Bent Friis Theisen

SIMPLICITY-CORRELATED SIZE GROWTH OF THE NUCLEAR 28S RIBOSOMAL RNA D3 EXPANSION SEGMENT IN THE CRUSTACEAN ORDER ISOPODA

The expansion segments within the eukaryote nuclear 23S-like ribosomal RNA molecule are now well characterized in many diverse organisms. A different base compositional bias, a higher propensity for size variability, and an increased evolutionary rate distinguish these regions from the universally conserved “core” regions of the molecule. In addition, some expansion segments of higher eukaryotes exhibit significant sequence simplicity which is hypothesized to occur by slippage-mediated mutational processes. We describe the discovery of extreme size variation of the D3 expansion segment in the crustacean order Isopoda. Among 11 species D3 varies in size from 180 to 518 nucleotides but maintains a homologous secondary structure. The D3 size is significantly positively correlated to relative simplicity factor (RSF), indicating that growth is most likely by insertion of simple sequences. D3 size and RSF correlate approximately with a morphology-based phylogeny, and within oniscideans RSF increases as more recent divergences occur. The D3 ofArmadillidium vulgare, with an RSF of 1.87, is the highest value recorded for any known expansion segment. Regions of high sequence simplicity in nuclear ribosomal RNA were previously only known from the higher vertebrate lineage. Here we demonstrate that this phenomenon occurs in a more extreme condition within a monophyletic invertebrate lineage. The extreme size changes identified could indicate that expansion segments are an extraneous element in the functioning ribosome.

Allozyme clines and evidence of strong selection in three loci in Mytilus edulis L. (Bivalvia) from Danish waters

Conspicuous differences in allozyme frequencies are found between Mytilus edulis populations from Bornholm in the Baltic and from the Kattegat and the North Sea in three allozyme loci (PGM: phospho...

The growth of Mytilus edulis L. (Bivalvia) from Disko and Thule district, Greenland

Abstract The growth in length of Mytilus edulis L. from Disko and the Tliule district is estimated by means of the very distinct winter growth checks. The growth is highly sigmoid and can be described by a combination of the Gomperz equation (valid for the growth until about half the ultimate length is attained) and the von Bertalanffy equation (valid for the growth from about one third of the ultimate length) as neither of the two growth equations covers the whole size range of Mytilus. The growth of the species at Greenland is slow compared with its growth in most temperate areas. Doubtlessly low temperature is the cause of the slow growth. When the growth rate is related to day-degrees, growth at Greenland almost equals that found in similar habitats in temperate regions. An apparent size-dependent mortality occurs among the very small Mytilus living on Fucus. However, this phenomenon is probably caused by differential emigration among the small individuals. A conspicuous lack of young individuals in t...

Variation in size of gills, labial palps, and adductor muscle in Mytilus edulis L. (Bivalvia) from Danish waters

Abstract Large variation is found in the size of gills, labial palps, and posterior adductor muscle in samples of Mytilus edulis L. from different parts of Danish waters. The differences in gill size and palp size can be explained as adaptation to waters of different turbidity, and most of the variation in adductor muscle size as adaptation to predation by Asterias.

Feeding rate of Mytilus edulis L. (Bivalvia) from different parts of Danish waters in water of different turbidity

Abstract The feeding rate of Mytilus edulis L. from different parts of Danish waters was measured in different concentrations of talcum simulating different concentrations of mud. Dyed yeast was used as food. The feeding rate decreased drastically with increased concentrations of talcum. At high concentrations of talcum Mytilus from the Wadden Sea fed at about twice the rate as Mytilus from other Danish waters. This is correlated with the size of the labial palps which are about twice as large in Mytilus from the Wadden Sea as in Mytilus from other Danish waters.

Shell cleaning and deposit feeding in Mytilus edulis L. (Bivalvia)

Abstract Mytilus edulis as a rule has shells with a clean and smooth periostracum. It is shown that the mussels actively clean their shells with the foot, which is morphologically adapted for the cleaning process. Particles removed from the shells during cleaning are taken into the mantle cavity and treated in the same way as particles strained from the water by the gills, i. e., eaten or rejected as pseudofaeces. Particles reached by the foot during creeping may be treated in the same way.

Mytilicola intestinalis Steuer and the condition of its host Mytilus edulis L.

Abstract The incidence of infestation of Mytilus edulis L. with Mytilicola intestinalis and the condition (meat content) of Mytilus was monitored 1976-1985. For the individual years the number of Mytilicola was positively correlated with meat content of Mytilus while comparison between individual years showed a negative relation between number of Mytilicola and the condition of Mytilus. It is concluded that Mytilicola has a strong adverse effect on the condition of its host, but that this effect is masked in samples with large variation in the condition of Mytilus.

Origin of clonal diversity in triploid parthenogenetic Trichoniscus pusillus pusillus (Isopoda, Crustacea) based upon allozyme and nucleotide sequence data

Variation in PGM (phosphoglucomutase) and MDH (malate dehydrogenase) allozymes and in mitochondrial and nuclear (ribosomal) DNA gives evidence of at least three independent origins of triploid Trichoniscus pusillus pusillus. Much of the genetic variation found may reflect variation within the parental diploid population(s), but it is argued that some of the variation in PGM allozymes have accumulated within the parthenogenetic lines. Based upon the variation at this locus, 15 genetically distinct clones are distinguished.