Gametogenesis in the Imposex-affected Oyster Drills, Thais Clavigera and Thais rufotincta

Abstract

Histological examination on gonads of Thais clavigera and T. rufotincta was conducted to evaluate the possible reproductive abnormality caused by imposex. Snails were collected from the west coast of Taiwan, including Shunsun, Taishi, Budai, Chiku and Tungkang. For T. clavigera, females from all of the surveyed populations have shown 'imposex' which refers to the development of additional male sex organs in females. The relative penis sizes (RPS values) of T. clavigera were greater than T. rufotincta, i.e. 9-28% vs. 0-1%, indicating a high degree of imposex in T. clavigera. Histological studies in T. clavigera and T. rufotincta showed that male testis tissues from all sampling sites contained sperm cells in various developing stages. In the ovary, there was no obvious abnormality in the imposex-affected T. rufotincta. However, some haemocytes were found in the ovary tissues of T. clavigera from Shunsun and Budai. Although the development of imposex and sterilization causing by the blockage of female opening are reported, the phenomena of ov o-testis and sex change do not occur in the species of Thais.