Evolution of a mate recognition system after hybridization between two Drosophila species

I investigated the genetic relationship between male and female components of the mate recognition system and how this relationship influenced the subsequent evolution of the two traits, in a series of replicate populations of interspecific hybrids. Thirty populations of hybrids between Drosophila serrata and Drosophila birchii were established and maintained for 24 generations. At the fifth generation after hybridization, the mating success of hybrid individuals with the D. serrata parent was determined. The genetic correlation between male and female components of the male recognition system, as a consequence of pleiotropy or tight physical linkage, was found to be significant but low (r = 0.388). This result suggested that pleiotropy may play only a minor role in the evolution of mate recognition in this system. At the twenty-fourth generation after hybridization, the mating success of the hybrids was again determined. The evolution of male and female components was investigated by analyzing the direction of evolution of each hybrid line with respect to its initial position in relation to the genetic regression. Male and female components appeared to converge on a single equilibrium point, rather than evolving along trajectories with slope equal to the genetic regression, toward a line of equilibria.

Renewing Australia's mental health strategy

The Second National Mental Health Plan, endorsed by Commonwealth, State and Territory governments on 30 July 1998, will pursue three key themes: (1) Promoting mental health, plus prevention of and early intervention in mental disorders, with a specific focus on depression; (2) continuing structural reform of mental health services, including better integration with general practice and the private psychiatric sector; and (3) implementing quality and outcome measures in mental health services, including evidence-based practice.

Evolution of three-dimensional folds for a non-Newtonian plate in a viscous medium

We derive analytical solutions for the three-dimensional time-dependent buckling of a non-Newtonian viscous plate in a less viscous medium. For the plate we assume a power-law rheology. The principal, axes of the stretching D-ij in the homogeneously deformed ground state are parallel and orthogonal to the bounding surfaces of the plate in the flat state. In the model formulation the action of the less viscous medium is replaced by equivalent reaction forces. The reaction forces are assumed to be parallel to the normal vector of the deformed plate surfaces. As a consequence, the buckling process is driven by the differences between the in-plane stresses and out of plane stress, and not by the in-plane stresses alone as assumed in previous models. The governing differential equation is essentially an orthotropic plate equation for rate dependent material, under biaxial pre-stress, supported by a viscous medium. The differential problem is solved by means of Fourier transformation and largest growth coefficients and corresponding wavenumbers are evaluated. We discuss in detail fold evolutions for isotropic in-plane stretching (D-11 = D-22), uniaxial plane straining (D-22 = 0) and in-plane flattening (D-11 = -2D(22)). Three-dimensional plots illustrate the stages of fold evolution for random initial perturbations or initial embryonic folds with axes non-parallel to the maximum compression axis. For all situations, one dominant set of folds develops normal to D-11, although the dominant wavelength differs from the Biot dominant wavelength except when the plate has a purely Newtonian viscosity. However, in the direction parallel to D-22, there exist infinitely many modes in the vicinity of the dominant wavelength which grow only marginally slower than the one corresponding to the dominant wavelength. This means that, except for very special initial conditions, the appearance of a three-dimensional fold will always be governed by at least two wavelengths. The wavelength in the direction parallel to D-11 is the dominant wavelength, and the wavelength(s) in the direction parallel to D-22 is determined essentially by the statistics of the initial state. A comparable sensitivity to the initial geometry does not exist in the classic two-dimensional folding models. In conformity with tradition we have applied Kirchhoff's hypothesis to constrain the cross-sectional rotations of the plate. We investigate the validity of this hypothesis within the framework of Reissner's plate theory. We also include a discussion of the effects of adding elasticity into the constitutive relations and show that there exist critical ratios of the relaxation times of the plate and the embedding medium for which two dominant wavelengths develop, one at ca. 2.5 of the classical Biot dominant wavelength and the other at ca. 0.45 of this wavelength. We propose that herein lies the origin of parasitic folds well known in natural examples.

Genetic structure and evolution of species in the mangrove genus Avicennia (Avicenniaceae) in the Indo-West Pacific

Allozyme variation in species of the mangrove genus Avicennia was screened in 25 populations collected from 22 locations in the Indo-West Pacific and eastern North America using 11 loci. Several fixed gene differences supported the specific status of Avicennia alba, A. integra, A. marina, and A. rumphiana from the Indo-West Pacific, and A. germinans from the Atlantic-East Pacific. The three varieties of A. marina, var. marina, var. eucalyptifolia, and var. australasica, had higher genetic similarities (Nei's I) and no fixed gene differences, confirming their conspecific status. Strong genetic structuring was observed in A. marina, with sharp changes in gene frequencies at the geographical margins of varietal distributions. The occurrence of alleles found otherwise in only one variety, in only immediately adjacent populations of another variety, provided evidence of introgession between varieties. The varieties appear to have diverged recently in the Pleistocene and are apparently not of ancient Cretaceous origin, as suggested earlier. Despite evidence of high degrees of outcrossing, gene flow among populations was relatively low (N(e)m less than or equal to 1-2), except where populations were geographically continuous, questioning assumptions that these widespread mangrove species achieve high levels of long-distance dispersal.

A bleach program for inmates in NSW: an HIV prevention strategy

Syringe cleaning guidelines for injecting drug users (IDUs) were revised in 1993. This paper examines efforts by IDUs in NSW prisons to adopt the revised guidelines in 1994. Consecutive inmates (229) nearing release were visited and asked to call a toll free number for an interview once released. Respondents (102) did not differ from non-respondents (127). Many respondents (64%) reported ever injecting and many of these reported injecting (58%), sharing (48%) and syringe cleaning (46%) when last in prison. Some (23%) respondents reported adopting the revised syringe cleaning guidelines. Tattooing (38%) was reported more often than sexual activity in prison (4%). A new methodology for prison research was found to be feasible in this study. The potential for HIV to spread in prison still poses major public health challenges.

Crystal structure of human T cell leukemia virus type 1 gp21 ectodomain crystallized as a maltose-binding protein chimera reveals structural evolution of retroviral transmembrane proteins

Retroviral entry into cells depends on envelope glycoproteins, whereby receptor binding to the surface-exposed subunit triggers membrane fusion by the transmembrane protein (TM) subunit. We determined the crystal structure at 2.5-Angstrom resolution of the ectodomain of gp21, the TM from human T cell leukemia virus type 1. The gp21 fragment was crystallized as a maltose-binding protein chimera, and the maltose-binding protein domain was used to solve the initial phases by the method of molecular replacement. The structure of gp21 comprises an N-terminal trimeric coiled coil, an adjacent disulfide-bonded loop that stabilizes a chain reversal, and a C-terminal sequence structurally distinct from HIV type 1/simian immunodeficiency virus gp41 that packs against the coil in an extended antiparallel fashion. Comparison of the gp21 structure with the structures of other retroviral TMs contrasts the conserved nature of the coiled coil-forming region and adjacent disulfide-bonded loop with the variable nature of the C-terminal ectodomain segment. The structure points to these features having evolved to enable the dual roles of retroviral TMs: conserved fusion function and an ability to anchor diverse surface-exposed subunit structures to the virion envelope and infected cell surface. The structure of gp21 implies that the N-terminal fusion peptide is in close proximity to the C-terminal transmembrane domain and likely represents a postfusion conformation.

Some new examples for nonuniqueness of the evolution problem of harmonic maps

We find some new examples to show nonuniquence for the heat flow of harmonic maps where weak solutions satisfy the same monotonicity property.

Rapid evolution towards equal sex ratios in a system with heterogamety

The equal sex ratios found in many species with heterogametic sex determination may be a consequence of selection for equality or the result of the Mendelian segregation of the two sex chromosomes. A lack of genetic variation in sex ratio in species with heterogamety has been the major obstacle in distinguishing between these two hypotheses. We overcome this obstacle by generating hybrids between two species of Drosophila. The resulting hybrid lines had biased sex ratios, allowing us to observe the evolution of sex ratio in replicate populations. Sex ratio converged towards 1:1 after 16 generations of natural selection. These changes in sex ratio were not due to differences in viability between the sexes and the loci underlying the variation in sex ratio were not sex-linked. Equal sex ratios may therefore be the result of natural selection as Fisher predicted.

Protein sequence threading, the alignment problem, and a two-step strategy

Conventionally, protein structure prediction via threading relies on some nonoptimal method to align a protein sequence to each member of a library of known structures. We show how a score function (force field) can be modified so as to allow the direct application of a dynamic programming algorithm to the problem. This involves an approximation whose damage can be minimized by an optimization process during score function parameter determination. The method is compared to sequence to structure alignments using a more conventional pair-wise score function and the frozen approximation. The new method produces results comparable to the frozen approximation, but is faster and has fewer adjustable parameters. It is also free of memory of the template's original amino acid sequence, and does not suffer from a problem of nonconvergence, which can be shown to occur with the frozen approximation. Alignments generated by the simplified score function can then be ranked using a second score function with the approximations removed. (C) 1999 John Wiley & Sons, Inc.

Electrochemistry of macrocyclic cobalt(III/II) hexaamines: Electrocatalytic hydrogen evolution in aqueous solution

The macrocyclic cobalt hexaamines [Co(trans-diammac)](3+) and [Co(cis-diammac)](3+) (diammac = 6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine) are capable of reducing the overpotential for hydrogen evolution on a mercury cathode in aqueous solution. Protons are reduced in a catalytic process involving reoxidation of the Co-II species to its parent Co-III complex. The cycle is robust at neutral pH with no decomposition of catalyst. The stability of the [Co(trans-diammac)](2+) and [Co(cis-diammac)](2+) complexes depends on the pH of the solution and the coordinating properties of the supporting electrolyte. Electrochemical studies indicate that the adsorbed Co-II complex on the surface of mercury is the active catalyst for the reduction of protons to dihydrogen.