@article{3920, abstract = {A particular Solid Injector needle, suitable for GC-MS analyses of small specimens, is described together with its application in a study on ants.}, author = {Turillazzi, Stefano and Sledge, Matthew and Cremer, Sylvia and Heinze, Jürgen}, journal = {Insect Social Life}, pages = {169 -- 175}, publisher = {Elsevier}, title = {{A method for analysing small-size specimens in GC-MS}}, volume = {4}, year = {2002}, } @article{3924, abstract = {Males of the ant Cardiocondyla show a dispersal dimorphism of a winged and wingless morph. The loss of flight has lead to morphological reductions in the wingless (ergatoid) males and also affected body size, eye size and pigmentation. As ergatoid males mate exclusively inside the maternal nest, they underlie increased male-male competition and therefore have also evolved additional changes in behaviour and physiology: in contrast to winged males, ergatoid males are highly aggressive towards each other and their spermatogenesis is prolonged compared to all other hymenopteran males. In addition to these two male morphs, we found males with an intermediate appearance. These "intermorphic" males provide a transitional stage between normal males in most investigated morphological and physiological parameters. As they are produced extremely rarely and only in colonies that switch between pure ergatoid to mixed male production, we argue that they likely represent a developmental mistake. Parallels between the determination of male morphs and female castes (queen-worker dimorphism and worker polymorphism) might help to understand how the large potential of phenotypic plasticity in both sexes of social insects is realised during development.}, author = {Cremer, Sylvia and Lautenschläger, Birgit and Heinze, Jürgen}, issn = {0020-1812}, journal = {Insectes Sociaux}, number = {3}, pages = {221 -- 228}, publisher = {Springer}, title = {{A transitional stage between the ergatoid and winged male morph in the ant Cardiocondyla obscurior}}, doi = {10.1007/s00040-002-8305-z}, volume = {49}, year = {2002}, } @article{3925, abstract = {Males of the tropical ant Cardiocondyla obscurior are either wingless and aggressive or winged and docile, and both compete for access to virgin queens in the nest1, 2. Although the fighter males (ergatoids) attack and kill other ergatoids, they tolerate and even attempt to mate with their winged rivals. Here we show that the winged males avoid the aggression of wingless males by mimicking the chemical bouquet of virgin queens, but that their mating success is not reduced as a result. This example of female mimicry by vigorous males is surprising, as in other species it is typically used as a protective strategy by weaker males, and may explain the coexistence and equal mating success of two male morphs.}, author = {Cremer, Sylvia and Sledge, Matthew and Heinze, Jürgen}, issn = {0028-0836}, journal = {Nature}, pages = {897 -- 897}, publisher = {Nature Publishing Group}, title = {{Chemical mimicry: Male ants disguised by the queen's bouquet}}, doi = {10.1038/419897a}, volume = {419}, year = {2002}, } @article{3995, abstract = {This article is a survey of research areas in which motion plays a pivotal role. The aim of the article is to review current approaches to modeling motion together with related data structures and algorithms, and to summarize the challenges that lie ahead in producing a more unified theory of motion representation that would be useful across several disciplines.}, author = {Agarwal, Pankaj and Guibas, Leonidas and Edelsbrunner, Herbert and Erickson, Jeff and Isard, Michael and Har Peled, Sariel and Hershberger, John and Jensen, Christian and Kavraki, Lydia and Koehl, Patrice and Lin, Ming and Manocha, Dinesh and Metaxas, Dimitris and Mirtich, Brian and Mount, David and Muthukrishnan, Sankara and Pai, Dinesh and Sacks, Elisha and Snoeyink, Jack and Suri, Subhash and Wolefson, Ouri}, issn = {0360-0300}, journal = {ACM Computing Surveys}, number = {4}, pages = {550 -- 572}, publisher = {ACM}, title = {{Algorithmic issues in modeling motion}}, doi = {10.1145/592642.592647}, volume = {34}, year = {2002}, } @article{3996, abstract = {We formalize a notion of topological simplification within the framework of a filtration, which is the history of a growing complex. We classify a topological change that happens during growth as either a feature or noise depending on its lifetime or persistence within the filtration. We give fast algorithms for computing persistence and experimental evidence for their speed and utility.}, author = {Edelsbrunner, Herbert and Letscher, David and Zomorodian, Afra}, issn = {0179-5376}, journal = {Discrete & Computational Geometry}, number = {4}, pages = {511 -- 533}, publisher = {Springer}, title = {{Topological persistence and simplification}}, doi = {10.1007/s00454-002-2885-2}, volume = {28}, year = {2002}, } @article{3998, abstract = {We present results on a two-step improvement of mesh quality in three-dimensional Delaunay triangulations. The first step refines the triangulation by inserting sinks and eliminates tetrahedra with large circumradius over shortest edge length ratio. The second step assigns weights to the vertices to eliminate slivers. Our experimental findings provide evidence for the practical effectiveness of sliver exudation.}, author = {Edelsbrunner, Herbert and Guoy, Damrong}, issn = {0177-0667}, journal = {Engineering with Computers}, number = {3}, pages = {229 -- 240}, publisher = {Springer}, title = {{An experimental study of sliver exudation}}, doi = {10.1007/s003660200020}, volume = {18}, year = {2002}, } @article{4000, abstract = {We present fast implementations of a hybrid algorithm for reporting box and cube intersections. Our algorithm initially takes a divide-and-conquer approach and switches to simpler algorithms for low numbers of boxes. We use our implementations as engines to solve problems about geometric primitives. We look at two such problems in the category of quality analysis of surface triangulations.}, author = {Zomorodian, Afra and Edelsbrunner, Herbert}, issn = {0218-1959}, journal = {International Journal of Computational Geometry and Applications}, number = {1-2}, pages = {143 -- 172}, publisher = {World Scientific Publishing}, title = {{Fast software for box intersections}}, doi = {10.1142/S0218195902000785}, volume = {12}, year = {2002}, } @inproceedings{4003, abstract = {The writhing number measures the global geometry of a closed space curve or knot. We show that this measure is related to the average winding number of its Gauss map. Using this relationship, we give an algorithm for computing the writhing number for a polygonal knot with n edges in time roughly proportional to n(1.6). We also implement a different, simple algorithm and provide experimental evidence for its practical efficiency.}, author = {Agarwal, Pankaj and Edelsbrunner, Herbert and Wang, Yusu}, booktitle = {Proceedings of the 13th annual ACM-SIAM symposium on Discrete algorithms}, isbn = {9780898715132}, location = {San Francisco, CA, USA}, pages = {791 -- 799}, publisher = {SIAM}, title = {{Computing the writhing number of a polygonal knot}}, year = {2002}, } @article{4139, abstract = {Pilot studies in England by Stopka and Macdonald revealed that allogrooming in the Old World wood mouse, Apodemus sylvaticus, is a commodity that males can trade for reproductive benefits with females. This study, which used a combination of field study and observations in experimental enclosures, revealed that specific experimental conditions such as group-size and sex-ratio manipulations have a significant effect on the pattern of allogrooming exchanged between individuals. Furthermore, females from the Czech population were more likely to associate with each other as revealed by the clustering of activity centers of females (i.e., as opposed to almost exclusive ranges in English populations), and also by the higher intensity of allogrooming exchanged between females (i.e., virtually lacking in the previous experiment with English mice). Therefore, geographic variation and specific social conditions seem to be important driving factors for allogrooming behavior. Together with changes in overall grooming patterns, allogrooming between males and females remained invariably asymmetrical over all four experimental groups (i.e., two conditions for each sex) in that males provided more allogrooming to females than they received from them.}, author = {Polechova, Jitka and Stopka, P.}, issn = {0008-4301}, journal = {Canadian Journal of Zoology}, number = {8}, pages = {1383 -- 1388}, publisher = {NRC Research Press}, title = {{Geometry of social relationships in the Old World wood mouse, Apodemus sylvaticus}}, doi = {10.1139/z02-128}, volume = {80}, year = {2002}, } @article{4148, abstract = {Members of the Wnt family have been implicated in a variety of developmental processes including axis formation, Patterning of the central nervous system and tissue morphogenesis. Recent studies have shown that a Wnt signalling pathway similar to that involved in the establishment of planar cell polarity in Drosophila regulates convergent extension movements during zebrafish and Xenopus gastrulation. This finding provides a good starting point to dissect the complex cell biology and genetic regulation of vertebrate gastrulation movements.}, author = {Tada, Masazumi and Concha, Miguel and Heisenberg, Carl-Philipp J}, issn = {1084-9521}, journal = {Seminars in Cell & Developmental Biology}, number = {3}, pages = {251 -- 260}, publisher = {Academic Press}, title = {{Non-canonical Wnt signalling and regulation of gastrulation movements}}, doi = {10.1016/S1084-9521(02)00052-6}, volume = {13}, year = {2002}, } @article{4194, abstract = {Cells at the anterior boundary of the neural plate (ANB) can induce telencephalic gene expression when transplanted to more posterior regions. Here, we identify a secreted Frizzled-related Wnt antagonist, Tic, that is expressed in ANB cells and can cell nonautonomously promote telencephalic gene expression in a concentration-dependent manner. Moreover, abrogation of Tlc function compromises telencephalic development. We also identify Wnt8b as a locally acting modulator of regional fate in the anterior neural plate and a likely target for antagonism by Tic. Finally, we show that tlc expression is regulated by signals that establish early antero-posterior and dorso-ventral ectodermal pattern. From these studies, we propose that local antagonism of Wnt activity within the anterior ectoderm is required to establish the telencephalon.}, author = {Houart, Corinne and Caneparo, Luca and Heisenberg, Carl-Philipp J and Barth, K Anukampa and Take Uchi, Masaya and Wilson, Stephen}, issn = {0896-6273}, journal = {Neuron}, number = {2}, pages = {255 -- 265}, publisher = {Elsevier}, title = {{Establishment of the telencephalon during gastrulation by local antagonism of Wnt signaling}}, doi = {10.1016/S0896-6273(02)00751-1}, volume = {35}, year = {2002}, } @article{4196, abstract = {During vertebrate gastrulation, large cellular rearrangements lead to the formation of the three germ layers, ectoderm, mesoderm and endoderm. Zebrafish offer many genetic and experimental advantages for studying vertebrate gastrulation movements. For instance, several mutants, including silberblick, knypek and trilobite, exhibit defects in morphogenesis during gastrulation. The identification of the genes mutated in these lines together with the analysis of the mutant phenotypes has provided new insights into the molecular and cellular mechanisms that underlie vertebrate gastrulation movements.}, author = {Heisenberg, Carl-Philipp J and Tada, Masazumi}, issn = {1084-9521}, journal = {Seminars in Cell & Developmental Biology}, number = {6}, pages = {471 -- 479}, publisher = {Academic Press}, title = {{Zebrafish gastrulation movements: bridging cell and developmental biology}}, doi = {10.1016/S1084952102001003}, volume = {13}, year = {2002}, } @article{4199, abstract = {Recent studies on vertebrate homologues of the van gogh/strabismus (vang/stbm) gene, a key player in planar cell polarity signalling in Drosophila, show that vang/stbm is involved in patterning and morphogenesis during vertebrate gastrulation where it modulates two distinct Wnt signals.}, author = {Heisenberg, Carl-Philipp J and Tada, Masazumi}, issn = {0960-9822}, journal = {Current Biology}, number = {4}, pages = {R126 -- R128}, publisher = {Cell Press}, title = {{Wnt signalling: A moving picture emerges from van gogh}}, doi = {10.1016/S0960-9822(02)00704-2}, volume = {12}, year = {2002}, } @article{4207, abstract = {Vertebrate homologues of the Strabismus/van Gogh (stbm/vang) gene have been implicated in patterning and morphogenesis during gastrulation. Recent work shows that stbm/vang is mutated in zebrafish trilobite mutants and that stbm/vang is required for morphogenesis but not patterning during zebrafish gastrulation.}, author = {Heisenberg, Carl-Philipp J}, issn = {0960-9822}, journal = {Current Biology}, number = {19}, pages = {R657 -- R659}, publisher = {Cell Press}, title = {{Wnt signalling: Refocusing on Strabismus}}, doi = {10.1016/S0960-9822(02)01160-0}, volume = {12}, year = {2002}, } @article{4209, abstract = {We have identified widerborst (wdb), a B' regulatory subunit of PP2A, as a conserved component of planar cell polarization mechanisms in both Drosophila and in zebrafish. In Drosophila, wdb acts at two steps during planar polarization of wing epithelial cells. It is required to organize tissue polarity proteins into proximal and distal cortical domains, thus determining wing hair orientation. It is also needed to generate the polarized membrane outgrowth that becomes the wing hair. Widerborst activates the catalytic subunit of PP2A and localizes to the distal side of a planar microtubule web that lies at the level of apical cell junctions. This suggests that polarized PP2A activation along the planar microtubule web is important for planar polarization. In zebrafish, two wdb homologs are required for convergent extension during gastrulation, supporting the conjecture that Drosophila planar cell polarization and vertebrate gastrulation movements are regulated by similar mechanisms.}, author = {Hannus, Michael and Feiguin, Fabian and Heisenberg, Carl-Philipp J and Eaton, Suzanne}, issn = {0950-1991}, journal = {Development}, number = {14}, pages = {3493 -- 3503}, publisher = {Company of Biologists}, title = {{Planar cell polarization requires Widerborst, a B′ regulatory subunit of protein phosphatase 2A}}, doi = {10.1242/dev.129.14.3493}, volume = {129}, year = {2002}, } @article{4258, abstract = {We studied the effect of multilocus balancing selection on neutral nucleotide variability at linked sites by simulating a model where diallelic polymorphisms are maintained at an arbitrary number of selected loci by means of symmetric overdominance. Different combinations of alleles define different genetic backgrounds that subdivide the population and strongly affect variability. Several multilocus fitness regimes with different degrees of epistasis and gametic disequilibrium are allowed. Analytical results based on a multilocus extension of the structured coalescent predict that the expected linked neutral diversity increases exponentially with the number of selected loci and can become extremely large. Our simulation results show that although variability increases with the number of genetic backgrounds that are maintained in the population, it is reduced by random fluctuations in the frequencies of those backgrounds and does not reach high levels even in very large populations. We also show that previous results on balancing selection in single-locus systems do not extend to the multilocus scenario in a straightforward way. Different patterns of linkage disequilibrium and of the frequency spectrum of neutral mutations are expected under different degrees of epistasis. Interestingly, the power to detect balancing selection using deviations from a neutral distribution of allele frequencies seems to be diminished under the fitness regime that leads to the largest increase of variability over the neutral case. This and other results are discussed in the light of data from the Mhc.}, author = {Navarro, Arcadio and Barton, Nicholas H}, issn = {0016-6731}, journal = {Genetics}, number = {2}, pages = {849 -- 863}, publisher = {Genetics Society of America}, title = {{The effects of multilocus balancing selection on neutral variability}}, doi = {10.1093/genetics/161.2.849}, volume = {161}, year = {2002}, } @article{4259, abstract = {We extend current multilocus models to describe the effects of migration, recombination, selection, and nonrandom mating on sets of genes in diploids with varied modes of inheritance, allowing us to consider the patterns of nuclear and cytonuclear associations (disequilibria) under various models of migration. We show the relationship between the multilocus notation recently presented by Kirkpatrick, Johnson, and Barton (developed from previous work by Barton and Turelli) and the cytonuclear parameterization of Asmussen, Arnold, and Avise and extend this notation to describe associations between cytoplasmic elements and multiple nuclear genes. Under models with sexual symmetry, both nuclear-nuclear and cytonuclear disequilibria are equivalent. They differ, however, in cases involving some type of sexual asymmetry, which is then reflected in the asymmetric inheritance of cytoplasmic markers. An example given is the case of different migration rates in males and females; simulations using 2, 3, 4, or 5 unlinked autosomal markers with a maternally inherited cytoplasmic marker illustrate how nuclear-nuclear and cytonuclear associations can be used to separately estimate female and male migration rates. The general framework developed here allows us to investigate conditions where associations between loci with different modes of inheritance are not equivalent and to use this nonequivalence to test for deviations from simple models of admixture. }, author = {Orive, Maria and Barton, Nicholas H}, issn = {0016-6731}, journal = {Genetics}, number = {3}, pages = {1469 -- 1485}, publisher = {Genetics Society of America}, title = {{Associations between cytoplasmic and nuclear loci in hybridizing populations}}, doi = {10.1093/genetics/162.3.1469}, volume = {162}, year = {2002}, } @article{4260, abstract = {We calculate the fixation probability of a beneficial allele that arises as the result of a unique mutation in an asexual population that is subject to recurrent deleterious mutation at rate U. Our analysis is an extension of previous works, which make a biologically restrictive assumption that selection against deleterious alleles is stronger than that on the beneficial allele of interest. We show that when selection against deleterious alleles is weak, beneficial alleles that confer a selective advantage that is small relative to U have greatly reduced probabilities of fixation. We discuss the consequences of this effect for the distribution of effects of alleles fixed during adaptation. We show that a selective sweep will increase the fixation probabilities of other beneficial mutations arising during some short interval afterward. We use the calculated fixation probabilities to estimate the expected rate of fitness improvement in an asexual population when beneficial alleles arise continually at some low rate proportional to U. We estimate the rate of mutation that is optimal in the sense that it maximizes this rate of fitness improvement. Again, this analysis relaxes the assumption made previously that selection against deleterious alleles is stronger than on beneficial alleles. }, author = {Johnson, Toby and Barton, Nicholas H}, issn = {0016-6731}, journal = {Genetics}, number = {1}, pages = {395 -- 411}, publisher = {Genetics Society of America}, title = {{The effect of deleterious alleles on adaptation in asexual populations}}, doi = {10.1093/genetics/162.1.395}, volume = {162}, year = {2002}, } @article{4261, abstract = {Until recently, it was impracticable to identify the genes that are responsible for variation in continuous traits, or to directly observe the effects of their different alleles. Now, the abundance of genetic markers has made it possible to identify quantitative trait loci (QTL) — the regions of a chromosome or, ideally, individual sequence variants that are responsible for trait variation. What kind of QTL do we expect to find and what can our observations of QTL tell us about how organisms evolve? The key to understanding the evolutionary significance of QTL is to understand the nature of inherited variation, not in the immediate mechanistic sense of how genes influence phenotype, but, rather, to know what evolutionary forces maintain genetic variability.}, author = {Barton, Nicholas H and Keightley, Peter}, issn = {1471-0056}, journal = {Nature Reviews Genetics}, pages = {11 -- 21}, publisher = {Nature Publishing Group}, title = {{Understanding quantitative genetic variation}}, doi = {10.1038/nrg700}, volume = {3}, year = {2002}, } @article{4262, abstract = {Natural populations are structured spatially into local populations and genetically into diverse ‘genetic backgrounds’ defined by different combinations of selected alleles. If selection maintains genetic backgrounds at constant frequency then neutral diversity is enhanced. By contrast, if background frequencies fluctuate then diversity is reduced. Provided that the population size of each background is large enough, these effects can be described by the structured coalescent process. Almost all the extant results based on the coalescent deal with a single selected locus. Yet we know that very large numbers of genes are under selection and that any substantial effects are likely to be due to the cumulative effects of many loci. Here, we set up a general framework for the extension of the coalescent to multilocus scenarios and we use it to study the simplest model, where strong balancing selection acting on a set of n loci maintains 2n backgrounds at constant frequencies and at linkage equilibrium. Analytical results show that the expected linked neutral diversity increases exponentially with the number of selected loci and can become extremely large. However, simulation results reveal that the structured coalescent approach breaks down when the number of backgrounds approaches the population size, because of stochastic fluctuations in background frequencies. A new method is needed to extend the structured coalescent to cases with large numbers of backgrounds.}, author = {Barton, Nicholas H and Navarro, Arcadio}, issn = {0016-6723}, journal = {Genetical Research}, number = {2}, pages = {129 -- 139}, publisher = {Cambridge University Press}, title = {{Extending the coalescent to multilocus systems: the case of balancing selection}}, doi = {10.1017/S0016672301005493}, volume = {79}, year = {2002}, }