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Egypt. J. Exp. Biol. (Zoo.). 2007; 3(0): 317-323


THE FECUNDITY OF STRESSED SOIL ORIBATID MITE POPULATIONS IN THE VICINITY OF METAL SMELTER

Lamiaa A. Sharra.




Abstract

The present study aims to determine the fecundity of stressed soil oribatid mite populations in the vicinity of metal smelter. To perform this study, abundance and number of eggs per individual were recorded for five species of common oribatid mites at two sampling sites, polluted and reference sites from a copper smelter at Seeger, Tanta, Al-Gharbia Governorate. Soil samples were taken every season from the two chosen sites for one year. The total number of individuals of each mite species was determined and the total number of eggs contained in their bodies was evaluated by pooling them over all sampling times. Student's t-test was applied to compare between the means of number of eggs per individual in polluted and unpolluted sites for each oribatid mite species. The correlation between population density and fecundity, also, the relationship between body size and number of eggs per individual were estimated using correlation coefficient analysis. The results showed significant differences between species in the number of eggs per individual. The five oribatid mites could be grouped into four categories, each comprising species with similar egg number. The ratios between gravid and ungravid individuals are significantly different due to the burden of the toxic stress. No significant differences could be observed between the density of gravid individuals and the egg number per individual at both studied sites. There was a positive correlation between the body size of individuals and the egg number per individual. Observed distributions of the eggs among stressed population of four studied oribatid species (Zygoribatula undulata, Lamellobates orientalis, Plakoribates multicuspidus and Scheloribates laevigatus) were significantly different from those expected ones (Poisson distribution). However, the reverse was true in case of Anachipteria aegyptiaca. In conclusion the present study suggests that the fecundity of oribatid mites, being a species-specific dependent and is rather sensitive to metal pollution. However, no relationship between the fecundity and the population density of the oribatid mites could be detected. Therefore the egg number within a species could emphasize a good indicator of the ecological performance of oribatid mites.

Key words: egg number, oribatid mite, metal pollution






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