A technique for predicting in-stream flow requirements of benthic macroinvertebrates

SUMMARY. A total of 225 benthic samples was taken at various riffles along the Tongue River in Montana during three separate weekly intervals in 1975. For each sample, depth, current velocity, substrate microprofile, turbulence (Froude number), and the number and kind of species present were considered.
The conditions of highest faunal diversity were 75–125 cm/s current velocity at 20–40cm depth. The optimum condition appeared to be 76 cm/s at a depth of 28 cm over medium cobble substrates.
The centroids for optimum conditions of depth and current velocity for thirty-six common macroinvertebrates are also presented.
Representative diagrams of the tolerance ranges of some common invertebrate species are presented. Rhithrogena hageni Eaton was chosen as the indicator species since its tolerances closely matched those of the highest community diversity. The presence of Rhithrogena in future samples would indicate maintenance of adequate flow conditions for the present benthic community.
A method for applying these data to produce a minimum flow recommendation is discussed. If the optimum conditions can be plotted on composite hydrologic maps of depth and velocity in riffle areas at various discharges, one can predict the discharge at which the optimum conditions are eliminated and, thus, the recommended minimum discharge.     

Change in Methylation of 16S Ribosomal RNA Associated with Mutation to Kasugamycin Resistance in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Resistance to a drug acting on the 30S ribosomal subunit is attributed to non-methylation of 16S RNA.     

A Freeze-Fracture Study of the Microcyst Wall,Plasma Membrane,and Intramembrane Components of Physarum polycephalum1

ABSTRACT. Freeze-cleave replicas of encysted cells of the myxamoebae of Physarum polycephalum were examined to determine the intrawall substructure and to compare the intramembrane structural components. Cleaved areas of the cyst wall revealed a laminated substructure devoid of the macromolecular interruptions (intramembrane particles or IMP) visible in the cleaved cell membranes. The cyst wall adjacent to the cell membrane appears laminated, and a loose branching network of fibers and fibrils occurs at the wall periphery. The absence of intrawall particles is interpreted as a lack of protein or polypeptide components, thus suggesting additional support for the conclusion that polysaccharides are the major wall constituents. When cleaved cell membranes of encysted cells were examined, more intramembrane particles per unit area were observed on the extracellular membrane leaflet than on the protoplasmic membrane leaflet. In addition, homogeneous as well as aggregated particle distributions were visible on cleaved membrane leaflets. Moreover, the presence of aggregated and unaggregated particles on the same membrane leaflets similarly suggests asynchrony of the cell population. This paper examines and compares biological processes involving the cell membrane that may be related to different stages in the cell cycle or to periods of temporary stasis during the cell cycle.     

The Origin of the Mammalian Middle Ear

A functional explanation is presented for the shift of the reptilianarticular and quadrate into the mammalian middle ear to becomethe malleus and incus. Modification of the masticatory apparatusof therapsids results in reduction of stresses on the jaw jointand consequently in reduction of posterior elements of the jaw.In the late therapsid, Bienotherium, the quadrate and post-dentaryjaw bones resemble the mammalian malleus and incus which togetherform a lever. The therapsid articular possesses a downturnedretroarticular process (for insertion of M. depressor mandibulae)homologous with the manubrium (force lever arm) of the malleus.About the time of origin of the mammalian (dentarysquamosal)jaw joint and following the origin of the mammalian depressor,the reptilian depressor is lost. This allows the enlarging reptiliantympanum to become attached to the retroarticular process. Thenew lever system thus formed by articular and quadrate increasesthe sensitivity of the ear and the reptilian one-bone systemis replaced. In early mammals the reflected lamina of the angularmigrates posteriorly with the angle of the dentary so that itcontacts and assumes support of the tympanum. Non-homology ofthe monotreme and therian depressors indicates a multiple originof the mammalian middle ear.