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R D Ward

Publications and source records attributed to R D Ward.

At least 109 records · Page 6Linked to original sources
PubMed1989

Changing localizations of site-specific sperm surface antigens during sea urchin fertilization.

Indirect immunofluorescence studies show that monoclonal antibody (mAb) J18/2 binds site-specifically to surface antigens localized over the acrosome and tail regions of mature Strongylocentrotus purpuratus spermatozoa. Within 5 min after induction of the acrosome reaction by exposure to egg jelly or ionophore A23187, these surface antigens become detectable over the lateral region of the head so that the entire surface of the spermatozoon is labeled. Polyspermically fertilized S. purpuratus eggs fixed at varying times after insemination and exposed to mAb J18/2 reveal that these surface antigens are quickly incorporated into the egg plasma membrane and begin to disperse as early as 1.5 min after insemination. At subsequent times, they undergo further dispersal so that by 45 min they are distributed over the entire surface of the egg. These results suggest that the sperm surface components recognized by mAb J18/2 gain the ability to disperse laterally during the acrosome reaction and proceed to do so in the egg plasma membrane after fertilization.

Acrosome↗
PubMed1989

Laboratory response of female Lutzomyia longipalpis sandflies to a host and male pheromone source over distance.

A nylon net cage (260 x 40 x 40 cm) provided with unidirectional air flow was used to demonstrate the response of female sandflies, Lutzomyia longipalpis Lutz & Neiva (Diptera: Psychodidae) to a host and extract of male pheromone glands over a distance of 240 cm. Females responded more rapidly and in greater numbers to the host if male pheromone was present. Results suggest that one function of the pheromone may be to attract females from some distance to a common mating site, on or near the host.

Animals↗
PubMed1988

Schistosoma mansoni: relationship between cercarial production levels and snail host susceptibility.

Two populations of Biomphalaria glabrata snails differing slightly in their susceptibility to Schistosoma mansoni infection showed dramatic differences in cercarial output per snail. Exposed to five or more miracidia, snails from a group with a 90-100% susceptibility rate (Group A) produced nearly twice the number of cercariae as those from a group with a 70-80% susceptibility rate (Group B). Exposure of individual snails to known numbers of miracidia resulted in higher numbers of primary (mother) sporocysts in Group A snails than in Group B snails. However, monomiracidial exposure of snails from both groups resulted in equivalent numbers of cercariae produced per positive snail, indicating that, once established, all primary sporocysts possess a similar reproductive potential. Morphometric analysis of serially sectioned 9-day-old primary sporocysts supported this conclusion; the size of the primary sporocysts and the size and numbers of secondary (daughter) sporocysts within each primary sporocyst were comparable in snails from both groups. The data indicate cercarial production in this system is regulated prior to, and/or during, early development of the primary sporocyst.

Animals↗
PubMed1987

A simulation study of the neutral evolution of heterozygosity and genetic distance.

This paper considers a statistical test of neutral theory which can be applied to allozyme variation in natural populations. Computer simulation is used to derive the theoretical relationship between genetic distance and heterozygosity under a variety of neutral models employing stepwise mutation. It is shown that the relationship between these variables is robust to variation in the parameters of the models, and that a test of neutral theory can therefore be derived. Applications of the test in the analysis of data from natural populations are discussed in the light of the simulation results.

Biological Evolution↗
PubMed1987

A method for the purification of Leishmania promastigotes from infected phlebotomine sandflies.

We describe a method for the purification of Leishmania promastigotes, isolated from infected sandflies (Lutzomyia longipalpis) using a discontinuous density centrifugation gradient (Percoll/Homem). The sandflies, infected seven days previously with Leishmania donovani chagasi or Leishmania mexicana mexicana from culture, were homogenized and centrifuged on a Percoll discontinuous gradient. Five interface bands were formed, and most of the promastigotes settled out at the interface between the (30% and 40%) Percoll concentrations. An extraction of 3.5 x 10(4) promastigotes from 90 female flies was achieved using this technique.

Animals↗
PubMed1986

Purine nucleoside phosphorylase polymorphism in the genus Littorina (Prosobranchia: Mollusca).

Examination of eight Atlantic species of the genus Littorina by starch gel electrophoresis of purine nucleoside phosphorylase revealed extensive polymorphism within the L. saxatilis complex. In this group, four alleles have been identified. Heterozygotes are four banded, and thus, as in vertebrates, the enzyme is likely to be a trimer. Breeding experiments confirmed the genetic interpretation of the phenotype patterns. Where species of the saxatilis complex [L. saxatilis (=L. rudis), L. arcana, L. nigrolineata, L. neglecta] are sympatric, there are sometimes significant allele frequency differences between them. A fifth allele was present at a high frequency in L. obtusata and L. mariae, and L. littorea and L. neritoides each possessed unique alleles. A total of eight alleles was identified. Densitometric scanning of heterozygote patterns pointed to activity differences between alleles and also showed that, while the heterotrimeric bands were never less intense than the homotrimeric bands, the heterotrimeric bands were sometimes less intense than expected. It is not clear whether this represents nonrandom association of subunits, decreased stability of heterotrimers, or simply an artifact of the staining and quantifying process.

Animals↗
PubMed1985

Population genetics of polymorphisms in Cardiff newborn. Relationship between blood group and allozyme heterozygosity and birth weight.

A newborn population of Cardiff, Wales, was screened for variation at three blood group loci (ABO, Rhesus and MN) and four enzyme loci (ACP-1, PGM-1, ADA and EST-D). Birth weights were measured. There were no significant differences between mean birth weights or birth weight variances for individuals homozygous or heterozygous at the MN and the four enzyme loci. (ABO and Rhesus loci cannot be used in these tests.) There was no significant heterogeneity in contingency tables relating phenotypes at the seven loci to birth weight. There were no significant differences in mean heterozygosity per locus between babies placed in different birth weight categories, ranging from 2.5 to 4.2 kg. The genetic variation screened appears therefore to be neutral with respect to this character.

Acid Phosphatase↗
PubMed1984

Ecology of leishmaniasis in the south of France. 20. Dispersal of Phlebotomus ariasi Tonnoir, 1921 as a factor in the spread of visceral leishmaniasis in the Cévennes.

The dispersal of Phlebotomus ariasi was studied in mark-release-recapture experiments in the summer of 1980 in a valley on the north-eastern slopes of the Oiselette range in the Cévennes mountains, in the commune of Roquedur, Gard, 50 km north of Montpellier, France. More than 5,000 specimens of P. ariasi were marked with fluorescent powders and released in 9 batches at 3 different places. Seven batches were engorged females and two were unengorged females and males. From 1-29 days after release, 497 marked sandflies (approximately 9%) were recaptured by active searches with UV lamps or in 58 CDC light traps set up in groups of 4 or 5 at 12 recapture stations. Females released engorged generally remained within 250 m of the release point for the first eight days while the bloodmeal was being digested after which there was a tendency to disperse to distances greater than 350 m presumably in a search for oviposition sites or another bloodmeal. The furthest distance to which a female released engorged was shown to move was 925 m; it was caught 12 days after release. Some of the females released unfed quickly moved away from release points, sometimes to distances of 1,000 m or more. One of these was caught 68.5 hrs after release at a station 2,200 m from the release point. Male sandflies tended to stay near the point of release and were not recaptured at distances greater than 600 m. There was no evidence that the movement of the sandflies was assisted by wind. Observations on the dispersal of female sandflies confirm that leishmaniasis can be more widely spread than generally assumed by the movements of the vector.

Animals↗