Macrophyte communities of European streams with altered physical habitat

The impact of altering hydro-morphology on three macrophyte community types was investigated at 107 European stream sites. Sites were surveyed using standard macrophyte and habitat survey techniques (Mean Trophic Rank Methodology and River Habitat Survey respectively). Principal Components Analysis shows the macrophyte community of upland streams live in a more structurally diverse physical habitat than lowland communities. Variables representing the homogeneity and diversity of the physical environment were used to successfully separate un-impacted from impacted sites, e.g. homogeneity of depth and substrate increased with decreasing quality class for lowland sites (ANOVA p < 0.05). Macrophyte attribute groups and structural metrics such as species richness were successfully linked to hydro-morphological variables indicative of impact. Most links were specific to each macrophyte community type, e.g., the attribute group liverworts, mosses and lichens decreased in abundance with increasing homogeneity of depth and decreasing substrate size at lowland sites but not at upland sites. Elodea canadensis, Sparganium emersum and Potamogeton crispus were indicative of impacted lowland sites. Many of the indicator species are also known to be tolerant to other forms of impact. The potential for a macrophyte tool indicative of hydro-morphological impact is discussed. It is concluded one could be constructed by combining indicator species and metrics such as species richness and evenness.     

Metabolism of the polysaccharides of human dental plaque. Part II. Purification and properties of Cladosporium resinae (1 leads to 3)-alpha-D-glucanase, and the enzymic hydrolysis of glucans synthesised by extracellular D-glucosyltransferases of oral streptococci.

Cladosporium resinae (1 leads to 3)-alpha-D-glucanase has been characterized as an endoglucanase capable of completely hydrolysing insoluble (1 leads to 3)-alpha-D-glucans isolated from fungal cell-walls. D-Glucose was the major product, but a small amount of nigerose was also produced. The enzyme was specific for the hydrolysis of (1 leads to 3) bonds that occur in sequence, and nigerotetraose was the smallest substrate that was rapidly attacked. Isolated (1 leads to 3)-alpha-D-glucosidic linkages that occur in mycodextran, isolichein, dextrans, and oligosaccharides derived from dextran were not hydrolysed. Insoluble glucan synthesised from sucrose by culture filtrates of Streptococcus spp. were all hydrolysed to various limits; the range was 11-61%. A soluble glucan, synthesised by an extracellular D-glucosyltransferase of S. mutans OMZ176, was not a substrate, whereas insoluble glucans synthesised by a different D-glucosyltransferase, isolated from S. mutans strains OMZ176 and K1-R, were extensively hydrolysed (84 and 92%, respectively). It is suggested that dextranase-CB, a bacterial endo(1 leads to 6)-alpha-D-glucanase that does not release D-glucose from any substrate, could be used together with C. resinae (1 leads to 3)-alpha-D-glucanase to determine the relative proportions of (1 leads to 6)-linked to (1 leads to 3)-linked sequences of D-glucose residues in the insoluble glucans produce by oral streptococci. The simultaneous action of the two D-glucanoses was highly effective in solubilizing the glucans.     

Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves

A puzzling population-genetic phenomenon widely reported in allozyme surveys of marine bivalves is the occurrence of heterozygote deficits relative to Hardy-Weinberg expectations. Possible explanations for this pattern are categorized with respect to whether the effects should be confined to protein-level assays or are genomically pervasive and expected to be registered in both protein- and DNA-level assays. Anonymous nuclear DNA markers from the American oyster were employed to reexamine the phenomenon. In assays based on the polymerase chain reaction (PCR), two DNA-level processes were encountered that can lead to artifactual genotypic scorings: (a) differential amplification of alleles at a target locus and (b) amplification from multiple paralogous loci. We describe symptoms of these complications and prescribe methods that should generally help to ameliorate them. When artifactual scorings at two anonymous DNA loci in the American oyster were corrected, Hardy-Weinberg deviations registered in preliminary population assays decreased to nonsignificant values. Implications of these findings for the heterozygote-deficit phenomenon in marine bivalves, and for the general development and use of PCR-based assays, are discussed.      

The Effects of Sub-Regional Climate Velocity on the Distribution and Spatial Extent of Marine Species Assemblages

Many studies illustrate variable patterns in individual species distribution shifts in response to changing temperature. However, an assemblage, a group of species that shares a common environmental niche, will likely exhibit similar responses to climate changes, and these community-level responses may have significant implications for ecosystem function. Therefore, we examine the relationship between observed shifts of species in assemblages and regional climate velocity (i.e., the rate and direction of change of temperature isotherms). The assemblages are defined in two sub-regions of the U.S. Northeast Shelf that have heterogeneous oceanography and bathymetry using four decades of bottom trawl survey data and we explore temporal changes in distribution, spatial range extent, thermal habitat area, and biomass, within assemblages. These sub-regional analyses allow the dissection of the relative roles of regional climate velocity and local physiography in shaping observed distribution shifts. We find that assemblages of species associated with shallower, warmer waters tend to shift west-southwest and to shallower waters over time, possibly towards cooler temperatures in the semi-enclosed Gulf of Maine, while species assemblages associated with relatively cooler and deeper waters shift deeper, but with little latitudinal change. Conversely, species assemblages associated with warmer and shallower water on the broad, shallow continental shelf from the Mid-Atlantic Bight to Georges Bank shift strongly northeast along latitudinal gradients with little change in depth. Shifts in depth among the southern species associated with deeper and cooler waters are more variable, although predominantly shifts are toward deeper waters. In addition, spatial expansion and contraction of species assemblages in each region corresponds to the area of suitable thermal habitat, but is inversely related to assemblage biomass. This suggests that assemblage distribution shifts in conjunction with expansion or contraction of thermal habitat acts to compress or stretch marine species assemblages, which may respectively amplify or dilute species interactions to an extent that is rarely considered. Overall, regional differences in climate change effects on the movement and extent of species assemblages hold important implications for management, mitigation, and adaptation on the U.S. Northeast Shelf.     

Nuclear alterations in mammalian cells induced by L-canavanine

Mammalian cells treated four hours with the L-arginine analogue, L-canavanine (Cana), develop alterations in nuclear architecture characterized by the formation of irregular aggregates of nucleoplasmic contents, frequently attached to the nuclear membrane. On the basis of previous studies showing that Cana is incorporated into nuclear proteins and inhibits DNA synthesis over similar periods of exposure, it is postulated that the formation of canavanyl protein-DNA aggregates interfere with DNA replication.     

Variations in microviscosity values induced by different rotational behaviour of fluorescent probes in some aliphatic environments

Recently there have been large developments in the indirect estimation of phospholipid bilayer and membrane microviscosities through the use of fluorescent probes with the help of paraffin oils as standard solvents.Before applying this semi-empirical method to membrane systems, it seemed necessary to test: first, a large variety of probes (this has been done by many authors) and secondly, a large variety of aliphatic oils (there is little literature on these tests).The present paper shows the variations of the rotational relaxation rates of three probes in relation to the viscosities of some aliphatic oils. When changing the oil but keeping constant the macroscopic viscosity, large differences appear in the relaxation rates of a given fluorphore (a ratio of 30/1 is observed in the extreme cases).The microviscosities of membranes deduced from the probe motion will consequently exhibit large uncertainty, as is shown with dipalmitoyl phosphatidylcholine.The cause of these different behaviours must be looked for in the properties of the oil. Particularly, the anisotropy of the solute-solvent interaction in the site where the probe is located depends in part on the internal order of the solvent which is used as a reference.