Phylogenetics and Evolution of theDaphnia longispinaGroup (Crustacea) Based on 12S rDNA Sequence and Allozyme Variation

Although members of the crustacean genusDaphniahave been the target of much research, there is little understanding of the group's evolutionary history. We addressed this gap by inferring a phylogeny for one of the major species groups (longispina) using nucleotide sequence variation of a 525-bp segment of the mitochondrial 12S rDNA and allozyme variation at 21 loci. We identified the major lineages and their relationships, assessed the phylogenetic utility of the few morphological characters in the group, and examinedDaphniaphylogeography. Nuclear and mtDNA phylogenies were generally concordant in recognizing the same four species complexes. An exception was the position ofDaphnia galeata mendotae.The allozyme tree paired this species with theDaphnia rosealineage, whereas the mtDNA trees groupedD. g. mendotaewithDaphnia galeata galeata.This discordance was consistent with the reticulate evolution of nuclear genes supporting the hypothesis thatD. g. mendotaerepresents a case of homoploid hybrid speciation. Striking morphological stasis in thelongispinagroup was evidenced by its very limited morphological divergence over an estimated 100 MY, and by the unusual transitional saturation of the conservative 12S rRNA gene within a species group. Phylogenetic inference also provided evidence that similarities in cephalic crest shape likely resulted from convergent or parallel evolution among species. Endemism at the continental level was indicated for previously cosmopolitan species, but the estimated times of these divisions were inconsistent with vicariance events suggesting recent dispersal among continents. A significant role for divergent selection in new habitats during speciation was suggested by the neighboringly sympatric distributions of four sister species pairs over broad geographic areas.     

Performance of 18S rRNA in Littorinid Phylogeny (Gastropoda: Caenogastropoda)

In the past, 18S rRNA sequences have proved to be very useful for tracing ancient divergences but were rarely used for resolving more recent ones. Moreover, it was suggested that the molecule does not contain useful information to resolve divergences which took place during less than 40 Myr. The present paper takes littorinid phylogeny as a case study to reevaluate the utility of the molecule for resolving recent divergences. Two data sets for nine species of the snail family Littorinidae were analyzed, both separately and combined. One data set comprised 7 new complete 18S rRNA sequences aligned with 2 published littorinid sequences; the other comprised 12 morphological, 1 biochemical, and 2 18S rRNA secondary structure characters. On the basis of its ability to confirm generally accepted relationships and the congruence of results derived from the different data sets, it is concluded that 18S rRNA sequences do contain information to resolve ``rapid' cladogenetic events, provided that they occurred in the not too distant past. 18S rRNA sequences yielded support for (1) the branching order (L. littorea, (L. obtusata, (L. saxatilis, L. compressa))) and (2) the basal position of L. striata in the Littorina clade. Received: 6 February 1998 / Accepted: 20 March 1998     

The branching pattern of major groups of land plants inferred from parsimony analysis of ribosomal RNA sequences

The parsimony and bootstrap branching pattern of major groups of land plants derived from relevant 5S rRNA sequence trees have been discussed in the light of paleobotanical and morphological evidences. Although 5S rRNA sequence information is not useful for dileneating angiosperm relationships, it does capture the earlier phase of land plant evolution. The consensus branching pattern indicates an ancient split of bryophytes and vascular plants from the charophycean algal stem. Among the bryophytes,Marchantia andLophocolea appear to be phylogenetically close and together withPlagiomnium form a monophyletic group.Lycopodium andPsilotum arose early in vascular land plant evolution, independent of fem-sphenopsid branch. Gymnosperms are polyphyletic; conifers, Gnetales and cycads emerge in that order with ginkgo joiningCycas. Among the conifers,Metasequoia,Juniperus andTaxus emerge as a branch independent ofPinus which joins Gnetales. The phylogeny derived from the available ss-RNA sequences shows that angiosperms are monophyletic with monocots and dicots diverging from a common stem. The nucleotide replacements during angiosperm descent from the gymnosperm ancestor which presumably arose around 370 my ago indicates that monocots and dicots diverged around 180 my ago, which is compatible with the reported divergence estimate of around 200 my ago deduced from chloroplast DNA sequences. Since deceased.     

Phylogeny of Ultra-Rapidly Evolving Dinoflagellate Chloroplast Genes: A Possible Common Origin for Sporozoan and Dinoflagellate Plastids

Complete chloroplast 23S rRNA and psbA genes from five peridinin-containing dinoflagellates (Heterocapsa pygmaea, Heterocapsa niei, Heterocapsa rotun-data, Amphidinium carterae, and Protoceratium reticulatum) were amplified by PCR and sequenced; partial sequences were obtained from Thoracosphaera heimii and Scrippsiella trochoidea. Comparison with chloroplast 23S rRNA and psbA genes of other organisms shows that dinoflagellate chloroplast genes are the most divergent and rapidly evolving of all. Quartet puzzling, maximum likelihood, maximum parsimony, neighbor joining, and LogDet trees were constructed. Intersite rate variation and invariant sites were allowed for with quartet puzzling and neighbor joining. All psbA and 23S rRNA trees showed peridinin-containing dinoflagellate chloroplasts as monophyletic. In psbA trees they are related to those of chromists and red algae. In 23S rRNA trees, dinoflagellates are always the sisters of Sporozoa (apicomplexans); maximum likelihood analysis of Heterocapsa triquetra 16S rRNA also groups the dinoflagellate and sporozoan sequences, but the other methods were inconsistent. Thus, dinoflagellate chloroplasts may actually be related to sporozoan plastids, but the possibility of reproducible long-branch artifacts cannot be strongly ruled out. The results for all three genes fit the idea that dinoflagellate chloroplasts originated from red algae by a secondary endosymbiosis, possibly the same one as for chromists and Sporozoa. The marked disagreement between 16S rRNA trees using different phylogenetic algorithms indicates that this is a rather poor molecule for elucidating overall chloroplast phylogeny. We discuss possible reasons why both plastid and mitochondrial genomes of alveolates (Dinozoa, Sporozoa and Ciliophora) have ultra-rapid substitution rates and a proneness to unique genomic rearrangements. Received: 27 December 1999 / Accepted: 24 March 2000     

POLYPHASIC CHARACTERIZATION OF DOLICHOSPERMUM SPP. AND SPHAEROSPERMOPSIS SPP. (NOSTOCALES,CYANOBACTERIA): MORPHOLOGY, 16S rRNA GENE SEQUENCES AND FATTY ACID AND SECONDARY METABOLITE PROFILES1

The genera Dolichospermum (Ralfs ex Bornet et Flahault) Wacklin, L. Hoffm. et Komárek and Sphaerospermopsis Zapomělová, Jezberová, Hrouzek, Hisem, K. ?eháková et Komárk.‐Legn. represent a highly diversified group of planktonic cyanobacteria that have been recently separated from the traditional genus Anabaena Bory ex Bornet et Flahault. In this study, morphological diversity, phylogeny of the 16S rRNA gene, production of fatty acids, and secondary metabolite profiles were evaluated in 33 strains of 14 morphospecies isolated from the Czech Republic. Clustering of the strains based on 16S rRNA gene sequences corresponded to wider groups of species in terms of morphology. The overall secondary metabolite and fatty acid profiles, however, were not correlated to each other and neither were they correlated to the 16S rRNA phylogeny nor the morphology of the strains. Nevertheless, a minor part of the detected secondary metabolites (19% of all compounds) was present only in close relatives and can be thus considered as autapomorphic features.     

Morphological variation among members of theStellaria longipes complex:S. longipes,S. longifolia,andS. porsildii (Caryophyllaceae)

Morphological relationships were investigated among diploidStellaria porsildii, polyploidS. longipes, and diploidS. longifolia. Canonical discriminant analysis, based on a priori assumptions to maximize differences among groups, showed thatS. longipes clusters equally distant between the two diploid species along an axis connecting the diploids' centroids, but it differs along an axis perpendicular to this axis. The intermediacy along the former axis is evidence thatS. longipes is an amphiploid derived fromS. longifolia andS. porsildii. The divergence along the latter axis may be attributable to adaptively valuable heterotic traits which were retained following amphidiploidization. The only morphological discontinuity occurred between the two diploids, whereas the morphological range ofS. longipes overlapped the range of both diploids forming a continuum. The lack of discrete clusters is likely due to hybridization and introgression withS. longifolia on one hand, and convergence of traits betweenS. longipes var.monantha andS. porsildii on the other. High a posteriori assignments in classificatory discriminant analysis supports the separation ofS. longipes var.monantha from otherS. longipes specimens. AlthoughS. longipes var.monantha grouped close toS. porsildii, the two groups separate based on leaf shape traits. Overall results support, firstly, the hypothesis thatS. porsildii is a diploid parent species which by hybridizing withS. longifolia gave rise to polyploidS. longipes. Secondly, results suggest thatS. longipes var.monantha converged morphologically towardsS. porsildii relatively recently due to ecological specialization, and merits distinction at least as a variety ofS. longipes.     

New considerations on the phylogeny of cyrtophorian ciliates (Protozoa,Ciliophora): expanded sampling to understand their evolutionary relationships

To rationalize the confusing relationships among the cyrtophorian ciliates, we expanded the taxon sampling by sequencing the small subunit ribosomal RNA (SSU rRNA) gene of representatives of 12 genera (20 species, 23 new sequences). The SSU rRNA sequences of Spirodysteria, Agnathodysteria, Brooklynella and Odontochlamys are reported for the first time. Phylogenetic trees were constructed, and secondary structures of variable region 4 (V4) of all genera for which SSU rRNA gene sequence data are available were predicted. The results indicate that (i) Brooklynella is likely an intermediate taxon between Dysteriidae and Hartmannulidae; (ii) the genus Dysteria is paraphyletic with Spirodysteria and Mirodysteria nested within it; (iii) the genus Agnathodysteria is well separated from Dysteria based on both molecular and morphological data; and (iv) Trithigmostoma is a basal genus of Chilodonellidae, based on both the morphological and molecular data.     

Secondary structure and patterns of evolution among mammalian mitochondrial 12S rRNA molecules

Forty-nine complete 12S ribosomal RNA (rRNA) gene sequences from a diverse assortment of mammals (one monotreme, 11 marsupials, 37 placentals), including 11 new sequences, were employed to establish a ``core' secondary structure model for mammalian 12S rRNA. Base-pairing interactions were assessed according to the criteria of potential base-pairing as well as evidence for base-pairing in the form of compensatory mutations. In cases where compensatory evidence was not available among mammalian sequences, we evaluated evidence among other vertebrate 12S rRNAs. Our results suggest a core model for secondary structure in mammalian 12S rRNAs with deletions as well as additions to the Gutell (1994: Nucleic Acids Res. 22) models for Bos and Homo. In all, we recognize 40 stems, 34 of which are supported by at least some compensatory evidence within Mammalia. We also investigated the occurrence and conservation in mammalian 12S rRNAs of nucleotide positions that are known to participate in the decoding site in E. coli. Twenty-four nucleotide positions known to participate in the decoding site in E. coli also occur among mammalian 12S rRNAs and 17 are invariant for the same base as in E. coli. Patterns of nucleotide substitution were assessed based on our secondary structure model. Transitions in loops become saturated by approximately 10–20 million years. Transitions in stems, in turn, show partial saturation at 20 million years but divergence continues to increase beyond 100 million years. Transversions accumulate linearly beyond 100 million years in both stems and loops although the rate of accumulation of transversions is three- to fourfold higher in loops. Presumably, this difference results from constraints to maintain pairing in stems. Received: 21 June 1995 / Accepted: 25 March 1996     

Phylogenetic relationships ofPythium species based on ITS and 5.8S sequences of the ribosomal DNA

The sequences of ITS regions in 30 species and two groups of the genusPythium were resolved. In the phylogenetic trees, the species were generally divided into two clusters, referred to here as the F and S groups. The species in the two groups correspond in terms of their sporangial morphology, with the F group being filamentous/lobulate and the S group being spherical. Genetic divergence within the F group was lower than that within the S group. Other morphological characteristics such as oogonial structure and sexual nature appeared to be unrelated to the groupings in these trees. An alignment analysis revealed common sequences to all the species and arrangements specific to each F or S group. It was found that the ITS region was a good target in designing species-specific primers for the identification and detection ofPythium species. In the tree based on 5.8S rDNA sequences, oomycetes are distantly related to other fungi but separated from algae in Chromista.     

Reconciling classical and molecular phylogenies in the stichotrichines (Ciliophora, Spirotrichea), including new sequences from some rare species

We performed a comparative morphological and molecular study on oxytrichid and urostylid stichotrichs (=part of the former hypotrichs). Included are new small subunit (18S) ribosomal RNA (rRNA) gene sequences from five rare oxytrichids (Gonostomum namibiense, Cyrtohymena citrina, Hemiurosoma terricola, Onychodromopsis flexilis, Orthoamphisiella breviseries) and published sequences, based on cultures provided by the senior author, of two key stichotrichid genera, viz., Gastrostyla and Engelmanniella. These and other sequences, altogether 27 species representing 23 genera, were used to analyze how 18S rRNA-based phylogenetic trees can be reconciled with the morphological and ontogenetical data. In 18S rRNA trees, the oligotrichine family Halteriidae invariably clusters within the oxytrichid clade, usually near Oxytricha granulifera, type species of the genus. This position is hardly supported by morphological and ecological evidence and, especially, it contradicts the current ontogenetic findings; possibly, it is an artifact caused by taxa undersampling and/or special molecular evolutionary events. In contrast, most morphological and DNA sequence data of the stichotrichs can be harmonized with the CEUU (Convergent Evolution of Urostylids and Uroleptids) hypothesis which suggests that the urostylid midventral pattern evolved from an oxytrichine ancestor, developing a second time within the Oxytrichidae. The systematic position of one of the two key genera could be clarified with the 18S rRNA sequences: Gastrostyla is a stylonychine oxytrichid. Based on the molecular data and a reassessment of ontogenesis, a new genus, Styxophrya nov. gen., is established for Onychodromus quadricornutus Foissner, Schlegel & Prescott, 1987.     

Molecular phylogeny of silk-producing insects based on 16S ribosomal RNA and cytochrome oxidase subunit I genes

We have examined the molecular-phylogenetic relationships between nonmulberry and mulberry silkworm species that belong to the families Saturniidae, Bombycidae and Lasiocampidae using 16S ribosomal RNA (16S rRNA) and cytochrome oxidase subunit I (coxI) gene sequences. Aligned nucleotide sequences of 16S rRNA andcoxI from 14 silk-producing species were used for construction of phylogenetic trees by maximum likelihood and maximum parsimony methods. The tree topology on the basis of 16S rRNA supports monophyly for members of Saturniidae and Bombycidae. Weighted parsimony analysis weighted towards transversions relative to transitions (ts, tv4) forcoxI resulted in more robust bootstrap support over unweighted parsimony and favours the 16S rRNA tree topology. Combined analysis reflected clear biogeographic pattern, and agrees with morphological and cytological data.     

Genotypic and phenotypic diversity of cyanobacteria assigned to the genus <Emphasis Type="Italic">Phormidium</Emphasis> (Oscillatoriales) from different habitats and geographical sites

In this study, 30 strains of filamentous, non-heterocystous cyanobacteria from different habitats and different geographical regions assigned to diverse oscillatorian genera but here collectively referred to as members of the Phormidium group have been characterized using a polyphasic approach by comparing phenotypic and molecular characteristics. The phenotypic analysis dealt with cell and filament morphology, ultrastructure, phycoerythrin content, and complementary chromatic adaptation. The molecular phylogenetic analyses were based on sequences of the 16S rRNA gene and the adjacent intergenic transcribed spacer (ITS). The sequences were located on multiple branches of the inferred cyanobacterial 16S rRNA tree. For some, but not all, strains with identical 16S rDNA sequences, a higher level of discrimination was achieved by analyses of the less conserved ITS sequences. As shown for other cyanobacteria, no correlation was found between position of the strains in the phylogenetic tree and their geographic origin. Genetically similar strains originated from distant sites while other strains isolated from the same sampling site were in different phylogenetic clusters. Also the presence of phycoerythrin was not correlated with the strains’ position in the phylogenetic trees. In contrast, there was some correlation among inferred phylogenetic relationship, original environmental habitat, and morphology. Closely related strains came from similar ecosystems and shared the same morphological and ultrastructural features. Nevertheless, structural properties are insufficient in themselves for identification at the genus or species level since some phylogenetically distant members also showed similar morphological traits. Our results reconfirm that the Phormidium group is not phylogenetically coherent and requires revision.     

Molecular evidence for the presence of novel actinomycete lineages in a temperate forest soil

PCR primers were designed to selectively recover partial (1100 bp) actinomycete 16S ribosomal DNA sequences from a temperate forest soil. A gene library was made and colony PCR was used to identify clones containing inserts. Unique clones were identified and partial or complete insert sequences were determined for 53 clones. Phylogenetic analyses revealed that 46 (87%) of the clones sampled contained 16S rDNA sequences which fell within the actinomycete radiation. The largest group of 34 sequences formed two closely related monophyletic groups in the 16S rRNA tree, which in turn formed a weakly supported sister group with the sequence fromActinomadura madurae. Four novel 16S rDNA lineages were detected inMycobacterium, one inPropionibacterium and one inCorynebacterium. Three novel sequences weakly grouped withSporichthya polymorpha. Two sequences formed an isolated lineage not closely related to any of the reference actinomycetes. Our results lend strong support to the hypothesis that cultured (and sequenced) actinomycetes do not adequately describe the diversity of this group in the environment.     

Molecular evolution of the mitochondrial 12S rRNA in Ungulata (mammalia)

The complete 12S rRNA gene has been sequenced in 4 Ungulata (hoofed eutherians) and 1 marsupial and compared to 38 available mammalian sequences in order to investigate the molecular evolution of the mitochondrial small-subunit ribosomal RNA molecule. Ungulata were represented by one artiodactyl (the collared peccary, Tayassu tajacu, suborder Suiformes), two perissodactyls (the Grevy's zebra, Equus grevyi, suborder Hippomorpha; the white rhinoceros, Ceratotherium simum, suborder Ceratomorpha), and one hyracoid (the tree hyrax, Dendrohyrax dorsalis). The fifth species was a marsupial, the eastern gray kangaroo (Macropus giganteus). Several transition/transversion biases characterized the pattern of changes between mammalian 12S rRNA molecules. A bias toward transitions was found among 12S rRNA sequences of Ungulata, illustrating the general bias exhibited by ribosomal and protein-encoding genes of the mitochondrial genome. The derivation of a mammalian 12S rRNA secondary structure model from the comparison of 43 eutherian and marsupial sequences evidenced a pronounced bias against transversions in stems. Moreover, transversional compensatory changes were rare events within double-stranded regions of the ribosomal RNA. Evolutionary characteristics of the 12S rRNA were compared with those of the nuclear 18S and 28S rRNAs. From a phylogenetic point of view, transitions, transversions and indels in stems as well as transversional and indels events in loops gave congruent results for comparisons within orders. Some compensatory changes in double-stranded regions and some indels in single-stranded regions also constituted diagnostic events. The 12S rRNA molecule confirmed the monophyly of infraorder Pecora and order Cetacea and demonstrated the monophyly of suborder Suiformes. However, the monophyly of the suborder Ruminantia was not supported, and the branching pattern between Cetacea and the artiodactyl suborders Ruminantia and Suiformes was not established. The monophyly of the order Perissodactyla was evidenced, but the relationships between Artiodactyla, Cetacea, and Perissodactyla remained unresolved. Nevertheless, we found no support for a Perissodactyla + Hyracoidea clade, neither with distance approach, nor with parsimony reconstruction. The 12S rRNA was useful to solve intraordinal relationships among Ungulata, but it seemed to harbor too few informative positions to decipher the bushlike radiation of some Ungulata orders, an event which has most probably occurred in a short span of time between 55 and 70 MYA. Correspondence to: E. Douzery     

Congruence between molecular phylogeny and cuticular design in Echiniscoidea (Tardigrada,Heterotardigrada)

Although morphological characters distinguishing echiniscid genera and species are well understood, the phylogenetic relationships of these taxa are not well established. We thus investigated the phylogeny of Echiniscidae, assessed the monophyly of Echiniscus, and explored the value of cuticular ornamentation as a phylogenetic character within Echiniscus. To do this, DNA was extracted from single individuals for multiple Echiniscus species, and 18S and 28S rRNA gene fragments were sequenced. Each specimen was photographed, and published in an open database prior to DNA extraction, to make morphological evidence available for future inquiries. An updated phylogeny of the class Heterotardigrada is provided, and conflict between the obtained molecular trees and the distribution of dorsal plates among echiniscid genera is highlighted. The monophyly of Echiniscus was corroborated by the data, with the recent genus Diploechiniscus inferred as its sister group, and Testechiniscus as the sister group of this assemblage. Three groups that closely correspond to specific types of cuticular design in Echiniscus have been found with a parsimony network constructed with 18S rRNA data. © 2013 The Linnean Society of London     

Taxonomic re-evaluation of Aphanizomenon flos-aquae NH-5 based on morphology and 16S rRNA gene sequences

The taxonomy of Aphanizomenon flos-aquae strain NH-5, a producer of cyanotoxins, was re-evaluated by comparison with six other Aphanizomenon strains using morphological characteristics and 16S rRNA gene sequences. Strain NH-5 was concluded to be improperly identified as Aph. flos-aquae based upon (1) lack of bundle formation in the trichomes, (2) location of akinetes next to heterocytes, (3) lower similarities (less than 97.5%) in the 16S rRNA gene sequences relative to Aph. flos-aquae strains, and (4) comparison within a phylogenetic tree constructed from 16S rRNA gene sequences. The Aphanizomenon strains investigated in this study are classified to four morphological groups as described by the classical taxonomy of Komárek & Kovácik (1989). This classification was supported from the phylogenetic results of 16S rRNA gene sequences. This study also discusses the generic boundaries between Aphanizomenon and Anabaena.     

The 5S DNA units of bread wheat (Triticum aestivum)

A collection of 44 cloned 5S DNA units fromTriticum aestivum cv. Chinese Spring were grouped into 12 sequence-types based on sequence similarity and the respective consensus sequences were then produced. The relationship between these 12 consensus sequences (T. aestivum S 1-S 8 andT. aestivum L 1-L 4), together with two clones sequenced byGerlach andDyer, and the 5S DNA consensus sequences from diploidTriticum spp. were then determined by numerical methods. Both phenetic and cladistic analyses were carried out. The following wheat 5S DNA sequences were found to group with respective sequences from diploidTriticum spp.:T. aestivum S 4, S 6 withT. tauschii S;T. aestivum S 3 withT. monococcum S andT. monococcum S-Rus 7;T. aestivum L 1 andT. aestivum L-G&D withT. speltoides L;T. aestivum L 2, L 3 withT. tauschii L;T. aestivum L 4 withT. monococcum L andT. monococcum L-Rus 12. The analyses suggested that 5 out of the 65S Dna loci present in wheat were identified at the sequence level. The locus that could not be identified in this analysis was the5S Dna-B 1 locus. A group ofT. aestivum sequences (T. aestivum S 1, S 7, S 8, S-G&D) were found to be distinct from the other 5S DNA sequences in the data base. The existence of the distinct group of 5S DNA sequences suggests that there is a gap in our current understanding of wheat evolution with respect to the5S Dna loci.     

16S rRNA及rpoC1基因用于螺旋藻、节旋藻系统发育的比较北大核心CSCD

【目的】利用16S rRNA和rpoC1基因分子标记研究螺旋藻、节旋藻的系统发育关系,并对其区分能力进行比较。【方法】以84株螺旋藻、节旋藻为研究对象,对其进行16S rRNA、rpoC1基因序列的扩增、测序及分析,并对构建的系统发育树进行对比。【结果】rpoC1基因序列保守位点所占比例49.7%、平均G+C百分含量47.7%和序列相似度76%–100%明显低于16S rRNA基因序列的79.4%、55.6%和91%–100%,其变异程度高于16S rRNA基因;基于16S rRNA、rpoC1基因构建的系统发育NJ树拓扑结构基本一致,84株实验藻株分为2个属3个类群,其中仅F-351、F-904-2、F-1070和TJBC14-1藻株为螺旋藻,其余均为节旋藻;虽然2个基因都不能区分形态种和地理种,但rpoC1基因NJ树的置信度(100%)高于16S rRNA基因(99%),属内分群效果也明显优于16S rRNA基因。【结论】支持了螺旋藻、节旋藻为两个不同属的结论,且在属内分类时rpoC1基因比16S rRNA基因具有更高的区分度。     

Phylogenetic relationships of Steinernema Travassos, 1927 (Nematoda: Cephalobina: Steinernematidae) based on nuclear, mitochondrial and morphological data

Entomopathogenic nematodes of the genus Steinernema are lethal parasites of insects that are used as biological control agents of several lepidopteran, dipteran and coleopteran pests. Phylogenetic relationships among 25 Steinernema species were estimated using nucleotide sequences from three genes and 22 morphological characters. Parsimony analysis of 28S (LSU) sequences yielded a well-resolved phylogenetic hypothesis with reliable bootstrap support for 13 clades. Parsimony analysis of mitochondrial DNA sequences (12S rDNA and cox 1 genes) yielded phylogenetic trees with a lower consistency index than for LSU sequences, and with fewer reliably supported clades. Combined phylogenetic analysis of the 3-gene dataset by parsimony and Bayesian methods yielded well-resolved and highly similar trees. Bayesian posterior probabilities were high for most clades; bootstrap (parsimony) support was reliable for approximately half of the internal nodes. Parsimony analysis of the morphological dataset yielded a poorly resolved tree, whereas total evidence analysis (molecular plus morphological data) yielded a phylogenetic hypothesis consistent with, but less resolved than trees inferred from combined molecular data. Parsimony mapping of morphological characters on the 3-gene trees showed that most structural features of steinernematids are highly homoplastic. The distribution of nematode foraging strategies on these trees predicts that S. hermaphroditum, S. diaprepesi and S. longicaudum (US isolate) have cruise forager behaviours.     

Phylogenetic relationship of the green alga Nanochlorum eukaryotum deduced from its chloroplast rRNA sequences

The marine green coccoidal alga Nanochlorum eukaryotum (N.e.) is of small size with an average diameter of 1.5 m. It is characterized by primitive-appearing biochemical and morphological properties, which are considerably different from those of other green algae. Thus, it has been proposed that N.e. may be an early developed algal form. To prove this hypothesis, DNA of N.e. was isolated by a phenol extraction procedure, and the chloroplast DNA separated by preparative CsCl density-gradient centrifugation. The kinetic complexity of the nuclear and of the chloroplast DNA was evaluated by reassociation kinetics to 3 × 10⁷ by and 9 × 10⁴ bp, respectively. Several chloroplast genes, including the rRNA genes, were cloned on distinct fragments. The order of the rRNA genes corresponds to the common prokaryotic pattern. The 16S rRNA gene comprises 1,548 bases and is separated from the 23S rRNA gene with its 2,920 bases by a short spacer of 460 bases, which also includes the tRNA^Ile and tRNA^Ala genes. The 5S rRNA gene has not been found; it must start further than 500 bases downstream from the 3-end of the 23S rRNA gene. From the chloroplast rRNA sequences, we have deduced secondary structures of the 16S and 23S rRNAs, which are in agreement with standard models. The rRNA sequences were aligned with corresponding chloroplast sequences; phylogenetic relationships were calculated by several methods. From these calculations, we conclude that N.e. is most closely related to Chlorella vulgaris. Therefore, N.e. does not represent an early developed algal species; the primitive-appearing morphological and biochemical characteristics of N.e. must rather be explained by secondary losses. Correspondence to: D. Weinblum