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Biomedical subjects

D M Bird

Publications and source records attributed to D M Bird.

At least 19 recordsLinked to original sources
PubMed2005

A risk assessment approach to DDE exposure based on the case of the eastern screech-owl (Megascops asio) in apple orchards of southern Quebec,Canada.

As part of a larger study assessing exposure of the Eastern screech-owl to pesticides in apple orchards from consumption of contaminated small-mammal prey, we evaluated the potential for owls in orchards of southern Quebec to be exposed to persistent contaminants with emphasis on DDE. Levels were highest in short-tailed shrews (0.94 to 26.29 microg/g wet wt). Based on a worst-case scenario, it is possible that consumption of small-mammal prey in orchards of the study area may result in exposure to DDE at a level associated with significant eggshell thinning; however, consumption of other prey, (e.g., robins) may represent a more important threat. Other organochlorines and persistent contaminants such as trace metals and PCBs, reported elsewhere, were found at negligible levels only. Based on an evaluation of the data used, we identify critical information required to enhance the proposed risk assessment.

Animals↗
PubMed2005

Electronic nonadiabatic effects in the adsorption of hydrogen atoms on metals.

The time-dependent, mean-field Newns-Anderson model for a spin-polarized adsorbate approaching a metallic surface is solved in the wide-band limit. Equations for the time evolution of the occupation of the spin dependent adsorbate states and for the nonadiabatic and nearly adiabatic adsorbate-surface energy transfer rates are derived. Numerical solutions are obtained using characteristic parameters derived from density functional theory calculations for the H/Cu(111) system. The time evolution of the model system is shown to be strongly nonadiabatic in the vicinity of the transition point between spin-polarized and nonpolarized ground states. Away from the spin transition the nonadiabatic energy transfer is in close agreement with the nearly adiabatic limit. Near the transition, nonadiabatic effects are large and the nearly adiabatic approximation fails.

Journal Article↗
PubMed2004

All-solid photonic bandgap fiber.

We describe the design and fabrication of a photonic bandgap fiber formed with two different glasses. As in a hollow-core fiber, light is guided in a low-index core region because of the antiresonances of the high-index strands in the fiber cladding. The structure described represents an ideal bandgap fiber that exhibits no interface modes and guides over the full width of multiple bandgaps.

Journal Article↗
PubMed2002

Energy loss of atoms at metal surfaces due to electron-hole pair excitations: first-principles theory of "chemicurrents".

A method is presented for calculating electron-hole pair excitation due to an incident atom or molecule interacting with a metal surface. Energy loss is described using an ab initio approach that obtains a position-dependent friction coefficient for an adsorbate moving near a metal surface from a total energy pseudopotential calculation. A semiclassical forced oscillator model is constructed to describe excitation of the electron gas due to the incident molecule. This approach is applied to H and D atoms incident on a Cu(111) surface, and we obtain theoretical estimates of the "chemicurrents" measured by Nienhaus et al. [Phys. Rev. Lett. 82, 446 (1999)] for these atoms incident on the surface of a Schottky diode.

Journal Article↗
PubMed2002

Computer simulations to determine the efficacy of different genome resource banking strategies for maintaining genetic diversity.

Genome resource banks (GRBs) and assisted reproductive techniques are increasingly recognized as useful tools for the management and conservation of biodiversity, including endangered species. Cryotechnology permits long-term storage of valuable genetic material. Although, the actual application to endangered species management requires technical knowledge about sperm freezing and thawing, a systematic understanding of the quantitative impacts of various germ plasm storage and use scenarios is also mandatory. In this study, various GRB strategies were analyzed using the historical data from three managed populations of endangered species with varied pedigrees (Eld's deer, Przewalski's horse, and Sumatran tiger). The following types of sperm banks were assessed: (1) a "Wild Bank" consisting of sperm (i.e., genes) from 5 to 10 males unrelated to the managed population and to each other; and (2) a "Best Male" bank containing sperm from only the most genetically valuable males alive in the ex situ population at the time the bank was established. These different bank types were then used to evaluate the effectiveness of different bank usage frequencies. The efficiency of each scenario was assessed by examining the level of inbreeding and gene diversity in the population. Overall, a sperm usage frequency of five times per year was determined to be the most efficient and "wild banks" were highly successful at enhancing genetic diversity. The value of a GRB established from the ex situ population depends on how closely related the banked males are to future generations. A GRB will have significantly less benefit when banked males also produce many successful offspring, or when donors are already genetically over-represented in the population at the time of establishing the GRB.

Animals↗
PubMed2001

Sperm capacitation in vitro in the eld's deer.

Sperm capacitation was examined in the endangered Eld's deer (Cervus eldi thamin). Sperm motility and viability (percentage of sperm cells with intact membranes) were assessed in vitro over time after attempting to induce capacitation in TALP alone and TALP supplemented with calcium (10 mM CaCl2), dibutyryl cAMP (1 mM dbcAMP), or fetal calf serum (20% FCS). Sperm aliquots were evaluated at 0, 3, 6, 9, and 12 h for motility, viability, and ability to acrosome react after exposure to calcium ionophore (A23187, CI; 10 microM) or lysophosphatidylcholine (LC; 100 microg/mL). Fresh sperm aliquots in TALP + 10 mM CaCl2 exposed to CI had fewer (P < 0.05) intact acrosomes than the TALP control (TALP alone) or dbcAMP and FCS treatments after 9 h. Mean (+/- SEM) percentage of intact acrosomes of spermatozoa incubated in medium with increased CaCl2 declined (P < 0.05) from 80.2 +/- 2.6% (0 h) to 49.7 +/- 7.3% after prolonged incubation (9 h). The proportion of capacitated fresh spermatozoa was not influenced by LC treatment. Capacitation was not induced (P > 0.05) by any of the presumptive sperm capacitators after freeze-thawing. Likewise, neither CI nor LC induced the acrosome reaction (AR) in these spermatozoa, suggesting that the freeze-thawing process may have caused membrane damage. Results revealed that the supplementation of medium with CaCl2 evokes capacitation in some spermatozoa. However, Eld's deer spermatozoa appear remarkably resistant to conventional stimulators of capacitation and the AR.

Acrosome Reaction↗
PubMed2001

Evidence of oxidative stress in American kestrels exposed to electromagnetic fields.

Exposure to electromagnetic fields (EMFs) alters melatonin, behavior, growth, and reproduction of captive American kestrels (Falco sparverius), particularly of males. EMF exposure is a "possible" human carcinogen and associated with some neurodegenerative diseases. Oxidative stress contributes to cancer, neurodegenerative diseases, and immune disorders. We tested whether EMF exposure elicits an avian immune response and alters oxidative stress levels. Captive male kestrels were bred under control or EMF conditions equivalent to those experienced by wild kestrels. Short-term EMF exposure (one breeding season) suppressed plasma total proteins, hematocrits, and carotenoids in the first half of the breeding season. It also suppressed erythrocyte cells and lymphocyte proportions, but elevated granulosa proportions at the end of the breeding season. Long-term EMF exposure (two breeding seasons) suppressed hematocrits in the first half of the reproductive period too. Results indicate that only short-term EMF birds experience an immune response, particularly during the early half of the breeding season. The elevation of granulocytes, and the suppression of carotenoids, total proteins, and previously melatonin in the same kestrels, signifies that the short-term EMF male kestrels had higher levels of oxidative stress, due to an immune response and/or EMF exposure. Long-term EMF exposure may be linked to higher levels of oxidative stress through EMF exposure only.

Animals↗
PubMed2001

In ovo exposure to polychlorinated biphenyls: reproductive effects on second-generation American kestrels.

The reproductive success of wild birds has been affected by exposure to multiple contaminants. Reproduction of captive American kestrels (Falco sparverius) was suppressed when adult birds were exposed to dietary polychlorinated biphenyls (PCBs). In this study, the reproductive effects of in ovo exposure to PCBs is explored, along with determining effects on reproduction in second-generation birds indirectly exposed to PCBs. Reproductive changes in this subsequent generation are examined separately in male and female birds. Captive American kestrels (F. sparerius) were hatched from clutches with eggs containing environmentally relevant levels of total PCBs (34.0 microg/g whole egg WW versus 0 microg/g controls); parent birds had been fed PCB-spiked (Aroclor 1248:1254:1260) food (7 mg/kg BW day(-1)) for 100 days until their eggs hatched. In 1999, the second-generation PCB birds were paired with unexposed kestrels having reproductive experience. In ovo PCB exposure suppressed egg laying completely in 25% of PCB females and resulted in delays in clutch initiation and smaller clutch sizes for PCB male and female pairs. There was no evidence in this study of in ovo PCB treatment effects on fertility or hatching success. The decline in reproductive success was also reflected in the reduced fledging success and higher incidence of complete brood mortality of PCB nestlings. Differences between in ovo-exposed PCB males and females but not between controls were evident in reproductive success. In ovo PCB exposure appears to have had greater effects on female kestrels until clutch completion, with a greater time lag between pairing and egg laying, reduced numbers of pairs laying eggs, and smaller clutches being laid. In ovo PCB exposure has greater effects later in the breeding season on male kestrels, which had poorer hatching and fledging success relative to the PCB females. Possible behavioral and physiological mechanisms involved in these reproductive changes are discussed.

Animals↗
PubMed2001

Courtship behavior of captive American kestrels (Falco sparverius) exposed to polychlorinated biphenyls.

Polychlorinated biphenyls (PCBs) adversely affect reproduction in birds. Captive adult male and female American kestrels (Falco sparverius) were studied to investigate the potential behavioral and hormonal alterations during the courtship period resulting from clinical exposure to PCBs. American kestrels ingested 7 mg/kg/body weight/bird/day of a 1:1:1 mixture of Aroclors 1248, 1254, and 1260 through their diet of day-old cockerels. The dietary dosage of Aroclors resulted in environmentally relevant total PCB residues in the eggs, averaging 34.1 microg/g wet weight (geometric mean). There was no difference between treatment and control birds in the circulating levels of total androgens (p = 0.44) or in 17 beta-estradiol (p = 0.29), one week following pairing. Male kestrels exposed to dietary PCBs exhibited significantly more sexual behaviors (p = 0.034) and flight behaviors (p = 0.026) than the control males. Sexual behaviors of male kestrels included; nest-box inspections, solicitation of copulation, the offer of food to the female, and giving the female food. The flight behaviors of the male included; flying from one perch to another and aerial display. In addition, the frequency of male sexual behaviors were correlated (r = 0.605, p = 0.001) with total PCB residues in the eggs of their mates. A concurrent study found that these same PCB-exposed kestrels experienced a delay in clutch initiation as well as a greater number of completely infertile clutches.

Animals↗
PubMed2001

Cytochrome c is not essential for viability of the fungus Aspergillus nidulans.

The filamentous fungus Aspergillus nidulans is an obligate aerobe, which is capable of anaerobic survival, but not anaerobic growth. Since cytochrome c forms an essential part of the oxidative respiratory pathway it was expected that mutants lacking this component would be non-viable. Gene replacement of one homologue of the cycA (cytochrome c) gene was carried out in a diploid strain. Benomyl-induced haploidisation of this diploid yielded all cycA+ haploid colonies, initially suggesting that loss of cycA was indeed lethal. However, use of an alternative unbiased method to recover haploids yielded viable, but slow-growing, cycA- mutants. Replacement of the cycA locus in the cycA- mutants was verified by Southern blotting. Spectral analysis confirmed the absence of detectable levels of cytochrome c, and respiratory insensitivity to cyanide suggested the absence of cytochrome c-dependent respiration. Growth parameters were consistent with those expected of a CycA- mutant. Compared to the wild type, the mutants grew slowly on fermentable carbon sources, did not grow on non-fermentable carbon sources, and produced higher levels of ethanol. To our knowledge, this is the first report of a filamentous fungus that remains viable after complete elimination of a functional cytochrome c gene. We propose that the mutants are viable due to their ability to ferment and to use alternative respiratory pathways.

Aspergillus nidulans↗
PubMed2001

Reproduction success of American kestrels exposed to dietary polychlorinated biphenyls.

While reproduction of wild birds is adversely affected by multiple environmental contaminants, we determined that polychlorinated biphenyls (PCBs) alone alter reproduction. Captive American kestrels (Falco sparverius), fed PCB-spiked (Aroclor 1248:1254:1260) food (7 mg/kg body weight/d) prior to and during the first breeding season only (100 d) laid eggs with environmentally relevant levels of total PCBs (34.0 microg/g whole egg wet wt vs 0 microg/g for controls). Reproduction changed during, not after, PCB exposure in this two-year study. The PCB-exposed pairs laid smaller clutches later in the season and laid more totally infertile clutches. Hatching success was reduced in PCB-exposed pairs, and 50% of PCB nestlings died within 3 d of hatching. Nearly 60% of PCB-exposed pairs with hatchlings failed to produce fledglings. Higher levels of total PCB residues and congeners were associated with later clutch initiation and fewer fertile eggs, hatchlings, and fledglings. We suggest that nonpersistent PCB congeners have a greater influence on reproduction than do persistent congeners.

Animals↗
PubMed2001

Bioaccumulation and toxicokinetics of 42 polychlorinated biphenyl congeners in American kestrels (Falco sparverius).

The bioaccumulation and toxicokinetics of 42 polychlorinated biphenyls (PCBs) was determined in male American kestrels exposed to an Aroclor-contaminated diet for 120 d followed by a 348-d depuration period. The birds were housed under ambient outdoor temperatures to permit normal fluctuations in body weight during the study. Whole body PCB clearance, plasma/fat distribution coefficients, and plasma PCB clearance constants were determined for individual PCBs to calibrate a two-compartment rate constant model in order to describe PCB elimination in the birds. Plasma/fat partition coefficients (K(PF)) averaged 0.0060 +/- 0.0001 for all congeners of study, were not dependent on chemical hydrophobicity, and did not change in summer versus winter sacrificed animals. Plasma clearance constants (k'pc) for PCBs were observed to be dependent on both chlorine substitution patterns and congener hydrophobicity. Polychlorinated biphenyl congeners categorized as readily cleared congeners contained vicinal meta-para hydrogen substituents on at least one phenyl ring, while slowly cleared congeners were chlorine hindered at these positions. A general equation was derived to predict plasma clearance constants for all tri- to octachlorobiphenyls based on the presence of an open meta-para site on one of the phenyl rings and from the n-octanol-water partition coefficient of the chemical. The equation was validated by comparing predicted versus measured relative biomagnification factors of PCBs determined in birds at the end of the dosing period. The two-compartment model calibrated for PCB elimination in American kestrels may be used to describe PCB toxicokinetics in wild birds provided that seasonal fluctuations in the fat content of the modeled population is known.

Animals↗
PubMed2000

Behavior of free-ranging and captive American kestrels under electromagnetic fields.

Wild birds, particularly raptors, commonly use electrical transmission structures for nesting, perching, hunting, and roosting. Consequently, birds are exposed to electromagnetic fields (EMFs). The amount of time that wild reproducing American kestrels (Falco sparverius) were exposed to EMFs was determined, and the effects of EMFs on the behavior of captive reproducing kestrels were examined. Wild kestrels were exposed to EMFs for 25% to 75% of the observed time. On a 24-h basis, estimated EMF exposure of wild kestrels ranged from 71% during courtship, to 90% during incubation, similar to that experienced by captive kestrels (88% of a 24-h period). Additionally, captive kestrels were exposed to EMF levels experienced by wild kestrels nesting under 735-kV power lines. Captive EMF females were more active, more alert, and perched on the pen roof more frequently than control females during courtship. EMF females preened and rested less often during brood rearing. EMF male kestrels were more active than control males during courtship, and more alert during incubation. Increased activity of kestrels during courtship may be linked to changes in corticosterone, but likely not melatonin. Observed behavioral changes were unlikely to directly result in the better growth of nestlings and fledging success, or poorer hatching success, of the EMF group, as previously reported. Behavioral changes of captive EMF kestrels may be observed in wild kestrels.

Animals↗
PubMed2000

Epistatic repression of PHANTASTICA and class 1 KNOTTED genes is uncoupled in tomato.

Class 1 KNOTTED genes (KNOX) and PHANTASTICA (PHAN) are both central to meristem establishment and maintenance and, in maize and Antirrhinum, it has been proposed that PHAN acts as an epigenetic repressor of KNOX. In tomato, a distinct spatial distribution of Tkn2 KNOX transcripts compared to Antirrhinum and maize suggests either a different spatial distribution of tomato PHAN (Le-phan) transcripts, or that PHAN alone is insufficient for KNOX repression in tomato. We established the pattern of Le-phan expression, including a first demonstration of PHAN expression in healthy roots, and found Le-phan and Tkn2 transcripts to be temporally and spatially coincidental, with PHAN exhibiting an expression pattern in tomato distinct from that in plants with simple leaves. Our results imply that the expression of Le-phan is insufficient for the repression of Tkn2 in tomato and suggest an expanded role for either gene in the establishment of cell identity in plant development.

Base Sequence↗
PubMed2000

High throughput cellular localization of specific plant mRNAs by liquid-phase in situ reverse transcription-polymerase chain reaction of tissue sections.

Advances in high throughput DNA sequencing and bioinformatic gene discovery far outpace our ability to analyze gene function, necessitating development of more efficient means to examine expression at the cellular level. Here we present a polymerase chain reaction-based method to detect mRNA species in situ in which essentially all of the steps are carried out in liquid phase in a 96-well microtiter tray and only the final signal detection is performed on a microscope slide. We demonstrate the sensitivity of the method by the cellular localization of mRNA for the Tkn2 transcription factor in a wide variety of plant tissues, and its selectivity in discriminating a single gene family member by the in situ localization of rbcs3 transcripts. Furthermore, we demonstrate the utility of the in-well in situ method in detecting FDL and IFL1 transcripts in Arabidopsis sections, thus establishing the method as a tool to determine spatial expression pattern of sequences obtained from genomic sequencing projects. Being amenable to robotic processing, in-well in situ reverse transcription-polymerase chain reaction permits a great enhancement in the number of tissue samples that can be processed. Consequently, this method may become a powerful tool for functional genomics studies, permitting the cellular site of transcription of large numbers of sequences obtained from databases to be rapidly established.

Arabidopsis↗
PubMed2000

Changes in egg composition of American kestrels exposed to dietary polychlorinated biphenyls.

Changes in the quality of eggs of birds exposed to polychlorinated biphenyls (PCBs) have been described, but have never been directly attributed to PCBs. Polychlorinated biphenyl residues in eggs have been associated with reduced reproductive success and embryonic deformities in wild birds. Egg size and composition, specifically the amount of albumen, yolk, and water in an egg, also influence the growth and viability of embryos and hatchlings, and consequently the reproductive success of birds. To deter mine whether PCB exposure of adult birds affected the size and composition of their eggs, 25 pairs of captive American kestrels (Falco sparverius) were fed a mixture of PCB-spiked (1248:1254:1260) food to give an approximate exposure of 7 mg/kg body weight/d, beginning 1 mo prior to pairing, and continuing throughout the courtship, egg-laying, and incubation periods. This dietary level in the adult female kestrels resulted in mean total PCB residues in the eggs of 34.1 microg/g wet weight (geometric mean), which is environmentally relevant. PCB residues in eggs increased with the time of female exposure to the contaminated diet and laying date. Variation in egg size within PCB clutches was significantly greater than within control clutches, although absolute egg mass and volume did not differ markedly by treatment. Only infertile eggs and only one egg per clutch were used for egg composition analysis. Yolks in the PCB-contaminated eggs were heavier, with less wet and dry albumen relative to control eggs. Water content and eggshell thickness were not significantly affected by PCB exposure. These results suggest that eggs from the PCB treatment have relatively more lipid and less protein available for embryonic development. Changes in egg composition were not associated with egg size, lay date, ambient temperature, humidity, or precipitation, which are factors known to affect these variables in bird eggs. The PCB-induced changes in egg composition described here provide insight into possible mechanisms contributing to reduced reproductive performance in wild birds exposed to PCBs.

Administration, Oral↗
PubMed1999

THE CAENORHABDITIS ELEGANS GENOME: A Guide in The Post Genomics Age.

The completion of the entire genome sequence of the free-living nematode, Caenorhabditis elegans is a tremendous milestone in modern biology. Not only will scientists be poring over data mined from this resource, but techniques and methodologies developed along the way have changed the way we can approach biological questions. The completion of the C. elegans genomic sequence will be of particular importance to scientists working on parasitic nematodes. In many cases, these nematode species present intractable challenges to those interested in their biology and genetics. The data already compared from parasites to the C. elegans database reveals a wealth of opportunities for parasite biologists. It is likely that many of the same genes will be present in parasites and that these genes will have similar functions. Additional information regarding differences between free-living and parasitic species will provide insight into the evolution and nature of parasitism. Finally, genetic and genomic approaches to the study of parasitic nematodes now have a clearly marked path to follow.

Journal Article↗