Bottlenecks, population differentiation and apparent selection at microsatellite loci in Australian Drosophila buzzatii.

Species colonizing new areas disjunct from their original habitat may be subject to novel selection pressures, and exhibit adaptive genetic changes. However, if colonization occurs through a small number of founders, the genetic composition of the colonized population may differ from that of the original population simply due to genetic drift. Disentangling the effects of founder drift and selection after colonization is crucial to understanding the adaptive process. Drosophila buzzatii colonized Australia some 600-700 generations ago, and spread rapidly over a wide geographical range. Genetic variation for 15 microsatellite loci in each of nine populations in eastern Australia was used to estimate the size of the bottleneck, and to determine if any of these microsatellites marked genomic regions subject to recent selection. We estimate that on its introduction to Australia, D. buzzatii went through a moderate bottleneck (approximately 30-40 founders). Linkage disequilibrium was common, both intrachromosomal and between loci on different chromosomes. Of the 15 loci, 2 showed evidence of selection, one exhibiting local adaptation in different populations and the other balancing selection. We conclude that linkage disequilibria may be far more common in natural populations than is generally assumed, and the loci apparently affected by selection may well be marking selection in large genome regions including many loci that are not necessarily closely linked.

Field trial of a staphylococcal mastitis vaccine in dairy herds: clinical, subclinical and microbiological assessments.

OBJECTIVE: To assess the efficacy of a new staphylococcal mastitis vaccine under commercial dairying conditions. DESIGN: A field trial involving 1819 cows and heifers conducted on seven dairy herds in Victoria. The trial was done 'blind'; approximately half the animals were vaccinated and the remainder were untreated controls. PROCEDURE: The vaccine was given twice during the last 10 weeks of pregnancy. Effects of vaccination were assessed, during the ensuing lactation, on the basis of clinical and sub-clinical mastitis and microbiological investigations of the milk. RESULTS: A total of 273 cases of clinical mastitis were recorded. Staphylococcus aureus was isolated from 112 of these, 45 cases in vaccinates and 67 cases in controls; the difference was not statistically significant. One herd was notable in having a high incidence of clinical staphylococcal mastitis. This herd accounted for 15.8% of the animals in the field trial but 54.5% of cases of clinical staphylococcal mastitis. For this herd, vaccinated animals had significantly lower incidence of clinical staphylococcal mastitis and prevalence of subclinical mastitis, relative to controls. An unexpected feature of the trial as a whole was the low incidence of clinical mastitis from which S aureus was isolated in pure culture (26.3% of cases) and the high incidence of clinical Streptococcus uberis mastitis (22.7% of cases). CONCLUSIONS: The trial showed that the vaccine was efficacious in reducing the incidence of clinical mastitis and prevalence of subclinical mastitis in a herd that had a serious staphylococcal mastitis problem.

Influence of adjuvants on the immune response of sheep to a novel Staphylococcus aureus vaccine.

Sheep were immunized twice with two Staphylococcus aureus vaccines which contained either killed bacterial cells shrouded with pseudocapsules or toxoided beta haemolysin, together with various adjuvants. Circulating antibody responses were monitored using an ELISA (anti-pseudo-capsule responses) and an anti-beta haemolysin assay. Combining a killed cell/pseudocapsule/dextran sulphate (DXS) vaccine and the toxoid vaccine did not cause any diminution of antibody responses compared with separate injection of the two preparations. Addition of calcium phosphate to DXS as an adjuvant for the combined vaccine did not extend the duration of anti-pseudocapsule responses compared with those obtained with dextran sulphate alone. Nor was there any benefit in terms of durability of the response by increasing the amount of DXS: doses of DXS of 10-20 mg/kg liveweight provoked significantly higher peak responses but caused acute clinical reactions at the vaccination site and did not prolong the antibody response. In contrast, the combined vaccine given with DXS and emulsified in Freund's Incomplete Adjuvant (FIA) resulted in a large anti-pseudocapsule response with elevated levels of antibody being sustained for at least one year; there was a significant IgG2 anti-pseudocapsule response in animals receiving the vaccine with DXS and FIA. In the above experiments, 10(10) pseudocapsule-shrouded bacterial cells were used in the vaccine. Reducing the concentration of cells to 10(9) caused a slightly reduced anti-pseudocapsule response (not significant) whereas increasing the concentration to 10(11) did not increase the response.

Survival times and resistance to sea snake (Aipysurus laevis) venom by five species of prey fish.

The LD50 values and survival times of three pomacentrid species and two blennies were measured after being subjected to the venom of one of their predators, the olive sea snake, Aipysurus laevis. The species differed significantly in the speed of their responses to the venom. At high venom doses, blennies had higher survival times than pomacentrids, and in the latter group Dascyllus survived longer than did species of Chromis. In part, this may be related to differences between blennies and pomacentrids in degree of cutaneous respiration. Relative survival time was influenced by venom dosage; ranking order of species' survival times was different at low doses than at high ones, and taxonomic correlations broke down.

Some cutaneous responses to mitogen injection in sheep, with special reference to eosinophil leucocytes.

Research in laboratory animals suggests that eosinophil numbers in some cutaneous reactions may reveal inherent differences in resistance to parasite infection. An intradermal injection with 10 microgram of the mitogen phytohaemagglutinin, followed by counting eosinophils in the deep dermis of skin biopsies removed 24 hours later, appears to be a practical and reproducible way of comparing the ability of individual sheep to marshal eosinophils in a tissue. This procedure will allow study of the relationship between eosinophil response and resistance to parasite infection in sheep.

Survey of intramammary infections in ewes on the New England Tableland of New South Wales.

Samples of mammary secretion were collected aseptically from 1093 ewes in 8 separate flocks. Most of the ewes were suckling lambs 4 to 6 weeks old. Standard bacteriological tests were carried out on the samples to identify the organisms involved in intramammary infections. Data on age, breed, lactational status and clinical status of the gland and its secretion were recorded at the time of sampling. The prevalence of intramammary infection was 14% of ewes (8% of glands). There was a tendency for prevalence of intramammary infection to be positively correlated with age of the ewe (two-year-old and six-year-old ewes had, respectively, 4.4% and 14.0% of glands infected). This relationship was highly significant for Border Leicester x Merino ewes. There were also significant differences in infection prevalence between breeds. infected glands had a higher prevalence of clinical abnormalities of udder, teat and secretion than did non-infected glands. Staphylococcus aureus was overwhelmingly the most frequently isolated bacterium being responsible for 40% of all intramammary infections.

Immunophysiological activity of supramammary lymph nodes of the ewe during the very early phase of staphylococcal mastitis.

Efferent mammary lymph was collected from lactating ewes which were unimmunised (controls) or immunised during pregnancy with two doses of an attenuated live Staphylococcus aureus vaccine either in the hindlimb ("directly primed' supramammary nodes) or in the brisket ("indirectly primed' supramammary nodes). Mammary lymph was also collected from unimmunised animals in which the supramammary nodes had been extirpated several months before. Ewes in which the supramammary nodes had been directly primed by staphylococcal vaccination before challenge had a significantly greater output of IgM- and IgG2-containing cells in lymph and higher concentrations of IgG1 and IgG2 antibody against S aureus surface antigens than did other groups. Lymphadenectomised ewes had fewer leucocytes in mammary lymph but a much higher proportion of neutrophils than other ewes, indicating that afferent mammary lymph has an unusually high number of neutrophils and most of these cells are filtered out in the supramammary lymph nodes under normal circumstances. The results indicated that most of the leucocytes in efferent lymph were derived from the supramammary nodes. After induction of experimental staphylococcal mastitis there was a rapid drop in leucocyte output in lymph within one to four hours after infection; the data indicated that events within the supramammary nodes were responsible for this phenomenon. The output of immunoglobulin-containing cells was reduced during this phase. No significant increases in output of lymphoblasts, immunoglobulin-containing cells or specific antibody occurred during the six hours immediately following infection.