Performance trade-off across a natural resource gradient

An important environmental factor determining both phytoplankton and zooplankton community composition is lake depth and thermal stratification. However, there is little information on how the interaction between zooplankton grazers and their phytoplankton food changes along an environmental gradient of lake depth. We contrasted resource availability for daphniid zooplankton populations living in two shallow, unstratified lakes and in two deep, stratified lakes using a novel growth bioassay. Stratified lakes had consistently lower resource richness than shallow unstratified lakes. To test whether resources were important in explaining differences in daphniid composition of shallow and deep lakes, we performed reciprocal transplant experiments. We raised daphniids typical of shallow (Ceriodaphnia reticulata) and deep (Daphnia dentifera) lakes in the resources from replicate shallow and deep lakes and monitored survival and reproduction. The two species exhibited a performance trade-off, measured by life table r and R ₀, across a gradient in natural resource richness. D. dentifera had higher relative fitness than C. reticulata when raised in the poorest resource environment from a deep lake. However, under richer resource conditions typical of shallow lakes, C. reticulata outperformed D. dentifera. We further created a gradient in natural resource quantity (by dilution) to test whether this trade-off in species relative fitness involved aspects of resource quality. No trade-off in species performance was evident across the dilution gradient, indicating that resource quality was important to the trade-off. We conclude that shifts in daphniid species composition along a gradient of lake depth involve an adaptive trade-off in ability to exploit rich versus poor resource quality. Received: 11 May 1998 / Accepted: 15 January 1999     

A new model of forelimb ecomorphology for predicting the ancient habitats of fossil turtles

Various morphological proxies have been used to infer habitat preferences among fossil turtles and their early ancestors, but most are tightly linked to phylogeny, thereby minimizing their predictive power. One particularly widely used model incorporates linear measurements of the forelimb (humerus + ulna + manus), but in addition to the issue of phylogenetic correlation, it does not estimate the likelihood of habitat assignment. Here, we introduce a new model that uses intramanual measurements (digit III metacarpal + non‐ungual phalanges + ungual) to statistically estimate habitat likelihood and that has greater predictive strength than prior estimators. Application of the model supports the hypothesis that stem‐turtles were primarily terrestrial in nature and recovers the nanhsiungchelyid Basilemys (a fossil crown‐group turtle) as having lived primarily on land, despite some prior claims to the contrary.     

Length–weight relationships of eight Asian freshwater fish species in Nam Theun 2 Reservoir (Laos PDR)

Length–weight relationships (LWRs) were determined for eight Asian freshwater fish species that were not yet recorded in any peer‐reviewed journal indexed in the Web of Science or the FishBase database. Fish specimens from Nam Theun 2 reservoir in Lao PDR, were collected from April 2012 to August 2016 using several methods to cover a large size‐spectrum for each species. For LWRs using the general equation from Beckman (1948), the parameter b (slope value on the growth pattern) ranges from 2.908 (Puntius brevis) to 3.429 (Rasbora paviana). This study provides an update in maximum lengths for two species and first LWRs for eight common freshwater species found mainly in reservoirs, and thus represents a means for further population dynamic evolution analyses and local fisheries management.     

Structure and thermotropic phase behaviour of detergent-resistant membrane raft fractions isolated from human and ruminant erythrocytes

Detergent-resistant membrane raft fractions have been prepared from human, goat, and sheep erythrocyte ghosts using Triton X-100. The structure and thermotropic phase behaviour of the fractions have been examined by freeze-fracture electron microscopy and synchrotron X-ray diffraction methods. The raft fractions are found to consist of vesicles and multilamellar structures indicating considerable rearrangement of the original ghost membrane. Few membrane-associated particles typical of freeze-fracture replicas of intact erythrocyte membranes are observed in the fracture planes. Synchrotron X-ray diffraction studies during heating and cooling scans showed that multilamellar structures formed by stacks of raft membranes from all three species have d-spacings of about 6.5 nm. These structures can be distinguished from peaks corresponding to d-spacings of about 5.5 nm, which were assigned to scattering from single bilayer vesicles on the basis of the temperature dependence of their d-spacings compared with the multilamellar arrangements. The spacings obtained from multilamellar stacks and vesicular suspensions of raft membranes were, on average, more than 0.5 nm greater than corresponding arrangements of erythrocyte ghost membranes from which they were derived. The trypsinization of human erythrocyte ghosts results in a small decrease in lamellar d-spacing, but rafts prepared from trypsinized ghosts exhibit an additional lamellar repeat 0.4 nm less than a lamellar repeat coinciding with rafts prepared from untreated ghosts. The trypsinization of sheep erythrocyte ghosts results in the phase separation of two lamellar repeat structures (d = 6.00; 5.77 nm), but rafts from trypsinized ghosts produce a diffraction band almost identical to rafts from untreated ghosts. An examination of the structure and thermotropic phase behaviour of the dispersions of total polar lipid extracts of sheep detergent-resistant membrane preparations showed that a reversible phase separation of an inverted hexagonal structure from coexisting lamellar phase takes place upon heating above about 30 °C. Non-lamellar phases are not observed in erythrocytes or detergent-resistant membrane preparations heated up to 55 °C, suggesting that the lamellar arrangement is imposed on these membrane lipids by interaction with non-lipid components of rafts and/or that the topology of lipids in the erythrocyte membrane survives detergent treatment.     

Extension of the GLYCAM06 Biomolecular Force Field to Lipids, Lipid Bilayers and Glycolipids

GLYCAM06 is a generalisable biomolecular force field that is extendible to diverse molecular classes in the spirit of a small-molecule force field. Here we report parameters for lipids, lipid bilayers and glycolipids for use with GLYCAM06. Only three lipid-specific atom types have been introduced, in keeping with the general philosophy of transferable parameter development. Bond stretching, angle bending, and torsional force constants were derived by fitting to quantum mechanical data for a collection of minimal molecular fragments and related small molecules. Partial atomic charges were computed by fitting to ensemble-averaged quantum-computed molecular electrostatic potentials.In addition to reproducing quantum mechanical internal rotational energies and experimental valence geometries for an array of small molecules, condensed-phase simulations employing the new parameters are shown to reproduce the bulk physical properties of a DMPC lipid bilayer. The new parameters allow for molecular dynamics simulations of complex systems containing lipids, lipid bilayers, glycolipids, and carbohydrates, using an internally consistent force field. By combining the AMBER parameters for proteins with the GLYCAM06 parameters, it is also possible to simulate protein-lipid complexes and proteins in biologically relevant membrane-like environments.     

Multinuclear magnetic resonance study of Pt(II) compounds with sulfoxide ligands and crystal structures of complexes of the types [Pt(R2SO)X3] and Pt(R2SO)2Cl2

Pt(II) complexes of the types K[Pt(R₂SO)X₃], NR₄[Pt(R₂SO)X₃] and Pt(R₂SO)₂Cl₂ (where X = Cl or Br) were characterized by multinuclear magnetic resonance spectroscopy (¹⁹⁵Pt, ¹H and ¹³C). In ¹⁹⁵Pt NMR, the chloro ionic compounds have shown signals between −2979 and −3106 ppm, while the cis disubstituted complexes were observed at higher fields, between −3450 and −3546 ppm. The signal of the compound trans-Pt(DPrSO)₂Cl₂ was found at higher field (−3666 ppm) than its cis analogue (−3517 ppm), since π-back-donation is considerably less effective in the trans geometry. In ¹H NMR, a single signal was observed for the sulfoxide in [Pt(DMSO)Cl₃]⁻, but for the other more sterically hindered ligands, two series of resonances were observed for the protons in α and β positions. The coupling constant ³J(¹⁹⁵Pt-¹H) are between 15 and 33 Hz. The ¹³C NMR results were interpreted in relation to the concept of inversed polarization of the π sulfoxide bond. The ²J(¹⁹⁵Pt-¹³C) values vary between 35 and 66 Hz, while a few ³J(¹⁹⁵Pt-¹³C) couplings were observed (13-26 Hz). The crystal structures of five monosubstituted ionic compounds N(n-Bu)₄[Pt(TMSO)Cl₃], N(Me)₄[Pt(DPrSO)Cl₃], K[Pt(EMSO)Cl₃], K[Pt(TMSO)Br₃] · H₂O and N(Et)₄[Pt(DPrSO)Br₃] and one disubstituted complex cis-Pt(DBuSO)₂Cl₂ were determined. The trans influence of the different ligands is discussed.     

Quality matters: resource quality for hosts and the timing of epidemics

Epidemiologists increasingly realize that species interactions (e.g. selective predation) can determine when epidemics start and end. We hypothesize here that resource quality can also strongly influence disease dynamics: epidemics can be inhibited when resource quality for hosts is too poor and too good. In three lakes, resource quality for the zooplankton host ( Daphnia dentifera ) was poor when fungal epidemics ( Metschnikowia bicuspidata ) commenced and increased as epidemics waned. Experiments using variation in algal food showed that resource quality had conflicting effects on underlying epidemiology: high-quality food induced large production of infective propagules (spores) and high birth rate but also reduced transmission. A model then illustrated how these underlying correlations can inhibit the start of epidemics (when spore production/birth rate are too low) but also catalyse their end (when transmission becomes too low). This resource quality mechanism is likely to interface with other ones controlling disease dynamics and warrants closer evaluation.     

Generation of an OMgp allelic series in mice

The very limited ability to regenerate axons after injury in the mature mammalian central nervous system (CNS) has been partly attributed to the growth restrictive nature of CNS myelin. Oligodendrocyte myelin glycoprotein (OMgp) was identified as a major myelin‐derived inhibitor of axon growth. However, its role in axon regeneration in vivo is poorly understood. Here we describe the generation and molecular characterization of an OMgp allelic series. With a single gene targeting event and Cre/FLP mediated recombination, we generated an OMgp null allele with a LacZ reporter, one without a reporter gene, and an OMgp conditional allele. This allelic series will aid in the study of OMgp in adult CNS axon regeneration using mouse models of spinal cord injury. The conditional allele will overcome developmental compensation when employed with an inducible Cre, and allows for the study of temporal and tissue/cell type‐specific roles of OMgp in CNS injury‐induced axonal plasticity. genesis 47:751–756, 2009. © 2009 Wiley‐Liss, Inc.