Extrinsic versus intrinsic factors in the decline and extinction of Australian marsupials

Recent attempts to explain the susceptibility of vertebrates to declines worldwide have largely focused on intrinsic factors such as body size, reproductive potential, ecological specialization, geographical range and phylogenetic longevity. Here, we use a database of 145 Australian marsupial species to test the effects of both intrinsic and extrinsic factors in a multivariate comparative approach. We model five intrinsic (body size, habitat specialization, diet, reproductive rate and range size) and four extrinsic (climate and range overlap with introduced foxes, sheep and rabbits) factors. We use quantitative measures of geographical range contraction as indices of decline. We also develop a new modelling approach of phylogenetically independent contrasts combined with imputation of missing values to deal simultaneously with phylogenetic structuring and missing data. One extrinsic variable-geographical range overlap with sheep-was the only consistent predictor of declines. Habitat specialization was independently but less consistently associated with declines. This suggests that extrinsic factors largely determine interspecific variation in extinction risk among Australian marsupials, and that the intrinsic factors that are consistently associated with extinction risk in other vertebrates are less important in this group. We conclude that recent anthropogenic changes have been profound enough to affect species on a continent-wide scale, regardless of their intrinsic biology.

True measures of GDP and convergence

Widely used ''purchasing power parity'' comparisons of per capita GDP are not true quantity indexes and are subject to systematic substitution bins. This bias may distort measurement of convergence and divergence. Extending Varian's nonparametric construction of a true index gives the set of true indexes, including the new Ideal Afriat Index. These indexes are utility-consistent and independent of arbitrary reference price vectors. We establish bounds on the dispersion of true multilateral indexes, hence bounds on convergence. International price indexes understate both true GDP dispersion and, where prices are converging over time, the rate of true quantity convergence.

Alternatives for parallel Krylov subspace basis computation

Numerical methods related to Krylov subspaces are widely used in large sparse numerical linear algebra. Vectors in these subspaces are manipulated via their representation onto orthonormal bases. Nowadays, on serial computers, the method of Arnoldi is considered as a reliable technique for constructing such bases. However, although easily parallelizable, this technique is not as scalable as expected for communications. In this work we examine alternative methods aimed at overcoming this drawback. Since they retrieve upon completion the same information as Arnoldi's algorithm does, they enable us to design a wide family of stable and scalable Krylov approximation methods for various parallel environments. We present timing results obtained from their implementation on two distributed-memory multiprocessor supercomputers: the Intel Paragon and the IBM Scalable POWERparallel SP2. (C) 1997 by John Wiley & Sons, Ltd.

The intrinsic antinociceptive effects of oxycodone appear to be kappa-opioid receptor mediated

Our previous studies in the Sprague-Dawley rat showed that the intrinsic antinociceptive effects of oxycodone are naloxone reversible in a manner analogous to morphine but that in contrast to morphine, oxycodone's antinociceptive effects have a rapid onset of maximum effect (approximate to 5-7 min compared to 30-45 min for morphine), comprise one antinociceptive phase (compared to two phases) and are of relatively short duration (approximate to 90 min compared to approximate to 180 min). In the present study, administration of a range of selective opioid receptor antagonists has shown that the intrinsic antinociceptive effects of oxycodone (171 nmol) are not attenuated by i.c.v. administration of (i) naloxonazine, a mu(1)-selective opioid receptor antagonist, or (ii) naltrindole, a delta-selective opioid receptor antagonist, in doses that completely attenuated the intrinsic antinociceptive effects of equipotent doses of the respective mu- and delta-opioid agonists, morphine and enkephalin-[D-Pen(2,5)] (DPDPE). Although beta-funaltrexamine (beta-FNA) attenuated the antinociceptive effects of oxycodone (171 nmol i.c.v.), it also attenuated the antinociceptive effects of morphine and bremazocine (kappa-opioid agonist) indicative of non-selective antagonism. Importantly, the antinociceptive effects of oxycodone (171 nmol i.c.v.) were markedly attenuated by the prior i.c.v. administration of the selective kappa-opioid receptor antagonist, norbinaltorphimine (nor-BNI), in a dose (0.3 nmol) that did not attenuate the antinociceptive effects of an equipotent dose of i.c.v. morphine (78 nmol). Taken together, these data strongly suggest that the intrinsic antinociceptive effects of oxycodone are mediated by K-opioid receptors, in contrast to morphine which interacts primarily with mu-opioid receptors. (C) 1997 International Association for the Study of Pain. Published by Elsevier Science B.V.

Spontaneous and stimulus-evoked intrinsic optical signals in primary auditory cortex of the cat

Spontaneous and tone-evoked changes in light reflectance were recorded from primary auditory cortex (A1) of anesthetized cats (barbiturate induction, ketamine maintenance). Spontaneous 0.1-Hz oscillations of reflectance of 540- and 690-nm light were recorded in quiet. Stimulation with tone pips evoked localized reflectance decreases at 540 nm in 3/10 cats. The distribution of patches activated by tones of different frequencies reflected the known tonotopic organization of auditory cortex. Stimulus-evoked reflectance changes at 690 nm were observed in 9/10 cats but lacked stimulus-dependent topography. In two experiments, stimulus-evoked optical signals at 540 nm were compared with multiunit responses to the same stimuli recorded at multiple sites. A significant correlation (P < 0.05) between magnitude of reflectance decrease and multiunit response strength was evident in only one of five stimulus conditions in each experiment. There was no significant correlation when data were pooled across all stimulus conditions in either experiment. In one experiment, the spatial distribution of activated patches, evident in records of spontaneous activity at 540 nm, was similar to that of patches activated by tonal stimuli. These results suggest that local cerebral blood volume changes reflect the gross tonotopic organization of A1 but are not restricted to the sites of spiking neurons.

Calculation of product state distributions from resonance decay via Lanczos subspace filter diagonalization: Application to HO2

Resonance phenomena associated with the unimolecular dissociation of HO2 have been investigated quantum-mechanically by the Lanczos homogeneous filter diagonalization (LHFD) method. The calculated resonance energies, rates (widths), and product state distributions are compared to results from an autocorrelation function-based filter diagonalization (ACFFD) method. For calculating resonance wave functions via ACFFD, an analytical expression for the expansion coefficients of the modified Chebyshev polynomials is introduced. Both dissociation rates and product state distributions of O-2 show strong fluctuations, indicating the dissociation of HO2 is essentially irregular. (C) 2001 American Institute of Physics.

Lanczos subspace filter diagonalization: Homogeneous recursive filtering and a low-storage method for the calculation of matrix elements

We develop a new iterative filter diagonalization (FD) scheme based on Lanczos subspaces and demonstrate its application to the calculation of bound-state and resonance eigenvalues. The new scheme combines the Lanczos three-term vector recursion for the generation of a tridiagonal representation of the Hamiltonian with a three-term scalar recursion to generate filtered states within the Lanczos representation. Eigenstates in the energy windows of interest can then be obtained by solving a small generalized eigenvalue problem in the subspace spanned by the filtered states. The scalar filtering recursion is based on the homogeneous eigenvalue equation of the tridiagonal representation of the Hamiltonian, and is simpler and more efficient than our previous quasi-minimum-residual filter diagonalization (QMRFD) scheme (H. G. Yu and S. C. Smith, Chem. Phys. Lett., 1998, 283, 69), which was based on solving for the action of the Green operator via an inhomogeneous equation. A low-storage method for the construction of Hamiltonian and overlap matrix elements in the filtered-basis representation is devised, in which contributions to the matrix elements are computed simultaneously as the recursion proceeds, allowing coefficients of the filtered states to be discarded once their contribution has been evaluated. Application to the HO2 system shows that the new scheme is highly efficient and can generate eigenvalues with the same numerical accuracy as the basic Lanczos algorithm.

Subspace wavepacket evolution with Newton polynomials

Time-dependent wavepacket evolution techniques demand the action of the propagator, exp(-iHt/(h)over-bar), on a suitable initial wavepacket. When a complex absorbing potential is added to the Hamiltonian for combating unwanted reflection effects, polynomial expansions of the propagator are selected on their ability to cope with non-Hermiticity. An efficient subspace implementation of the Newton polynomial expansion scheme that requires fewer dense matrix-vector multiplications than its grid-based counterpart has been devised. Performance improvements are illustrated with some benchmark one and two-dimensional examples. (C) 2001 Elsevier Science B.V. All rights reserved.

Adult mouse intrinsic laryngeal muscles express high levels of the myogenic regulatory factor, MYF-5

The intrinsic laryngeal muscles display unique structural and functional characteristics that distinguish them from the skeletal muscle of the trunk and limbs. These features include relatively small muscle fibers, super-fast contraction speed, and fatigue resistance. The molecular basis of tissue-specific functions and other characteristics is differential gene expression. Accordingly, we have investigated the molecular basis of the functional specialization of the intrinsic laryngeal muscles by examining the expression of two key genes in the larynx, known to be important for skeletal muscle development and function: (a) the muscle regulatory factor, Myf-5, and (b) the superfast-contracting myosin heavy chain (EO-MyHC). We have found that the adult thyroarytenoid muscles express much higher levels of both Myf-5 and EO-MyHC messenger ribonucleic acid (mRNA), compared to lower hindlimb skeletal muscle where Myf-5 mRNA levels are very low and EO-MyHC is not detectable. These findings suggest that the unique functional characteristics of the intrinsic laryngeal muscles may be based in laryngeal muscle-specific gene expression directed by a unique combination of muscle regulatory factors. Such laryngeal muscle-specific genes may allow the future development of new treatments for laryngeal muscle dysfunction.

Characterization of two HKT1 homologues from Eucalyptus camaldulensis that display intrinsic osmosensing capability

Plants have multiple potassium (K+) uptake and efflux mechanisms that are expressed throughout plant tissues to fulfill different physiological functions. Several different classes of K+ channels and carriers have been identified at the molecular level in plants. K+ transporters of the HKT1 superfamily have been cloned from wheat (Triticum aestivum), Arabidopsis, and Eucalyptus camaldulensis. The functional characteristics as well as the primary structure of these transporters are diverse with orthologues found in bacterial and fungal genomes. In this report, we provide a detailed characterization of the functional characteristics, as expressed in Xenopus laevis oocytes, of two cDNAs isolated from E. camaldulensis that encode proteins belonging to the HKT1 superfamily of K+/Na+ transporters. The transport of K+ in EcHKT-expressing oocytes is enhanced by Na+, but K+ was also transported in the absence of Na+. Na+ is transported in the absence of K+ as has been demonstrated for HKT1 and AtHKT1. Overall, the E. camaldulensis transporters show some similarities and differences in ionic selectivity to HKT1 and AtHKT1. One striking difference between HKT1 and EcHKT is the sensitivity to changes in the external osmolarity of the solution. Hypotonic solutions increased EcHKT induced currents in oocytes by 100% as compared with no increased current in HKT1 expressing or uninjected oocytes. These osmotically sensitive currents were not enhanced by voltage and may mediate water flux. The physiological function of these osmotically induced increases in currents may be related to the ecological niches that E. camaldulensis inhabits, which are periodically flooded. Therefore, the osmosensing function of EcHKT may provide this species with a competitive advantage in maintaining K+ homeostasis under certain conditions.

A critical appraisal of the intrinsic pancreatic angiotensin-generating system

The pancreas is a relative newcomer to the stable of tissues with an intrinsic angiotensin-generating system. The involvement of this system in pancreatic activity will be dependent on the angiotensin-generating paths present in the pancreas and their precise cellular location. Thus far, renin, angiotensin-converting enzyme (ACE), angiotensin II and AT1 and AT2 receptors have been found. These are components of the "classical" renin-angiotensin system. But there is uncertainty as to their location and site of action. Furthermore, it is not known which, if any, alternative enzymes to renin and ACE are present, which angiotensins in addition to angiotensin II are generated and whether or not there are receptors to angiotensin IV and angiotensin-(1-7). Future research should focus on these aspects in order to provide a mechanistic basis to pancreatic physiological functions and to pathological conditions of clinical relevance.