Dichotomous Tree Research Articles

RATIONAL CONTROL BY TEMPERATURE IN VORTEX ENERGY SEPARATOR UNDER DESTABILIZING EFFECTS

The focus of this study is the arrangement of a rational control technique used to maintain the airflow temperature in a vortex energy separator (VES) under destabilizing effects. The objectives include the development of tools for the rational control of temperature in the cold and hot air flows of a VES. Methods used: Discrete state space, production rule statement, resolution of two-valued predicate equations, dichotomous trees, diagnosis, and recovery of dynamic objects. Problems settled: the studied features of the vortex energy separation process, architecture, and operation links of the rational control system were considered, mathematical models were deduced, and tools for diagnosing and recovering the efficiency of the vortex energy separator as a rational control object were developed. The scientific novelty of the study lies in the formation of instrumental tools to provide rational control of the airflow condition in the VES, where the control object is subjected to the substantial influence of various destabilizing effects.

Rational control of the temperature of vortex energy separator under destabilizing influence

The object of study in this article is the formation process of a rational control of the temperature of a vortex energy separator under destabilizing influences. The subject matter of the article is the process of forming a dichotomous tree by two-digit predicates from diagnostic models a vortex energy-separator device as a rational control object when destabilizing influences appear, and its further recovery. The goal is to develop an analytical approach to the formation of digital algorithms for the rational control of cold and hot air flow temperatures of a vortex energy separator. The tasks are to study the features of the process in the vortex energy-separator device; to describe a rational control system of the vortex energy-separator device; to analyze the experimental characteristics of the vortex energy-separator device; to form linear mathematical models of the nominal mode of the vortex energy-separator device; to develop linear diagnostic models that describe the inoperable states of the vortex energy separator as a rational control object; to form logical signs of diagnosing using diagnostic models, to develop recovering algorithms for the vortex energy separator. The methods used are transfer functions, discrete state space, forming production rules, two-digit predicate equations, dichotomous trees, diagnosing and recovering the operability of dynamic objects. The following results were obtained: the vortex energy-separation process features analysis, the rational control system structure and function description, the experimental characteristics analysis, the development of mathematical models, diagnostic and recovering tool development for the emergency operation process of a vortex energy separator as a rational control object for a given destabilizing influence set. Conclusions. Scientific novelty is the development of an analytical approach to the development of rational control of the vortex separation process of the air flow under the significant influence of various kinds of destabilizing influences.

<strong><em>Cocconeis tsara sp. nov.</em>, <em>C. santandrea sp. nov.</em> and allied taxa pertaining to the new section <em>Loculatae</em></strong>

The genus Cocconeis is highly diverse and composed of several groups with distinctive morphologies. Several Cocconeis, characterized by complex areola occlusions, are here grouped under the new section Loculatae. The complex loculate areolae are either present on both valves, or most often only on the sternum valve (SV). Among the Loculatae taxa, some were described as varieties of Cocconeis scutellum, whereas others were assigned species rank. Critical SEM examination is required to correctly discriminate members of this section. Cocconeis tsara sp. nov. and C. santandrea sp. nov. are marine tropical benthic diatoms with loculate areolae justifying their membership to the proposed section. Based on ultrastructure, a cladistic analysis is performed to determine the relationships between these taxa. A traditional dichotomous tree based on the most particular features encountered on this group is constructed to aid in species determination. Several of the Loculatae taxa are epiphytic, one was observed as epizoic. The necessity of high resolution SEM to discern details of the SV areola occlusions and the raphe valve valvocopula (RVVC), and the nomenclatural descriptive terms used by authors, are discussed to better compare recent and historical descriptions.

METHOD OF SYNTHESIS OF THE INTEGRATED ASSESSMENT SYSTEM

Systems of complex estimation (CO) based on a dichotomous tree of criteria and a set of criteria convolution matrices (generalized criteria) are widely used in the evaluation of a wide variety of ob-jects. Purpose of the study. To build a CO system for a given set of criteria, you need to solve two problems: 1. To choose the structure of the dichotomous tree of criteria. 2. To define matrix convolutions of pairs of criteria (generalized criteria) at each vertex of the tree (except for hanging ones). The article deals with the second problem, i.e. the problem of determining matrices the criteria convolution. In practice, this task is often solved based on expert opinions. Materials and methods. Let us assume that there are a set of options (a variant is a set of criteria estimates) and experts have defined complex estimates for each option from this set. The task is to define matrix convolu-tions at each vertex of the tree such that the CO of each variant in the resulting system CO is equal to the EXPERT estimate. The paper defines a class of unified CO mechanisms that meet the following conditions: 1. All matrices of the unified complex estimation mechanism have the same dimension. 2. For any matrix all rows are different and all columns are different. 3. All matrices are monotonous in rows and columns; 4. If all the variant scores are equal to a certain score, then the complex score is equal to this score. Results. Two cases are considered. In the first case, experts can give estimates of options with any set of criteria estimates. In the second case, experts can give a CO of only complete options, that is, options that contain estimates of all criteria. For the first case, an efficient algorithm with an estimate of computational complexity of the order of lm2 is proposed, where l is the number of crite-ria, and m is the number of gradations of the rating scale. The algorithm makes significant use of the 4 property of unified mechanisms. For the second case, we propose a method for solving the problem by constructing “top-down” matrices, i.e. constructing a matrix for the root vertex, then for adjacent ones, and so on. Conclu-sion. Thus, the paper proposes algorithms for the synthesis of unified mechanisms for complex eva-luation, in which the number of required expert options is minimal.

RATIONAL CONTROL OF OBJECTS WITH UNCERTAIN DYNAMICS

The reasons causing uncertainty in the dynamics of objects are considered on the example of aerospace engineering. Objects of automatic control, consisting of control objects, servo drives, and sensors, are subjects to the influence of indefinite external and internal disturbing influences, which destabilize their performance. Classical methods of automatic control of such objects do not allow obtaining the desired quality indicators. For the rational control of such objects with uncertain dynamics, a new approach has been proposed, which is based on a deep diagnosis of the causes of destabilization and flexible restoration of working capacity. The main provisions of the method of rational control are described. A new class of mathematical models called diagnostic is presented. In-depth diagnostic procedures are formed using formalized and weakly formalized models of the processes of regular and abnormal operation of the control system. For the formation of a priori and a posteriori knowledge of the causes of malfunctioning, structures of developing dichotomous trees are used, representing a kind of product knowledge bases with a design in nodes “if ... then ...”, with logical rules for obtaining a diagnosis of the causes of destabilizing effects. A method for solving diagnostic problems for objects with uncertain dynamics is described. To restore the performance of objects with uncertain dynamics, the use of redundant means has been proposed: signal and parametric adjustment, reconfiguration of algorithms and hardware. The process of parrying destabilization, which was diagnosed, is formed using the second method A. M. Lyapunov. This method ensures the stability of the system and the specified quality control. Rational adaptation to destabilizing effects is based on the use of intelligent procedures for in-depth diagnosis of the causes of a malfunction of the control system and a flexible restoration of working capacity in real time. Such procedures allow for productive training in order to preserve the efficiency of the control system throughout the entire life cycle. The results of applying the method of rational control to a number of model samples of aircraft are given.

A Machine Learning Based Morphological Classification of 14,245 Radio AGNs Selected from the Best–Heckman Sample

Abstract We present a morphological classification of 14,245 radio active galactic nuclei (AGNs) into six types, i.e., typical Fanaroff–Riley Class I/II (FRI/II), FRI/II-like bent-tailed, X-shaped radio galaxy, and ringlike radio galaxy, by designing a convolutional neural network based autoencoder, namely MCRGNet, and applying it to a labeled radio galaxy (LRG) sample containing 1442 AGNs and an unlabeled radio galaxy (unLRG) sample containing 14,245 unlabeled AGNs selected from the Best–Heckman sample. We train MCRGNet and implement the classification task by a three-step strategy, i.e., pre-training, fine-tuning, and classification, which combines both unsupervised and supervised learnings. A four-layer dichotomous tree is designed to classify the radio AGNs, which leads to a significantly better performance than the direct six-type classification. On the LRG sample, our MCRGNet achieves a total precision of ∼93% and an averaged sensitivity of ∼87%, which are better than those obtained in previous works. On the unLRG sample, whose labels have been human-inspected, the neural network achieves a total precision of ∼80%. Also, using Sloan Digital Sky Survey Data Release 7 to calculate the r-band absolute magnitude (M opt) and using the flux densities to calculate the radio luminosity (L radio), we find that the distributions of the unLRG sources on the L radio–M opt plane do not show an apparent redshift evolution and could confirm with a sufficiently large sample that there could not exist an abrupt separation between FRIs and FRIIs as reported in some previous works.

A New Perspective on Reticulate Evolution of the Genus <i>Homo</i>

No consensus exists in human evolution research regarding the definition of genus Homo and its mode of evolution. We address these two questions with an integrated phylogenetic reconstruction approach applied to craniodental characters of 22 hominin species, combining Maximum Parsimony dichotomous tree and Phylogenetic Networks methods. Three Homo most parsimonious tree-based definitions are identified, with cumulative distinguishing feature changes in support of hypothetical last common ancestors highlighted by a novel elliptic representation. We analyze the complexity of the genus Homo evolutionary process by means of a Phylogenetic Networks method, and show its probable web-like reticulate mode of evolution that gave rise to the emergence of the only surviving paleospecies, Homo sapiens, further to the extinctions of preceding archaic human species such as Homo neanderthalensis. Our results confirm a paradigm shift in the study of human evolution in favor of reticulation, in accord with recent findings of introgressive hybridization in paleogenomics.

Phylogenomic Analysis of the Explosive Adaptive Radiation of the Espeletia Complex (Asteraceae) in the Tropical Andes.

The subtribe Espeletiinae (Asteraceae), endemic to the high-elevations in the Northern Andes, exhibits an exceptional diversity of species, growth-forms, and reproductive strategies. This complex of 140 species includes large trees, dichotomous trees, shrubs and the extraordinary giant caulescent rosettes, considered as a classic example of adaptation in tropical high-elevation ecosystems. The subtribe has also long been recognized as a prominent case of adaptive radiation, but the understanding of its evolution has been hampered by a lack of phylogenetic resolution. Herein, we produce the first fully resolved phylogeny of all morphological groups of Espeletiinae, using whole plastomes and about a million nuclear nucleotides obtained with an original de novo assembly procedure without reference genome, and analyzed with traditional and coalescent-based approaches that consider the possible impact of incomplete lineage sorting and hybridization on phylogenetic inference. We show that the diversification of Espeletiinae started from a rosette ancestor about 2.3 Ma, after the final uplift of the Northern Andes. This was followed by two independent radiations in the Colombian and Venezuelan Andes, with a few trans-cordilleran dispersal events among low-elevation tree lineages but none among high-elevation rosettes. We demonstrate complex scenarios of morphological change in Espeletiinae, usually implying the convergent evolution of growth-forms with frequent loss/gains of various traits. For instance, caulescent rosettes evolved independently in both countries, likely as convergent adaptations to life in tropical high-elevation habitats. Tree growth-forms evolved independently three times from the repeated colonization of lower elevations by high-elevation rosette ancestors. The rate of morphological diversification increased during the early phase of the radiation, after which it decreased steadily towards the present. On the other hand, the rate of species diversification in the best-sampled Venezuelan radiation was on average very high (3.1 spp/My), with significant rate variation among growth-forms (much higher in polycarpic caulescent rosettes). Our results point out a scenario where both adaptive morphological evolution and geographical isolation due to Pleistocene climatic oscillations triggered an exceptionally rapid radiation for a continental plant group.

Reaction-diffusion-advection equation in binary tree networks and optimal size ratio.

A simple reaction-diffusion-advection equation is proposed in a dichotomous tree network to discuss an optimal network. An optimal size ratio r is evaluated by the principle of maximization of total reaction rate. In the case of reaction-limited conditions, the optimal ratio can be larger than (1/2)(1/3) for a fixed value of branching number n, which is consistent with observations in mammalian lungs. We find furthermore that there is an optimal branching number nc when the Péclet number is large. Under the doubly optimal conditions with respect to the size ratio and branching number, the optimal value of r is close to (1/2)(1/3).

Discriminating micropathogen lineages and their reticulate evolution through graph theory-based network analysis: the case of Trypanosoma cruzi, the agent of Chagas disease.

Micropathogens (viruses, bacteria, fungi, parasitic protozoa) share a common trait, which is partial clonality, with wide variance in the respective influence of clonality and sexual recombination on the dynamics and evolution of taxa. The discrimination of distinct lineages and the reconstruction of their phylogenetic history are key information to infer their biomedical properties. However, the phylogenetic picture is often clouded by occasional events of recombination across divergent lineages, limiting the relevance of classical phylogenetic analysis and dichotomic trees. We have applied a network analysis based on graph theory to illustrate the relationships among genotypes of Trypanosoma cruzi, the parasitic protozoan responsible for Chagas disease, to identify major lineages and to unravel their past history of divergence and possible recombination events. At the scale of T. cruzi subspecific diversity, graph theory-based networks applied to 22 isoenzyme loci (262 distinct Multi-Locus-Enzyme-Electrophoresis -MLEE) and 19 microsatellite loci (66 Multi-Locus-Genotypes -MLG) fully confirms the high clustering of genotypes into major lineages or “near-clades”. The release of the dichotomic constraint associated with phylogenetic reconstruction usually applied to Multilocus data allows identifying putative hybrids and their parental lineages. Reticulate topology suggests a slightly different history for some of the main “near-clades”, and a possibly more complex origin for the putative hybrids than hitherto proposed. Finally the sub-network of the near-clade T. cruzi I (28 MLG) shows a clustering subdivision into three differentiated lesser near-clades (“Russian doll pattern”), which confirms the hypothesis recently proposed by other investigators. The present study broadens and clarifies the hypotheses previously obtained from classical markers on the same sets of data, which demonstrates the added value of this approach. This underlines the potential of graph theory-based network analysis for describing the nature and relationships of major pathogens, thereby opening stimulating prospects to unravel the organization, dynamics and history of major micropathogen lineages.

MODELS AND ALGORITHMS FOR FINDING ERRORS WHILE SOLVING TASKS USING COMPUTER-ASSISTED LEARNING

An algorithm for diagnosing errors in a computer training program for solutions of the control system characteristic equation using a numerical method is offered. Its feature is the formation of a product knowledge base for searching errors and using dichotomous tree in the process of diagnosis.

Utility, or not, of estimates of glomerular filtration rate in modifying drug dosage, with particular reference to enoxaparin

A reduced clearance of some drugs in renal failure is a problem, particularly with drugs that are excreted by the kidney substantially unmetabolised and also have significant toxicity and a low therapeutic ratio. The problem is compounded by the significant inaccuracy of estimated glomerular filtration rate (eGFR). The aim was to develop general recommendations to reduce the risk of drug toxicity in renal failure, with particular reference to enoxaparin. The substantial inaccuracies in eGFR (eGFR in 32% of patients is different from measured GFR by 20-30%) are compounded when using a dichotomous decision tree (renal failure or not). As the eGFR approaches the GFR decision boundary, for classification as renal failure or not, misclassification approaches 50%. Recommendations, when patients are at risk, include the following: acknowledge inaccuracies of eGFR, particularly in anthropometrically diverse populations; measure drug levels wherever possible; realise that drug levels after early doses relate more to volume of distribution, rather than renal function, allowing time for modification of the drug dose; where accurate urine collection is feasible, use creatinine clearance as an estimate of GFR; and use eGFR as a (more) continuous, rather than dichotomous, variable to adjust dosage, exampled by enoxaparin.

Examination of Potential Measures of Vine Maturity in Potato

Plant maturity is a complex physiological trait routinely evaluated by plant breeders because of its agronomic, economic, and breeding implications. In potato, plant maturity is typically estimated by monitoring vine characteristics. This study investigates several reported measures of vine maturity in potato cultivars, including examination of flower development, leaf chlorophyll content, and leaf peroxidase activity to see what method is most appropriate for maturity classification in temperate production regions. These three measures were evaluated multiple times throughout a single growing season across two locations. The data were analyzed using canonical discriminant and dichotomous tree analyses. Both methods revealed that flower development is not an accurate indicator of maturity, even though it is a common component of maturity screening protocols. Peroxidase measures were slightly better, but the optimal period of time to assess this trait was variable across locations and a considerable time commitment is required to collect and process samples. Monitoring leaf chlorophyll content throughout plant development was most appropriate for predicting vine maturity under these conditions, as this trait showed the most consistency and greatest prediction accuracy (69% - 71%) relative to peroxidase activity and flowering development. Additionally, chlorophyll measurements are a more practical method of measuring maturity due to the ease of data collection. Leaf chlorophyll content best distinguished late cultivars from early-medium and medium-late cultivars. However, it did not separate early-medium from medium-late cultivars. Combining chlorophyll monitoring with peroxidase and flowering measures improved the ability to distinguish among the early-medium and medium-late maturity classes. However, doing so only increased classification accuracy by 3%.

Clinical interventions on the major vascular risk factors (RIVANA study)

To describe the diagnostic frequency of classical vascular risk factors, dietary and therapeutic interventions and their control. Within the project Vascular Risk in Navarre (RIVANA), a transversal study was made of a random sample of 4,354 people between the ages of 35 and 84; antecedents were gathered by interview and clinical and analytical exploration was carried out. The subjects were classified for each risk factor into: diagnosed by information--when health personnel had informed them that they presented a risk factor; by intervention--when they take medication for it; and by detection in asymptomatic people. The variables of intervention were identified by dichotomic trees expressed by relative frequencies. Forty-five point three percent of the subjects are hypertense: 27% previously diagnosed and 18.3% at the time of the exploration. Thirty-nine percent are hypercholesterolemic: 33.4% previously diagnosed and 5.6% at the time of the exploration. Twenty-one point two percent presented hyperglycemia: 9.7% previously diagnosed and 11.6% at the time of the exploration. Sixty-five point six percent were diagnosed as overweight or obese: 25.9% previously and 39.6% at the time of the exploration. They received dietary counselling and pharmacological treatment respectively: 79.8% and 70.3% of the hypertense; 75.4% and 35% of the hypercholesterolemic; 83.1% and 47.4% of those who presented hyperglycemia and 68.5% and 4% of those who showed overweight or obesity. The frequency of cardiovascular risk factors is high. There is a margin for significant improvement in the detection, intervention and control of the risk factors.

Intervención clínica sobre los principales factores de riesgo vascular (estudio RIVANA)

Background. To describe the diagnostic frequency of classical vascular risk factors, dietary and therapeutic interventions and their control. Methods. Within the project Vascular Risk in Navarre (RIVANA), a transversal study was made of a random sample of 4,354 people between the ages of 35 and 84; antecedents were gathered by interview and clinical and analytical exploration was carried out. The subjects were classified for each risk factor into: diagnosed by information –when health personnel had informed them that they presented a risk factor–; by intervention –when they take medication for it–; and by detection in asymptomatic people. The variables of intervention were identified by dichotomic trees expressed by relative frequencies. Results. Forty-five point three percent of the subjects are hypertense: 27% previously diagnosed and 18.3% at the time of the exploration. Thirty-nine percent are hypercholesterolemic: 33.4% previously diagnosed and 5.6% at the time of the exploration. Twenty-one point two percent presented hyperglycemia: 9.7% previously diagnosed and 11.6% at the time of the exploration. Sixty-five point six percent were diagnosed as overweight or obese: 25.9% previously and 39.6% at the time of the exploration. They received dietary counselling and pharmacological treatment respectively: 79.8% and 70.3% of the hypertense; 75.4% and 35% of the hypercholesterolemic; 83.1% and 47.4% of those who presented hyperglycemia and 68.5% and 4% of those who showed overweight or obesity. Conclusions. The frequency of cardiovascular risk factors is high. There is a margin for significant improvement in the detection, intervention and control of the risk factors.

Flow distribution and mass transfer in a parallel microchannel contactor integrated with constructal distributors

AbstractFlow distribution and mass transfer characteristics during CO2‐water flow through a parallel microchannel contactor integrated with two constructal distributors have been investigated numerically and experimentally. Each distributor comprises a dichotomic tree structure that feeds 16 microchannels with hydraulic diameters of 667 μm. It was found that constructal distributors could ensure a nearly uniform gas–liquid distribution at high gas flow rates where the ideal flow pattern was slug‐annular flow. Nevertheless, at small gas flow rates where the ideal flow pattern was slug flow, a significant flow maldistribution occurred primarily due to the lack of large pressure barrier inside each distributor, indicating that dynamic pressure fluctuation in parallel microchannels greatly disturbed an otherwise good flow distribution therein. It was further shown that the present parallel microchannel contactor could realize the desired mass transfer performance previously achieved in one single microchannel under relatively wide operational ranges due to the integration of constructal distributors. © 2009 American Institute of Chemical Engineers AIChE J, 2010

Constructal optimization of arborescent structures with flow singularities

Abstract This article presents analytical resolutions of the problem of optimal channel size distribution for arborescent (ramified, branched, tree-like) networks used as flow distributors or collectors. The distributor network connects a single inlet port to an array of outlet ports distributed over a specified square or rectangular surface (point-to-surface problem), and the reverse for a collector. The optimization problem is formulated as follows: find the distribution of channel radii that minimizes total viscous dissipation (or entropy production, pumping power, pressure drop) under constraints of uniform irrigation and of total volume of channels (or of average residence time) and the assumption that the flow is split equally between branches at each junction. With respect to earlier work, the present approach does not assume Poiseuille flow, but accounts instead for singular pressure losses in T-type junctions. Different situations are investigated, with the pressure loss coefficient being either a constant for the whole structure, or depending on local flow conditions. The case where both Poiseuille and singular pressure losses are present is also addressed. Also two types of networks are taken as illustrations: a dichotomic tree (a branch divides into two sub-branches), and a tetratomic tree (a branch divides into four sub-branches). The analytical results are in the form of scaling relations between the different levels of the arborescence, and in the form of distributions for channel radii, dissipation, pressure drop, porous volumes. A so-called “constructal function” is introduced that depends on the network structure and on the pressure loss relation, and is calculable as the sum of a geometric series. All explicit relations for the above quantities may then be expressed in a compact fashion in terms of the constructal function. A remarkable property of the optimized structures concerns the distribution of dissipation density (i.e. dissipation divided by volume): when the singular pressure loss coefficient is independent of local flow conditions, this quantity is uniform over the whole structure, thus satisfying “equipartition of entropy production”. A weaker form of this property is found when the singular pressure drop coefficient depends on local conditions (parity dependence).

Comparing chromosomal and mitochondrial phylogenies of sportive lemurs (Genus Lepilemur, Primates)

In recent years several new sportive lemur species (genus Lepilemur) have been described. In contrast to other lemur taxa, the genus shows comparatively high chromosomal variability, which, in addition to molecular data, can be used to infer phylogenetic relationships within the genus. By comparing R-banding patterns and fluorescence in-situ hybridization data, we detected chromosomal rearrangements that occurred during speciation within the genus. The analysis of these data with cladistic methods resulted in a dichotomic phylogenetic tree comparable to that obtained from mitochondrial sequence data. However, a phase of reticulation can not be excluded from the evolution of Lepilemur. Although some incongruences were detected, both phylogenies show similar patterns concerning relationships of the basal and terminal splits. We therefore hypothesize that both, chromosome rearrangements and molecular mutations, alone or in combination, contributed to the speciation process in sportive lemurs.

Forest landscape models: Definitions, characterization, and classification

Previous model classification efforts have led to a broad group of models from site-scale (non-spatial) gap models to continental-scale biogeographical models due to a lack of definition of landscape models. Such classifications become inefficient to compare approaches and techniques that are specifically associated with forest landscape modeling. This paper provides definitions of key terminologies commonly used in forest landscape modeling to classify forest landscape models. It presents a set of qualitative criteria for model classification. These criteria represent model definitions and key model implementation decisions, including the temporal resolution, number of spatial processes simulated, and approaches to simulate site-level succession. Four approaches of simulating site level succession are summarized: (1) no site-level succession (spatial processes as surrogates), (2) successional pathway, (3) vital attribute, and (4) model coupling. Computational load for the first three approaches is calculated using the Big O Notation, a standard method. Classification criteria are organized in a hierarchical order that creates a dichotomous tree with each end node representing a group of models with similar traits. The classified models fall into various groups ranging from theoretical and empirical to strategic and tactical. The paper summarizes the applications of forest landscape models into three categories: (1) spatiotemporal patterns of model objects, (2) sensitivities of model object to input parameters, and (3) scenario analyses. Finally, the paper discusses two dilemmas related to the use of forest landscape models: result validation and circular reasoning.

Insights on speciation patterns in the genus Iberochondrostoma (Cyprinidae): Evidence from mitochondrial and nuclear data

In this paper, the patterns of cladogenesis in the cyprinid fish genus Iberochondrostoma were analysed using a mitochondrial (cytochrome b) and a nuclear (beta-actin) gene fragment. The two genes yielded discordant results. While the cytochrome b gene yielded a fully dichotomous tree, where all species of the genus are monophyletic, the much slower beta-actin gene yielded star-like relationships. However, when information from both genes was considered together, the data suggested the persistence of a very large central unit from which at least two peripheral clades arose at different times. This pattern which is akin to peripatric speciation was shown to be compatible with the paleogeographical information available. It is suggested that combining the techniques of phylogeny and phylogeography and the use of multiple markers varying in their rate of evolution may enrich our understanding of speciation and evolution of clades beyond species level.