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Biomedical subjects

G Dwyer

Publications and source records attributed to G Dwyer.

11 recordsLinked to original sources
PubMed2001

Hybrid zone dynamics and species replacement between Orconectes crayfishes in a northern Wisconsin lake.

Hybrid zones that result in the genetic assimilation (replacement) of one species by another are underrepresented in the animal literature, most likely due to their transient nature. One such zone involves the rusty crayfish, Orconectes rusticus, and its congener O. propinquus. Orconectes rusticus was recently introduced into northern Wisconsin and Michigan lakes and streams, where it is hybridizing with and displacing resident O. propinquus. Here we report on a study investigating the dynamics of a hybrid zone between the two crayfish in Trout Lake, Wisconsin, where both the time (circa 1979) and location of the initial introduction are known. Our prediction was that hybridization should hasten the demise of O. propinquus because we expected that male O. rusticus (which are larger than congeners) would outcompete male O. propinquus for mates of both species. If hybrid progeny are unfit, then the result would be decreased reproductive output of O. propinquus females. However, we found a pattern of cytonuclear disequilibrium between allozymes and mtDNA suggesting that a majority (94.5%) of F1 hybrids resulted from matings between O. rusticus females and O. propinquus males. Also contrary to expectations, fecundity (O. rusticus and O. propinquus) and early hybrid survivorship did not differ significantly from nonhybrids. Moreover, adults of mixed ancestry were superior to both O. rusticus and O. propinquus in competition for a limiting food resource. Using a single-locus model, we estimated that hybridization increases the advance of O. rusticus genes in Trout Lake between 4.8% and 36.3% above that due to the previously documented ecological interactions. Consequently, whereas hybridization may be hastening the elimination of genetically pure O. propinquus, introgression is nevertheless slowing the loss of O. propinquus nuclear genes. Although our results suggest that O. rusticus and O. propinquus may not be true species under the biological concept, their ecological differences are of great conservation importance.

Animals↗
PubMed2001

Models and data on plant-enemy coevolution.

Although coevolution is complicated, in that the interacting species evolve in response to each other, such evolutionary dynamics are amenable to mathematical modeling. In this article, we briefly review models and data on coevolution between plants and the pathogens and herbivores that attack them. We focus on "arms races," in which trait values in the plant and its enemies escalate to more and more extreme values. Untested key assumptions in many of the models are the relationships between costs and benefits of resistance in the plant and the level of resistance, as well as how costs of virulence or detoxification ability in the enemy change with levels of these traits. A preliminary assessment of these assumptions finds only mixed support for the models. What is needed are models that are more closely tailored to particular plant-enemy interactions, as well as experiments that are expressly designed to test existing models.

Biological Evolution↗
PubMed1999

Dynamics of disease resistance polymorphism at the Rpm1 locus of Arabidopsis.

The co-evolutionary 'arms race' is a widely accepted model for the evolution of host-pathogen interactions. This model predicts that variation for disease resistance will be transient, and that host populations generally will be monomorphic at disease-resistance (R-gene) loci. However, plant populations show considerable polymorphism at R-gene loci involved in pathogen recognition. Here we have tested the arms-race model in Arabidopsis thaliana by analysing sequences flanking Rpm1, a gene conferring the ability to recognize Pseudomonas pathogens carrying AvrRpm1 or AvrB. We reject the arms-race hypothesis: resistance and susceptibility alleles at this locus have co-existed for millions of years. To account for the age of alleles and the relative levels of polymorphism within allelic classes, we use coalescence theory to model the long-term accumulation of nucleotide polymorphism in the context of the short-term ecological dynamics of disease resistance. This analysis supports a 'trench warfare' hypothesis, in which advances and retreats of resistance-allele frequency maintain variation for disease resistance as a dynamic polymorphism.

Arabidopsis↗
PubMed1995

Nucleotide and deduced amino acid sequence of the 3' end of the BYMV-MI genome.

We have cloned and sequenced cDNA transcribed from the 3' 1,239 nucleotides of the genomic RNA of a Western Australian isolate (MI) of bean yellow mosaic potyvirus (BYMV). This sequence contains 246 nucleotides of the NIb (replicase) gene and 819 nucleotides representing the entire coding region of the viral coat protein gene, followed by a 3' non-coding region of 174 nucleotides. The coding region of the coat protein gene is identical in length (273 amino acids) to that already reported for other isolates of this virus. The sequence identities obtained for BYMV-MI and published sequences of BYMV isolates range between 85% and 92% for the coding region of the coat protein and 90% to 98% for the 3' non-coding region. Likewise, the region of the NIb gene sequenced shows 99% and 97% sequence identity in the deduced amino acid and the nucleotide sequences, respectively.

Amino Acid Sequence↗
PubMed1992

Developmental changes in continuity and stability of breathing in the fetal lamb.

Developmental changes in the continuity and stability of fetal breathing patterns were studied in 27 fetal lambs with chronically implanted electromyographic electrodes in the diaphragm throughout the third trimester (102-140 days). The results showed that there was a progressive decrease in the incidence of fetal breathing movements throughout the third trimester (P less than 0.001). This reduction in incidence of fetal breathing movements was due, in part, to a 20% decrease in the total number of breathing bursts at approximately 125 days (P = 0.05). The breathing patterns in both immature (less than 120 days) and mature fetal lambs were fragmented by a large number of pauses (interburst interval 6-10 s) and apneas (interburst interval greater than 10 s). Increase in gestational age was associated with a decrease in the number of pauses and apneas but longer apnea durations. The breathing pattern in fetuses less than 120 days old was more continuous than that in those greater than 120 days old, as demonstrated by significantly longer epoch durations (P = 0.013). There was no significant change in the continuity of the breathing pattern after 120 days. However, there was a significant increase in the stability of the instantaneous breathing rates throughout the third trimester. This was indicated by a significant increase in the percent of breathing bursts that occurred in stable clusters (P = 0.046), the number of bursts per cluster (P = 0.013), and cluster duration (P = 0.018). Thus an increase in stability appears to be the major developmental change in breathing control in late gestation.

Animals↗
PubMed1992

Fractal properties in fetal breathing dynamics.

The dynamic pattern of fetal breathing was studied in 17 fetal lambs with chronically implanted electromyographic electrodes in the diaphragm. The instantaneous breathing rate time series appeared similar on different time scales, with clusters of faster breathing rates interspersed with periods of relative quiescience, suggesting self-similarity. Distribution histograms of the interbreath intervals (IBIs) showed log-normal distribution for IBIs less than 1 s and inverse power-law distribution for IBIs greater than 1 s. The ratio of log-normal distribution to power-law distribution varied from approximately 2 at 102 days to approximately 30 by 130 days of gestation. Fast Fourier transform of the breathing rate time series revealed 1/f beta power spectra for all animals, with beta increasing linearly from 0.43 to 0.88 between 102 and 139 days. Studies in the newborn lamb showed further maturation in both the distribution characteristics of the IBIs, as well as in the 1/f power spectra, with beta approaching 1.0 at 2 days after birth. The inverse power-law relationship in the distribution of the IBIs, together with the 1/f beta power spectra, indicate scale invariance and suggest that fractal mechanisms are involved in the regulation of fetal breathing.

Animals↗
PubMed1991

Morphine-induced stimulation of fetal breathing: role of mu 1-receptors and central muscarinic pathways.

The mechanism of action of low doses of morphine on breathing dynamics in the fetus was studied in 16 fetal lambs with chronically implanted electromyographic electrodes in the diaphragm. Morphine (0.15-2.5 mg/h) caused a significant dose-dependent increase in the number of diaphragmatic bursts per hour, with either an increase or no change in instantaneous breathing rate. There was also a significant dose-related increase in the continuity of the breathing pattern, as indicated by a decrease in the number of apneas per hour, and an increase in epoch duration. Morphine also had a significant effect on the stability of the breathing pattern, with an increase in the percentage of bursts that occurred in stable clusters. All of these effects were completely abolished by concurrent intracerebroventricular administration of either methylnaloxone or methylatropine or by pretreatment with intravenous naloxonazine. These results suggest that stimulation and stabilization of ventilatory activity in the fetal lamb by low doses of morphine are mediated via mu 1-receptors and involve central muscarinic pathways.

Animals↗
PubMed1988

Dual action of morphine on fetal breathing movements.

Morphine has been reported to both stimulate and suppress fetal breathing movements (FBM). In light of these conflicting reports, we have conducted a systematic dose-response analysis of the effects of morphine on FBM in 27 fetal lambs. Morphine was infused directly to the fetus in doses ranging from 0.075 to 80 mg/hr. Low doses (0.075-2.5 mg/hr) resulted in a progressive increase in the relative incidence of FBM, whereas higher doses (greater than 2.5 mg/hr) decreased FBM with total apnea observed at 80 mg/hr. This biphasic response can be fitted as the sum of two sigmoidal log dose-response curves. Both stimulation and suppression of FBM by morphine were abolished by naloxone pretreatment, indicating that both responses are mediated by activation of opioid receptors. The dual action of morphine on FBM may be due to different opioid receptor subtypes or different sites of action.

Animals↗
PubMed1986

A distributed microcomputer-controlled system for data acquisition and power spectral analysis of EEG.

A relatively powerful and inexpensive microcomputer-based system for the spectral analysis of the EEG is presented. High resolution and speed is achieved with the use of recently available large-scale integrated circuit technology with enhanced functionality (INTEL Math co-processors 8087) which can perform transcendental functions rapidly. The versatility of the system is achieved with a hardware organization that has distributed data acquisition capability performed by the use of a microprocessor-based analog to digital converter with large resident memory (Cyborg ISAAC-2000). Compiled BASIC programs and assembly language subroutines perform on-line or off-line the fast Fourier transform and spectral analysis of the EEG which is stored as soft as well as hard copy. Some results obtained from test application of the entire system in animal studies are presented.

Animals↗
PubMed1985

The ontogeny of fetal lamb electrocortical activity: a power spectral analysis.

With the use of a relatively inexpensive microcomputer-based system for power spectral analysis, we have been able to provide quantitative information on maturational changes in electrocorticogram waveforms in the third-trimester fetal lamb. Twenty-six electrocorticogram recordings were obtained from nine fetal lambs, with gestational ages ranging from 114 to 139 days' gestation. The transition from disorganized to cyclic electrocorticogram activity (high-voltage slow activity and low-voltage fast activity) occurred at approximately 115 to 120 days' gestation. However, quantitative changes in waveform characteristics of the electrocorticogram continued throughout the rest of gestation. These maturational changes occurred primarily in the low-voltage fast activity periods, with a decrease in power density in the delta (0.3 to 3 Hz) band and an increase in the maximum frequencies detected in the beta (15 to 30 Hz) band. There were no significant changes in the power spectrum of the high-voltage slow activity periods as a function of gestational age.

Analog-Digital Conversion↗