Dédoublement revisited: towards a renewed interpretation of the androecium of the Magnoliophytina

RONSE DECRAENE, L. P. & SMETS, E F., 1993. Dedoublement revisited: towards a renewed interpretation of the androecium of the Magnoliophytina. There has been much controversy about dedoublement in the past. Dedoublement was originally described as a process of doubling of a (stamen) primordium up to two equivalent primordia. Later, it was extended to explain occurrences of higher stamen numbers, even without evidence of a division. Different interpretations from both opponents and protagonists of dedoublement are critically examined and concepts such as negative, positive, serial, lateral and congenital dedoublement are discussed. Some case studies are presented to evaluate the concept of dedoublement. Paired stamens are not necessarily the result of splitting; they can also arise by a spatial shift, connected with the cyclization of a spiral flower. Two smaller stamen primordia replacing a stamen without visible splitting and a primordium dividing ontogenetically into a stamen pair are essentially similar. The morphological difference between both configurations can be explained by the principle of variable proportions. Radial dedoublement and stamen-petal complexes are examples of meristem fusion (absorption) and may be defined by the term 'negative dedoublement' in the sense of Celakovsky (1894). A distinction between 'dedoublement' sensu stricto and 'polygenesis' is proposed.     

Bayesian Neural Network Models for Censored Data

Neural networks are considered by many to be very promising tools for classification and prediction. The flexibility of the neural network models often result in over-fit. Shrinking the parameters using a penalized likelihood is often used in order to overcome such over-fit. In this paper we extend the approach proposed by FARAGGI and SIMON (1995a) to modeling censored survival data using the input-output relationship associated with a single hidden layer feed-forward neural network. Instead of estimating the neural network parameters using the method of maximum likelihood, we place normal prior distributions on the parameters and make inferences based on derived posterior distributions of the parameters. This Bayesian formulation will result in shrinking the parameters of the neural network model and will reduce the over-fit compared with the maximum likelihood estimators. We illustrate our proposed method on a simulated and a real example.     

Larval experience induces adult aversion to rearing host plants: a novel behaviour contrary to Hopkins' host selection principle

1. Hopkins' host selection principle (HSP) states that insects should prefer foliage from their rearing host plant over that of an alternative host. 2. The current study tested whether eastern spruce budworm, Choristoneura fumiferana (Clem.) (Lepidoptera: Tortricidae), that were laid and developed on, respectively, resistant and susceptible white spruce Picea glauca (Moench) Voss, showed differences in their feeding and oviposition preferences for these two hosts. 3. The data revealed that previous experience of spruce budworm on a host tree type does not influence the host acceptance and feeding behaviour of later larval stages. However, adult budworm reared on resistant white spruce needles preferentially selected susceptible white spruce needles as the host for their progeny, whereas those reared on susceptible needles showed no preference. 4. To the authors' knowledge, this is the first report of an insect showing an oviposition preference for the non‐rearing host plant. This would tend to increase mixing between insects from susceptible and resistant trees. The present results thus argue against Hopkins' HSP and suggest that learned aversion to resistant foliage experienced by larvae is carried into the adult stage.     

Diversity partitioning of Rao’s quadratic entropy

Many applications of diversity indices are only valid if they are first transformed into their equivalent number of species. These equivalent numbers of species can be multiplicatively partitioned into independent alpha, beta and gamma components, and can be formed into mathematically consistent similarity measures. The utility of beta diversity and similarity measures that incorporate information about the degree of ecological dissimilarity between species is becoming increasingly recognized. The concept of equivalent number of species is here extended to Rao’s quadratic entropy, opening the way to methods of diversity partitioning that take into account taxonomic or ecological differences between species.     

Qualitatively distinct phenotypes in the design space of biochemical systems

Although characterization of the genotype has undergone revolutionary advances as a result of the successful genome projects, the chasm between our understanding of a fully characterized gene sequence and the phenotypic repertoire of the organism is as broad and deep as it was in the pre-genomic era. There are two fundamental unsolved problems that provide the context for the challenges in relating genotype to phenotype. We address one of these and describe a generic method for constructing a system design space in which qualitatively distinct phenotypes can be identified and counted, their relative fitness analyzed and compared, and their tolerance to change measured.     

应用主成分分析法研究缺Zn症患儿的样本特征

本文测定了150例缺Z_n症患儿发样中的Z_n、C_a、M_g及F_e元素水平，将原始数据经对数─中心化变换后，应用主成分分析法将高维空间中的样本点映射到低维空间，研究其样本特征，为缺Z_n症患儿的正确诊治提供依据．     

Decoupling vigour and quality in the autumn colours game: Weak individuals can signal, cheating can pay

According to the coevolution theory, autumn colours are a warning signal to insects, signalling the level of chemical defences or availability of nutrients. Because in the original model tree vigour and defences were positively correlated, it is not clear whether signalling would still be stable when they are decoupled, and the fact that weak trees often display bright autumn colours is usually presented as evidence against the coevolution theory. I show that in a theoretical model of insect-tree coevolution, signalling is still stable when vigour and defences are decoupled. Weak trees can signal. Moreover, partial cheating is possible. The different equilibria depend on the importance of vigour and defences against insect attack, of vigour in the production of the signal, and of pleiotropic effects between colour and defences. These results provide precise predictions that can be used for planning future empirical test.     

Signal verification can promote reliable signalling

The central question in communication theory is whether communication is reliable, and if so, which mechanisms select for reliability. The primary approach in the past has been to attribute reliability to strategic costs associated with signalling as predicted by the handicap principle. Yet, reliability can arise through other mechanisms, such as signal verification; but the theoretical understanding of such mechanisms has received relatively little attention. Here, we model whether verification can lead to reliability in repeated interactions that typically characterize mutualisms. Specifically, we model whether fruit consumers that discriminate among poor- and good-quality fruits within a population can select for reliable fruit signals. In our model, plants either signal or they do not; costs associated with signalling are fixed and independent of plant quality. We find parameter combinations where discriminating fruit consumers can select for signal reliability by abandoning unprofitable plants more quickly. This self-serving behaviour imposes costs upon plants as a by-product, rendering it unprofitable for unrewarding plants to signal. Thus, strategic costs to signalling are not a prerequisite for reliable communication. We expect verification to more generally explain signal reliability in repeated consumer–resource interactions that typify mutualisms but also in antagonistic interactions such as mimicry and aposematism.     

Effective communication in technology sharing

Abstract

The paper emphasizes the importance of communication for the success of technology sharing and information dissemination programs. The concept of the “gatekeeper”; is discussed and placed in the organizational perspective. Several characteristics by which this vital individual can be identified are delineated.

The flow of information across and within organizations, communities and regions of interest is studied in the context of the gatekeeper, the liasion and the communication isolate—three groups of people identifiable within an organization. Information channels are next explored and a method of evaluating their effectiveness presented.

The authors suggest that a technology sharing program needs to deal with certain distinct audiences termed politicians, managers, scientists, technologists and workers. Patterns of communication among these audiences together with a system of communicating with outside expertise needs to be analyzed at the outset of any extension or cooperative endeavor.

This basic structure is then applied to a model indicating the role of a hypothetical International Sea Grant effort. The authors suggest that such an international program could best succeed when integrated with existing extension networks. Evaluation, feedback and follow‐up are mentioned as areas vital to the success of an extension or sharing program.

The paper then proceeds to present some perspectives on communication and change agents and warns against the possible dangers which could plague an extension system.

The authors conclude with some thoughts on an extension strategy.