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R H Richardson

Publications and source records attributed to R H Richardson.

At least 19 recordsLinked to original sources
PubMed1987

Dynamics and stability in coevolutionary ecological systems. I. Community stability and coevolutionarily stable states.

An extension of J. Roughgarden's [1979, Theor. Pop. Biol. 9, 388; 1979, "An Introduction to Evolutionary Ecology and Population Genetic Theory," Macmillan, New York] formalism for investigating the effects of coevolution on community structure is presented. The extension assumes the result that a coevolved community is asymptotically stable when coevolution takes place at a genetically noninvasible boundary. This is proved for the general case of n interacting species. From this a community persistence function, phi (P), is defined that allows measuring the domain of attraction for the community as well as the resilience time, that is, the time taken for a perturbation to decay to 1-1/e (63%) of its initial value.

Animals↗
PubMed1982

Autocidal control of screwworms in North America.

The larva of the blowfly Cochliomyia hominivorax, also known as the screwworm, eats the living flesh of cattle and sheep and other warm-blooded animals. A program to eradicate the screwworm in the United States was initiated in the 1950's. The program was very effective until 1968, but severe screwworm outbreaks occurred in 1972 to 1976 and in 1978. Although the program has again been effective since 1979, the possibility of outbreaks recurring in the future has highlighted the need for a broader understanding of the pest. Studies of screwworm populations in the United Stated and Mexico indicate that much of the genetic diversity of this insect is distributed among sympatric non-interbreeding populations. A new approach may be required to retain the effectiveness of the control program and to prevent a serious outbreak from threatening the economic viability of the U.S. livestock industry.

Animals↗
PubMed1981

The synthesis of dihydroxylated vitamin D metabolites by human renal mitochondria.

Mitochondrial preparations from 4 human kidneys produced 1,25-dihydroxycholecalciferol and 24,25 dihydroxycholecalciferol at rates of 0.019 - 0.114 and 0.029 - 0.164 pmol/mg/min respectively at a 25-hydroxycholecalciferol concentration of 1 mumol per litre. Mitochondria from a fifth kidney failed to produce either metabolite.

24,25-Dihydroxyvitamin D 3↗
PubMed1977

Gene regulation in Drosophila mulleri, D. arizonensis, and their hybrids: The nucleolar organizer.

Typically, Drosophila have nucleolar organizer regions (NORs) confined to the sex chromosomes. Salivary gland cells of hybrids between Drosophila mulleri females and D. arizonensis males exhibit features in nucleolar organizer regulation that differentiate the species on one hand, and which show an interplay between the X and the microchromosome on the other hand.In the hybrid females only the X chromosome from D. arizonensis appears to be attached to the nucleolus. In the hybrid males the X chromosome, from D. mulleri, also does not seem to contain a functional NOR. However, in hybrid males the microchromosome from D. arizonensis increases greatly in size and appears to be associated with the nucleolus. The increase in size of the microchromosome involves a 4-fold increase in DNA content. In D. arizonensis and in hybrid females the NOR of the microchromosome appears to be suppressed. In the absence of an arizonensis X chromosome, the NOR of the microchromosome typically is active, while the NOR on the mulleri X chromosome remains suppressed. Therefore, the ribosomal cistrons and interchromosomal regulator element appears to be duplicated on both the X chromosome and microchromosome of D. arizonensis, but with epistatic suppression of the microchromosomal NOR by the arizonensis X-linked NOR. Either arizonensis NOR, X linked or microchromosomal, suppresses the mulleri NOR.

Journal Article↗
PubMed1977

Patterns of molecular variation. II. associations of electrophoretic mobility and larval substrate within species of the Drosophila mulleri complex.

Electromorphic variation among populations of Drosophila mojavensis, D. arizonensis and D. longicornis was examined for seven genetic loci. The average electrophoretic mobility for a population was used as the metric. D. mojavensis and D. arizonensis use larval substrates in different parts of their geographic ranges, while D. longicornis is more narrowly restricted to different species of the cactus Opuntia in different localities. There is marked electromorphic variation among populations of either D. mojavensis of D. arizonensis, and the bulk of this variation is accounted for by differences in laval substrate. There is somewhat less variation among populations of D. longicornis, and only a moderate portion of this is accounted for by larval substrate differences. There appears to be an association between the taxonomic diversity of the larval substrates and the electromorphic diversity of the Drosophila populations utilizing those substrates. Evidence is reviewed that suggests physiological mechanisms for these possibly adaptive associations.

Alcohol Oxidoreductases↗
PubMed1977

The detection of sympatric sibling species using genetic correlation analysis. I. Two loci, two gamodemes.

Four models are presented describing zygotic frequencies at two loci for one or two sympatric but genetically differentiated populations of "gamodemes." Linkage disequilibrium within gamodemes is allowed in two of the models. Maximum likelihood criteria are used to fit the models to the observed numbers of zygotes in a sample. A fitting-testing sequence for choosing a best model is described and the power of the test is analyzed. The statistical characteristics of the genetic parameter estimates were examined by simulation studies. In general, estimates were reliable when allele frequency differences between gamodemes were greater than 0.30 at both loci. This method may be used to study the population structure of samples with fewer heterozygotes than expected for Hardy-Weinberg populations, including the detection and genetic description of sibling species having overlapping ranges.--An example is given for Drosophila longicornis and D. propachuca, two sibling species within the mulleri complex of the repleta group which have been studied in detail using more conventional techniques. The reanalysis using the approach derived in this paper confirmed the reproductive isolation of these two species, and hinted at the possibility of further subdivision within D. propachuca.

Alleles↗
PubMed1976

Patterns of molecular variation. I. Interspecific comparisons of electromorphs in the Drosophila mulleri complex.

The average mobility of electromorphs at an enzyme locus in a single population was defined as the weighted average mobility of the electromorphs in that population, where the electromorph frequencies are the weights. A derivative distance measure was defined whose taxonomic utility was determined in the Drosophila mulleri species complex. Most of the variation in this metric was at the interspecific level, primarily among clusters of sibling species. The electromorphs of some loci were equally and regularly spaced, while those of other loci were less regular in their spacing. Overall, these minor perturbations from regular spacing did not noticeably detract from the taxonomic utility of average mobility, and cluster analysis yielded the same taxonomic relationships as more conventional nonmolecular treatments. On the other hand, electromorph spacing may be related to functional constraints on the enzyme molecules. Some possible implications of the results for the modes of selection during evolution of the different enzymes are discussed.

Alcohol Oxidoreductases↗
PubMed1976

Multiple pheromone system controlling mating in Drosophila melanogaster.

The signals essential to Drosophila melanogaster courtship include pheromones emitted by the female which stimulate the male to court and pheromones emitted by the courting male which stimulate the female to accept. Genetic variation among these phermones is a common (if not universal) requirement for stimulation of either sex. The signal from the courting male to the female involves both a volatile and a nonvolatile component. The volatile component is associated with loci on the second and/or third chromosomes, while the monvolatile component is associated with the X and/or fourth chromosomes. This widespread distribution in the genome of loci controlling various components in the communication network inevitably results in linkage associations with other loci. The genetic array of gametes was limited. When combined with the negative assortitative mating pattern produced by the stimulation by dissimilar pheromones, linkage disequilibrium creates a strong counterforce to inbreeding during population bottlenecks.

Animals↗
PubMed1976

Evolution of Hawaiian drosophilidae. II. Patterns and rates of chromosome evolution in an antopocerus phylogeny.

The phylogenetic relationships of seven species of the genus Antopocerus (Family Drosophilidae) have been determined by means of a study of the metaphase configurations and polytene chromosomes. Based on biogeographical, behavioral and cytogenetic information A. longiseta from Molokai is tentatively identified as the primitive species of the genus. The metaphase karyotypes of all Antopocerus species are either five pairs of rod chromosomes and a pair of dots (5R1D), or six rods (6R). Heterochromatin additions converted the dots to rods. Chromosome breakpoints for inversions also are clustered at heterochromatic loci. The chromosome segments between heterochromatic loci may represent sets of functionally related loci, evolving as a unit. The rate of chromosomal inversion substitution is estimated in the origin of the taxon (probably a subgenus of Drosophila rather than a separate genus). It averages no greater than one substitution per 1,000 years, or one per 5,000 generations. The average genetic death rate per generation of one individual per hundred is required to achieve this substitution rate. The rate of inversion substitution during radiation of this taxon may be only 4.4 X 10(-3) times as fast as that present in forming the taxon. Alternatively, radiation may have required only 250,000 years if rates of substitution are the same as in the origination of the taxon. Average rates of substitution reflect genetic accidents, selection pressures and rates of adaptation to new niches, as well as the rate of encountering new niches. Rate of adaptation probably is much greater in this instance than rate of encountering new niches. Rate of adaptation probably is much greater in this instance than rate of encountering new niches. Therefore, the average rate of evolution reflects more nearly biogeographic and ecological factors than genetic factors.

Animals↗
PubMed1975

Heterochromatic chromosomes and satellite DNAs of Drosophila nasutoides.

Drosophila nasutoides is distinguished from other Drosophila species in that the metaphase karyotype shows a pair of very large V-shaped chromosomes. With Giemsa, a distinctive C-banding pattern is revealed along the arms of this large chromosome, indicating a largely heterochromatic nature. Furthermore, the banding patterns of the arms are symmetrical, indicating that it is an iso-chromosome. A comparison between the metaphase karyotype and polytene chromosomes suggests that the large V chromosome appears as the dot chromosome in polytene squash. One autosome has twice the arm length of typical Drosophila polytene chromosomes and arose either by centric fusion and a pericentric inversion, or by translocation connecting distal ends with a subsequent loss of one centromere. This chromosome appears to have a short arm which ectopically pairs with the proximal region of the long arm, representing a duplication of about ten bands. When the nuclear DNA is examined by neutral CsCl gradient, four satellites are observed. As much as sixty percent of the total DNA appears as satellites in the lysate of larval brains. No satellite was detectable in the lysate of salivary glands. These observations led us to suggest that the heterochromatic nature of the large V chromosome is due to the presence of all four satellites in this chromosome and that this large chromosome appears as the dot because of the under-reduplication of the satellites during polytenization.

Animals↗