@inproceedings{11803, abstract = {We present the first fully dynamic algorithm for maintaining a minimum spanning tree in time o(√n) per operation. To be precise, the algorithm uses O(n 1/3 log n) amortized time per update operation. The algorithm is fairly simple and deterministic. An immediate consequence is the first fully dynamic deterministic algorithm for maintaining connectivity and, bipartiteness in amortized time O(n 1/3 log n) per update, with O(1) worst case time per query.}, author = {Henzinger, Monika H and King, Valerie}, booktitle = {24th International Colloquium on Automata, Languages and Programming}, isbn = {9783540631651}, issn = {1611-3349}, location = {Bologna, Italy}, pages = {594–604}, publisher = {Springer Nature}, title = {{Maintaining minimum spanning trees in dynamic graphs}}, doi = {10.1007/3-540-63165-8_214}, volume = {1256}, year = {1997}, } @article{11849, abstract = {This paper describes the DIGlTAL Continuous Profiling Infrastmcture, a sampling-based profiling system designed to run continuously on production systems. The system supports multiprocessors, works on unmodified executable& and collects profiles for entire systems, including user programs, shared libraries, and the operating system kernel. Samples are collected at a high rate (over 5200 samples/secper333-MHz processor), yet with low overhead (l-3% slowdown for most workloads). Analysis tools supplied with the profiling system use the sample data to produce an accurate accounting, down to the level of pipeline stalls incurred by individual instructions, of where time is being spent. When instructions incur stalls, the tools identify possible reasons, such as cache misses, branch mispredictions, and functional unit contention. The fine-grained instruction-level analysis guides users and automated optimizers to the causes of performance problems and provides important insights for fixing them. }, author = {Anderson, Jennifer M. and Berc, Lance M. and Dean, Jeffrey and Ghemawat, Sanjay and Henzinger, Monika H and Leung, Shun-Tak A. and Sites, Richard L. and Vandevoorde, Mark T. and Waldspurger, Carl A. and Weihl, William E.}, issn = {0163-5980}, journal = {ACM SIGOPS Operating Systems Review}, number = {5}, pages = {1--14}, publisher = {Association for Computing Machinery}, title = {{Continuous profiling: Where have all the cycles gone?}}, doi = {10.1145/269005.266637}, volume = {31}, year = {1997}, } @article{11883, abstract = {In dynamic graph algorithms the following provide-or-bound problem has to be solved quickly: Given a set S containing a subset R and a way of generating random elements from S testing for membership in R, either (i) provide an element of R, or (ii) give a (small) upper bound on the size of R that holds with high probability. We give an optimal algorithm for this problem. This algorithm improves the time per operation for various dynamic graph algorithms by a factor of O(log n). For example, it improves the time per update for fully dynamic connectivity from O(log3n) to O(log2n).}, author = {Henzinger, Monika H and Thorup, Mikkel}, issn = {1098-2418}, journal = {Random Structures and Algorithms}, number = {4}, pages = {369--379}, publisher = {Wiley}, title = {{Sampling to provide or to bound: With applications to fully dynamic graph algorithms}}, doi = {10.1002/(sici)1098-2418(199712)11:4<369::aid-rsa5>3.0.co;2-x}, volume = {11}, year = {1997}, } @article{3482, abstract = {AMPA- and NMDA-type glutamate receptors (AMPARs and NMDARs) mediate excitatory synoptic transmission in the basal ganglia and may contribute to excitotoxic injury. We investigated the functional properties of AMPARs and NMDARs expressed by six main types of basal ganglia neurons in acute rat brain slices (principal neurons and cholinergic interneurons of striatum, GABAergic and dopaminergic neurons of substantia nigra, globus pallidus neurons, and subthalamic nucleus neurons) using fast application of glutamate to nucleated and outside-out membrane patches, AMPARs in different types of basal ganglia neurons were functionally distinct. Those expressed in striatal principal neurons exhibited the slowest gating (desensitization time constant τ = 11.5 msec, 1 mM glutamate, 22°C), whereas those in striatal cholinergic interneurons showed the fastest gating (desensitization time constant τ = 3.6 msec). The lowest Ca2+ permeability of AMPARs was observed in nigral dopaminergic neurons (P(CA)/P(NA) = 0.10), whereas the highest Ca2+ permeability was found in subthalamic nucleus neurons (P(Ca)/P(Na) = 1.17). NMDARs of different types of basal ganglia neurons were less variable in their functional properties; those expressed in nigral dopaminergic neurons exhibited the slowest gating (deactivation time constant of predominant fast component τ1 150 msec, 100 μM glutamate), and those of globus pallidus neurons showed the fastest gating (τ1 = 67 msec). The Mg2+ block of NMDARs was similar; the average chord conductance ratio g(+60mv)/g(+40mV) was 0.18-0.22 in 100 μM external Mg2+. Hence, AMPARs expressed in different types of basal ganglia neurons are markedly diverse, whereas NMDARs are less variable in functional properties that are relevant for excitatory synoptic transmission and neuronal vulnerability.}, author = {Götz, Thomas and Kraushaar, Udo and Geiger, Jörg and Lubke, Joachim and Berger, Thomas and Jonas, Peter M}, issn = {0270-6474}, journal = {Journal of Neuroscience}, number = {1}, pages = {204 -- 215}, publisher = {Society for Neuroscience}, title = {{Functional properties of AMPA and NMDA receptors expressed in identified types of basal ganglia neurons}}, doi = {10.1523/JNEUROSCI.17-01-00204.1997}, volume = {17}, year = {1997}, } @article{3483, abstract = {The main excitatory pathway of the hippocampal formation is controlled by a network of morphologically distinct populations of GABAergic interneurons. Here we describe a novel type of GABAergic interneuron located in the outer molecular layer (OML) of the rat dentate gyrus with a long- range forward projection from the dentate gyrus to the subiculum across the hippocampal fissure, OML interneurons were recorded in hippocampal slices by using the whole-cell patch-clamp configuration. During recording, cells were filled with biocytin for subsequent light and electron microscopic analysis. Neurons projecting to the subiculum were distributed throughout the entire OML. They had round or ovoid somata and a multipolar dendritic morphology. Two axonal domains could be distinguished: an extensive, tangential distribution within the OML and a long-range vertical and tangential projection to layer 1 and stratum pyramidale of the subiculum. Symmetric synaptic contacts were established by these interneurons on dendritic shafts in the OML and subiculum. OML interneurons were characterized physiologically by short action potential duration and marked afterhyperpolarization that followed the spike. On sustained current injection, they generated high- frequency (up to 130 Hz, 34°C) trains of action potentials with only little adaptation. In situ hybridization and single-call RT-PCR analysis for GAD67 mRNA confirmed the GABAergic nature of OML interneurons. GABAergic interneurons in the OML projecting to the subiculum connect the input and output regions of the hippocampus. Hence, they could mediate long-range feed- forward inhibition and may participate in an oscillating cross-regional interneuron network that may synchronize the activity of spatially distributed principal neurons in the dentate gyrus and the subiculum.}, author = {Ceranik, Katya and Bender, Roland and Geiger, Jörg and Monyer, Hannah and Jonas, Peter M and Frotscher, Michael and Lubke, Joachim}, issn = {0270-6474}, journal = {Journal of Neuroscience}, number = {14}, pages = {5380 -- 5394}, publisher = {Society for Neuroscience}, title = {{A novel type of GABAergic interneuron connecting the input and the output regions of the hippocampus.}}, doi = {10.1523/JNEUROSCI.17-14-05380.1997}, volume = {17}, year = {1997}, } @article{3484, abstract = {Glutamatergic transmission at a principal neuroninterneuron synapse was investigated by dual whole-cell patch-clamp recording in rat hippocampal slices combined with morphological analysis. Evoked EPSPs with rapid time course (half duration ≃ 4 ms; 34°C) were generated at multiple synaptic contacts established on the interneuron dendrites close to the soma. The underlying postsynaptic conductance change showed a submillisecond rise and decay, due to the precise timing of glutamate release and the rapid deactivation of the postsynaptic AMPA receptors. Simulations based on a compartmental model of the interneuron indicated that the rapid postsynaptic conductance change determines the shape and the somatodendritic integration of EPSPs, thus enabling interneurons to detect synchronous principal neuron activity.}, author = {Geiger, Jörg and Lubke, Joachim and Roth, Arnd and Frotscher, Michael and Jonas, Peter M}, issn = {0896-6273}, journal = {Neuron}, number = {6}, pages = {1009 -- 1023}, publisher = {Elsevier}, title = {{Submillisecond AMPA receptor-mediated signaling at a principal neuron-interneuron synapse}}, doi = {10.1016/S0896-6273(00)80339-6}, volume = {18}, year = {1997}, } @article{3485, abstract = {1. GABAergic interneurones differ from glutamatergic principal neurones in their ability to discharge high-frequency trains of action potentials without adaptation. To examine whether Na+ channel gating contributed to these differences, Na+ currents were recorded in nucleated patches from interneurones (dentate gyrus basket cells, BCs) and principal neurones (CA1 pyramidal cells, PCs) of rat hippocampal slices. 2. The voltage dependence of Na+ channel activation in BCs and PCs was similar. The slope factors of the activation curves, fitted with Boltzmann functions raised to the third power, were 11.5 and 11.8 mV, and the mid-point potentials were -25.1 and -23.9 mV, respectively. 3. Whereas the time course of Na+ channel activation (-30 to +40 mV) was similar, the deactivation kinetics (-100 to -40 mV) were faster in BCs than in PCs (tail current decay time constants, 0.13 and 0.20 ms, respectively, at -40 mV). 4. Na+ channels in BCs and PCs differed in the voltage dependence of inactivation. The slope factors of the steady-state inactivation curves fitted with Boltzmann functions were 6.7 and 10.7 mV, and the mid-point potentials were -58.3 and -62.9 mV, respectively. 5. The onset of Na+ channel inactivation at -55 mV was slower in BC's than in PCs; the inactivation time constants were 18.6 and 9.3 ms, respectively. At more positive potentials the differences in inactivation onset were smaller. 6. The time course of recovery of Na+ channels from inactivation induced by a 30 ms pulse was fast and mono-exponential (τ = 2.0 ms at -120 mV) in BCs, whereas it was slower and biexponential in PCs (τ1 = 2.0 ms and τ2 = 133 ms; amplitude contribution of the slow component, 15%). 7. We conclude that Na+ channels of BCs and PCs differ in gating properties that contribute to the characteristic action potential patterns of the two types of neurones.}, author = {Martina, Marco and Jonas, Peter M}, issn = {0022-3751}, journal = {Journal of Physiology}, number = {3}, pages = {593 -- 603}, publisher = {Wiley-Blackwell}, title = {{Functional differences in Na+ channel gating between fast-spiking interneurones and principal neurones in rat hippocampus}}, doi = {10.1111/j.1469-7793.1997.593ba.x}, volume = {505}, year = {1997}, } @article{3486, abstract = {1. Dendritic patch-clamp recordings were obtained from mitral cells in rat olfactory bulb slices, up to 350 μm from the soma. Simultaneous dendritic and somatic whole-cell recordings indicated that action potentials (APs) evoked by somatic or dendritic current injection were initiated near the soma. Both the large amplitude (100.7 ± 1.1 mV) and the short duration (1.38 ± 0.07 ms) of the AP were maintained as the AP propagated back into the primary mitral cell dendrites. 2. Outside-out patches isolated from mitral cell dendrites contained voltage-gated Na+ channels (peak conductance density, 90 pS μm-2 at -10 mV). When an AP was used as a somatic voltage-clamp command in the presence of 1 μM tetrodotoxin (TTX), the amplitude of the dendritic potential was attenuated to 48 ± 14 mV. This shows that dendritic Na+ channels support the active back-propagation of APs. 3. Dendritic patches contained voltage-gated K+ channels with high density (conductance density, 513 pS μm-2 at 30 mV. Dendritic K+ currents were reduced to 35% by 1 mM external tetraethylammonium chloride (TEACl). When an AP was used as a somatic voltage clamp command in the presence of TEACl, the dendritic potential was markedly prolonged. This indicates that dendritic K+ channels mediate the fast repolarization of dendritic APs. 4. We conclude that voltage gated Na+ and K+ channels support dendritic APs with large amplitudes and short durations that may trigger fast transmitter release at dendrodendritic synapses in the olfactory bulb.}, author = {Bischofberger, Joseph and Jonas, Peter M}, issn = {0022-3751}, journal = {Journal of Physiology}, number = {Pt 2}, pages = {359 -- 365}, publisher = {Wiley-Blackwell}, title = {{Action potential propagation into the presynaptic dendrites of rat mitral cells}}, doi = {10.1111/j.1469-7793.1997.359be.x}, volume = {504}, year = {1997}, } @article{3541, abstract = {The contribution of the various hippocampal regions to the maintenance of epileptic activity, induced by stimulation of the perforant path or commissural system, was examined in the awake rat. Combination of multiple-site recordings with silicon probes, current source density analysis and unit recordings allowed for a high spatial resolution of the field events. Following perforant path stimulation, seizures began in the dentate gyrus, followed by events in the CA3-CA1 regions. After commissural stimulation, rhythmic bursts in the CA3-CA1 circuitry preceded the activation of the dentate gyrus. Correlation of events in the different subregions indicated that the sustained rhythmic afterdischarge (2-6 Hz) could not be explained by a cycle-by-cycle excitation of principal cell populations in the hippocampal-entorhinal loop. The primary afterdischarge always terminated in the CA1 region, followed by the dentate gyrus, CA3 region and the entorhinal cortex. The duration and pattern of the hippocampal afterdischarge was essentially unaffected by removal of the entorhinal cortex. The emergence of large population spike bursts coincided with a decreased discharge of interneurons in both CAI and hilar regions. The majority of hilar interneurons displayed a strong amplitude decrement prior to the onset of population spike phase of the afterdischarge. These findings suggest that (i) afterdischarges can independently arise in the CA3-CA1 and entorhinal-dentate gyrus circuitries, (ii) reverberation of excitation in the hippocampal-entorhinal loop is not critical for the maintenance of afterdischarges and (iii) decreased activity of the interneuronal network may release population bursting of principal cells. }, author = {Bragin, Anatol and Csicsvari, Jozsef L and Penttonen, Markku and Buzsáki, György}, issn = {0306-4522}, journal = {Neuroscience}, number = {4}, pages = {1187 -- 1203}, publisher = {Elsevier}, title = {{Epileptic afterdischarge in the hippocampal-entorhinal system: Current source density and unit studies}}, doi = {10.1016/S0306-4522(96)00446-0}, volume = {76}, year = {1997}, } @article{3630, abstract = {This paper derives the long-term effective size, Ne, for a general model of population subdivision, allowing for differential deme fitness, variable emigration and immigration rates, extinction, colonization, and correlations across generations in these processes. We show that various long-term measures of Ne are equivalent. The effective size of a metapopulation can be expressed in a variety of ways. At a demographic equilibrium, Ne can be derived from the demography by combining information about the ultimate contribution of each deme to the future genetic make-up of the population and Wright's FST's. The effective size is given by Ne = 1/(1 + var (upsilon) ((1 - FST)/Nin), where n is the number of demes, theta i is the eventual contribution of individuals in deme i to the whole population (scaled such that sigma theta i = n), and < > denotes an average weighted by theta i. This formula is applied to a catastrophic extinction model (where sites are either empty or at carrying capacity) and to a metapopulation model with explicit dynamics, where extinction is caused by demographic stochasticity and by chaos. Contrary to the expectation from the standard island model, the usual effect of population subdivision is to decrease the effective size relative to a panmictic population living on the same resource.}, author = {Whitlock, Michael and Barton, Nicholas H}, issn = {0016-6731}, journal = {Genetics}, number = {1}, pages = {427 -- 441}, publisher = {Genetics Society of America}, title = {{The effective size of a subdivided population}}, doi = {10.1093/genetics/146.1.427}, volume = {146}, year = {1997}, } @article{3631, abstract = {In spatially heterogeneous environments, natural selection for maintenance of adaptation to habitats that contribute little to the population's reproduction is weak. In this paper we model a mechanism that can result in loss of fitness in such marginal habitats, and thus lead to specialisation on the main habitat. It involves accumulation of mutations that are deleterious in the marginal habitat but neutral or nearly so in the main habitat (mutations deleterious in the main habitat and neutral in the marginal habitat have a negligible influence). If the contribution of the marginal habitat to total reproduction in the absence of the mutations is less than a threshold value, selection is too weak to counter accumulation of such mutations. A positive feedback then results in loss of fitness in the marginal habitat. This mechanism does not require antagonistic pleiotropy in adaptation to different habitats, although antagonistic pleiotropy facilitates the mutational collapse of fitness in the marginal habitat. We suggest that deleterious mutations with habitat-specific expression may play a role in the evolution of ecological specialisation and promote evolutionary conservatism of ecological niches.}, author = {Kawecki, Tadeusz and Barton, Nicholas H and Fry, James}, issn = {1010-061X}, journal = {Journal of Evolutionary Biology}, number = {3}, pages = {407 -- 430}, publisher = {Wiley-Blackwell}, title = {{Mutational collapse of fitness in marginal habitats and the evolution of ecological specialisation}}, doi = {10.1046/j.1420-9101.1997.10030407.x}, volume = {10}, year = {1997}, } @article{3632, abstract = {An important but controversial class of hypotheses concerning the evolution of female preferences for extreme male mating displays involves 'indirect selection.' Even in the absence of direct fitness effects, preference for males with high overall fitness can spread via a genetic correlation that develops between preference alleles and high fitness genotypes. Here we develop a quantitative expression for the force of indirect selection that (i) applies to any female mating behavior, (ii) is relatively insensitive to the underlying genetics, and (iii) is based on measurable quantities. In conjunction with the limited data now available, it suggests that the evolutionary force generated by indirect selection on preferences is weak in absolute terms. This finding raises the possibility that direct selection on preference genes may often be more important than indirect selection, but more data on the quantities identified by our model and on direct selection are needed to decide the question.}, author = {Kirkpatrick, Mark and Barton, Nicholas H}, issn = {0027-8424}, journal = {PNAS}, number = {4}, pages = {1282 -- 1286}, publisher = {National Academy of Sciences}, title = {{The strength of indirect selection on female mating preferences}}, doi = {10.1073/pnas.94.4.1282}, volume = {94}, year = {1997}, } @article{3633, abstract = {Gene flow from the center of a species' range can stymie adaptation at the periphery and prevent the range from expanding outward. We study this process using simple models that track both demography and the evolution of a quantitative trait in a population that is continuously distributed in space. Stabilizing selection acts on the trait and favors an optimum phenotype that changes linearly across the habitat. One of three outcomes is possible: the species will become extinct, expand to fill all of the available habitat, or be confined to a limited range in which it is significantly adapted to allow population growth. When the environment changes rapidly in space, increased migration inhibits local adaptation and so decreases the species' total population size. Gene flow can cause enough maladaptation that the peripheral half of a species' range acts as an demographic sink. The trait's genetic variance has little effect on species persistence or the size of the range when gene flow is sufficiently strong to keep population densities far below the carrying capacity throughout the range, but it can increase the range width and population size of an abundant species. Under some conditions, a small parameter change can dramatically shift the balance between gene flow and local adaptation, allowing a species with a limited range to suddenly expand to fill all the available habitat.}, author = {Kirkpatrick, Mark and Barton, Nicholas H}, issn = {0003-0147}, journal = {American Naturalist}, number = {1}, pages = {1 -- 23}, publisher = {University of Chicago Press}, title = {{Evolution of a species' range}}, doi = {10.1086/286054}, volume = {150}, year = {1997}, } @article{4018, abstract = {Given a subspace X subset of or equal to R-d and a finite set S subset of or equal to R-d, we introduce the Delaunay complex, D-X, restricted by X. Its simplices are spanned by subsets T subset of or equal to S for which the common intersection of Voronoi cells meets X in a non-empty set. By the nerve theorem, boolean OR D-X and X are homotopy equivalent if all such sets are contractible. This paper proves a sufficient condition for boolean OR D-X and X be homeomorphic.}, author = {Edelsbrunner, Herbert and Shah, Nimish}, issn = {0925-7721}, journal = {International Journal of Computational Geometry & Applications}, number = {4}, pages = {365 -- 378}, publisher = {World Scientific Publishing}, title = {{Triangulating topological spaces}}, doi = {10.1142/S0218195997000223}, volume = {7}, year = {1997}, } @article{4021, abstract = {A homeomorphism from R-2 to itself distorts metric quantities, such as distance and area. We describe an algorithm that constructs homeomorphisms with prescribed area distortion. Such homeomorphisms can be used to generate cartograms, which are geographic maps purposely distorted so their area distributions reflects a variable different from area, as for example population density. The algorithm generates the homeomorphism through a sequence of local piecewise linear homeomorphic changes. Sample results produced by the preliminary implementation of the method are included.}, author = {Edelsbrunner, Herbert and Waupotitsch, Roman}, issn = {0925-7721}, journal = {Computational Geometry: Theory and Applications}, number = {5-6}, pages = {343 -- 360}, publisher = {Elsevier}, title = {{A combinatorial approach to cartograms}}, doi = {10.1016/S0925-7721(96)00006-5}, volume = {7}, year = {1997}, } @article{4022, abstract = {A halving hyperplane of a set S of n points in R(d) contains d affinely independent points of S so that equally many of the points off the hyperplane lie in each of the two half-spaces. We prove bounds on the number of halving hyperplanes under the condition that the ratio of largest over smallest distance between any two points is at most delta n(1/d), delta some constant. Such a set S is called dense. In d = 2 dimensions the number of halving lines for a dense set can be as much as Omega(n log n), and it cannot exceed O (n(5/4)/log* n). The upper bound improves over the current best bound of O (n(3/2)/log* n) which holds more generally without any density assumption. In d = 3 dimensions we show that O (n(7/3)) is an upper bound on the number of halving planes for a dense set, The proof is based on a metric argument that can be extended to d greater than or equal to 4 dimensions, where it leads to O (n(d-2/d)) as an upper bound for the number of halving hyperplanes.}, author = {Edelsbrunner, Herbert and Valtr, Pavel and Welzl, Emo}, issn = {0179-5376}, journal = {Discrete & Computational Geometry}, number = {3}, pages = {243 -- 255}, publisher = {Springer}, title = {{Cutting dense point sets in half}}, doi = {10.1007/PL00009291}, volume = {17}, year = {1997}, } @article{4023, abstract = {Let B be a finite pseudodisk collection in the plane. By the principle of inclusion-exclusion, the area or any other measure of the union is [GRAPHICS] We show the existence of a two-dimensional abstract simplicial complex, X subset of or equal to 2(B), so the above relation holds even if X is substituted for 2(B). In addition, X can be embedded in R(2) SO its underlying space is homotopy equivalent to int Boolean OR B, and the frontier of X is isomorphic to the nerve of the set of boundary contributions.}, author = {Edelsbrunner, Herbert and Ramos, Edgar}, issn = {0179-5376}, journal = {Discrete & Computational Geometry}, number = {3}, pages = {287 -- 306}, publisher = {Springer}, title = {{Inclusion-exclusion complexes for pseudodisk collections}}, doi = {10.1007/PL00009295}, volume = {17}, year = {1997}, } @article{4174, abstract = {The epiphysial region of the dorsal diencephalon is the first site at which neurogenesis occurs in the roof of the zebrafish forebrain. We show that the homeobox containing gene floating head (flh) is required for neurogenesis to proceed in the epiphysis. In flh(-) embryos, the first few epiphysial neurons are generated, but beyond the 18 somite stage, neuronal production ceases. In contrast, in masterblind(-) (mbl(-)) embryos, epiphysial neurons are generated throughout the dorsal forebrain. We show that mbl is required to prevent the expression of flh in dorsal forebrain cells rostral to the epiphysis. Furthermore, epiphysial neurons are not ectopically induced in mbl(-)/flh(-) embryos, demonstrating that the epiphysial phenotype of mbl(-) embryos is mediated by ectopic Flh activity. We propose a role for Flh in linking the signaling pathways that regulate regional patterning to the signaling pathways that regulate neurogenesis.}, author = {Masai, Ichiro and Heisenberg, Carl-Philipp J and Barth, K Anukampa and Macdonald, Rachel and Adamek, Sylwia and Wilson, Stephen}, issn = {0896-6273}, journal = {Neuron}, number = {1}, pages = {43 -- 57}, publisher = {Elsevier}, title = {{Floating head and masterblind regulate neuronal patterning in the roof of the forebrain}}, doi = {10.1016/S0896-6273(01)80045-3}, volume = {18}, year = {1997}, } @article{4201, abstract = {In zebrafish, as in other vertebrates, an initially singular eye held within the neural plate has to split during morphogenesis to allow the development of two separated eyes. It has been suggested that anterior progression of midline tissue within the neural plate is involved in the bilateralization of the eye held. Mutations in the recently identified silberblick (slb) gene cause an incomplete separation of the eyes. During gastrulation and early somitogenesis, the ventral midline of the central nervous system (CNS) together with the underlying axial mesendoderm is shortened and broadened in slb embryos. While in wild-type embryos the ventral CNS midline extends to the anterior limit of the neural plate at the end of gastrulation, there is a gap between the anterior tip of the ventral CNS midline and the anterior edge of the neural plate in slb. To investigate the cause for the shortening of the ventral CNS midline in slb we determined the fate of labeled ventral CNS midline cells in wild-type and slb embryos at different stages of development. In slb, anterior migration of ventral CNS midline cells is impaired, which indicates that migration of these cells is needed for elongation of the ventral CNS midline. The anterior shortening of the ventral CNS midline in slb leads to medial instead of bilateral induction of optic stalks followed by a partial fusion of the eyes at later developmental stages. The analysis of the sIb phenotype indicates that anterior migration of midline cells within the neural plate is required for proper induction and subsequent bilateralization of an initially singular eye field. These findings may therefore provide a starting point in elucidating the role of neural plate morphogenesis in positioning of the eyes. (C) 1997 Academic Press.}, author = {Heisenberg, Carl-Philipp J and Nüsslein Volhard, Christiane}, issn = {0012-1606}, journal = {Developmental Biology}, number = {1}, pages = {85 -- 94}, publisher = {Elsevier}, title = {{The function of silberblick in the positioning of the eye anlage in the zebrafish embryo}}, doi = {10.1006/dbio.1997.8511}, volume = {184}, year = {1997}, } @inbook{4284, abstract = {The evolutionary processes responsible for adaptation and speciation on islands differ in several ways from those on the mainland. Most attention has been given to the random genetic drift that arises when a population is founded from just a few colonizing genomes. Theoretical obstacles to ‘founder effect speciation’ are discussed, together with recent proposals for avoiding them. It is argued that although certain kinds of epistasis can facilitate the evolution of strong reproductive isolation, this favours divergence by selection as much as by random drift.}, author = {Barton, Nicholas H}, booktitle = {Evolution on islands}, isbn = {9780198501718}, pages = {102 -- 123}, publisher = {Oxford University Press}, title = {{Natural selection and random genetic drift as causes of evolution on islands}}, doi = {10.1098/rstb.1996.0073}, year = {1997}, }