Identification and characterisation of thirteen new microsatellites for Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis> L.) from a repeat-enriched library

A total of 13 polymorphic microsatellite markers were developed for Atlantic cod (Gadus morhua L.) from a repeat-enriched library. Polymorphism of each locus was assessed in 96 unrelated individuals from a natural population. The number of alleles per locus varied from 8 to 45. The ranges of observed and expected heterozygosity were 0.122–0.907 and 0.673–0.965, respectively. Four of the loci (Gmo-G24, Gmo-G40, Gmo-G46 and Gmo-G49) followed Hardy–Weinberg expectation. No evidence for linkage disequilibrium between pairs of loci was found in any combination of loci pairs, except between Gmo-G40 and Gmo-G43. These microsatellite markers provide useful tools for studies of population genetics, reproductive ecology and for constructing linkage maps of Atlantic cod. Jon-Ivar Westgaard and Tekle Tafese have contributed equally to the work.     

Subcellular localization of hexadecanedioic acid activation in human liver

The activation of hexadecanedioic acid has been studied in subcellular fractions of human liver. The activation capacity in a total homogenate of human liver was found to be 0.5 micro mole/min/g wet wt of tissue, about 10% of that for palmitic acid. Hexadecanedioic acid was activated by the mitochondrial and microsomal fractions. The mitochondrial enzyme is probably localized outside the inner mitochondrial compartment. The subcellular distribution of the hexadecanedioic acid activation was almost identical with the distribution of palmitic acid activation. Hexadecanedioic and palmitic acids seemed to compete for the same enzyme.     

Does collembolan grazing influence nitrogen fixation by cyanobacteria in the high Arctic?

A field experiment was performed to test whether cyanobacterial nitrogen fixation rates increase or decrease when exposed to low and moderate microarthropod grazing intensities. The densities of naturally occurring Collembola, i.e. Hypogastrura viatica, were manipulated on a salt marsh covered with cyanobacteria in the high Arctic, Svalbard. Nitrogen-fixation rates in grazed cyanobacterial crust were measured and used as an indirect measurement of cyanobacterial biomass on three dates during one summer. After 30 days, a second order polynomial regression gave a good fit to the data, indicating an increase in nitrogen-fixation rates at low/intermediate grazing pressures and a decrease at high grazing pressures. Thus, grazing collembolans may influence the nitrogen-fixation rates in an arctic salt-marsh community. Although based on a small set of data, the study indicates a compensatory fixation at low grazing pressures followed by a reduction at high grazing pressures. Accepted: 21 March 2000     

Refractive index of phytoplankton derived from its metabolite composition

The refractive index of phytoplankton is calculated from itsmetabolite composition. The mean index of the algal dry mass,relative to the index of water, seems to vary from 1.146 forgreen algae to 1.167 for coccolithophonds. This difference of0.021 reduces to 0.007 and 0.003 when the partial water volumesof the algae are 0.6 and 0.8, respectively. The most importantfactor for the variation of the refractive index is the algalwater content. If a reasonable average range of the partialwater volume is 0.6 ± 0.2, the corresponding range ofthe refractive index relative to sea water becomes 1.06 ±0.04. This result is in excellent agreement with estimates basedon optical measurements of pure algal cultures. The normal dispersionof the refractive index is negligible, but anomalous dispersionin the vicinity of strong absorption bands may be of importancefor the light scattering properties of small phytoplankton.