Effects of temperature, salinity and fish in structuring the macroinvertebrate community in shallow lakes: implications for effects of climate change

Climate warming may lead to changes in the trophic structure and diversity of shallow lakes as a combined effect of increased temperature and salinity and likely increased strength of trophic interactions. We investigated the potential effects of temperature, salinity and fish on the plant-associated macroinvertebrate community by introducing artificial plants in eight comparable shallow brackish lakes located in two climatic regions of contrasting temperature: cold-temperate and Mediterranean. In both regions, lakes covered a salinity gradient from freshwater to oligohaline waters. We undertook day and night-time sampling of macroinvertebrates associated with the artificial plants and fish and free-swimming macroinvertebrate predators within artificial plants and in pelagic areas. Our results showed marked differences in the trophic structure between cold and warm shallow lakes. Plant-associated macroinvertebrates and free-swimming macroinvertebrate predators were more abundant and the communities richer in species in the cold compared to the warm climate, most probably as a result of differences in fish predation pressure. Submerged plants in warm brackish lakes did not seem to counteract the effect of fish predation on macroinvertebrates to the same extent as in temperate freshwater lakes, since small fish were abundant and tended to aggregate within the macrophytes. The richness and abundance of most plant-associated macroinvertebrate taxa decreased with salinity. Despite the lower densities of plant-associated macroinvertebrates in the Mediterranean lakes, periphyton biomass was lower than in cold temperate systems, a fact that was mainly attributed to grazing and disturbance by fish. Our results suggest that, if the current process of warming entails higher chances of shallow lakes becoming warmer and more saline, climatic change may result in a decrease in macroinvertebrate species richness and abundance in shallow lakes.     

Horizontal distribution of cladocerans in arctic Greenland lakes – impact of macrophytes and fish

Submerged macrophytes may play an important role as a refuge for zooplankton against predators. However, a recent study suggests that their importance depends on the trophic state of the lake. We studied the impact of fish and macrophytes on the horizontal distribution of pelagic cladocerans in 56 oligotrophic arctic Greenland lakes. In north-east and western Greenland, zooplankton was sampled in the near-shore (littoral) and central (pelagial) part of all lakes and fish were sampled with multiple mesh-sized gill nets. Macrophytes were visually estimated in the littoral. In north-east Greenland, 5 taxa of cladocerans were found, while 14 taxa were recorded in western Greenland. Daphnia pulex occurred only in fishless lakes in both northeast and western Greenland and avoided the near-shore areas in the shallow and deep lakes. Bosmina spp. and Holopedium gibberum were evenly distributed between the littoral and the pelagial in the deep and shallow fishless lakes. However, their near-shore density was lowest in the presence of fish. Macrophyte-related and benthic cladocerans concentrated either in the littoral or were evenly distributed between the littoral and the pelagial, irrespective of depth and fish presence or absence. Macrophytes had no impact on the horizontal distribution of pelagic cladocerans. Thus, it is concluded that horizontal heterogeneity of Bosmina spp. and Holopedium gibberum might be affected by the presence of fish.     

Welcome by the Dean Henrik Jeppesen at the 8th International Symposium on Tardigrada

Mr. Chairman. Distinguished ladies and gentlemen. As Dean of Science it is a great honour on behalf of the University of Copenhagen and the Faculty of Science to welcome all of you here to the 8th International Symposium on Tardigrada. We are especially happy to have you here at the August Krogh Institute (named after our well-known Nobel Prize winner in Physiology), because on September 1st we celebrate the establishment of the Faculty. So coming here and honouring our 150 year anniversary jubilee help us to promote the importance of science in our society. The University was founded in 1479 as a theological catholic school. It broke down in 1530 and was reestablished in 1537 after the reformation. Right from the start in 1479 there was science thought of at the university. Mathematics and Astronomy. And Zoology became a subject over the centuries together with other subjects which are today regarded as science. But only in 1850 did we become an independent Faculty thanks to the effort and progress done by the Danish Chemist H.C. Ørsted.The animals, which you study, are marvellous in the sense that they can survive under severe conditions for centuries. Under extreme dry conditions in Sahara, in extreme cold conditions (they can survive minus 273 °C, or survive in vacuum). This has practical implications for people who need to excuse their scientific interest, for medicine if we can freeze human tissue, or for space study how to survive under extreme conditions. The study of Tardigrada is an important field here at the Institute of Zoology, at the Zoological Museum, and at the University of Roskilde, 30 km west of Copenhagen. Some of our most distinguished zoologists take part in this research. That might be the reason why you have chosen to have the symposium here in Copenhagen. They are doing research on tardigrades in marine areas, and in Greenland on the ice cap. Especially interesting are the studies done in the Ikka Fjord in Greenland, where the unique Ikkaite Tufa columns made of calcium carbonate hexahydrate originating from alkaline cold springs at the bottom of the fjord create very specific environments with nearly brackish conditions in the center and sea water salinity on the outside. And this creates varied conditions for different species of Tardigrada.We also celebrate this year the 50th anniversary of the 2. Galathea expedition which went round the world and specifically looked for deep sea fauna. There are Tardigrades here. It has been interesting to look through the 54 abstracts in the programme and read the names and work places for the 65 participants listed. In English tardigrades are called water bears, in Danish “bjørnedyr” meaning bear animals. I prefer the Danish version, this sounds more like pet bears.The symposium is followed by a field trip to the faculty's research station on Disko in Greenland. In 1994 I arrived on the new research vessel “Porsild” to Disko to deliver the new boat some of you will sail in during the workshop up there. I stayed there some days, and there was this man Professor Reinhardt Møbjerg Kristensen, looking into his microscope. It was fascinating to see the joy which he expressed explaining his animals. His engagement was so impressive and his talk so marvellous. It was really his pet animals he caressed all day and night. If all of you are looking on the water bears with the same fascination and engagement, then this will be one of the most entertaining symposiums ever held. One can fear that you are so engaged that you will forget everything around you, even to listen to the contributions of the others, and to be careful that maybe a new group will be announced.I wish you some very good days here at the Faculty of Science and some very fruitful days. I should like to thank the sponsors of the meeting, The Danish Science Foundation, The Carlsberg Foundation and Dr. Bøje Benzon Foundation. I would like to express my gratitude to the organizing committee for attracting the conference here and making the programme so wide and interesting. I can promise the committee will do all their best to help you all way through. And for those going to Disko — you will have a most splendid experience.I shall ask my colleagues at my own institute, Geography, to arrange some bad weather except on Thursday where you join the excursion. This to prevent you from sneaking away and enjoy the wonders of Copenhagen.By this once again welcome and a wish for a fruitfulconference.     

Sub-fossils of cladocerans in the surface sediment of 135 lakes as proxies for community structure of zooplankton,fish abundance and lake temperature

To elucidate the possibilities of using zooplankton remains in the surface sediment to describe present-days community structure and population dynamics of zooplankton, fish abundance and temperature, we compared contemporary data sampled in the pelagial during summer with the sediment record from the upper 1 cm of the sediment in 135 lakes covering a latitude gradient from Greenland in the north to New Zealand in the south. The abundance of three genera Bosmina, Daphnia and Ceriodaphnia of the total pool of ephippia was significantly related to the total abundance of the same taxa in the pelagic zone. However, in most lakes the abundance of Ceriodaphnia was higher in the sediment than in the water, which may be attributed to the overall preference by this genus for the littoral habitat. Using contemporary data from 27 Danish lakes sampled fortnightly during summer for 10 years, we found substantial inter-annual variations in the abundance of Daphnia spp., Ceriodaphnia spp., B. longirostris and B. coregoni. Yet, the sediment record mimicked the medium level well for most of the lakes, which suggests that the sediment record provides an integrated picture of the pelagic cladoceran community, which otherwise can be obtained only by long-term frequent contemporary sampling for several years. The contribution of Daphnia to the sum of Daphnia and Bosmina ephippia was negatively correlated with the abundance of fish expressed as catch per night in multi-mesh sized gill nets (CPUE). Yet, region-specific differences occurred, which partly could be eliminated by including nutrient state expressed as total phosphorus (TP) in a multiple regression. The average ratio of ephippia to the sum of ephippia and carapaces of Bosmina varied 40-fold between the sampling regions and was significantly negatively related to summer mean air temperature, and for Danish lakes also, albeit weakly, to fish CPUE but not to chlorophyll a. Apparently, temperature is the most important factor determining the ratio of parthenogenetic to ephippia producing specimens of Bosmina. We conclude that the sediment record of cladocerans is a useful indicator of community structure of pelagic cladocerans and the abundance of fish and temperature.     

The severe phenotype of females with tiny ring X chromosomes is associated with inability of these chromosomes to undergo X inactivation.

Molecular typing of HLA class II loci has been performed on a sample of 196 patients with Hodgkin lymphoma. Division of patients into two histological categories--nodular sclerosing Hodgkin disease versus all other types--shows significant overall association of the nodular sclerosing group with the HLA class II region. Haplotypes and alleles defined for the four loci typed--DRB1, DQA1, DQB1, and DPB1--were present in both excess and deficit in the nodular sclerosing sample. Some of the effects are attributable to particular DRB1 and DQB1 alleles, while other effects are best explained by haplotypes marking the entire class II region. The latter effects might be due to variation in additional, as-yet-unexamined loci in the class II region or to particular combinations of alleles from two or more loci. These data also explain why earlier studies showed HLA linkage but not association, and they substantiate the specific involvement of the immune system in certain neoplastic diseases.     

Histone acetylation: A possible mechanism for the inheritance of cell memory at mitosis

Immunofluorescent labelling demonstrates that human metaphase chromosomes contain hyperacetylated histone H4. With the exception of the inactive X chromosome in female cells, where the bulk of histone H4 is under-acetylated, H4 hyperacetylation is non-uniformly distributed along the chromosomes and clustered in cytologically resolvable chromatin domains that correspond, in general, with the R-bands of conventional staining. The strongest immunolabelling is often found in T-bands, the subset of intense R-bands having the highest GC content. The majority of mapped genes also occurs in R-band regions, with the highest gene density in T-bands. These observations are consistent with a model in which hyperacetylation of histone H4 marks the position of potentially active gene sequences on metaphase chromosomes. Since acetylation is maintained during mitosis, progeny cells receive an imprint of the histone H4 acetylation pattern that was present on the parental chromosomes before cell division. Histone acetylation could provide a mechanism for propagating cell memory, defined as the maintenance of committed states of gene expression through cell lineages.     

Size diversity and species diversity relationships in fish assemblages of Western Palearctic lakes

Body size, coupled with abundance and taxonomy, may help to understand the mechanisms shaping community structure. Since the body size of fish is closely related to their trophic niche, size diversity (based on individual body size) of fish communities may capture intraspecific variations in fish trophic niches that are not detected by species diversity. Thus, the relationship between size diversity and species diversity may help to integrate variation at both intraspecific and interspecific levels. We studied the relationship between species diversity and size diversity as a measure of the degree of overlap in size among species and thereby the potential overlap in niches in a community. We hypothesized that the relationship between size diversity and species would be different across the European continent due to different levels of size overlap in fish communities. The data were derived from samplings of fish communities using standardised benthic gill nets in 363 lakes. At the continental scale, size diversity increased with species diversity; at the ecoregion scale, the slope of the relation changed across the continent, with the greatest mismatch occurring in northern Europe where communities comprised only one or a few species, but each of which exhibited a great range in size. There was an increase in slope towards the south with significant relations for four out of six ecoregions. The steeper size diversity‐species diversity slope at lower latitudes is attributable to a lower overlap in fish size and thus likely to finer niche separation. Our results also suggest that size diversity is not a strong surrogate for species diversity in European lake fish communities. Thus, particularly in fish communities composed of few species, measuring size diversity may help to detect potential functional variation which may be neglected by measuring species diversity alone.     

<Emphasis Type="Italic">Cortinarius</Emphasis> sect. <Emphasis Type="Italic">Riederi</Emphasis>: taxonomy and phylogeny of the new section with European and North American distribution

Cortinarius is one of the most species-rich genera of mushroom-forming fungi. Based on phylogenetic and morphological evidence, Cortinarius, sect. Riederi, is introduced at sectional level (= subsect. Riederi sensu Brandrud & Melot). The taxonomy, phylogeny, ecology and distribution of not only mainly European but also including some North American taxa of this section are treated, which includes nine species and two varieties. Of these, three taxa are described as new (C. burlinghamiae, C. pallidoriederi and C. argenteolilacinus var. dovrensis). The sect. Riederi species possess morphological features similar to Phlegmacium group(s) and forms a phylogenetically isolated lineage, with no supported affinity to other phlegmacioid groups. Three taxa are known from both Europe and North America, two species are known only from North America and five only from Europe. Altogether, eight of the ten taxa are associated with conifers or northern (boreal-subalpine) deciduous trees (Betula spp.). Only two species occur in more temperate forests (Fagus forests), and no species have so far been found in thermophilous Quercus forests     

A method for separating DNA fragments by electrophoresis in polyacrylamide concentration gradient slab gels

Electrophoresis on slab gels containing a linear gradient of polyacrylamide concentration has been used to separate DNA fragments obtained by restriction of viral DNAs. A simple method of preparing gradient gels using a sucrose density-gradient mixer and preexisting slab gel apparatus is described. DNA fragments of molecular weights 7 × 10⁴–14 × 10⁶ have been fractionated on gels of 3.5–7.5% and 2.5–7.5% acrylamide concentration. In addition to the wide range of fragment sizes which may be run on a single gel, a further advantage of the system is that much sharper bands are obtained compared to conventional constant concentration gels, thus improving resolution.In the molecular-weight range below 5 × 10⁶, for bands whose terminal velocities in the polyacrylamide concentration gradient approach zero, an approximately linear relationship holds between the logarithms of the molecular weights of the fragments and the logarithms of the distances they have migrated in the gel. Thus, by choosing a suitable upper limit to the concentration gradient, the gel system provides a method for estimating approximate molecular weights of unknown DNA fragments, by comparing their mobilities to known standards.     

Nucleotide sequences of two fragments from the coat-protein cistron of bacteriophage R17 ribonucleic acid

Bacteriophage R17 RNA was labelled with ³²P and was subjected to partial digestion with ribonuclease T₁. The products were fractionated by ionophoresis on polyacrylamide gel. Two fragments were purified and their nucleotide sequences determined by methods involving complete and further partial digestion with ribonucleases A and T₁. Fragment 20 had a sequence that coded for the amino acids in positions 32–53 of the coat protein of the bacteriophage. Fragment 20X, on further purification in 7m-urea, gave rise to two smaller nucleotides whose sequences coded for the amino acids in positions 56–66 and 67–76 of the coat protein. The sequence of the two fragments was such that they could be written in the form of loops stabilized by base-pairing.