposta de Facultat de Biociències. Investidura 06/06/2007. Padrina: Isabel Esteve Martíne
Specialty fibres and components for advanced microscopy
No full textWe investigate fibre basic functions like SHG and pulse gating. We achieved 5.2% conversion efficiency into green light with 50 W peak pump power and demonstrated in-fibre pulse gating at 1 MHz repetition rat
Avatars of Margulis invariants and proper actions
No full textIn this article, we provide a necessary and sufficient criterion for proper actions on in terms of certain special Anosov representations in . Moreover, we show that affine Anosov representations of any word hyperbolic group in are infinitesimal versions of such special Anosov representations. Finally, using the above two results we interpret Margulis spacetimes as infinitesimal versions of quotient manifolds of .
In the appendix, we give a description of the appropriate cross-ratios in our setting and their infinitesimal versions.42 pages, final version, accepted for publication in Annales de l\u27Institut Fourie
Spirochete attachment ultrastructure : implications for the origin and evolution of cilia
No full textThe fine structure of spirochete attachments to the plasma membrane of anaerobic protists displays variations here interpreted as legacies of an evolutionary sequence analogous to that from free-living spirochetes to undulipodia (eukaryotic "flagella" and homologous structures). Attached spirochetes form a vestment, a wriggling fringe of motile cells at the edge of the plasma membrane of unidentified cellulolytic protist cells in the hypertrophied hindgut of the digestive system of Mastotermes darwinien- sis, the large wood-feeding termite from northern Australia. From the membrane extend both undulipodia and a complex of comparably sized (10-12 μm × 0.2-0.3 μn) ectosymbiotic spirochetes that resembles unruly ciliated epithelium. In the intestines are helical (swimming) and round-body morphotypes. Round bodies (RBs) are slow or immotile spirochetes, propagules known to revert to typical swimming helices under culture conditions favorable for growth. The surfaces of both the spirochete gram-negative eubacteria and the parabasalid protists display distinctive attachment structures. The attached hypertrophied structures, some of which resemble ciliate kinetids, are found consistently at sites where the spirochete termini contact the protist plasma membranes
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