Glacial-driven vicariance in the amphipod Gammarus duebeni.

We have examined the genetic diversity using mitochondrial COI and ND2 sequence data from 306 specimens of the amphi-Atlantic-distributed amphipod Gammarus duebeni. Marine populations from the Atlantic Ocean, the Baltic and North Sea, as well as freshwater populations from Ireland, Cornwall and Brittany were analysed. G. duebeni is a complex of five allopatric lineages. Freshwater populations result from multiple invasions of marine ancestors, represented by distinct lineages. We interpret the recent distribution of lineages as the outcome of a series of spatio-temporal vicariant events caused by Pleistocene glaciations and sea level changes. The freshwater lineages are therefore regarded as 'glacial relicts'. Furthermore, inter-specific competition with, for example, Gammarus pulex (which is absent in Ireland and western Brittany) may be another important determinant in the distribution of freshwater G. duebeni. In Ireland and Brittany, three freshwater refugia are suggested. The significantly limited gene flow detected among marine populations is more likely due to inter-specific competition than to salinity. The G. duebeni-complex represents a model system for the study of allopatric speciation accompanied by major habitat shifts. The pattern of spatio-temporal origins of the freshwater entities we describe here provides an excellent system for investigating evolutionary adaptations to the freshwater environment. Our data did not confirm the presently used subspecies classification but are only preliminary in the absence of nuclear genetic analyses.

Stress protein response in two sibling species of Marenzelleria (Polychaeta: Spionidae): is there an influence of acclimation salinity?

The induction and synthesis of stress proteins in the polychaete sibling species Marenzelleria viridis and M. neglecta was investigated at two different acclimation salinities (10 and 25 ppt). By in vitro labeling of dissected metameres with (35)S-methionine/cysteine and electrophoretic separation, four size classes of heat shock proteins (Hsps) were detected corresponding to 86, 78, 75 and 27 kDa. All Hsps, with the exception of Hsp86, represent a complex of multiple isoforms. The sibling species differed in three aspects of their heat shock response: (1) the induction temperature for Hsp75 synthesis was 25 degrees C and 30 degrees C in M. viridis and M. neglecta, respectively; (2) the relative level of synthesis of Hsp75 was higher in M. viridis; (3) the heat shock response was inactivated at a higher temperature in M. neglecta compared to M. viridis. The results showed that acclimation salinity had no explicit effect on Hsp synthesis in either species and that M. viridis was thermally more sensitive than its sibling species. We proposed that temperature, alone or in combination with other abiotic factors, plays a far greater role in the biogeographic distribution in Marenzelleria spp. than has been estimated so far.

Locomotory capacity of Baltic Sea and freshwater populations of the threespine stickleback (Gasterosteus aculeatus).

Two freshwater populations and one marine population (Baltic Sea) of threespine stickeback (Gasterosteus aculeatus) from Northeastern Germany were studied with regard to locomotory capacity: sustained swimming performance, activities of key enzymes in axial muscle, pectoral fin muscle and heart, and morphology. We postulated that life history differences between migratory Baltic Sea and resident freshwater populations could have led to a divergence in their locomotory capacity. The activity of citrate synthase (CS) in pectoral muscle correlated with critical swimming speed. Critical swimming speed, aerobic and anaerobic capacity of the pectoral fin muscle were population-specific. The Baltic Sea sticklebacks had a higher locomotory capacity (activity of CS in pectoral muscle, critical swimming speed) than sticklebacks of one freshwater population. However, another freshwater population expressed a similar locomotory capacity as the Baltic Sea population. In addition, Baltic Sea sticklebacks had a greater mass and lower anaerobic capacity of the pectoral fin muscle than the freshwater sticklebacks. The results are interpreted as an indication of a proceeding divergence between marine and resident freshwater populations and between freshwater populations of G. aculeatus originating from marine ancestors. The migratory Baltic Sea sticklebacks had better morphological prerequisites for sustained swimming than both freshwater populations, but there was no general difference in the locomotory capacity between marine and freshwater sticklebacks. However, their morphology could favour a more effective locomotion in the Baltic Sea sticklebacks.

A new molecular phylogenetic hypothesis for the evolution of freshwater eels.

Phylogenetic analysis of a segment of the mitochondrial 16S rDNA of eight Anguilla species from the Indo-Pacific region and from the North Atlantic revealed that the genus Anguilla appears to be surprisingly young, based upon the small observed maximum genetic distance of 4.8% and the high degree of morphological similarity among the species. The placement of A. marmorata as the most ancestral lineage suggests that the genus is likely to have originated in the Indo-Malayian region, from which it quickly spread. Two Pacific species, A. obscura and A. japonica, branched next. A. japonica was placed as sister group to all remaining species, which formed three clades: the first comprising A. australis, the second A. reinhardti and A. mossambica, and the third A. anguilla and A. rostrata. All analyzed specimens of A. rostrata originating from southern New Jersey to Nova Scotia had identical mitotypes, while five mitochondrial genotypes were found in Europe differing by zero to two substitutions. The two Atlantic eel species are very closely related; all surveyed specimens of A. anguilla differ by three to five substitutions from their American allies, corroborating the existence of two distinct biological species. This was also confirmed by restriction analysis of a 350-bp segment of the cytochrome b, in which American specimens were distinct in sharing a single diagnostic restriction site of HinfI. Our results suggest little to no gene flow between the two nominal Atlantic eel species.

Cryptic species in marine polychaete and their independent introduction from North America to Europe.

The vast body of ballast water carried across oceans by freight ships represents a major source for the introduction of foreign species into marine ecosystems. The worm Marenzelleria viridis, originally found only in North America, appeared in estuaries of the North Sea in 1979 and 6 years later also in the Baltic, where it has developed into a major faunal element. Two competing hypotheses are discussed here: either both populations owe their presence to a single introductory event in the North Sea, or each population originated from a separate introduction. Our phylogeographic analysis of Baltic, North Sea and American Marenzelleria, based on mitochondrial 16S rDNA sequences (326-bp segment) of 98 individuals from 17 localities on the North American, North Sea, and Baltic coasts not only favors the two-event hypothesis, but also separates the locations of origin for the introductions. Eighteen mitochondrial genotypes were identified altogether. In agreement with allozyme data, three lineages were identified: genotypes assigned to the same lineage differed from each other by up to 5 point mutations, and those assigned to different lineages differed by up to 17. The existence of three morphologically indistinguishable, and thus cryptic, species is therefore suggested. The individuals from the Baltic Sea probably originated from the Atlantic coast of the United States between Chesapeake Bay and Georgia, and the North Sea populations may stem from the U.S. coast region north of Chesapeake Bay to Nova Scotia. Despite their similar morphologies, the two European Marenzelleria species may differ ecologically with respect to their preference for habitat salinity. Assuming that transport via ballast water occurs quite frequently, we hypothesize that both European cryptic species of Marenzelleria may originally have been introduced to both the North Sea and the Baltic Sea but that neither of them was able to proliferate in both water bodies owing to their differential physiological performances at high and low salinities.

Biochemical parameters as a measure of food availability and growth in immature rainbow trout (Oncorhynchus mykiss).

1. Rainbow trout held in brackish water (15 parts per thousand) were starved or fed different amounts of food. 2. A significant correlation was found between the growth rates of the different animals and the feed rates. 3. The RNA:DNA ratio in the white epaxial muscle is lowest in starved fish and increases in proportion to the feed rate and individual specific growth rate. The correlations are significant at the P less than 0.01 level. 4. Liver metabolism varies according to food availability. 5. The protein synthesis capacity of the liver (RNA:DNA ratio) and liver somatic index increase as the feeding rate increases. It also correlates significantly with the specific growth rates of the different animals. 6. The intermediary metabolism of the central metabolic organ, the liver, varies in the same way. 7. The activities of the NADPH producing liver enzymes glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), isocitrate dehydrogenase (IDH) and malic enzyme (ME) increase as the feed rate (and therefore the specific growth rate) increases. 8. G6PDH and IDH activity in the kidney is influenced to a much lower degree by food intake. 9. Summarizing, it can be stated that biochemical parameters can be used to describe comprehensively the metabolic status and growth of rainbow trout.

The role of elongation factors in protein synthesis rate variation in white teleost muscle.

Protein synthesis-stimulating activity was assayed in the cytosolic fraction of white muscle from teleost fish (rainbow trout, carp) and of rat liver. In vitro protein synthesis-stimulating activity in the cytosolic fraction is reduced by food deprivation. The addition of elongation factors EF1, EF2, or EF1 + EF2 compensates for the starvation-induced loss of protein synthesis-stimulating activity in trout muscle cytosol. The action of EF2 is stronger than that of EF1 in this respect. However, EF1 enhances in vitro protein synthesis-stimulating activity in rat liver cytosol more than EF2. The EF2 concentration in the cytosolic fraction of white muscle from starved trout is significantly lower than in fed specimens.

Effects of salinity on vitamin B6 deficiency in rainbow trout (Salmo gairdneri Richardson).

1. The link between vitamin B6 deficiency and sea water adaptation in rainbow trout was investigated. 2. A plasma-hyperosmotic salinity (20%) exacerbates the effect of vitamin B6 deficiency in rainbow trout. 3. Na/K-ATPase activity in the gill and kidney of the rainbow trout is not affected by vitamin B6 deficiency.

Effects of temperature, food deprivation and salinity on growth, RNA/DNA ratio and certain enzyme activities in rainbow trout (Salmo gairdneri Richardson).

1. The connection between feeding regime (food deprivation and restricted diet) and thermal acclimation (1-2, 6, 11 and 16 degrees C) was studied in rainbow trout held in diluted seawater (20% S). 2. At 1 degree C, food deprivation effects on all parameters are slight, and on RNA and certain enzymes they are masked by thermal acclimation effects. 3. At a salinity of 20% rainbow trout on a restricted diet and held at 11 degrees C have the highest growth rate. 4. Owing to increasing RNA levels, the RNA/DNA quotient is significantly higher than normal in rainbow trout held at 1 degree C although the fishes do not grow at this temperature. 5. Temperature and feeding both affect the enzymes we studied (liver: G1DH, AspT, arginase, G6PDH, and 6PGDH; kidney: G1DH, AspT, arginase, and Na/K-ATPase; white muscle: AspT and A1T; gill: Na/K-ATPase) differently. Interactions between these two factors also occur in some cases.

Influence of salinity and ratio of lipid to protein in diets on certain enzyme activities in rainbow trout (Salmo gairdneri Richardson).

The connection between metabolic and sea water adaptation of the rainbow trout was investigated. The rainbow trout were kept in fresh water and diluted sea water of 8 and 20 0/00 S at 16 degrees C and fed on three different diets for 51 days. Hyperosmotic salinity (20 0/00) tends to inhibit growth in rainbow trout by reducing the food conversion efficiency. A higher protein concentration in the diet can partly compensate for this effect. The liver IDH, G6PDH and 6PGDH activities of the rainbow trout are influenced only by food quality, whereas the liver G1DH, AspT and A1T activities, like the muscle A1T, are also affected by salinity. The salinity had no significant effect on the activities of the kidney enzymes we investigated (Na/K-ATPase, G1DH, A1T, AspT) or of the muscle AspT in these experiments.

Influence of nutrition on biochemical sea water adaptation of the rainbow trout (Salmo gairdneri richardson).

Glutamate dehydrogenase activity in the liver of the rainbow trout increases when the animals are starved for four weeks. Glutamate dehydrogenase, alanine aminotransferase and aspartate aminotransferase activity in the kidney of rainbow trout kept in sea water (20% S) is significantly higher than in the kidney of rainbow trout kept in fresh water. Gill Na/K-ATPase activity in the rainbow trout is reduced significantly (44%) by starvation for four weeks. Most of the free amino acids investigated in the white muscle of the rainbow trout were present in significantly higher concentrations in animals fed in sea water than in animals fed in fresh water. The concentrations of these amino acids are even higher in the muscle of starved animals held in sea water than in fed animals held in sea water.

Effects of temperature, salinity, and feeding on aminotransferase activity in the liver and white muscle of rainbow trout (Salmo gairdneri Richardson).

1. The liver-somatic index of rainbow trout is governed by temperature and salinity, and by the interaction of these two factors. 2. The overall liver-alanine aminotransferase activity (in units/100 g body weight) increases slightly with increasing salinity of the surroundings in the case of rainbow trout. 3. The overall liver-aspartate aminotransferase activity (in units/100 g body weight) in rainbow trout depends on their food and the temperature at which they are kept. 4. Salinity adaptation leads to reductions in the specific alanine and aspartate aminotransferase activity in the liver of rainbow trout. 5. The specific alanine aminotransferase activity in the muscle of starving rainbow trout kept in diluted seawater (580 mOsm/l, 18 degrees C) is clearly higher than in control animals kept in tapwater.