Methanogenesis produces strong 13C enrichment in stromatolites of Lagoa Salgada, Brazil: a modern analogue for Palaeo-/Neoproterozoic stromatolites?

Holocene stromatolites characterized by unusually positive inorganic δ(13) CPDB values (i.e. up to +16‰) are present in Lagoa Salgada, a seasonally brackish to hypersaline lagoon near Rio de Janeiro (Brazil). Such positive values cannot be explained by phototrophic fixation of CO2 alone, and they suggest that methanogenesis was a dominating process during the growth of the stromatolites. Indeed, up to 5 mm methane was measured in the porewater. The archaeal membrane lipid archaeol showing δ(13) C values between -15 and 0‰ suggests that archaea are present and producing methane in the modern lagoon sediment. Moreover, (13) C-depleted hopanoids diplopterol and 3β-methylated C32 17β(H),21β(H)-hopanoic acid (both -40‰) are preserved in lagoon sediments and are most likely derived from aerobic methanotrophic bacteria thriving in the methane-enriched water column. Loss of isotopically light methane through the water column would explain the residual (13) C-enriched pool of dissolved inorganic carbon from where the carbonate constituting the stromatolites precipitated. The predominance of methanogenic archaea in the lagoon is most likely a result of sulphate limitation, suppressing the activity of sulphate-reducing bacteria under brackish conditions in a seasonally humid tropical environment. Indeed, sulphate-reduction activity is very low in the modern sediments. In absence of an efficient carbonate-inducing metabolic process, we propose that stromatolite formation in Lagoa Salgada was abiotically induced, while the (13) C-enriched organic and inorganic carbon pools are due to methanogenesis. Unusually, (13) C-enriched stromatolitic deposits also appear in the geological record of prolonged periods in the Palaeo- and Neoproterozoic. Lagoa Salgada represents a possible modern analogue to conditions that may have been widespread in the Proterozoic, at times when low sulphate concentrations in sea water allowed methanogens to prevail over sulphate-reducing bacteria.

Models of intellectual disability: towards a perspective of (poss)ability

BACKGROUND

The social and medical models of disability configure the relationship between disability and impairment differently. Neither of these models has provided a comprehensive theoretical or practical basis for talking about intellectual disability (ID). Models that emphasise the interactive nature of disability appear to be more promising. This study explores the ways in which models of disability are reflected in disability discourse in an empirical discourse analysis conducted in the Eastern Cape Province of South Africa.

METHODS

Q methodology was used in this study as a discourse analysis tool. Adults with ID, parents of children with ID and professionals who work with people with ID completed a sorting task where they stated the degree to which they agreed or disagreed with statements that are made about people with ID. This exercise resulted in a pattern of responses for each participant, termed a Q sort and these were used as data in a factor analysis using dedicated Q method software. A second order factor analysis was then performed on the resulting factors.

RESULTS

Four discourses were identified: the Social Model/Human Rights Discourse, the Medical Model/Professional Religious Discourse, the Community Model/Community Religious Discourse and the Interactive Discourse. Except for the last one, each of these discourses adopts a model of disability with a static view of impairment as fixed. The Interactive Discourse appears to be related to dynamic, environmental conceptions of disability where competence is built through social interaction.

CONCLUSIONS

A theory of (poss)ability is proposed and some of its concerns are suggested. This perspective views impairment as an interaction between individuals and their environment and postulates that competence is a function of context, rather than a property of the individual.

Obstructive sleep apnoea and perioperative complications in bariatric patients

BACKGROUND

The objective of this study was to determine the relationship between perioperative complications and the severity of obstructive sleep apnoea (OSA) in patients undergoing bariatric surgery who had undergone preoperative polysomnography (PSG).

METHODS

The records of 797 patients, age >18 yr, who underwent bariatric operations (442 open and 355 laparoscopic procedures) at Mayo Clinic and were assessed before operation by PSG, were reviewed retrospectively. OSA was quantified using the apnoea-hypopnoea index (AHI) as none (≤ 4), mild (5-15), moderate (16-30), and severe (≥ 31). Pulmonary, surgical, and 'other' complications within the first 30 postoperative days were analysed according to OSA severity. Logistic regression was used to assess the multivariable association of OSA, age, sex, BMI, and surgical approach with postoperative complications.

RESULTS

Most patients with OSA (93%) received perioperative positive airway pressure therapy, and all patients were closely monitored after operation with pulse oximetry on either regular nursing floors or in intensive or intermediate care units. At least one postoperative complication occurred in 259 patients (33%). In a multivariable model, the overall complication rate was increased with open procedures compared with laparoscopic. In addition, increased BMI and age were associated with increased likelihood of pulmonary and other complications. Complication rates were not associated with OSA severity.

CONCLUSIONS

In obese patients evaluated before operation by PSG before bariatric surgery and managed accordingly, the severity of OSA, as assessed by the AHI, was not associated with the rate of perioperative complications. These results cannot determine whether unrecognized and untreated OSA increases risk.

Mass mortality and its environmental and evolutionary consequences

The latest Mesozoic and earliest Tertiary sediments at Deep Sea Drilling Project site 524 provide an amplified record of environmental and biostratographic changes at the end of Cretaceous. Closely spaced samples, representing time intervals as short as 10(2) or 10(3) years, were analyzed for their bulk carbonate and trace-metal compositions, and for oxygen and carbon isotopic compositions. The data indicate that at the end of Cretaceous, when a high proportion of the ocean's planktic organisms were eliminated, an associated reduction in productivity led to a partial transfer of dissolved carbon dioxide from the oceans to the atmosphere. This resulted in a large increase of the atmospheric carbon dioxide during the next 50,000 years, which is believed to have caused a temperature rise revealed by the oxygen-isotope data. The lowermost Tertiary sediments at site 524 include fossils with Cretaceous affinities, which may include both reworked individuals and some forms that survived for a while after the catastrophe. Our data indicate that many of the Cretaceous pelagic organisms became extinct over a period of a few tens of thousands of years, and do not contradict the scenario of cometary impact as a cause of mass mortality in the oceans, as suggested by an iridium anomaly at the Cretaceous-Tertiary boundary.

Retina-specific LDH isozyme in blueback herring, Alosa aestivalis (Mitchell), and alewife, Alosa pseudoharengus (Wilson)

The retina of 390 Alosa aestivalis and 410 Alosa pseudoharengus have been examined by means of starch-gel electrophoresis. The retina-specific E4 isozyme has been found to occur in all the fish examined. This study demonstrates for the first time that the E4 isozyme occurs in A. aestivalis. Because the E4 isozyme is not polymorphic and has an identical mobility in A. pseudoharengus and in A. aestivalis it is neither suitable for use as a species identification characteristic nor a population marker.

Positional cloning of a cyromazine resistance gene in Drosophila melanogaster

Cyromazine is an effective insecticide used to control dipteran insects. Its precise mode of action is yet to be determined, although it has been suggested that it interferes with the hormone system, sclerotization of the cuticle, or nucleic acid metabolism. To understand the way in which cyromazine acts, we have positionally cloned a cyromazine resistance gene from Drosophila melanogaster. Six cyromazine resistance alleles had previously been generated by ethyl methanasulphonate treatment. Two of these failed to complement each other and here we identify them as having independent non-sense mutations in CG32743, which is an ortholog of Smg1 of worms and mammals and encodes a phosphatidylinositol kinase-like kinase (PIKK). RNAi experiments confirm that cyromazine resistance can be achieved by knocking down CG32743. These are the first cyromazine resistant mutations identified at the nucleotide level. In mammals Smg1 phosphorylates P53 in response to DNA damage. This finding supports the hypothesis that cyromazine interferes with nucleic acid metabolism.

Molecular systematics and biogeography of the bent-wing bat complex Miniopterus schreibersii (Kuhl, 1817) (Chiroptera: Vespertilionidae)

The complete mitochondrial ND2 gene (1037 bp) was sequenced to examine relationships within the bent-wing bat complex, Miniopterus schreibersii (Family Vespertilionidae). It was found that M. schreibersii is a paraphyletic assemblage comprising several species. Two major lineages were identified, one of which was restricted to the Palearctic-Ethiopian regions and the other to the Oriental-Australasian regions. This pattern of differentiation was mirrored by the genus as a whole. Speciation and differentiation within the genus Miniopterus appears to have a hierarchical geographical pattern. The earliest divergence corresponds to the Ethiopian-Palearctic and the Oriental-Australasian biogeographical zones. This early divergence is then followed by radiations within each of the Ethiopian, Oriental and Australasian regions. The study also revealed that the number of species currently recognized (11 or 13) is a gross underestimate of the number of actual species. The emerging picture is one of a relatively speciose genus with most species having relatively restricted distributions; few, if any, occur in more than one biogeographical region.

The genetic, molecular and phenotypic consequences of selection for insecticide resistance

Studies of insecticide resistance allow theories of the adaptive process to be tested where the selective agent, the insecticide, is unambiguously defined. Thus, the consequences of selection of phenotypic variation can be investigated in genetic, biochemical, molecular, population biological and, most recently, developmental contexts. Are the options limited biochemically and molecularly? Is the genetic mechanism monogenic or polygenic, general or population/species specific? Are fitness and developmental patterns associated? These questions of general evolutionary significance can be considered with experimental approaches to determine how insecticide resistance evolves.

Oligonucleotides with bistranded abasic sites interfere with substrate binding and catalysis by human apurinic/apyrimidinic endonuclease

Apurinic/apyrimidinic endonuclease (AP endo) is a key enzyme in oxidative damage DNA repair. The enzyme, which repairs abasic sites, makes a single nick 5' to the phosphodeoxyribose, leaving a free 3'-hydroxyl. We recently described single turnover kinetics for human recombinant AP endo acting on an oligonucleotide with a single abasic site. We hypothesized that the structural changes induced by the presence of a second abasic site might provide insight into how AP endo recognizes the first abasic site. Here we performed steady state and single turnover experiments using bistranded abasic site substrates, with the second site located on the complementary strand to the one being followed and either opposite to the first or displaced in the 5' direction. All sites on the complementary strand were within half a helical turn of the first. The catalytic efficiency was reduced 80 to 96% and the Kd for substrate binding and dissociation was elevated 40- to 125-fold. The smaller changes occurred when the second site was opposite the first site or displaced by four nucleotides. In addition, if the second abasic site was directly across the helix or displaced by 1 or 3 nucleotides from the first abasic site, cleavage of the first abasic site was subject to apparent substrate inhibition, which did not occur if the second abasic site was displaced by four nucleotides from the first. While a substrate containing a nick without a phosphodeoxyribose on the contralateral strand abasic site did not inhibit nicking of the first strand, a substrate with a nicked abasic site on the contralateral strand was an even stronger inhibitor of enzyme action than an oligonucleotide containing the corresponding abasic site on each strand. Consequently, the inhibitory effect of the second abasic site is probably the result of prior cleavage of the abasic site on the contralateral strand with resulting distortions to the DNA helix that interfere with enzyme binding and/or cleavage.

A method for the extraction of ammonium from freshwaters for nitrogen isotope analysis

The measurement of delta15N values of inorganic nitrogen species is an important analytical tool to trace nitrogen species in order to understand nitrogen cycling in aquatic systems. Nitrogen isotope analysis of freshwater ammonium has, however, been hindered by the lack of a simple and reliable technique to measure delta15N values at natural abundance levels. We present a simple and rapid method to concentrate ammonium from freshwater samples for on-line N-isotope ratio determination. Ammonium is collected by adsorption on N-free cation exchange resins. The dried N-loaded exchange resin is then directly combusted to produce N2 gas for subsequent delta15N analysis. The method was evaluated with simulated freshwater solutions containing varying amounts of standard NH4+-N (delta15N = 2.1 per thousand) and potentially interfering inorganic and organic compounds. In general, the cation exchange resin method gives accurate and reproducible delta15N values (sigma1 < 0.3 per thousand; n = 10). Because of adsorption interference, high concentrations of cations in solution may cause ammonium loss but do not result in measurable isotope fractionation. Replicate extractions of the ammonium standard added to water collected from four Swiss lakes demonstrate the good performance of this method when applied to low ionic strength natural water samples with modest concentrations of dissolved organic nitrogen.

Fluctuating asymmetry for specific bristle characters in notch mutants of Drosophila melanogaster

Asymmetry has been used as a measure of developmental stability for bilaterally symmetrical organisms. Most studies have failed to partition the genetic and environmental contributions to the asymmetry phenotype due to the limitations of the systems used or the shortcomings in experimental design. The Notch mutants of Drosophila melanogaster were used to study the genetic contribution to asymmetry for six different bristle characters. Asymmetry response was character specific for the mutants examined. For Nspl, N(Co), N264-47, Ax71d, Ax9B2, AxE2, 1(1)N(B) and nd2 significant asymmetry responses, relative to wildtype Canton-S, were observed for some characters. N60g11 and nd1 did not exhibit significant asymmetry for any of the characters examined. All of the mutants except N60g11 and nd1 showed thoracic bristle asymmetry. However, when asymmetry scores were pooled over the five bristle characters which individually exhibited fluctuating asymmetry, no significant differences were found between any genotypes. Therefore pooling asymmetry values across characters obscures the significant character specific asymmetry values observed. Thus caution is necessary when using the asymmetry phenotype of specific characters to draw organism wide conclusions about developmental stability.

Biogeochemistry. Sulfate reducers--dominant players in a low-oxygen world?

Sulfate reducing bacteria can adapt to extreme physical and chemical conditions and play an important role in global geochemical cycles, but their role in the formation of ore deposits has remained controversial. Strong support for such a role is provided by Labrenz et al., who have discovered sulfate-reducing bacteria that can tolerate low levels of oxygen and can precipitate zinc sulfide minerals. The results may have implications for bioremediation and may provide clues to processes that may have been more widespread in the geologic past.

Wings and bristles: character specificity of the asymmetry phenotype in insecticide-resistant strains of Lucilia cuprina

We investigated the hypothesis that observed higher levels of asymmetry displayed by insecticide-resistance genotypes of Lucilia cuprina are restricted to bristle characters, due to the action of resistance genes in bristle cell development, rather than through the disruption of genomic coadaptation. We compared the level of asymmetry of three bristle characters and three wing characters in non-modified and modified-resistance genotypes. Consistent with previous studies, resistance genotypes displayed greater levels of bristle asymmetry than either susceptible or modified genotypes. However, there were no differences among genotypes for any of the wing characters. To confirm that this result is attributable to the action of the resistance and modifier genes themselves, we also examined the responses of both bristle and wing characters to the more general developmental stress of extreme temperature. Sub-optimal temperature was shown to increase both bristle and wing asymmetry, suggesting that there are no underlying differences between the two character types which could, of themselves, explain the differential response observed in the resistance genotypes.

Evaluation of the cleaning and disinfection efficacy of the DEKO-190; award-based automated washer/disinfector

The DEKO-190 Washer-Disinfector combines both automatic washing and thermal disinfection functions and is designed for the decontamination of ward utensils (such as bedpans and urine bottles) and instruments used in minor surgery prior to sterilization. We undertook a microbiological evaluation of the disinfection efficacy of the machine, using its short wash plus disinfection programme and sealed suspensions of test organisms placed at various points within the instrument. Suspensions of Enterococcus faecalis and Poliovirus were totally inactivated, the counts of aerobic organisms within a stool specimen being reduced by a factor of 10(4)whilst spores of Clostridium perfringens were unaffected. The cleaning efficacy of the DEKO-190 was also evaluated under clinical conditions by visual inspection and was found to be satisfactory. Ward-based combined washer-disinfection machines, such as the DEKO-190, have the potential to improve the efficacy of cleaning protocols within healthcare institutions.

A genetic analysis of cyromazine resistance in Drosophila melanogaster (Diptera: Drosophilidae)

Flies resistant to the insect growth regulator cyromazine were selected in the F1 generation from a cyromazine-susceptible strain of Drosophila melanogaster (Meigen) treated with ethyl methanesulfonate. Four resistant strains were isolated by screening with cyromazine at a concentration > LC100 of susceptibles. In each strain, resistance is conferred by a single gene mutation. Cyromazine resistance in two of the mutants (rst(1a)cyr1 and rst(1a)cyr2) localizes to map position 17 of the X chromosome. Evidence is presented that these mutations are alleles of the gene rst(1a)cyr. Cyromazine resistance in another of the mutants (Rst(1b)Cyr) is also X-linked, and localizes to map position 49 of the X chromosome. The location of the gene conferring cyromazine resistance in the other mutant (Rst(2b)Cyr) is map position 66 of chromosome II. This is possibly an allele of a previously characterized cyromazine resistance gene, Rst(2)Cyr. Dosage-mortality analyses demonstrate a low level of cyromazine resistance is conferred in all strains.

Dieldrin resistance in Lucilia cuprina (the australian sheep blowfly): chance, selection and response

Discrete-generation population cages of Lucilia cuprina were initiated with dieldrin-resistant allele (Rdl ) frequencies of 1 or 5% and maintained for 17 generations on media with concentrations of dieldrin in the range 0-0.006% (w/v). The probability of the initial establishment of the Rdl allele in a population was consistently greater at the 5% frequency and dependent on the concentration of dieldrin in the medium for both starting frequencies. Once the resistant allele was established responses to selection were concentration-dependent. It was concluded that in the absence of dieldrin the susceptible allele was selectively favoured, at 0. 00005% (w/v) concentration selection and random genetic drift influenced changes in allele frequency and at concentrations above this the Rdl allele was at a selective advantage. Fixation of Rdl occurred at the higher concentrations. The influence of random genetic drift and selection on the genetic response during the evolution of insecticide resistance is discussed.

The character or the variation: the genetic analysis of the insecticide-resistance phenotype

In this critique it is argued that the genetic basis of the evolution of resistance is dependent on how the phenotypic, and underlying genotypic, variation is channelled during a selective response. A polygenic response is preferentially favoured if selection acts within the phenotypic distribution of susceptibles; a monogenic response is predicted if selection screens rare mutations with phenotypes outside that susceptible distribution. The relevance of this model to the method of genetic analysis, the prediction of resistance mechanisms to novel insecticides, the generation of resistant beneficial insects and the development of the most effective resistance and integrated pest management programmes is discussed.

Risk-assessment scores, prevention strategies, and the incidence of pressure ulcers among the elderly in four Canadian health-care facilities

The accurate prediction of pressure ulcer (PU) development among hospitalized elderly patients is a complex endeavour. A prospective, longitudinal, cohort study of 330 patients over age 65 in 2 Canadian tertiary-care teaching hospitals and 2 long-term-care facilities examined the association between risk-assessment scores, prevention strategies, and PU incidence. The overall PU incidence rate was 9.7%, with half of the subjects who developed a PU doing so in the first week of hospitalization. The incidence rate for "at risk" patients (10.1%) was similar to the rate for "not at risk" patients (9.3%). The number of prevention strategies used was related to risk-assessment scores and to PU development. Paradoxically, the incidence rate increased with the number of prevention strategies employed. The total risk-assessment score that appeared to have the best balance of sensitivity (69%) and specificity (55%) was 19. Four of the 6 risk-assessment subscales were associated with PU development. Logistic regression modelling confirmed the univariate results that the number of prevention strategies used was the best single predictor of PU development. The data confirm that predicting PU development for individual patients is difficult at best. Results suggest that use of a risk-assessment scale alone is not sufficient to accurately predict PU development. The clinical judgement and experience of nurses are required in providing supplementary information to standard measurement instruments.

Predicting insecticide resistance: mutagenesis, selection and response

Strategies to manage resistance to a particular insecticide have usually been devised after resistance has evolved. If it were possible to predict likely resistance mechanisms to novel insecticides before they evolved in the field, it might be feasible to have programmes that manage susceptibility. With this approach in mind, single-gene variants of the Australian sheep blowfly, Lucilia cuprina, resistant to dieldrin, diazinon and malathion, were selected in the laboratory after mutagenesis of susceptible strains. The genetic and molecular bases of resistance in these variants were identical to those that had previously evolved in natural populations. Given this predictive capacity for known resistances, the approach was extended to anticipate possible mechanisms of resistance to cyromazine, an insecticide to which L. cuprina populations remain susceptible after almost 20 years of exposure. Analysis of the laboratory-generated resistant variants provides an explanation for this observation. The variants show low levels of resistance and a selective advantage over susceptibles for only a limited concentration range. These results are discussed in the context of the choice of insecticides for control purposes and of delivery strategies to minimize the evolution of resistance.

Molecular characterization of the Notch homologue from the Australian sheep blowfly, Lucilia cuprina

The Drosophila melanogaster Notch gene product as a receptor of intercellular signals and is central to cell fate specification. The Scalloped wings (Scl) gene is the homologue of Notch in the Australian sheep blowfly, Lucilia cuprina. An allele of Scl is thought to be involved in the modification of Darwinian fitness and bristle asymmetry in flies resistant to organophosphorous chemicals (OPs). As a first step towards the testing of this hypothesis we cloned and sequenced Scl. A full-length cDNA segment representing the mRNA of Scl is 8503 bp and encodes a protein of 2653 amino acids, which shares 73.6% identity with Notch. All functional motifs including EGF-like repeats, LNR repeats, cdc 10/ankyrin repeats, opa and PEST elements are present in the same order as in Notch and the sequence identities peak in these motifs. With respect to genomic structure, intron/exon boundaries are conserved but, in most cases, the Scl introns are larger. Sequence analysis of the upstream genomic region reveals that the gene has a TATA-less promoter. Consistent with a central role in embryogenesis and imaginal development, high levels of Scl expression were detected in the early embryonic and pupal stages.

Genotypically dependent effects of cyromazine on reproduction and offspring development in the Australian Lucilia cuprina (Diptera: Calliphoridae)

The effects of cyromazine on egg production and subsequent egg-to-adult survival were examined on susceptible, heterozygous, and homozygous cyromazine-resistant genotypes of the Australian sheep blowfly Lucilia cuprina (Wiedemann) by administering to adults 10 ppm of cyromazine in drinking water. Cyromazine reduced egg production, hatch, and subsequent larval survival in susceptible genotypes by acting at the embryonic stage of development. Resistance negated these effects dominantly for egg production and egg hatch and in a partially dominant manner for egg-to-adult survivorship.

Stress and asymmetry during arrested development of the Australian sheep blowfly

The dieldrin and diazinon resistance systems of the Australian sheep blowfly (Lucilia cuprina) have been used previously to relate stress, departures from bilateral symmetry, developmental stability and relative fitness. These systems are now used to consider stress and asymmetry in a developmental context. Larval to adult development is shown to be significantly impaired after arrested development at 8 degrees C, however the asymmetry score of adults of a given genotype is similar after arrested or continuous development. Selection against dieldrin-resistant and unmodified diazinon-resistant genotypes occurs during arrested development because greater proportions of these genotypes pupae at 8 degrees C than do susceptible or modified diazinon-resistant genotypes. Pre-pupae of all genotypes complete development equally successfully when transferred from 8 degrees C to 27 degrees C. Adults fail to emerge when pupae formed at 8 degrees C undergo this temperature transition. Temperature-shift experiments show the asymmetry score is determined between pre-pupal and pupal stages of the life cycle. This stage occurs at 27 degrees C in arrested and continuously developing cultures providing an explanation for the independence of stress, selective mortality during developmental arrest and asymmetry score. The results emphasize the need for genetic, environmental and developmental data before an asymmetry phenotype can be directly related to developmental stability and relative fitness.

Fatal association between dieldrin-resistant and susceptible Australian sheep blowflies,Lucilia cuprina

A novel phenomenon of interactions between genotypes of the dieldrin-resistance (Rdl) locus of the Australian sheep blowfly (Lucilia cuprina) is described. Susceptible adult flies exposed to dieldrin-resistant (Rdl/Rdl or Rdl/S) adults, raised from larvae grown on media containing sublethal concentrations of dieldrin, display mortality related to the concentration on which the resistant flies developed. The resistant flies excrete quantities of dieldrin that are toxic to susceptible flies. These observations provide an additional mechanism to those previously identified for the rapid evolution of resistance to dieldrin by L. cuprina.

Asymmetry--where evolutionary and developmental genetics meet

The mechanisms responsible for the fine tuning of development, where the wildtype phenotype is reproduced with high fidelity, are not well understood. The difficulty in approaching this problem is the identification of mutant phenotypes indicative of a defect in these fine-tuning control mechanisms. Evolutionary biologists have used asymmetry as a measure of developmental homeostasis. The rationale for this was that, since the same genome controls the development of the left and right sides of a bilaterally symmetrical organism, departures from symmetry can be used to measure genetic or environmental perturbations. This paper examines the relationship between asymmetry and resistance to organophosphorous insecticides in the Australian sheep blowfly, Lucilia cuprina. A resistance gene, Rop-1, which encodes a carboxylesterase enzyme, also confers a significant increase in asymmetry. Continued exposure of resistant populations to insecticide has selected a dominant suppressor of the asymmetry phenotype. Genetic evidence indicates that the modifier is the L. cuprina Notch homologue.

Environmental and genetic effects on the asymmetry phenotype: Diazinon resistance in the Australian sheep blowfly, Lucilia cuprina

The asymmetry phenotype of diazinon-resistant flies lacking a fitness/asymmetry Modifier (+/+; R/-) was dominant and independent of developmental temperature, larval density and diazinon concentration. Asymmetry score, pooled over three bristle characters, was approximately 50% greater for these phenotypes than for those of modified genotypes (M/+; +/+) and unmodified susceptibles (+/+; S/S) reared under standard laboratory conditions. Modified and susceptible phenotypes showed increased asymmetry score for temperatures and larval densities above and below standard rearing conditions; a positive correlation was observed between diazinon concentration and asymmetry score. Single and multiple environmental stresses resulted in similar scores that approached, but never exceeded, those of unmodified resistant phenotypes. Irrespective of the developmental conditions anti-symmetry and fluctuating asymmetry were typically observed for each bristle character of unmodified resistant and the modified and susceptible phenotypes, respectively. Thus while similar asymmetry scores could arise from genetic or environmental effects, asymmetry pattern was genetically based. Population cage analyses at different temperatures and larval densities showed a negative association between mean asymmetry and relative fitness.

Scalloped wings is the Lucilia cuprina Notch homologue and a candidate for the modifier of fitness and asymmetry of diazinon resistance

The Scalloped wings (Scl) gene of the Australian sheep blowfly, Lucilia cuprina, is shown to be the homologue of the Drosophila melanogaster Notch gene by comparison at the DNA sequence and genetic levels. A L. cuprina genomic fragment, which shows strong identity with the Notch (N) gene at the molecular level, hybridizes to the location of the Scl gene on polytene chromosomes. The two genes are functionally homologous; the dominant and recessive Notch-like phenotypes produced by mutations in the Scl gene allow these alleles to be classed as N-like or Abruptex-like. The Scl gene is under investigation as a candidate for the fitness and asymmetry Modifier (M) of diazinon resistance. We show that M affects the penetrance of wing and bristle phenotypes associated with two Scl alleles in a manner consistent with the M being an allele of Scl. In addition, we report a phenotypic interaction between the diazinon-resistance mutation, Rop-1, and the same alleles of Scl. We propose that the product of Rop-1, an esterase, may be involved in cell adhesion in developmental processes involving the Scl gene product.

Predicting resistance and managing susceptibility to cyromazine in the Australian sheep blowfly Lucilia cuprina

Four cyromazine-resistant variants of Lucilia cuprina were selected after ethyl methanesulfonate mutagenesis and screening above the concentration of cyromazine lethal to susceptibles. Resistance is controlled by a single gene in each variant. Two resistance loci have been identified, one (Cyr 4) closely linked to the marker 'reduced eyes' on chromosome IV, the other (Cyr 5) closely linked to the 'stubby bristles' marker on chromosome V. Concentration-mortality line analysis shows resistance ratios are low (1.5-3x). One variant [Cyr 4(2)] is viable as a homozygote, the others are lethal [Cyr 4(1)] or, at best subvital [Cyr 5(1) and Cyr 5(2)]. Competition experiments between resistant heterozygotes and susceptibles show that resistance to cyromazine is selected for over a limited range of concentrations. The capacity of laboratory studies to predict likely resistance mechanisms before they evolve in the field is discussed. The use of genetic, toxicological and relative fitness data arising from these studies to devise the most effective strategies of insecticide usage while minimising the evolution of resistance is emphasised.

Genotype, environment and the asymmetry phenotype. Dieldrin-resistance in Lucilia cuprina (the Australian sheep blowfly)

Dieldrin-resistant (Rdl/Rdl and Rdl/+) and susceptible (+/+) phenotypes of Lucilia cuprina were scored for departures from bilateral symmetry for bristle characters after development at different temperatures, larval densities or concentrations of dieldrin. The asymmetry phenotype of resistant flies was dominant and independent of developmental temperature and larval density. The asymmetry of susceptibles increased for temperatures and larval densities above and below standard rearing conditions. A positive correlation was observed between asymmetry score and dieldrin concentration for all genotypes. The susceptible phenotype did not attain the asymmetry score of resistant in any environment. Resistant phenotypes showed an antisymmetric pattern in each environment; fluctuating asymmetry was observed for susceptibles. The relevance of the results of genetic and general or specific environmental stresses to estimates of developmental perturbation is discussed.

Selection at the diazinon resistance locus in overwintering populations of Lucilia cuprina (the Australian sheep blowfly)

In excess of 70 per cent mortality is observed during the overwintering stage of the life cycle of L. cuprina. The mortality is selective in the absence of a fitness modifier; phenotypes resistant to diazinon overwinter less successfully than susceptibles. In the presence of the modifier the overwintering success of all genotypes is similar. The effect is dominant. Laboratory and field experiments show that selection against resistant individuals increases with time in arrested development. The relevance of these results to the evolution of insecticide resistance is discussed.

Perturbation of gene frequencies in a natural population of Drosophila melanogaster: evidence for selection at the Adh locus

The cellular population of Drosophila melanogaster at the Chateau Tahbilk Winery (Victoria, Australia) was perturbed for alcohol dehydrogenase (Adh) gene frequencies. Phenol oxidase (Phox) frequencies were also perturbed and monitored as a control. Subsequent gene frequency changes, together with information on population structure, indicated that selection acted on the chromosome regions of both loci. Adh gene frequencies returned to preperturbation levels in a predictable manner. A model in which the relative fitness of Adh phenotypes was determined by temperature-dependent specific activities of enzymes of Adh genotypes adequately accounts for the rate of gene frequency change at this locus. Thus temperature behaves as a selective agent in modulating Adh gene frequencies in this cellar environment.

Cyromazine resistance in Drosophila melanogaster (Diptera: Drosophilidae) generated by ethyl methanesulfonate mutagenesis

Flies resistant to cyromazine (CGA-72662) were selected in susceptible laboratory populations of Drosophila melanogaster (Meigen) treated with ethyl methane-sulfonate after growth on cyromazine concentrations > LC99. Two resistant lines were obtained. In each case, resistance was a result of a mutation in a single, but different, gene. The resistance genes, designated Rst(2)Cyr and Rst(3)Cyr, were localized to map positions 64 on chromosome II and 47 on chromosome III, respectively. Concentration-mortality analysis of each mutant revealed that both genes conferred a low level (< 5 times) of resistance to cyromazine. Rst(2)Cyr produced LC99s of 1.3 x 10(-4)% (wt/vol) for heterozygotes and 2.7 x 10(-4)% for homozygotes; Rst(3)Cyr values were 1.6 x 10(-4) and 1.8 x 10(-4)%, respectively. These values compare with an LC99 of 5 x 10(-5)% for wild-type. The role of D. melanogaster as a model for insecticide resistance studies is discussed, especially the comparison of laboratory-generated cyromazine resistance in D. melanogaster with field resistance in Musca domestica L.

The effect of sequence variations and structure on the cytolytic activity of melittin peptides

The importance of various amino acid residues in melittin for cytolytic function against mammalian cells was assessed by use of a monoclonal antibody to the C-terminal region, synthesis of peptide analogues and chemical modification of specific residues. A monoclonal anti-melittin antibody directed to the basic C-terminal region inhibited cytolytic activity. Consistent with this, deletion of one of the two Lys Arg sequences at the C terminal end of the peptide reduced cytolysis 8-fold, although significant activity was still present. A similar reduction in activity was also found with a synthetic analogue which had the reverse sequence to melittin. In contrast, when the last 6 residues of the C-terminal region were transferred to the N-terminus, a peptide with markedly reduced activity was obtained. Chemical modification of lysine and arginine residues of melittin indicated that lysine was only minimally important for functional activity compared with arginine which was essential. In particular, our results demonstrate that substitution of serine for lysine 7 has no significant effect on the activity of the peptide and suggest that this residue is important only in maintaining the amphipathic helix of the peptide.

Polygenic and single gene responses to selection for resistance to diazinon in Lucilia cuprina

Following mutagenesis with ethyl methanesulfonate, selection in a susceptible strain with a concentration of the insecticide diazinon (0.0004%, w/v) above that required to kill 100% of the susceptible strain, the LC100 of that strain, resulted in a single gene response. The resultant four mutant resistant strains have equivalent physiological, genetical and biochemical profiles to a diazinon-resistant strain derived from a natural population and homozygous for the Rop-1 allele. Modification of the microsomal esterase E3 is responsible for resistance in each case. The Rop-1 locus maps approximately 4.4 map units proximal to bu on chromosome IV. Selection within the susceptible distribution, at a concentration of diazinon [0.0001% (w/v)] less than the LC100, resulted in a similar phenotypic response irrespective of whether the base population had been mutagenized. The responses were polygenically based, unique to each selection line and independent of Rop-1. The relevance of the results to selection for insecticide resistance in laboratory and natural populations is discussed.

The provision of speech, language and hearing services in a rural district of South Africa

In this paper the delivery of a speech, language and hearing therapy (SLHT) service in a rural area is discussed. In the light of the need to relate the delivery of this service to principles of primary health care (PHC) and community based rehabilitation (CBR), a brief theoretical background is given. Obstacles to service delivery are then presented, followed by a description of some attempts to implement principles of PHC and CBR. The author concludes that many challenges need to be faced in providing SLHT services that will benefit the majority of the population of South Africa.

Levamisole resistance in Trichostrongylus colubriformis: a sex-linked recessive character

Reciprocal crosses between susceptible and levamisole resistant strains of Trichostrongylus colubriformis produced F1 offspring consistent with resistance being inherited as a sex-linked recessive character. The resistance status of the offspring of the backcrosses of the F1 to both parental strains supported this hypothesis. The results are consistent with resistance being controlled by a single gene, or a tightly linked group of genes, but indicate that other autosomal loci have minor effects. The results contrast with the reported observations that resistance to the benzimidazole anthelmintics is polygenic and autosomal. The results are discussed relative to a general evolutionary model for anthelmintic resistance which predicts that selection from the upper extreme of an anthelmintic tolerance distribution results in polygenicity.

Type I procollagen N-proteinase from chick embryo tendons. Purification of a new 500-kDa form of the enzyme and identification of the catalytically active polypeptides

Procollagen N-proteinase (EC 3.4.24.14), the enzyme that cleaves the NH2-terminal propeptides from type I procollagen, was purified over 20,000-fold with a yield of 12% from extracts of 17-day-old chick embryo tendons. The procedure involved precipitation with ammonium sulfate, adsorption on concanavalin A-Sepharose, and five additional column chromatographic steps. The purified enzyme was a neutral, Ca2+-dependent proteinase (5-10 mM) that was inhibited by metal chelators. It had a molecular mass of 500 kDa as determined by gel filtration. The enzyme contained unreduced polypeptides of 61, 120, 135, and 161 kDa that were separated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The 135- and 161-kDa polypeptides were catalytically active after elution from the polyacrylamide gel. Other properties of 500-kDa enzyme are: 1) the Km for type I procollagen is 54 nM at pH 7.5 and 35 degrees C, and the kappa cat is 350 h-1; 2) the activation energy for reaction with type I procollagen is 7,100 cal mol-1; 3) the isoelectric point is 3.6; and 4) the enzyme specifically cleaves the NH2-terminal propeptides of type I and II procollagen, but not of type III procollagen. A minor form of N-proteinase with a 300-kDa mass was also purified and was found to contain a 90-kDa polypeptide as the major active polypeptide. The enzyme appeared to be a degraded form of the 500-kDa N-proteinase. The properties of the 300-kDa enzyme were similar to those observed for the 500-kDa enzyme.

Intraruminal controlled release of cyromazine for the prevention of Lucilia cuprina myiasis in sheep

The efficacy of cyromazine, continuously released from intraruminal capsules at dose rates from 0.5 to 2 mg kg-1 d-1, was evaluated against implants of eggs and first instar larvae of Lucilia cuprina on Merino sheep. Estimates from the non-linear relationship between the success of implants and plasma concentrations showed that 95 per cent protection of sheep could be achieved at a mean release rate of 1.39 mg kg-1 d-1 cyromazine which gave rise to a mean plasma concentration of 0.26 mg litre-1. Present formulations allowed protection for about 90 days in a 40 kg sheep. The 'square wave' type of release profile provided negligible suboptimal dosing thus limiting the potential for selection of resistance. Systemic application of cyromazine provides control of covert and overt strike among sheep and could be used in ecologically based strategies for the control of L. cuprina populations.

Development of a bifunctional crosslinking agent with potential for the preparation of immunotoxins

A new protein crosslinking agent, 2,3-dibromopropionyl-N-hydroxysuccinimide ester, has been synthesized and characterized. The potential use of this compound as a temperature-controllable heterobifunctional crosslinking agent has been investigated using model systems and its reactivity compared with that of chlorambucil-N-hydroxysuccinimide ester. The coupling of 14C-labeled phenylethylamine to lysozyme has been used to illustrate the feasibility of the use of this crosslinking agent for the synthesis of immunotoxins.

Diazinon resistance, fluctuating asymmetry and fitness in the Australian sheep blowfly, lucilia cuprina

Genetic evidence suggests that the evolution of resistance to the insecticide diazinon in Lucilia cuprina initially produced an increase in asymmetry. At that time resistant flies were presumed to be at a selective disadvantage in the absence of diazinon. Subsequent evolution in natural populations selected modifiers to ameliorate these effects. The fitness and fluctuating asymmetry levels of resistant flies are currently similar to those of susceptibles. Previous genetic analyses have shown the fitness modifier to co-segregate with the region of chromosome III marked by the white eyes, w, locus, unlinked to the diazinon resistance locus, Rop-1, on chromosome IV. This study maps the asymmetry modifier to the same region, shows, as in the case of the fitness modifier, its effect to be dominant and presents data consistent with the fitness/asymmetry modifier being the same gene (gene complex). These results suggest changes in fluctuating asymmetry reflect changes in fitness.

Genetic Architecture and Adaptation: Quantitative Analysis of Sheep and Refuse Tip Populations of the Australian Sheep Blowfly, Lucilia cuprina

Phenotypic differentiation between geographic areas and between sheep and adjacent refuse tip populations was assessed by quantitative analysis of population samples of L. cuprina from New South Wales (Lismore) and Victoria (Mansfield). In addition the genetic structure of populations has been defined and compared by biometrical analysis techniques. For all morphological and fitness characters examined significant phenotypic differentiation was observed both between geographic localities and between sheep and non-sheep populations of each locality. Diallel analysis of the populations revealed architectural differences between sheep and non-sheep populations for both fecundity and egg hatchability. Sheep populations only, regardless of locality, displayed dominant gene effects on these fitness traits. The results suggest that refuse tip populations may be other than transients and that the differentiation may reflect differing patterns of adaptation and history of selection of the populations. The relevance of such differentiation to the successful establishment of a chemical and/or autocidal control zone is considered.

Associations between Alcohol Tolerance and the Quantity of Alcohol Dehydrogenase in Drosophila melanogaster Isolated from a Winery Population

Variation in alcohol dehyqrogenase (ADH) and alcohol tolerance was investigated in AdhF isofemale lines of D. melanogaster isolated from an Australian winery population. For three different tests of alcohol tolerance no association with levels of ADH activity was detected. However, among 156 lines a significant negative asso9iation occurred between larval ethanol tolerance and the quantity of ADH enzyme measured in adults. In addition, a positive relationship occurred between ADH quantity and adult survival in a sucrose-ethanol ingestion test carried out on 28 of the lines. No correlation of enzyme quantity occurred when aqults were acutely exposed to ethanol vapour. These data indicate that ADH quantity and not ADH activity may be a mor.e crucial physiological determinant of survival in high ethanol environments.