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Taxonomic System (taxonomic + system)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

TAXONOMIC REEXAMINATION OF 17 SPECIES OF NITELLA SUBGENUS TIEFFALLENIA (CHARALES, CHAROPHYCEAE) BASED ON INTERNAL MORPHOLOGY OF THE OOSPORE WALL AND MULTIPLE DNA MARKER SEQUENCES,

JOURNAL OF PHYCOLOGY, Issue 1 2005
Hidetoshi Sakayama
In an attempt to reconstruct the natural taxonomic system for Nitella, 17 species of Nitella subgenus Tieffallenia were reexamined using SEM observations of the internal morphology of the oospore wall (IMOW) and phylogenetic analyses of 4553 base pairs from multiple DNA markers (atpB, rbcL, psaB, and ITS-5.8S rRNA genes). Our SEM observations identified three types of IMOW: homogeneous (HG), weakly spongy (W-SG), and strongly spongy (S-SG) types. Based on differences in the IMOW, species with reticulate or tuberculate oospore wall ornamentation in the external morphology of the oospore wall (EMOW) were subdivided into two distinct groups (characterized by the HG or S-SG types of IMOW, respectively), which were robustly separated from each other in our molecular phylogenetic analyses. In our molecular phylogeny, the subgenus Tieffallenia consisted of four robust monophyletic groups,three clades of the HG type and a spongy (S-SG and W-SG) type clade,that were characterized by differences in the IMOW and EMOW. In addition, our SEM observations and sequence data verified the distinct status of five species (N. japonica Allen, N. oligospira A. Braun, N. vieillardii stat. nov., N. imperialis stat. nov., and N. morongii Allen) that R. D. Wood had assigned as infraspecific taxa. Moreover, our SEM observations of the IMOW also suggested that N. megaspora (J. Groves) Sakayama originally identified by LM includes at least two distinct species, characterized by W-SG and S-SG types of IMOW, respectively. [source]

Species identification of Alnus (Betulaceae) using nrDNA and cpDNA genetic markers

MOLECULAR ECOLOGY RESOURCES, Issue 4 2010
BAO-QING REN
Abstract One nuclear and three chloroplast DNA regions (ITS, rbcL, matK and trnH-psbA) were used to identify the species of Alnus (Betulaceae). The results showed that 23 out of all 26 Alnus species in the world, represented by 131 samples, had their own specific molecular character states, especially for three morphologically confused species (Alnus formosana, Alnus japonica and Alnus maritima). The discriminating power of the four markers at the species level was 10% (rbcL), 31.25% (matK), 63.6% (trnH-psbA) and 76.9% (ITS). For ITS, the mean value of genetic distance between species was more than 10 times the intraspecific distance (0.009%), and 13 species had unique character states that differentiated them from other species of Alnus. The trnH-psbA region had higher mean values of genetic distance between and within species (2.1% and 0.68% respectively) than any other region tested. Using the trnH-psbA region, 13 species are distinguished from 22 species, and seven species have a single diagnostic site. The combination of two regions, ITS and trnH-psbA, is the best choice for DNA identification of Alnus species, as an improvement and supplement for morphologically based taxonomy. This study illustrates the potential for certain DNA regions to be used as novel internet biological information carrier through combining DNA sequences with existing morphological character and suggests a relatively reliable and open taxonomic system based on the linked DNA and morphological data. [source]

16S rRNA GENE HETEROGENEITY IN THE FILAMENTOUS MARINE CYANOBACTERIAL GENUS LYNGBYA,

JOURNAL OF PHYCOLOGY, Issue 3 2010
Niclas Engene
The SSU (16S) rRNA gene was used to investigate the phylogeny of the cyanobacterial genus Lyngbya as well as examined for its capacity to discriminate between different marine species of Lyngbya. We show that Lyngbya forms a polyphyletic genus composed of a marine lineage and a halophilic/brackish/freshwater lineage. In addition, we found morphological and genetic evidence that Lyngbya spp. often grow in association with other microorganisms, in particular smaller filamentous cyanobacteria such as Oscillatoria, and propose that these associated microorganisms have led to extensive phylogenetic confusion in identification of Lyngbya spp. At the species level, the phylogenetic diversity obtained from the comparison of 16S rRNA genes exceeded morphological diversity in Lyngbya. However, the expectation that this improved phylogeny would be useful to species and subspecies identification was eliminated by the fact that phylogenetic species did not correlate in any respect with the species obtained from current taxonomic systems. In addition, phylogenetic identification was adversely affected by the presence of multiple gene copies within individual Lyngbya colonies. Analysis of clonal Lyngbya cultures and multiple displacement amplified (MDA) single-cell genomes revealed that Lyngbya genomes contain two 16S rRNA gene copies, and that these typically are of variable sequence. Furthermore, intragenomic and interspecies 16S rRNA gene heterogeneity was approximately of the same magnitude. Hence, the intragenomic heterogeneity of the 16S rRNA gene overestimates the microdiversity of different strains and does not accurately reflect speciation within cyanobacteria, including the genus Lyngbya. [source]

Clinical Diagnosis at the Crossroads

CLINICAL PSYCHOLOGY: SCIENCE AND PRACTICE, Issue 3 2006
David Watson
There is widespread dissatisfaction with the existing diagnostic system articulated in the Diagnostic and Statistical Manual of Mental Disorders (DSM). The current DSM system is atheoretical, cumbersome to use, and plagued by the problems of comorbidity and heterogeneity. We explore two possible alternative approaches: (a) reorganizing the diagnostic classes and (b) the implementation of fully dimensional schemes. We then discuss the possibility that DSM-V will be a hybrid system, with Axis I remaining categorical and Axis II becoming dimensional. We conclude with a discussion of the merits,as well as the disadvantages,of creating two different taxonomic systems, one designed for psychopathology researchers and the other for practicing clinicians. [source]