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R D Ward

Publications and source records attributed to R D Ward.

At least 73 records · Page 4Linked to original sources
PubMed1993

A quantitative test of the neutral theory using pooled allozyme data.

Neutral theory predicts a positive correlation between the amount of polymorphism within species and evolutionary rate. Previous tests of this prediction using both allozyme and DNA data have led to conflicting conclusions about the influence of selection and mutation drift. It is argued here that quantitative conclusions about the adequacy of neutral theory can be obtained by analyzing genetic data pooled from many sources. Using this approach, a large database containing information on allozyme variation in over 1500 species is used to examine the relationship between heterozygosity and genetic distance. The results provide support for the hypothesis that a major percentage of protein variation can be explained by variation in neutral mutation rate, and a minor percentage by strong selection.

Animals↗
PubMed1993

The application of random amplified polymorphic DNA for sandfly species identification.

We have applied the recently developed Random Amplified Polymorphic DNA (RAPD) method to produce species-specific, DNA profiles for two sympatric, Venezuelan sandfly species, thought to be the vectors responsible for recent outbreaks of cutaneous and mucocutaneous leishmaniasis in the Andean State of Tachira. Moreover, within the profile, it was possible to identify a diagnostic DNA band for Lu. youngi of 0.32 kb. Results showed that the size of this diagnostic DNA band remained constant and did not vary with sex or geographical distribution.

Animals↗
PubMed1993

Semiochemical mediation of oviposition by the phlebotomine sandfly Lutzomyia longipalpis.

Extracts of rabbit food, hay and rabbit faeces elicited a positive oviposition response from gravid female Lutzomyia longipalpis sandflies (Diptera: Phlebotominae). Combined extract of rabbit food and oviposition pheromone had a synergistic effect on sandfly egg-laying, greatly increasing the number of eggs laid and resulting in a highly targeted response. Individually tubed flies, exposed to the combined extract, were shown to be 3.5 times more likely to survive oviposition and laid 2.5 times more eggs than control flies. A laboratory oviposition trap baited with the combined extract was tested in a cage and caught 31 (62%) of 50 gravid L. longipalpis over a 72h period.

Animal Feed↗
PubMed1993

Seasonal changes in testicular structure and localization of a sperm surface glycoprotein during spermatogenesis in sea urchins.

Testes of the sea urchin, Strongylocentrotus purpuratus, undergo morphological changes consistent with a reproductive season that includes the winter months in the northern hemisphere (c. November to March). These changes can be observed in the basal germinal epithelia (BGE) of testicular acini as alterations in the gradients of meiosis and spermatogenesis from the peripheral (basal) to the inner (luminal) regions. Early in the season, large numbers of spermatogonia and primary spermatocytes along with large, spherical nutritive phagocytes (NPs) occupy most of the BGE. Relatively few secondary spermatocytes, spermatids, and spermatozoa are present. In the middle of the season more spermatocytes, spermatids, and spermatozoa are observed within well-defined spermatogenic columns that run between elongated NPs. Late in the season the BGE diminishes as the number of spermatogenic cells within it decreases dramatically and the lumen becomes distended with mature spermatozoa. To trace the origin and location of a 210 KD sperm surface antigen during spermatogenesis, a monoclonal antibody that recognizes this antigen, MAb J18/2, was used to probe testis sections. Indirect immunofluorescence microscopy detected the antigen throughout the BGE. Immunogold electron microscopy further localized it to the intracellular vesicles within spermatogenic cells of all stages. In mature spermatozoa the 210 KD surface antigen was detected not only on the sperm surfaces overlying the acrosomes and tails but also within the acrosome, suggesting the presence of an intracellular store of this antigen. Other than the occasional detection of antigen within the residual bodies of NPs, which contain phagocytosed spermatozoa, no antigen was detected in somatic cells of the testis, indicating that it is generated within the spermatogenic cells themselves.

Acrosome↗
PubMed1992

A study of interlocus allozyme heterozygosity correlations: implications for neutral theory.

Using a database of allozyme studies, correlations in heterozygosity between selected enzyme loci (MDH, alpha GPDH, IDH, 6PGDH, LDH, SOD, AAT, PGM, EST, PGI) were calculated across vertebrate species. Large and positive correlations were observed with untransformed heterozygosity values. However, after transformation to correct for mean species heterozygosity, correlations were substantially reduced and median values were closer to zero. Some enzymes were more often involved in significant correlations than others, and correlations calculated across species within vertebrate classes were significant for different enzyme pairs in different classes. There was no evidence that significant correlations occurred primarily between functionally related enzymes. It is suggested that the observed correlations are best explained by variation between enzyme loci in functional constraint and effective neutral mutation rate.

Animals↗
PubMed1992

The thigmotropic oviposition response of the sandfly Lutzomyia longipalpis (Diptera: Psychodidae) to crevices.

Two experiments were carried out to investigate if Lutzomyia longipalpis would be attracted and stimulated to lay eggs in crevices. In the first experiment, females were introduced into a chamber and offered the choice of oviposition in a test site consisting of artificial crevices, and an open control site. Significantly more eggs were laid in the crevices of the test site than in the control site. In the second experiment, females were individually isolated in vials containing vertically placed filter papers, either folded to provide artificial crevices or arranged to offer two flat surfaces. The females isolated with the folded papers laid significantly more eggs than those isolated with the flat papers. The post-oviposition survival rates of both groups of females were, however, similar. It is suggested that the oviposition preference of the fly for the surface crevices was due to thigmotropic behaviour.

Animals↗
PubMed1992

Oviposition attractants and stimulants for the sandfly Lutzomyia longipalpis (Diptera: Psychodidae).

Oviposition preferences of Lutzomyia longipalpis Lutz & Neiva for surfaces containing frass (colony remains), larval rearing medium, and rabbit feces were investigated in the laboratory. In oviposition choice chambers, significantly more eggs were laid on sites containing frass, larval rearing medium, or rabbit feces than on untreated control sites. Experiments using unwashed and washed materials indicated, for the first time, the presence of chemical oviposition attractants or stimulants or both in larval medium (consisting of equal weight proportions of rabbit feces, potting compost, sand, and Daphnia). In an olfactometer, aroma from rabbit feces strongly attracted ovipositing females, and significantly higher numbers of eggs were laid in the olfactometer test chamber containing the rabbit feces than in the untreated control chamber. In comparisons of oviposition responses to hexane and distilled water extracts of rabbit feces, only the water extract was attractive. Similarly, the distilled water extract of rabbit feces proved to be an oviposition stimulant. Females kept individually with filter papers impregnated with the extract of feces oviposited earlier and survived longer than females kept with untreated papers.

Animals↗