A mitogenomic approach to the taxonomy of pollocks: <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> and <Emphasis Type="Italic">T. finnmarchica</Emphasis> represent one single species

Background  

The walleye pollock (Theragra chalcogramma) and Norwegian pollock (T. finnmarchica) are confined to the North Pacific and North Atlantic Oceans, respectively, and considered as distinct species within the family Gadidae. We have determined the complete mtDNA nucleotide sequence of two specimens of Norwegian pollock and compared the sequences to that of 10 specimens of walleye pollock representing stocks from the Sea of Japan and the Bering Sea, 2 specimens of Atlantic cod (Gadus morhua), and 2 specimens of haddock (Melanogrammus aeglefinus).     

Oligochaete response to changes in water flow in the Dokka Delta,Lake Randsfjorden (Norway), caused by hydroelectric power development

The results reported here are part of a joint study on possible ecological effects in the delta area of Lake Randsfjorden, Southern Norway, caused by a reduction in water flow as a result of hydroelectric power development.From 1988 to 1990 the mean daily water flow decreased sharply and the total load of suspended matter was greatly reduced. During the same period there was an increase in oligochaete abundance from 6,096 ind. m^–2 in 1988 to 100,051 ind. m^–2 in 1989 and 154,345 ind. m^–2 in 1990. Piguetiella blanci was the dominant species in 1988 making up 48.5% of the total community. In 1989, Limnodrilus hoffmeisteri, Nais variabilis/Nais communis and enchytraeids were the most abundant oligochaetes, making up 29.3%, 26.1% and 28.2%, respectively of the total number. Reduced water flow from 1988 to 1989 and 1990 caused reduced disturbance of the bottom sediments and is considered the main reason for the change in species composition and abundances.     

Population genetic analysis of Euro-Arctic polar cod <Emphasis Type="Italic">Boreogadus saida</Emphasis> suggests fjord and oceanic structuring

Polar cod, Boreogadus saida, is a key species in Arctic marine ecosystems; however, its genetic population structure is largely undescribed. The population genetic structure of 472 B. saida specimens among nine locations in the north-east Atlantic was revealed using 12 microsatellite loci. Pairwise F _ST comparisons showed significant population differentiation between B. saida sampled inside fjords in Svalbard and north-east Greenland, as compared to B. saida from the shelf. The observed genetic variation was not a function of isolation by distance, and it is speculated that B. saida populations inhabiting fjords may have become reproductively isolated from shelf-dwelling B. saida during the last post-glacial recolonization.     

Natural selection and the genetic differentiation of coastal and Arctic populations of the Atlantic cod in northern Norway: a test involving nucleotide sequence variation at the pantophysin (PanI) locus

To examine the role of contemporary selection in maintaining significant allele frequency differences at the pantophysin (PanI) locus among populations of the Atlantic cod, Gadus morhua, in northern Norway, we sequenced 127 PanIA alleles sampled from six coastal and two Barents Sea populations. The distributions of variable sites segregating within the PanIA allelic class were then compared among the populations. Significant differences were detected in the overall frequencies of PanIA alleles among populations within coastal and Arctic regions that was similar in magnitude to heterogeneity in the distributions of polymorphic sites segregating within the PanIA allelic class. The differentiation observed at silent sites in the PanIA allelic class contradicts the predicted effects of widescale gene flow and suggests that postsettlement selection acting on cohorts cannot be responsible for the genetic differences described between coastal and Arctic populations. Our results suggest that the marked differences observed between coastal and Arctic populations of G. morhua in northern Norway at the PanI locus reflect the action of recent diversifying selection and that populations throughout the region may be more independent than suggested by previous studies.     

Population dynamics and body composition of the Arctic hyperiid amphipod Themisto libellula in Svalbard fjords

Population structure, growth and body composition (wet-, dry-, ash weight and total lipid) of the Arctic pelagic amphipod Themisto libellula were studied in four fjords on West Spitsbergen, Svalbard, from July to December 2000 and in April 2002. In one of the fjords, Kongsfjorden, growth of T. libellula was calculated as the change in mean length of the 0+ cohort from July to December. The young were released from the brood pouches in early spring (March–April). Summer growth was 3.5 mm month⁻¹, whereas growth during the autumn was only 0.6 mm month⁻¹. The size frequency distributions indicated a 2–2.5 year life-span. The size structure of the population in Hornsund, the southernmost fjord on Spitsbergen, indicated a delayed time of spawning. The storage of lipids in T. libellula occurred during late summer and towards the winter, when the food items contain the maximum amount of stored lipids.     

Mixed stock analysis and the power of different classes of molecular markers in discriminating coastal and oceanic Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis> L.) on the Lofoten spawning grounds,Northern Norway

Atlantic cod (Gadus morhua) encompasses many different populations or stocks, which in part are managed separately. In the northeast Atlantic cod is divided into two main management units; northeast Arctic cod and coastal cod. These two groups have traditionally been separated by otolith classification. In this study, the power of different classes of genetic markers in separating the two cod groups was investigated. The variation in thirteen genetic markers, including allozymes, haemoglobin, the scDNA locus Pantophysin (Pan I) and a number of microsatellites was investigated, and mixed stock analysis and individual assignment tests were performed on samples comprising a mixture of individuals of putative coastal and oceanic type cod. The genetic analyses showed a large genetic differentiation between outer stations and stations located closer to the mainland shore. Mixed stock analysis and individual assignment tests used for estimation of stock proportions gave results similar to those obtained by otolith classification. Guest editors: J. Davenport, G. Burnell, T. Cross, M. Emmerson, R. McAllen, R. Ramsay & E. Rogan Challenges to Marine Ecosystems     

A simple molecular approach to distinguish between two Arctic gadoid fishes <Emphasis Type="Italic">Arctogadus glacialis</Emphasis> (Peters, 1874) and <Emphasis Type="Italic">Boreogadus saida</Emphasis> (Lepechin, 1774)

Correct phenotypical identification of and discrimination between Boreogadus saida and Arctogadus glacialis is challenging, especially for larvae and young fish. We propose the use of a single microsatellite genetic marker, Gmo8, to distinguish between the two gadoid fish species. Amplified allele frequencies differed considerably, with B. saida (n = 97) being almost exclusively monomorphic at this locus, whereas A. glacialis (n = 136) is highly polymorphic. There was a clear separation between the amplified allele ranges for the two species. The species specific properties of Gmo8 enables the use of this marker to distinguish between B. saida and A. glacialis.     

Thermohaline tolerance and embryonic development in capelin eggs (Mallotus villosus) from the Northeast Atlantic Ocean

Capelin (Mallotus villosus) displays alternative reproductive modes throughout its circumpolar distribution. This predicts divergent thermohaline tolerance of eggs because they are incubated in either a steady offshore or variable intertidal environment. We investigate herein thermohaline tolerance of eggs from the offshore spawning Barents Sea capelin. Subsequently, we compare our data with those previously published on other offshore and intertidal spawning capelin populations across the Northeast Atlantic Ocean, with the aim of determining possible patterns in the thermohaline tolerance of eggs from the alternative reproductive modes. In a 2?×?4 factorial design various combinations of salinities and temperatures had only negligible effect on the survival of eggs until first hatch. The embryonic development rate from fertilisation until first hatch across populations and between the two reproductive modes suggested non-local thermohaline tolerance towards the physical factors during development. Finally, no differences were observed in salinity tolerance from fertilisation to first hatch between populations representing different reproductive modes. The present findings demonstrate wide thermohaline tolerance of capelin eggs regardless of population origin and reproductive mode.     

Littoral microcrustaceans (Cladocera and Copepoda) as indices of recovery of a limed water system

A 7 year study (1992–1998) of littoral microcrustaceans (Cladocera and Copepoda) in the watercourse of the River Rore, South Norway, illustrates that qualitative data on cladocerans and copepods are well suited to indicate the recovery of lakes following liming. Eight limed, two acid and two circum neutral reference lakes, were sampled twice a year (June/July and September/October). In the limed lakes, species associated with neutral lakes have become more common, whereas apparently acid-tolerant species have become rarer. In Lake Rore and Lake Syndle, the two largest limed lakes which exhibited a gradual increase in pH, the changes in species composition indicated that these lakes were about to recover. Species composition in Lake Røynelandsvatn, which has reacidified after liming, first reflected improved water quality, then reverted to dominance by acid-tolerant species. In the remaining lakes, the species composition reflects a fauna which has recovered compared with the preliming situation. There is strong evidence, however, that temporary fluctuations in pH have a negative influence on the speed of recovery, confirming the importance of keeping pH stable.