Andy Vierstraete

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 426xa0bp 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.

Intraspecific variation in Radopholus similis isolates assessed with restriction fragment length polymorphism and DNA sequencing of the internal transcribed spacer region of the ribosomal RNA cistron.

Restriction fragment length polymorphism and direct sequencing of the internal transcribed spacer rDNA region of 19 isolates of Radopholus similis yielded significant diversity, both among isolates and within some individuals. Restriction fragment length polymorphism with HaeIII, AluI and Tru9I yielded two sets of patterns. Digestion with RsaI revealed one or two supernumerary bands in single nematodes from five isolates, and sequencing confirmed microheterogeneity in four of these. Phylogenetic analysis grouped most isolates closely together, except for the five isolates with additional bands for RsaI. Our data reveal more population structure than previously found and lend further support to the synonymy of R. similis and Radopholus citrophilus.

Genome-wide analysis of the globin gene family of C. elegans

The aim of our study was to annotate sequences for 35 putative globins from the nematode Caenorhabditis elegans. All these proteins are expressed, but seven of these differ from the gene predictions in Wormbase. The entire polypeptide sequences for 31 genes and the core globin domain of four proteins were confirmed or corrected. All core globin domains were aligned manually following a procedure that was designed to fit the putative sequences to the crystal structure based alignment of 56 known globin crystal structures. Neighbor‐joining analysis of the resulting alignment showed that the majority of these globins are very divergent from each other, possibly suggesting a long evolutionary divergence. The surprisingly high number and low sequence conservation of putative globins in this small organism urges a detailed functional analysis. IUBMB Life, 56: 697‐702, 2004