Prevalence and intensity of Cephalobium microbivorum (Nematoda: Diplogasterida) infection in three species of Gryllus field crickets.

Here we report on the results of a survey for nematode parasites in three species of field cricket, Gryllus integer, Gryllus lineaticeps, and an undescribed Gryllus species. The nematode, Cephalobium microbivorum, was recovered from the intestine of the crickets. To our knowledge, this paper is just one of two to report on the biology of C. microbivorum. This nematode was first described from the cricket, Gryllus assimilis. It has not been documented in any other Gryllus species to date. G. integer were collected from two locations: Aguila, Arizona and Davis, California. G. lineaticeps were collected from Davis, CA and an undescribed species of Gryllus cricket was collected from Aguila, AZ. Results of the survey revealed the presence of nematodes in all three species of Gryllus, at all collection sites. The intensity of infection ranged from 1 to 113 nematodes.

Temperature preferences of male field crickets ( Gryllus integer) alter their mating calls.

Temperature affects the mating displays of many ectothermic animals, yet almost no information exists on the temperature preferences of ectotherms while they are displaying for mates. This study investigated the preferences of displaying male field crickets ( Gryllus integer) for microhabitats of different temperatures. G. integer males attract sexually receptive females by calling from cracks in the ground. We collected data from the field on the temperature of male calling sites (cracks in the ground), on the amount of herbaceous cover (which affects crack temperature) surrounding calling sites, and on the temporal properties of male calls at different temperatures. Laboratory experiments demonstrated that males prefer warmer sites and confirmed that temperature influences mating calls. We conclude that males of this ectothermic species prefer to call for mates from warmer sites, and that microhabitat choice on the basis of temperature affects their mating calls, and potentially their reproductive success.

Optical coherent reflectometry: a new technique to guide invasive procedures.

The success rate of percutaneous transluminal coronary angioplasty for chronic total arterial occlusions is still unsatisfactory. Inability to cross the lesion with a guidewire is a major cause of failure. Optical coherent reflectometry (OCR) is a new method of using laser light to measure the depth of tissue from the end of an optic fiber. This study tests whether an OCR prototype guidewire provides a guidance system that might be useful to assist reopening chronic total arterial occlusions. An OCR fiber optic within a 0.014" hypotube was developed using the interference pattern of two reflected light beams (wave length 1,300 nm). To determine if OCR can distinguish different tissue types, plaques of human lower extremity arterial segments were visually divided into three types (calcified, white, or yellow). The slope of the initial reflectance of the OCR curve was calculated and compared between the three groups. In six other arteries, the OCR wire was advanced longitudinally through occluded human artery segments in vitro. Guidewire position was determined by OCR and compared to the position of the guidewire tip observed simultaneously by intravascular ultrasound (IVUS) imaging. In 16 arterial surface segments, calcified plaques had a significantly steeper slope than white or yellow plaques (-227.2 +/- 82.2; -81.5 +/- 12.9; -103.6 +/- 19.6 dB/mm; P < 0.01). For the determination of the guidewire position, IVUS and OCR corresponded correctly in 82% of 28 measurements. Sensitivity and specificity of OCR for detection of plaque versus the media/adventitia boundary were 79% and 89%, respectively (P < 0.001). OCR can distinguish calcified from noncalcified plaque and may distinguish plaque from the media/adventitia boundary. This technology may be useful as a means to help navigate a guidewire safely through an occluded artery.

Crickets with extravagant mating songs compensate for predation risk with extra caution.

Modern models for the evolution of conspicuous male mating displays assume that males with conspicuous displays must bear the cost of enhanced predation risk. However, if males can compensate behaviourally for their increased conspicuousness by acting more cautiously towards predators, they may be able to lower this cost. In the field cricket Gryllus integer, males call to attract females, and differ in their durations of uninterrupted trilling (calling-bout lengths). Differences among males in calling-bout lengths are heritable, and females prefer males with longer calling bouts. In this study, males with longer, more conspicuous songs behaved more cautiously than males with shorter songs on two different tests of predator avoidance. They took longer to emerge from a safe shelter within a novel, potentially dangerous environment, and they ceased calling for a longer time when their calls were interrupted by a predator cue. Thus, these males appear to compensate behaviourally for their more conspicuous mating displays. Additionally, latencies to emerge from a shelter in the novel environment were consistent over time for both individual males from the field and males that had been reared in the laboratory, indicating that the differences in latency among males may be heritable.

Nonrandom association between Huntington disease and two loci separated by about 3 Mb on 4p16.3.

The gene for Huntington disease (HD) has been localized close to the telomere on the short arm of chromosome 4. However, refined mapping using recombinant HD chromosomes has resulted in conflicting findings and mutually exclusive candidate regions. Previously reported significant nonrandom allelic association between D4S95 and HD provided support for a more proximal location for the defective gene. In this paper, we have analyzed 17 markers, spanning approximately 6 Mb of DNA distal to locus D4S62, for nonrandom association to HD. We confirm the previous findings of nonrandom allelic association between D4S95 and HD. In addition, we provide new data showing significant nonrandom association between HD and 3 markers at D4S133 and D4S228, which are approximately 3 Mb telomeric to D4S95.

Isolation and characterization of new highly polymorphic DNA markers from the Huntington disease region.

The defect causing Huntington disease (HD) has been mapped to 4p16.3, distal to the DNA marker D4S10. Subsequently, additional polymorphic markers closer to the HD gene have been isolated, which has led to the establishment of predictive testing programs for individuals at risk for HD. Approximately 17% of persons presenting to the Canadian collaborative study for predictive testing for HD have not received any modification of risk, in part because of limited informativeness of currently available DNA markers. Therefore, more highly polymorphic DNA markers are needed, which will further increase the accuracy and availability of predictive testing, specifically for families with complex or incomplete pedigree structures. In addition, new markers are urgently needed in order to refine the breakpoints in the few known recombinant HD chromosomes, which could allow a more accurate localization of the HD gene within 4p16.3 and, therefore, accelerate the cloning of the disease gene. In this study we present the identification and characterization of nine new polymorphic DNA markers, including three markers which detect highly informative multiallelic VNTR-like polymorphisms with PIC values of up to .84. These markers have been isolated from a cloned region of DNA which has been previously mapped approximately 1,000 kb from the 4p telomere.

The effect of modifiers of position-effect variegation on the variegation of heterochromatic genes of Drosophila melanogaster.

Dominant modifiers of position-effect variegation of Drosophila melanogaster were tested for their effects on the variegation of genes normally located in heterochromatin. These modifiers were previously isolated as strong suppressors of the variegation of euchromatic genes and have been postulated to encode structural components of heterochromatin or other products that influence chromosome condensation. While eight of the modifiers had weak or no detectable effects, six acted as enhancers of light (lt) variegation. The two modifiers with the strongest effects on lt were shown to also enhance the variegation of neighboring heterochromatic genes. These results suggest that the wild-type gene products of some modifiers of position-effect variegation are required for proper expression of genes normally located within or near the heterochromatin of chromosome 2. We conclude that these heterochromatic genes have fundamentally different regulatory requirements compared to those typical of euchromatic genes.

Linkage disequilibrium and modification of risk for Huntington disease.

The major limitation in performing predictive testing for Huntington disease (HD) is the unavailability of DNA from crucial family members. In our program approximately 20% (36/183) of persons have been excluded from predictive testing because of this reason. The major aim of this study was to examine whether data derived from linkage disequilibrium could modify risk analysis for persons at risk for HD. As a first step, we assessed whether the previously reported linkage disequilibrium between alleles recognized by probe pBS674E-D at locus D4S95 remained significant in a much larger data set. A total of 1,150 chromosomes from 622 individuals--200 affected and 422 unaffected--from 118 families were assessed. Significant haplotype association was detected with AccI and MboI RFLPs at the locus D4S95, with all the families (P = .00003), as well as for a subset from the United Kingdom (P = .0037). Data derived from linkage disequilibrium studies using D4S95 modifies the risk for HD, especially in persons of U.K. descent. Utilization of this approach for risk modification of HD awaits both validation of these data and additional information concerning ethnic-specific alleles at the D4S95 locus.

Ethical and legal dilemmas arising during predictive testing for adult-onset disease: the experience of Huntington disease.

The goal of predictive testing is to modify the risk for currently healthy individuals to develop a genetic disease in the future. Such testing using polymorphic DNA markers has had major application in Huntington disease. The Canadian Collaborative Study of Predictive Testing for Huntington Disease has been guided by major principles of medical ethics, including autonomy, beneficence, confidentiality, and justice. Numerous ethical and legal dilemmas have arisen in this program, challenging these principles and occasionally casting them into conflict. The present report describes these dilemmas and offers our approach to resolving them. These issues will have relevance to predictive-testing programs for other adult-onset disorders.

Non-random association between alleles detected at D4S95 and D4S98 and the Huntington's disease gene.

Analysis of many families with linked DNA markers has provided support for the Huntington's disease (HD) gene being close to the telomere on the short arm of chromosome 4. However, analysis of recombination events in particular families has provided conflicting results about the precise location of the HD gene relative to these closely linked DNA markers. Here we report an investigation of linkage disequilibrium between six DNA markers and the HD gene in 75 separate families of varied ancestry. We show significant non-random association between alleles detected at D4S95 and D4S98 and the mutant gene. These data suggest that it may be possible to construct high and low risk haplotypes, which may be helpful in DNA analysis and genetic counselling for HD, and represent independent evidence that the gene for HD is centromeric to more distally located DNA markers such as D4S90. This information may be helpful in defining a strategy to clone the gene for HD based on its location in the human genome.

The evolution of sexual dimorphism in animals: Hypotheses and tests.

Three major hypotheses, based upon mechanisms of sexual selection, intersexual food competition and reproductive role division, have been advanced to explain the evolution of sexual dimorphism in body size and morphology of animals. Genetic models suggest that all of the hypotheses are plausible, and empirical studies demonstrate that each of the three mechanisms operates in natural populations. However, problems arise in testing hypotheses for the evolution of sexual dimorphism: more than one mechanism may be operating simultaneously, and the demonstrated occurrence of a mechanism does not indicate that it actually results in selection for dimorphism. A recent statistical technique offers a solution to these problems and provides a promising new approach to the study of sexual dimorphism, in which researchers can assess the relative importance of each mechanism in present-day selection for sexual dimorphism within a species.