Isolation and characterization of microsatellite markers in the periwinkle Littorina striata King & Broderip, 1832 (Mollusca, Gastropoda, Prosobranchia).
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Alleles↗
Biomedical subjects
T Backeljau
Publications and source records attributed to T Backeljau.
Bootstrap tests for specific hypotheses at single locus inbreeding coefficients.
Deviations of genotype distribution from Hardy-Weinberg expectations within a (sub)population can give valuable insight into the population structure, and can be quantified by means of F(is) values. Specific biological and/or genetical hypotheses regarding F(is) require particular statistical procedures to be able to perform the test with high power. The bootstrap offers a convenient way to test against a broad range of alternative hypotheses. It enables: a) comparison of an observed F(is) with any expected value between -1 and 1, and b) comparison of two or more observed F(is) values. However, it fails under numerous situations, and great caution should be taken before applying the bootstrap to estimate confidence intervals of F(is). We discuss under which conditions the bootstrap gives reliable results.
Gene Frequency↗
18S rRNA suggests that Entoprocta are protostomes, unrelated to Ectoprocta.
The Ento- and Ectoprocta are sometimes placed together in the Bryozoa, which have variously been regarded as proto- or deuterostomes. However, Entoprocta have also been allied to the pseudocoelomates, while Ectoprocta are often united with the Brachiopoda and Phoronida in the (super)phylum Lophophorata. Hence, the phylogenetic relationships of these taxa are still much debated. We determined complete 18S rRNA sequences of two entoprocts, an ectoproct, an inarticulate brachiopod, a phoronid, two annelids, and a platyhelminth. Phylogenetic analyses of these data show that (1) entoprocts and lophophorates have spiralian, protostomous affinities, (2) Ento- and Ectoprocta are not sister taxa, (3) phoronids and brachiopods form a monophyletic clade, and (4) neither Ectoprocta or Annelida appear to be monophyletic. Both deuterostomous and pseudocoelomate features may have arisen at least two times in evolutionary history. These results advocate a Spiralia-Radialia-based classification rather than one based on the Protostomia-Deuterostomia concept.
Animals↗
Investigation of molluscan phylogeny on the basis of 18S rRNA sequences.
The 18S rRNA sequences of 12 molluscs, representing the extant classes Gastropoda, Bivalvia, Polyplacophora, Scaphopoda, and Caudofoveata, were determined and compared with selected known 18S rRNA sequences of Metazoa, including other Mollusca. These data do not provide support for a close relationship between Platyhelminthes (Turbellaria) and Mollusca, but rather suggest that the latter group belongs to a clade of eutrochozoan coelomates. The 18S rRNA data fail to recover molluscan, bivalve, or gastropod monophyly. However, the branching pattern of the eutrochozoan phyla and classes is unstable, probably due to the explosive Cambrian radiation during which these groups arose. Similarly, the 18S rRNA data do not provide a reliable signal for the molluscan interclass relationships. Nevertheless, we obtained strong preliminary support for phylogenetic inferences at more restricted taxonomic levels, such as the monophyly of Polyplacophora, Caenogastropoda, Euthyneura, Heterodonta, and Arcoida.
Animals↗
Phylogeny of protostome worms derived from 18S rRNA sequences.
The phylogenetic relationships of protostome worms were studied by comparing new complete 18S rRNA sequences of Vestimentifera, Pogonophora, Sipuncula, Echiura, Nemertea, and Annelida with existing 18S rRNA sequences of Mollusca, Arthropoda, Chordata, and Platyhelminthes. Phylogenetic trees were inferred via neighbor-joining and maximum parsimony analyses. These suggest that (1) Sipuncula and Echiura are not sister groups; (2) Nemertea are protostomes; (3) Vestimentifera and Pogonophora are protostomes that have a common ancestor with Echiura; and (4) Vestimentifera and Pogonophora are a monophyletic clade.
Animals↗
18S rRNA data indicate that Aschelminthes are polyphyletic in origin and consist of at least three distinct clades.
The Aschelminthes is a collection of at least eight animal phyla, historically grouped together because the absence of a true body cavity was perceived as a pseudocoelom. Analyses of 18S rRNA sequences from six Aschelminth phyla (including four previously unpublished sequences) support polyphyly for the Aschelminthes. At least three distinct groups of Aschelminthes were detected: the Priapulida among the protostomes, the Rotifera-Acanthocephala as a sister group to the protostomes, and the Nematoda as a basal group to the triploblastic Eumetazoa.
Acanthocephala↗
CARD: a drawing tool for RNA secondary structure models.
A graphical editor was developed to create publication-quality representations of RNA secondary structure models. A user-defined model can be gradually assembled from structural elements such as helix segments and loops. The type of structural element to be drawn is chosen from a menu. Its nucleotide sequence has to be entered from the keyboard. Afterwards, drawings can be manipulated by moving, deleting, rotating, copying or changing the structural elements separately. An example of a secondary structure model is given for a complete 18S rRNA molecule.
Nucleic Acid Conformation↗
Complete small ribosomal subunit RNA sequence of the chiton Acanthopleura japonica (Lischke, 1873) (Mollusca, Polyplacophora).
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Animals↗
Extraction of high molecular weight DNA from molluscs.
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Animals↗
Structure of the small ribosomal subunit RNA of the pulmonate snail, Limicolaria kambeul, and phylogenetic analysis of the Metazoa.
The complete nucleotide sequence of the small ribosomal subunit RNA of the gastropod, Limicolaria kambeul, was determined and used to infer a secondary structure model. In order to clarify the phylogenetic position of the Mollusca among the Metazoa, an evolutionary tree was constructed by neighbor-joining, starting from an alignment of small ribosomal subunit RNA sequences. The Mollusca appear to be a monophyletic group, related to Arthropoda and Chordata in an unresolved trichotomy.
Animals↗
Seasonal dynamics of population genetic structure in cryptic taxa of the Pellioditis marina complex (Nematoda: Rhabditida).
The distribution patterns and genetic structure of the Pellioditis marina species complex in Belgium and The Netherlands were compared between four consecutive seasons. Different types of habitats (coast, estuary, semi-estuary and lake) with different degrees of connectivity were sampled. In addition, each habitat type was characterised by either temporal or permanent algal deposits. We screened 426 bp of the mitochondrial cytochrome oxidase c (COI) gene with the single-strand conformation polymorphism (SSCP) method in 1615 individuals of Pellioditis marina. The 51 haplotypes were divided into four (sympatric) lineages, with divergences ranging from 0.25 to 10.6%. Our results show that the lineages have different temporal dynamics, which may be linked to abiotic factors. Analysis of Molecular Variance (AMOVA) indicated a significant structuring in the PmI lineage, which correlated with habitat characteristics and which changed over time (Mantel, r = 0.51; p = 0.126). Intrapopulational diversity was similar in all locations, and temporal changes in haplotype frequencies were not higher in temporary than in permanent algal deposits. Instead, the results of the temporal survey indicated that (some) P. marina populations are characterised by a metapopulation structure. It is emphasized that a complete and correct interpretation of processes causing genetic structuring within species and of the genetic structure itself can only be done when analyses are performed at several time points.
Animals↗