[Molecular phylogeny of gastrotricha based on 18S rRNA genes comparison: rejection of hypothesis of relatedness with nematodes].

Gastrotrichs are meiobenthic free-living aquatic worms whose phylogenetic and intra-group relationships remain unclear despite some attempts to resolve them on the base of morphology or molecules. In this study we analysed complete sequences of the 18S rRNA gene of 15 taxa (8 new and 7 published) to test numerous hypotheses on gastrotrich phylogeny and to verify whether controversial interrelationships from previous molecular data could be due to the short region available for analysis and the poor taxa sampling. Data were analysed using both maximum likelihood and Bayesian inference. Results obtained suggest that gastrotrichs, together with Gnathostomulida, Plathelminthes, Syndermata (Rotifera + Acanthocephala), Nemertea and Lophotrochozoa, comprise a clade Spiralia. Statistical tests reject phylogenetic hypotheses regarding Gastrotricha as close relatives of Nematoda and other Ecdysozoa or placing them at the base of bilaterian tree close to acoels and nemertodermatides. Within Gastrotricha, Chaetonotida and Macrodasyida comprise two well supported clades. Our analysis confirmed the monophyly of the Chaetonotidae and Xenotrichulidae within Chaetonida as well as Turbanellidae and Thaumastodermatidae within Macrodasyida. Mesodasys is a sister group of the Turbanellidae, and Lepidodasyidae appears to be a polyphyletic group as Cephalodasys forms a separate lineage at the base of macrodasyids, whereas Lepidodasys groups with Neodasys between Thaumastodermatidae and Turbanellidae. To infer a more reliable Gastrotricha phylogeny many species and additional genes should be involved in future analyses.

[Phylogeny of protostome moulting animals (Ecdysozoa) inferred from 18 and 28S rRNA gene sequences].

Reliability of reconstruction of phylogenetic relationships within a group of protostome moulting animals was evaluated by means of comparison of 18 and 28S rRNA gene sequences sets both taken separately and combined. Reliability of reconstructions was evaluated by values of the bootstrap support of major phylogenetic tree nodes and by degree of congruence of phylogenetic trees inferred by various methods. By both criteria, phylogenetic trees reconstructed from the combined 18 and 28S rRNA gene sequences were better than those inferred from 18 and 28S sequences taken separately. Results obtained are consistent with phylogenetic hypothesis separating protostome animals into two major clades, moulting Ecdysozoa (Priapulida + Kinorhyncha, Nematoda + Nematomorpha, Onychophora + Tardigrada, Myriapoda + Chelicerata, Crustacea + Hexapoda) and unmoulting Lophotrochozoa (Plathelminthes, Nemertini, Annelida, Mollusca, Echiura, Sipuncula). Clade Cephalorhyncha does not include nematomorphs (Nematomorpha). Conclusion was taken that it is necessary to use combined 18 and 28S data in phylogenetic studies.

[Phylogeny of amphibia based on comparison of conserved segments of the 28S rRNA sequence]. / Filogeniia amfibii na osnovanii sravneniia konservativnykh uchastkov posledovatelnosti 28S rRNK.

The sequences of two regions flanking the 5'D1 domain of 28S rRNA of 13 vertebrate species were determined by direct rRNA sequencing through reverse transcriptase extension of DNA primers. Comparative treatment of these new data and previously reported rRNA sequences was undertaken with special reference to phylogenetic affinity of Amphibia by using some programs of Felsenstein's PHYLIP 3.3 package. The results obtained suggest that Amphibia is rather a biphyletic than a monophyletic group, and that birds and mammals are the closest relevant. These data were compared with those obtained on Vertebrata by using an analogous comparative analysis of 18S rRNA sequences.

[Repeating DNA sequences of closely related species of mosquitoes]. / Povtvoriaiushchiesiia posledovatel'nosti DNK blizkorodstvennykh vidov komarov.

Repeated DNA sequences of mosquitoes were studied by using of reassociation kinetics, molecular hybridization, restriction analysis and Southern blot-hybridization. Mosquitoes of two genera, the species of one of them being sibling species, were investigated. The content of all repeated families is the same both in sibling species and in species of different genera DNA. The percent of homologous sequences is low as compared to the high thermal stability of heterologous duplexes both in sibling species DNA and in different genera DNA. Restriction analysis of DNA and blot-hybridization with 35S repeated fraction revealed certain specific families of repeated sequences in the DNA of sibling species and of different genera of mosquitoes.

[Formation of the genome of the alligator gar Lepisosteus osseus (Ganoidomorpha) genome]. / Stroenie genoma pantsirnoi shchuki Lepisosteus osseus (kostnye ganoidy).

Genome structure of the alligator gar was studied by means of a comparison of reassociation kinetics of short and long DNA fragments, an estimation of hyperchromicity of reassociated repetitive DNA as a function of fragments length, and length estimation of S1-resistant duplexes by gel filtration. It was shown that most of the repeated sequences in the alligator gar DNA are no less than 2000 b.p. long and weakly divergent. Little or no interspersion of unique and short repeated sequences were observed in this genome. No highly divergent repeats were found in the alligator gar genome.

[Comparison of the genome of the alligator gar with the genomes of several other fish]. / Sravnenie genoma pantsirnoi shchuki s genomami nekotorykh drugikh ryb.

Hybridization of alligator gar (Lepisosteus osseus, Lepisosteiformes, Ganoidomorpha) [125I]- or [3H]DNA fractions with DNAs of more or less phylogenetically related fishes was studied. Almost all of the repeated and unique sequences of alligator gar DNA and DNA of the spotted gar (from the same genus) are highly homologous (1-2% of nucleotide substitutions). The degrees of homology between repeated and unique sequences of alligator gar DNA and DNAs of the representatives of Acipenseriformes (the same super-order Ganoidomorpha), Latimeria chalumnae (another subclass, Sarcopterygii) and a shark (another class, Chondrichthyes) are of the same order, and the levels of divergency of their DNAs sequences are similar. These results demonstrate, that the joining of Lepisosteiformes and Acipenseriformes in one and the same group of Ganoidomorpha is artificial, and that the superclass of fishes, Pisces, includes more taxons of the class rank then it has been taken in theory.

[Divergence of unique and repetitive sequences in the genomes of fish]. / Divergentsiia unikal'ykh i povtoriaiushchikhsia posledovatel' "nostei v genomakh ryb.

The sterlet (Acipenser acipenser) genome was compared with the genome of other fishes by molecular hybridization of its fractions. The genomes of all fishes of the family Acipenseridae are represented by the same sets of repetitive and single copy sequences. Single copy sequences contain 1.5-2.7% nucleotide mismatches, and repetitive sequences 0-2.6%, so the divergency rate of single copy sequences in this family is higher that of the repetitive sequences. The rates of evolution of the repetitive sequences with different intragenomic divergency are the same. The great similarity in the structure of genomes of Acipenseridae is the molecular basis for the formation of vital fertile hybrids between these fishes. The genomes of Acipenseridae contain some sequences homologous to teleostean and chondrostean fishes DNA. These sequences are 5% of single copy and 10-25% of repetitive sequences and are the most conservative sequences in the fishes genomes.

[Organization of nucleotide sequences in the genome of the sterlet Acipenser acipenser]. / Organizatsiia nukleotidnykh posledovatel' "nostei v genome sterliadi Acipenser acipenser.

Three fractions of repeated sequences with different thermal stability after reassociation and zero time and single copy fractions as well were isolated from a sterlet (acipenser acipenser) genome. Repeated sequences with different thermal stabilities are organized as homogeneous families not reassociating with one another when being repeatedly annealed. These fractions consist of the similar kinetic components; the exception is the slowly reassociating component which is found only in the low temperature fraction. The sterlet repeated sequences were also fractionated according to their length on agarose A-50 columns. The long (no less than 1350 nucleotides) sequences are heterogeneous by extent of their divergency, some part of them being highly divergent and contain sequences that are homologous to repeated sequences with low thermal stability. A suggestion is made that long and short repeated sequences in the sterlet genome are partly shared. The short (about 400-600 nucleotides) repeated sequences in the sterlet genome are interspersed within single copy ones.

[Primary structure of hairpin 35 and 48 small rRNA is proof that Trefusiidae is a subtaxon of marine Enoplida (Nemotoda)]. / Pervichnaia struktura petel' 35 i 48 maloi rRNK svidetel'stvuet, chto Trefusiidae iavliaiutsia subtaksonom morskikh Enoplida (Nematoda).

A rare nucleotide substitution was found in the evolutionarily conserved loop of hairpin 35 of the 18S rRNA gene of marine free-living nematode, Trefusia zostericola (Nematoda: Enoplida). The same substitution was found in all the marine Enoplida studied but not in other nematodes. Such a molecular synapomorphy indicates that marine enoplids are more closely related to T. zostericola than to freshwater Triplonchida. Maximum parsimony, neighbor-joining, and maximum likelihood analyses of complete nucleotide sequences of the gene, with the heterogeneity of nucleotide sites in evolution rates taken into account, support this conclusion. Hence, the hypothesis of particular primitiveness of Trefusiidae among nematodes should be rejected. Phylogenies based on molecular data support the morphological reduction of metanemes in Trefusiidae. Alongside with the unique change in hairpin 35 loop among marine Enoplida (including T. zostericola), hairpin 48 is also modified by a rare transversion which could be found among Mesorhabditoidea nematodes, in related genera Pelodera, Mesorhabditis, Teratorhabditis, Parasitorhabditis, Crustorhabditis, and Distolabrellus, and in 11 orders of Rhodophyta. Rare mutations in hairpins 35 and 48 tend to be fixed correlatively in evolution and could be found in all the Acanthocephala species. X-Ray data show that these regions (H31 and H43, in alternative nomenclature) are spatially brought together in native ribosomes. The nature and distribution of molecular autoapomorphies in phylogenetic trees of high-rank taxa are discussed.