bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Complexity of Computing and Learning with Multiplicative Neural Networks
Authors: Schmitt Michael
Published: July 2002

In a great variety of neuron models, neural inputs are combined using the summing operation. We introduce the concept of multiplicative neural networks that contain units that multiply their inputs instead of summing them and thus allow inputs to interact nonlinearly. The class of multiplicative neural networks comprises such widely known and well-studied network types as higher-order networks and product unit networks.

We investigate the complexity of computing and learning for multiplicative neural networks. In particular, we derive upper and lower bounds on the Vapnik-Chervonenkis (VC) dimension and the pseudo-dimension for various types of networks with multiplicative units. As the most general case, we consider feedforward networks consisting of product and sigmoidal units, showing that their pseudo-dimension is bounded from above by a polynomial with the same order of magnitude as the currently best-known bound for purely sigmoidal networks. Moreover, we show that this bound holds even when the unit type, product or sigmoidal, may be learned. Crucial for these results are calculations of solution set components bounds for new network classes. As to lower bounds, we construct product unit networks of fixed depth with super-linear VC dimension.

For sigmoidal networks of higher order, we establish polynomial bounds that, in contrast to previous results, do not involve any restriction of the network order. We further consider various classes of higher-order units, also known as sigma-pi units, that are characterized by connectivity constraints. In terms of these, we derive some asymptotically tight bounds.

Multiplication plays an important role in both neural modeling of biological behavior and computing and learning with artificial neural networks. We briefly survey research in biology and in applications where multiplication is considered an essential computational element. The results we present here provide new tools for assessing the impact of multiplication on the computational power and the learning capabilities of neural networks.
Adjusting the Outputs of a Classifier to New aPrioriProbabilities: A Simple Procedure
Authors: Saerens Marco , Latinne Patrice , Decaestecker Christine
Published: July 2002

It sometimes happens (for instance in case control studies) that a classifier is trained on a data set that does not reflect the true a priori probabilities of the target classes on real-world data. This may have a negative effect on the classification accuracy obtained on the real-world data set, especially when the classifier's decisions are based on the a posteriori probabilities of class membership. Indeed, in this case, the trained classifier provides estimates of the a posteriori probabilities that are not valid for this real-world data set (they rely on the a priori probabilities of the training set). Applying the classifier as is (without correcting its outputs with respect to these new conditions) on this new data set may thus be suboptimal. In this note, we present a simple iterative procedure for adjusting the outputs of the trained classifier with respect to these new a priori probabilities without having to refit the model, even when these probabilities are not known in advance. As a by-product, estimates of the new a priori probabilities are also obtained. This iterative algorithm is a straightforward instance of the expectation-maximization (EM) algorithm and is shown to maximize the likelihood of the new data. Thereafter, we discuss a statistical test that can be applied to decide if the a priori class probabilities have changed from the training set to the real-world data. The procedure is illustrated on different classification problems involving a multilayer neural network, and comparisons with a standard procedure for a priori probability estimation are provided. Our original method, based on the EM algorithm, is shown to be superior to the standard one for a priori probability estimation. Experimental results also indicate that the classifier with adjusted outputs always performs better than the original one in terms of classification accuracy, when the a priori probability conditions differ from the training set to the real-world data. The gain in classification accuracy can be significant.
Multiplicative Synaptic Normalization and a Nonlinear Hebb Rule Underlie a Neurotrophic Model of Competitive Synaptic Plasticity
Authors: Elliott T. , Shadbolt N. R.
Published: July 2002

Synaptic normalization is used to enforce competitive dynamics in many models of developmental synaptic plasticity. In linear and semilinear Hebbian models, multiplicative synaptic normalization fails to segregate afferents whose activity patterns are positively correlated. To achieve this, the biologically problematic device of subtractive synaptic normalization must be used instead. Our own model of competition for neurotrophic support, which can segregate positively correlated afferents, was developed in part in an attempt to overcome these problems by removing the need for synaptic normalization altogether. However, we now show that the dynamics of our model decompose into two decoupled subspaces, with competitive dynamics being implemented in one of them through a nonlinear Hebb rule and multiplicative synaptic normalization. This normalization is “emergent” rather than imposed. We argue that these observations permit biologically plausible forms of synaptic normalization to be viewed as abstract and general descriptions of the underlying biology in certain scaleless models of synaptic plasticity.
Approximate Statistical Tests for Comparing Supervised Classification Learning Algorithms
Authors: Dietterich Thomas G.
Published: July 2002

This article reviews five approximate statistical tests for determining whether one learning algorithm outperforms another on a particular learning task. These test sare compared experimentally to determine their probability of incorrectly detecting a difference when no difference exists (type I error). Two widely used statistical tests are shown to have high probability of type I error in certain situations and should never be used: a test for the difference of two proportions and a paired-differences t test based on taking several random train-test splits. A third test, a paired-differences t test based on 10-fold cross-validation, exhibits somewhat elevated probability of type I error. A fourth test, McNemar's test, is shown to have low type I error. The fifth test is a new test, 5 × 2 cv, based on five iterations of twofold cross-validation. Experiments show that this test also has acceptable type I error. The article also measures the power (ability to detect algorithm differences when they do exist) of these tests. The cross-validated t test is the most powerful. The 5×2 cv test is shown to be slightly more powerful than McNemar's test. The choice of the best test is determined by the computational cost of running the learning algorithm. For algorithms that can be executed only once, Mc-Nemar's test is the only test with acceptable type I error. For algorithms that can be executed 10 times, the 5 × 2 cv test is recommended, because it is slightly more powerful and because it directly measures variation due to the choice of training set.
Probability Density Estimation Using Entropy Maximization
Authors: Miller Gad , Horn David
Published: July 2002

We propose a method for estimating probability density functions and conditional density functions by training on data produced by such distributions. The algorithm employs new stochastic variables that amount to coding of the input, using a principle of entropy maximization. It is shown to be closely related to the maximum likelihood approach. The encoding step of the algorithm provides an estimate of the probability distribution. The decoding step serves as a generative mode, producing an ensemble of data with the desired distribution. The algorithm is readily implemented by neural networks, using stochastic gradient ascent to achieve entropy maximization.
Computation with Infinite Neural Networks
Authors: Williams Christopher K. I.
Published: July 2002

For neural networks with a wide class of weight priors, it can be shown that in the limit of an infinite number of hidden units, the prior over functions tends to a gaussian process. In this article, analytic forms are derived for the covariance function of the gaussian processes corresponding to networks with sigmoidal and gaussian hidden units. This allows predictions to be made efficiently using networks with an infinite number of hidden units and shows, somewhat paradoxically, that it may be easier to carry out Bayesian prediction with infinite networks rather than finite ones.
Bayesian Radial Basis Functions of Variable Dimension
Authors: Holmes C. C. , Mallick B. K.
Published: July 2002

A Bayesian framework for the analysis of radial basis functions (RBF) is proposed that accommodates uncertainty in the dimension of the model. A distribution is defined over the space of all RBF models of a given basis function, and posterior densities are computed using reversible jump Markov chain Monte Carlo samplers (Green, 1995). This alleviates the need to select the architecture during the modeling process. The resulting networks are shown to adjust their size to the complexity of the data.
Backward Projections in the Cerebral Cortex: Implications for Memory Storage
Authors: Renart Alfonso , Parga Néstor , Rolls Edmund T.
Published: July 2002

Cortical areas are characterized by forward and backward connections between adjacent cortical areas in a processing stream. Within each area there are recurrent collateral connections between the pyramidal cells. We analyze the properties of this architecture for memory storage and processing. Hebb-like synaptic modifiability in the connections and attractor states are incorporated. We show the following: (1) The number of memories that can be stored in the connected modules is of the same order of magnitude as the number that can be stored in any one module using the recurrent collateral connections, and is proportional to the number of effective connections per neuron. (2) Cooperation between modules leads to a small increase in memory capacity. (3) Cooperation can also help retrieval in a module that is cued with a noisy or incomplete pattern. (4) If the connection strength between modules is strong, then global memory states that reflect the pairs of patterns on which the modules were trained together are found. (5) If the intermodule connection strengths are weaker, then separate, local memory states can exist in each module. (6) The boundaries between the global and local retrieval states, and the nonretrieval state, are delimited. All of these properties are analyzed quantitatively with the techniques of statistical physics.
Comparison of Approximate Methods for Handling Hyperparameters
Authors: MacKay David J. C.
Published: July 2002

I examine two approximate methods for computational implementation of Bayesian hierarchical models, that is, models that include unknown hyperparameters such as regularization constants and noise levels. In the evidence framework, the model parameters are integrated over, and the resulting evidence is maximized over the hyperparameters. The optimized hyperparameters are used to define a gaussian approximation to the posterior distribution. In the alternative MAP method, the true posterior probability is found by integrating over the hyperparameters. The true posterior is then maximized over the model parameters, and a gaussian approximation is made. The similarities of the two approaches and their relative merits are discussed, and comparisons are made with the ideal hierarchical Bayesian solution.

In moderately ill-posed problems, integration over hyperparameters yields a probability distribution with a skew peak, which causes signifi-cant biases to arise in the MAP method. In contrast, the evidence framework is shown to introduce negligible predictive error under straightforward conditions. General lessons are drawn concerning inference in many dimensions.
Mixtures of Probabilistic Principal Component Analyzers
Authors: Tipping Michael E. , Bishop Christopher M.
Published: July 2002

Principal component analysis (PCA) is one of the most popular techniques for processing, compressing, and visualizing data, although its effectiveness is limited by its global linearity. While nonlinear variants of PCA have been proposed, an alternative paradigm is to capture data complexity by a combination of local linear PCA projections. However, conventional PCA does not correspond to a probability density, and so there is no unique way to combine PCA models. Therefore, previous attempts to formulate mixture models for PCA have been ad hoc to some extent. In this article, PCA is formulated within a maximum likelihood framework, based on a specific form of gaussian latent variable model. This leads to a well-defined mixture model for probabilistic principal component analyzers, whose parameters can be determined using an expectation-maximization algorithm. We discuss the advantages of this model in the context of clustering, density modeling, and local dimensionality reduction, and we demonstrate its application to image compression and handwritten digit recognition.
Hidden Neural Networks
Authors: Krogh Anders , Riis Søren Kamaric
Published: July 2002

A general framework for hybrids of hidden Markov models (HMMs) and neural networks (NNs) called hidden neural networks (HNNs) is described. The article begins by reviewing standard HMMs and estimation by conditional maximum likelihood, which is used by the HNN. In the HNN, the usual HMM probability parameters are replaced by the outputs of state-specific neural networks. As opposed to many other hybrids, the HNN is normalized globally and therefore has a valid probabilistic interpretation. All parameters in the HNN are estimated simultaneously according to the discriminative conditional maximum likelihood criterion. The HNN can be viewed as an undirected probabilistic independence network (a graphical model), where the neural networks provide a compact representation of the clique functions. An evaluation of the HNN on the task of recognizing broad phoneme classes in the TIMIT database shows clear performance gains compared to standard HMMs tested on the same task.
A Stochastic Self-Organizing Map for Proximity Data
Authors: Graepel Thore , Obermayer Klaus
Published: July 2002

We derive an efficient algorithm for topographic mapping of proximity data (TMP), which can be seen as an extension of Kohonen's self-organizing map to arbitrary distance measures. The TMP cost function is derived in a Baysian framework of folded Markov chains for the description of autoencoders. It incorporates the data by a dissimilarity matrix [Formula: see text] and the topographic neighborhood by a matrix [Formula: see text] of transition probabilities. From the principle of maximum entropy, a nonfactorizing Gibbs distribution is obtained, which is approximated in a mean-field fashion. This allows for maximum likelihood estimation using an expectation-maximization algorithm. In analogy to the transition from topographic vector quantization to the self-organizing map, we suggest an approximation to TMP that is computationally more efficient. In order to prevent convergence to local minima, an annealing scheme in the temperature parameter is introduced, for which the critical temperature of the first phase transition is calculated in terms of [Formula: see text] and [Formula: see text]. Numerical results demonstrate the working of the algorithm and confirm the analytical results. Finally, the algorithm is used to generate a connection map of areas of the cat's cerebral cortex.
Too Many Notes: Computers, Complexity and Culture in Voyager
Authors: Lewis George E.
Published: July 2002

The author discusses his computer music composition, Voyager, which employs a computer-driven, interactive & “virtual improvising orchestra” that analyzes an improvisor's performance in real time, generating both complex responses to the musician's playing and independent behavior arising from the program's own internal processes. The author contends that notions about the nature and function of music are embedded in the structure of software-based music systems and that interactions with these systems tend to reveal characteristics of the community of thought and culture that produced them. Thus, Voyager is considered as a kind of computer music-making embodying African-American aesthetics and musical practices.
Localization of a Time-Delayed, Monocular Virtual Object Superimposed on a Real Environment
Authors: McCandless Jeffrey W. , Ellis Stephen R. , Adelstein Bernard D.
Published: July 2002

Observers adjusted a pointer to match the depicted distance of a monocular virtual object viewed in a see-through, had-mounted display. Distance information was available through motion parallax produced as the observers rocked side to side. The apparent stability of the virtual object was impaired by a time delay between the observers' head motions and the corresponding change in the object position on the display. Localizations were made for four time delays (31 ms, 64 ms, 131 ms, and 197 ms) and three depicted distances (75 cm, 95 cm, and 113 cm). The errors in localizations increased systematically with time delay and depicted distance. A model of the results shows that the judgment error and lateral projected position of the virtual object are each linearly related to time delay.
The Experience of Presence: Factor Analytic Insights
Authors: Schubert Thomas , Friedmann Frank , Regenbrecht Holger
Published: July 2002

Within an embodied cognition framework, it is argued that presence in a virtual environment (VE) develops from the construction of a spatial-functional mental model of the VE. Two cognitive processes lead to this model: the representation of bodily actions as possible actions in the VE, and the suppression of incompatible sensory input. It is hypothesized that the conscious sense of presence reflects these two components as spatial presence and involvement. This prediction was confirmed in two studies (N = 246 and N = 296) assessing self-reports of presence and immersion experiences. Additionally, judgments of “realness” were observed as a third presence component. A second-order factor analysis showed a distinction between presence, immersion, and interaction factors. Building on these results, a thirteen-item presence scale consisting of three independent components was developed and verified using confirmatory factor analyses across the two studies.
A Touch/Force Display System for Haptic Interface
Authors: Yoshikawa Tsuneo , Nagura Akihiro
Published: July 2002

The importance of force and tactile display in virtual reality technology has been recognized recently, and much research has been undertaken, including development of various force and/or tactile display devices. However, many of these devices are always in contact with the fingers or hands of the operators, and it is impossible for an operator to feel the difference between a contact and a noncontact state with a virtual object directly from tactile sensory channel in his/her finger or hand. This paper presents a new haptic display device that we have developed that provides both touch and force feeling to the operator's fingers. The device tracks the operator's finger without contact when the finger is not in contact with any virtual object. When some virtual object is in contact with the finger, the device touches and displays force to the finger. A control algorithm for the system is given to display the dynamics of the virtual objects. Preliminary experimental results are also presented to show the feasibility of the device and the validity of the control algorithm.
Effect of Turning Strategy on Maneuvering Ability Using the Treadport Locomotion Interface
Authors: Vijayakar Abhijeet , Hollerbach John
Published: July 2002

Turning strategies on the Sarcos Treadport, a linear treadmill locomotion interface, are developed and compared in a tight maneuvering task. A rate control strategy employing sidestep is compared to a proportional control strategy employing head gaze and torso trigger. The maneuvering task involves walking down a narrow corridor and avoiding obstacles that are placed at different separations to change the task difficulty. The performance metric was the number of times a subject collided with the obstacles or the corridor's walls. Traversal time and traversal distance were also characterized. The proportional control strategy was clearly found to permit more-precise maneuvering.
Navigating Large-Scale Virtual Environments: What Differences Occur Between Helmet-Mounted and Desk-Top Displays?
Authors: Ruddle Roy A. , Payne Stephen J. , Jones Dylan M.
Published: July 2002

Participants used a helmet-mounted display (HMD) and a desk-top (monitor) display to learn the layouts of two large-scale virtual environments (VEs) through repeated, direct navigational experience. Both VEs were “virtual buildings” containing more than seventy rooms. Participants using the HMD navigated the buildings significantly more quickly and developed a significantly more accurate sense of relative straight-line distance. There was no significant difference between the two types of display in terms of the distance that participants traveled or the mean accuracy of their direction estimates. Behavioral analyses showed that participants took advantage of the natural, head-tracked interface provided by the HMD in ways that included “looking around” more often while traveling through the VEs, and spending less time stationary in the VEs while choosing a direction in which to travel.
Coevolving Predator and Prey Robots: Do “Arms Races” Arise in Artificial Evolution?
Authors: Nolfi Stefano , Floreano Dario
Published: July 2002

Coevolution (i.e., the evolution of two or more competing populations with coupled fitness) has several features that may potentially enhance the power of adaptation of artificial evolution. In particular, as discussed by Dawkins and Krebs [3], competing populations may reciprocally drive one another to increasing levels of complexity by producing an evolutionary “arms race.” In this article we will investigate the role of coevolution in the context of evolutionary robotics. In particular, we will try to understand in what conditions coevolution can lead to “arms races.” Moreover, we will show that in some cases artificial coevolution has a higher adaptive power than simple evolution. Finally, by analyzing the dynamics of coevolved populations, we will show that in some circumstances well-adapted individuals would be better advised to adopt simple but easily modifiable strategies suited for the current competitor strategies rather than incorporate complex and general strategies that may be effective against a wide range of opposing counter-strategies.
The Human Dimensions of Geomorphological Work in Britain
Authors: Douglas Ian , Lawson Nigel
Published: July 2002

The transfer of materials from the natural environment to the urban and industrially built environment produces two broad impacts on the landscape: a removal of materials from the earth's surface (a change in geomorphology) and the accumulation of a stock of concrete and other materials elsewhere in cities and industrial zones (a change in urban morphology). Thus, industrial activity transforms natural landscapes and, in doing so, has to be considered to be a geological and geomorphological agent. On the global scale, the deliberate shift of around 57,000 Mt (megatons)/yr of materials through mineral extraction processes exceeds the annual transport of sediment to the oceans by rivers (some 22,000 Mt/yr) by almost a factor of three. On the island of Britain, the total deliberate shift of earth‐surface materials is between 688 and 972 Mt/yr, depending on whether or not the replacement of overburden in opencast coal mining is taken into account. The export of sediment to the oceans by rivers is only 10 Mt/yr whereas the export of materials in solution is about 40 Mt/yr, making the deliberate materials shift nearly 14 times larger than the shift caused by natural processes. Processes examined by industrial ecology, such as direct excavation, urban development, and waste dumping are those most driving changes in the shape of the British landscape today. These transformations pose added costs. Industrial ecology will produce an understanding of the hidden costs associated with these transformations. Such an understanding will help in planning and encouraging the reuse of materials everywhere and in identifying the key areas for intervention to reduce off‐site geomorphological impacts and costs.
Industrial Ecology as a Cultural Phenomenon: On Objectivity as a Normative Position
Authors: Boons Frank , Roome Nigel
Published: July 2002

Taking a recent column by Braden Allenby in this journal as a starting point, we argue the need for researchers in the field of industrial ecology to reflect upon its normative aspects. We argue that the field will advance through an explicit discourse on such issues as epistemological positions, the inherent normative nature of using metaphors, and the way in which the field of study relates to the field of practice.

In “Culture and Industrial Ecology,” Allenby raises, and begins to address, some critical questions that define the field of industrial ecology. We suggest that his arguments dismiss too lightly issues that are central to this developing field. The purpose of this reply is to open up for further discussion what industrial ecology is, and what it is not.

We begin by summarizing Allenby's line of reasoning. We explore his arguments around the notion of objectivity and the questions he raises about the relationship among objective science, normative positions, opinions, and fads. While Allenby makes a strong plea for industrial ecology to maintain objectivity and avoid normative positions, we contend that any positions on what should or should not be included in a field of study carry normative intent. Although science might seek to be objective in its method, scientists are rarely free of such normative positions. These positions need to be explicit and open to debate. Also, Allenby's position implies that industrial ecology as a field of study should be separated from industrial ecology as a field of practice. We argue that the interrelation of these fields provides important advantages.

Our main concern is that Allenby's position forestalls discussion on important issues at the heart of the field of study. We examine some key issues around the concept of objectivity and propose an agenda for research on the cultural and ideological aspects of industrial ecology.
Product Environmental Life‐Cycle Assessment Using Input‐Output Techniques
Authors: Joshi Satish
Published: July 2002

Life‐cycle assessment (LCA) facilitates a systems view in environmental evaluation of products, materials, and processes. Life‐cycle assessment attempts to quantify environmental burdens over the entire life‐cycle of a product from raw material extraction, manufacturing, and use to ultimate disposal. However, current methods for LCA suffer from problems of subjective boundary definition, inflexibility, high cost, data confidentiality, and aggregation.

This paper proposes alternative models to conduct quick, cost effective, and yet comprehensive life‐cycle assessments. The core of the analytical model consists of the 498 sector economic input‐output tables for the U.S. economy augmented with various sector‐level environmental impact vectors. The environmental impacts covered include global warming, acidification, energy use, non‐renewable ores consumption, eutrophication, conventional pollutant emissions and toxic releases to the environment. Alternative models are proposed for environmental assessment of individual products, processes, and life‐cycle stages by selective disaggregation of aggregate input‐output data or by creation of hypothetical new commodity sectors. To demonstrate the method, a case study comparing the life‐cycle environmental performance of steel and plastic automobile fuel tank systems is presented.
Servicizing the Chemical Supply Chain
Authors: Reiskin Edward D. , White Allen L. , Johnson Jill Kauffman , Votta Thomas J.
Published: July 2002

Servicizing—the transformation from product‐to service‐based enterprise—is a major force in changing how firms manage material input, throughput, and output. Redefinition of the firm as a service provider instead of a product manufacturer means that function, not form, is the source of added value delivered to the customer. To realize the dematerialization benefits of such a transformation requires a fundamental realignment of the supplier‐customer relationship. Instead of the traditional incentives to maximize the volume of physical product sold, servicizing requires a partnership wherein the financial rewards of reduced material consumption are shared between supplier and customer. We illustrate this partnership concept with the example of chemical management services (CMS), an approach that is gaining momentum in the automobile and electronics sector. Compensation and gain‐sharing based on chemical efficiency and chemical use reduction, often tied to fixed price mechanisms, lie at the core of the CMS model. Diffusion of the servicizing model holds much promise for driving dematerialization while reducing the environmental burden of product manufacturers.
The Global Environment Facility—a Role Model for International Governance?
Authors: Streck Charlotte
Published: July 2002

Today's fragmented world demands creative institutional arrangements to allow governments, international organizations and civil society actors to address transboundary and international problems. This article examines if and how the Global Environment Facility (GEF) can serve as a testing ground to find new ways to address such global problems in multilateral cooperation. After outlining the GEF's history, institutional setting and participatory elements, the paper points out some of its crucial weaknesses and flaws, such as insufficient private sector involvement, and the problem of power asymmetries. At the same time, however, the GEF can serve as a role model for international cooperation in many ways. More than any other international agency, the GEF is able to adapt to a constantly changing environment. The governance system of the GEF brings together advantages of both the UN and the Bretton Woods institutional rules and cultures. And it has a strong participatory element that includes close cooperation with nongovernmental actors.
WHO GETS IT WHEN YOU GO: THE LEGAL CONSEQUENCES OF THE ENDING OF HOUSEHOLDS (JUEHU) IN THE SONG DYNASTY (960-1279 C.E.)
Authors: McKnight Brian
Published: July 2002

In imperial China the normal pattern for the passing on of property across generations, giving assets to daughters as dowry at marriage and bequeathing the family estate in equal portions to sons upon the deaths of the parents, was distorted when both parents died without there being a living son, a situation called the extinguishing of the household (jeuhu). Under some dynasties the state attempted to deal with this phenomenon by mandating the posthumous adoption of sons, but during the Song (960-1279 C.E.) the government accepted the fact of the frequent ending of household (and family) lines, and established an elaborate set of laws and policies to assure the orderly transfer of assets. Song policy in this regard was prompted by the state's desire to avoid the concentration of land in the hands of the rich and the potential loss of tax revenues. Song policies both reflected and supported two social trends, the increasing independence of smaller stem family units from the influence of larger kin groupings and the increasing control of property by women, because most of those receiving juehu assets were women.
STICKLEBACK MALES, ESPECIALLY LARGE AND RED ONES, ARE MORE LIKELY TO NEST CONCEALED IN MACROPHYTES
Authors: Kraak Sarah , Bakker Theo , Hočevar Sandra
Published: July 2002

Previous studies have shown (1) that stickleback males enjoy increased mating success when their nest is concealed, (2) that males reduce their courtship in the face of predation risk to a lesser extent when their nest is concealed, and (3) that eggs in concealed nests have higher hatching chances. Here we test the prediction that male sticklebacks prefer to establish a territory at a site with a macrophyte under which they can conceal their nest. We planted macrophytes at half of the potential nest sites at two depths, in a section of a channel in which sticklebacks naturally occur. Subsequently, we found significantly more nests with eggs at the sites concealed by macrophytes than at the control sites, suggesting that wild sticklebacks preferred to build their nests at sites that offer concealment. At the shallow depth, males occupying a site with a macrophyte were larger and redder than males at control sites, but not at the deeper level. This suggests that males of higher competitive ability and greater conspicuousness were more likely to settle at shallow sites where predation risk by the grey heron is high.
FEMALE MATE PREFERENCE AND REPRODUCTIVE ISOLATION IN POPULATIONS OF THE STRIPED MOUSE RHABDOMYS PUMILIO
Authors: Pillay Neville
Published: July 2002

Laboratory experiments were conducted to study female mate preference in three allopatric populations of the striped mouse Rhabdomys pumilio, an African murid rodent. The three populations (Alice, Goegap, Irene) represent the extremes of the distribution range of the species in South Africa. Using two-way choice tests, virgin females were exposed to: (i) males of the same population (homotype) and those of another population (heterotype) in whole animal choice tests, or (ii) the odiferous bedding of homotype and heterotype males. Generally, females significantly preferred homotype stimulus males or their odour. This preference was only evident when females were in oestrus, suggesting that females were choosing potential mates. In addition, prior association with males is not needed for the establishment of female mate preference, since females were never exposed to adult males of any of the populations prior to testing. The only exception was receptive Goegap females which showed equal preference for homotype and Alice heterotype males. Mate preference in these two populations is asymmetric since Alice females showed strong preference for homotype males over Goegap males. The results indicate that divergence has occurred in allopatry, resulting in populationspecific communication signals and in particular olfactory cues, assortative mate choice, and pre-mating reproductive isolation.
'BABBLING' IN PYGMY MARMOSETS: DEVELOPMENT AFTER INFANCY
Authors: Snowdon Charles , Elowson A. Margaret
Published: July 2002

Infant pygmy marmosets (Cebuella pygmaea) are extremely vocal with much of their calling occurring in long sequences of mixed call-types that appears to have several parallels to the babbling of human infants (Elowson et al., 1998b). We refer to this vocal behaviour as Pygmy Marmoset Babbling (PMB) (Elowson et al., 1998a). We followed several of our original subjects beyond infancy to adulthood. Babbling bouts continued to appear through the age of puberty though at a reduced rate from that seen in infancy, but babbling was rarely observed in adults. With increasing age the vocal bouts contained a greater diversity of call types per bout and a decrease in call series duration. In addition, with increasing age there were decreasing proportions of calls that were Adult Variant and Infant calls and an increase in Adult calls. Structural analyses of trills, the most common call type found in vocal bouts, showed increased proportions of well-formed trills and decreased proportions of poorly formed trills with increased age, with different features reaching adult form at different ages. Babbling by juvenile marmosets was associated with increased social interactions with other group members as we had observed with infants. 'Babbling' in both infant and juvenile marmosets might provide vocal practice as well as attract attention from other group members.
SELECTION AND THE MAINTENANCE OF A COLOUR PATTERN POLYMORPHISM IN THE GREEN SWORDTAIL (XIPHOPHORUS HELLERI)
Authors: Franck Dierk , Dikomey Marion , Schartl Manfred
Published: July 2002

Many Xiphophorus populations include a number of individuals with black spots on body sides or fins. In many cases such spots are composed of extremely large melanophore cells, the so-called macromelanophores. Macromelanophore pattern polymorphism is known in 10 out of 22 Xiphophorus species. In at least 8 species alleles of the macromelanophore determining locus Mdl are intimately linked to a dominant oncogene, ONC-Xmrk, which can give rise to malignant skin tumors (melanoma). We present, for the first time, evidence that macromelanophore pattern polymorphisms may be maintained by selection in a seasonally variable environment. In school-choice experiments single Xiphophorus helleri females spent more time with groups of spotted females than with non-spotted females under turbid, but not under clear water conditions. Similarly, receptive females preferred spotted males in turbid, but not in clear water. Thus, in nature, when the water becomes turbid after heavy rainfalls, school mates and reproductive partners can evidently find each other more easily with the help of macromelanophore spotting patterns. Intrasexual selection seems to be irrelevant because spotted and non-spotted males were equally successful in competition experiments. A genetic hitchhiking scenario is discussed which could explain the fact that the potentially injurious tumor gene ONC-Xmrk has been maintained in the genus Xiphophorus over a period of millions of years by its close linkage to positively selected macromelanophore alleles.
RELEASE EXPERIMENTS WITH WILD ROCK DOVES (COLUMBA L. LIVIA GM.)
Authors: Baldaccini N. Emilio , Giunchi Dimitri , Mongini Emanuele , Ragionieri Luisa
Published: July 2002

The homing behaviour of free-living birds has rarely been systematically investigated, and so it is difficult to give a satisfactory comparative picture. Data are here presented on the initial orientation of rock doves displaced inside and outside the area that they daily cross during their foraging flights. Inside the familiar area, the results show marked variability in the directional choices of the released birds, probably related to temporal variability in the location of food patches during the year. Indeed, in autumn, when the doves feed almost exclusively near the colony site, they tend to fly home, but in summer, when food patches are dispersed over a wide area around the colony, this behaviour is not evident. Outside the familiar area, no clear evidence of a homeward directedness is obtained. Two releases inside the familiar area with clock-shifted birds produced ambiguous results and it is difficult to attribute the behaviour of the animals to a change in their motivation to reach home in different times of the day, or to the use of a time-compensated sun compass. On the whole, the presented results point to the difficulties of comparing rock dove behaviour to that of the homing pigeon, and show the importance of considering the influence of ecological and motivational variables in evaluating the orienting performances of wild birds.
TWO NEW SPECIES OF ALBOSCIA SCHULTZ, 1995 FROM RIO GRANDE DO SUL, BRAZIL (ISOPODA, ONISCIDEA, PHILOSCIIDAE)
Authors: Araujo
Published: July 2002

Two new species of Alboscia Schultz, 1995, from Rio Grande do Sul, Brazil, are described. A. silveirensis is characterized by having 2 sub-apical and 2 apical aesthetascs on the antennule, by its antenna with the distal flagellar article the longest, and by having sexual dimorphism on pereopod 1, while A. ornata is distinguished by an eye of 3 ocelli and the complex structure of pleopods 1 and 2. A new diagnosis of the genus is provided. Deux especes nouvelles d'Alboscia Schultz, 1995, sont decrites de Rio Grande do Sul, Bresil. A. silveirensis est caracterise par la presence de deux aestetascs subapicaux et de deux apicaux sur l'antennule, par son antenne avec l'article flagellaire distal le plus long et par le dimorphisme sexuel du pereiopode 1, alors que A. ornata se distingue par un oeil a trois ocelles et la structure complexe des pleopodes 1 et 2. Une nouvelle diagnose du genre est fournie.
AGONISTIC CONTESTS IN MALE FORM I CAMBARUS BARTONII BARTONII (FABRICIUS, 1798) (DECAPODA, CAMBARIDAE) CRAYFISH AND A COMPARISON WITH CONTESTS OF THE SAME TYPE IN CAMBARUS ROBUSTUS GIRARD, 1852
Authors: Guiasu Radu Cornel , Dunham David
Published: July 2002

During contests between evenly size-matched Cambarus bartonii bartonii crayfish males of reproductive form (Form I), the eventual winners performed significantly more total initiation acts, Lunge and Claws Raised initiation behaviours than the eventual losers. There were no significant differences between the numbers of Ambivalent Contact initiation acts and tail flip escape behaviours, respectively, performed by the winners and the losers. During intraspecific, intra-form contests, C. b. bartonii Form I males used the same three main types of initiation acts as Form I males of the closely related species Cambarus robustus. The highly aggressive Lunge initiation act plays a much more important role in the establishment of the dominant-subordinate relationship in the C. robustus intraspecific, intra-form Form I contests than in the C. b. bartonii contests of the same type. The eventual C. b. bartonii losers were considerably less submissive in the intraspecific contests in comparison to the interspecific contests against C. robustus. The decline in both the number of fights and the time spent fighting, which accompanied the establishment of the dominant-subordinate relationship in the C. robustus intraspecific contests, did not take place during the C. b. bartonii intraspecific contests. Pendant les confrontations entre ecrevisses males de taille assortie de l'espece Cambarus bartonii bartonii, appartenant a la forme reproductive (Forme I), les gagnants eventuels accomplissent de facon significative un plus grand nombre total d'actes d'engagement ("Lunge" et "Claws Raised") que les perdants eventuels. Il n'y avait pas de differences significatives entre les nombres des actes d'engagement "Ambivalent Contact" et de degagement "en coup de queue", respectivement, accomplis par les gagnants et les perdants. Pendant les confrontations intraspecifiques, intraformes, les males de C. b. bartonii utilisaient les trois memes types principaux d'actes d'engagement que les males Forme I de l'espece tres proche Cambarus robustus. L'acte d'engagement hautement agressif "Lunge" joue un role beaucoup plus important dans l'etablissement de la relation dominant-domine dans les confrontations intraspecifiques, intraformes Forme I, chez C. robustus, que dans les confrontations de meme type chez C. b. bartonii. Les eventuels perdants de C. b. bartonii etaient considerablement moins soumis dans les combats intraspecifiques que dans les combats interspecifiques contre C. robustus. Le declin, a la fois dans le nombre des combats et dans le temps passe a combattre, qui accompagnait l'etablissement de la relation dominant-domine dans les rencontres intraspecifiques chez C. robustus, n'intervenait pas pendant les rencontres intraspecifiques chez C. b. bartonii.
Sedentary endoparasitic nematodes as a model for other plant parasitic nematodes
Authors: Gheysen Godelieve , Meutter Jan De , Tytgat Tom , Coomans August
Published: July 2002

Plant parasitic nematodes are known to cause a severe reduction in crop yield. Recently much effort is being put to engineering new nematode-resistant crop cultivars. Plant parasitic nematodes occur in three widely separated orders: Triplonchida, Dorylaimida and Tylenchida. All triplonchid and dorylaimid plant parasitic nematodes are migratory ectoparasites of roots. Within the Tylenchida, several different types of plant parasitism can be recognised. The sedentary endoparasites have the most complex interaction with their host, and are responsible for the vast majority of the agricultural damage. This causes most research to be concentrated on two groups of the sedentary endoparasitic nematodes: cyst- and root-knot nematodes. Both induce specialised feeding structures in the vascular cylinder of the plant root. The mechanism of phytoparasitism of the cyst- and root-knot nematodes is reviewed, of which some aspects will be applicable to the study of the other plant parasitic nematodes. Les nématodes parasites de plantes sont connus pour provoquer de sévères réductions dans les rendements des cultures. Actuellement, un effort se développe pour créer de nouveaux cultivars résistants aux nématodes. Les nématodes parasite de plantes appartiennent à trois ordres très éloignés: Triplonchida, Dorylaimida et Tylenchida. Tous les nématodes parasites de plantes chez les Triplonchida et Dorylaimida sont des ectoparasites migrateurs. Chez les Tylenchida, plusieurs types différents de parasitisme peuvent être identifiés. Les endoparasites sédentaires ont l’interaction la plus complexe avec leur hôte et sont responsables de la plus grande part des dégâts agricoles. C’est la raison pour laquelle la plupart des recherches sont concentrées sur deux groupes de nématodes endoparasites sédentaires, les nématodes à kystes et les nématodes galligènes. Ces deux groupes induisent des structures d’alimentation spécialisées dans les tissus vasculaires de la racine végétale. Le mécanisme parasitaire des nématodes à kystes et galligènes est revu, certaines de leurs caractéristiques pouvant être applicables à l’étude des autres nématodes phytoparasites.
Nematodes of the order Dorylaimida from Andalucía Oriental, Spain. Two new species of the genus Carcharodiscus Andrássy, 1991, with a key to its species
Authors: Liébanas Gracia María , Peña-Santiago Reyes
Published: July 2002

Two new species of the genus Carcharodiscus are described from southeastern Spain. Carcharodiscus procerus sp. n. is characterised by: a very slender (a = 52 - 62) body 1.67 - 2.17 mm long, lip region offset by constriction and 17 - 18 μm diam., anterior portion of the cheilostome 12 - 13× 7.0- 7.5 μm with abundant denticles on its walls, odontostyle 10 - 12 μm long or ca 66% of the lip region diam., presence of a dorsal cell chord behind the cardia, female genital system amphidelphic, vulva longitudinal and somewhat posterior (V = 52 - 58), presence of cuticular irregularities near the vulva area, tail rounded conoid (22 - 28 μm; c = 70 - 83; c′ = 1.0 - 1.2), and male unknown. Carcharodiscus olearum sp. n. is distinguished by its very slender (a = 51 - 55) and long (L = 2.36 2.79 mm) body, lip region offset by deep constriction and 22 - 27 μm in diam., anterior portion of the cheilostome 16.5- 18.0 × 8.0- 9.5 μm with abundant denticles on its walls, odontostyle 16.0- 17.5 μm long or 0.7 to 0.8 times the lip region in diam., presence of a dorsal cell chord behind the cardia, female genital system amphidelphic, vulva longitudinal and somewhat posterior (V = 50 - 58), tail rounded conoid (25 - 28 μm; c = 89 - 99; c′ = 0.8- 0.9), and male unknown. Carcharolaimus eximius is transferred to Carcharodiscus. A list of the species of the genus and key to their identification are also provided.