Thesis (M. Phil.)--University of Hong Kong, 2004. / Title from PDF t.p. (viewed on Dec. 19, 2005). Includes bibliographical references (leaves 248-266). Also issued as print manuscript.

Previous studies in the population genetics of the oyster drill Thais clavigera show that snails from the west coast of Taiwan belong to the same population. However, the genotype frequency of arginine kinase (Ark) in large snails is different among sites in the west coast. In general, changes of temperature and desiccation caused by tidal cycle are the most important twp environmental factors affect genetic variation of intertidal organisms. In the present study, the relationship between the frequency of Ark genotype and tide was evaluated through the following experiments. It has been found that the frequencies of Ark genotype of snails, collected in August with the size range of 25-35mm, were correlated to tides. A higher grequency of Ark63/100 (0.47~0.56) was in the upper intertidal and a higher frequency of Ark63/63 (0.49~0.66) was at the lower end. Moreover, the genotype frequency also varied with size, i.e. more Ark63/63 in small snails (<25mm) and more Ark63/100 in large snails (>35mm). Laboratory desiccative experiments indicated that snails with genotype of Ark63/100 preferred in the areas of high water level and Ark63/63 in areas of low water level. The laboratory results were consistent with the field data. To compare the enzyme activity, there was no difference among the genotypes of Ark63/63, Ark63/100 and Ark100/100at temperatures of 18, 24 and 30¢J. In summary, the frequencies of Ark genotype varied with tide and size and factors such as temperature, desiccation and reproduction may play important roles in the relationship.

Morphological and histological studies of imposex has been studied in the oyster drills, Thais clavigera and T. rufotincta. The sex ratios of the collected samples were close to 1:1 among sites of Shunsun, Taishi, Budai, Chiku and Donkang. The relative penis sizes (RPS values) of T. clavigera were higher than T. rufotincta, indicating a high imposex degree in T. clavigera. The RPS values of T. clavigera showed seasonal variations, because the penis length of males and females were longer in the reproductive season, but the trends were inconsistent among the sampling sites. The RPS values in Shunsun and Taishi were higher in March (reproductive season) and lower in August (non-reproductive season), but Budai and Chiku were in a contrary way. It is suggested that the inconsistent patterns may result from temporal and spacial variations of tributyltin (TBT) and triphenyltin (TPT) concentrations among sites. For imposex females, they all developed penis and vas deferens. In the heaviest affected female T. clavigera, aborted egg capsules within the capsule gland that renders the female sterile has been observed. The percentage of capsule gland blockage in Shunsun, Taishi, Budai and Chiku were 7.7%, 9.7%, 50% and 0%, respectively. Other accessory sex organs, i.e. the lengths of capsule gland and prostate glands were all longer in reproductive season, and the difference among sampling sites were also significant. In histological studies of T. clavigera and T. rufotincta, the male testis tissue from all sampling sites contained all developing stages sperm cells in March; as females from March, the ovary tissues were full with mature oocytes. However, in Shunsun and Budai, there were many hemocytes found in the ovary tissues of T. clavigera that might result from imposex. In lab-experiments, T. clavigera were treated with TBT and TPT for 44 days, there was no difference in female penis length between control and TBT or TPT treated groups. The ovary and testis tissues were all developed normally. In general, there is no obvious abnormality in imposexd T. rufotincta. On the contrary, in T. clavigera, the female opening (vulva) occluded by overgrowing vas deferens which might prevent the spawning of egg capsules. In addition, some hemocytes were found in the ovary tissues in T. clavigera and the phenomenon of sex change was not observed. Meanwhile, no obvious abnormality was observed in the testis tissues of T. clavigera.

The variation of Arginine kinase (Ark) genotype frequency among populations of Thais clavigera has been reported in previous study. However, the difference which is originated from self-seeding or differential selection after recruitment is not understood. To answer this question, the spatial (i.e. Shainsan, Taisi, Budai, and Chiku) and temporal (sell length: <15mm, 15-20mm, 20-30mm, 30-40mm, and >40mm; year: 2001 and 2003) variations of Ark allozyme were examined by starch gel electrophoresis. There was no significant difference in the ratio of Ark genotypes (ark63/63, ark63/100, ark100/100) in the size range of <15mm among Shainsan, Taisi and Chiku. The result indicated that the populations of T. clavigera is from the same recruitment. In the size range of 15-20mm, the frequency of ark63/63 increased from southern to northern populations, i.e. 0.21(Chiku) < 0.33(Budai) < 0.60(Taisi) < 0.66(Shainsan), respectively. It is proposed that the variation of Ark genotypes among populations is resulting from stress of temperature or dessication. A significant difference in the ratio of Ark genotypes was found in the population of Taisi with the size range of 30-40mm. Besides, the frequency of Ark genotypes among populations was not related to the degree of imposex.