Levels of intracellular free amino acids used for salinity tolerance by oysters (Crassostrea virginica) are altered by protozoan (Perkinsus marinus) parasitism

Free amino acid (FAA) levels were measured from May through October 1991 in gill tissues of two groups of juvenile oysters (Crassostrea virginica Gmelin), one transferred from a low salinity field site (8) to a field site of high salinity (20) and high Perkinsus marinus (Mackin, Owen, and Collier) prevalence, the other kept at the low salinity field site. Within 24 h, glycine levels in the oysters transferred to high salinity increased 8-fold, taurine concentrations doubled and the total FAA pool rose from 150 mol g^–1 dry wt to 400 mol g^–1 dry wt. Taurine levels reached a plateau within 20 d after transfer to high salinity and remained at that level until P. marinus infections were detected 85 d after transfer. Taurine and glycine levels declined by 40% in the high salinity population as infection intensity increased between 70 and 105 d. Total FAA declined by approximately 33% over this period. The oysters kept at low salinity were not infected and continued to grow while the infected high salinity oysters showed no increase in shell length after Day 85. FAA levels in the low salinity group remained relatively constant throughout the experiment except for an initial rise triggered by an increase in ambient salinity from 8 to 12. The results suggest that salinity tolerance mechanisms in C. virginica may be impaired by P. marinus infection.     

The impact of synthetic pyrethroid and organophosphate sheep dip formulations on microbial activity in soil

Sheep dip formulations containing organophosphates (OPs) or synthetic pyrethroids (SPs) have been widely used in UK, and their spreading onto land has been identified as the most practical disposal method. In this study, the impact of two sheep dip formulations on the microbial activity of a soil was investigated over a 35-d incubation. Microbial utilisation of [1-(14)C] glucose, uptake of (14)C-activity into the microbial biomass and microbial numbers (CFUs g(-1) soil) were investigated. In control soils and soils amended with 0.01% sheep dip, after 7d a larger proportion of added glucose was allocated to microbial biomass rather than respired to CO(2). No clear temporal trends were found in soils amended with 0.1% and 1% sheep dips. Both sheep dip formulations at 0.1% and 1% concentrations resulted in a significant increase in CFUs g(-1) soil and [1-(14)C] glucose mineralisation rates, as well as a decline in microbial uptake of [1-(14)C] glucose, compared to control and 0.01% SP- or OP-amended soils. This study suggests that the growth, activity, physiological status and/or structure of soil microbial community may be affected by sheep dips.     

Mitochondrial DNA analysis of native and selectively inbred Chesapeake Bay oysters,Crassostrea virginica

Mitochondrial DNA (mtDNA) genotypes were examined in 1989 in threeCrassostrea virginica (Gmelin) populations native to Chesapeake Bay, USA, and in one population selectively inbred for rapid growth for ten generations. We wished to determine whether this character would be useful as a genetic marker for distinguishing between the inbred line and the native oysters and to determine whether detectable genetic differences exist among present-day native populations ofC. virginica. Thirty mtDNA haplotypes were identified. The average percentage nucleotide difference between native haplotypes was 1.8%. Inbred oysters were characterized by mtDNA haplotypes distinctly different from ancestral native oysters, indicating a high degree of genetic differentiation between the two groups (average percentage mtDNA nucleotide sequence divergence,=21.8%). The common native haplotype was not present in the selectively inbred sample, and six of the seven haplotypes detected in the inbred oysters were not found in the survey of native oysters. Chi-square tests on haplotype frequencies indicated that the native populations were not significantly different from one another. However, the distribution and relatedness of haplotypes suggest that significant change in the oyster gene pool may have occurred over the past few decades.