The studies of the asiatic clams (Corbicula, Muhlfeld, 1811) in Thailand : electrophoretic estimates of enzyme variation and the use of anatomy as a species indicator

Abstract

Freshwater bivalves of the genus Corbicula found in forty localities throughout Thailand were compared in regard to morphology anatomy and biochemistry. Shell morphological study revealed twenty two species of Brandts taxa and one unknown taxon. One form has a white nacre with purple highlights (the white form) and the other form has a deep purple nacre (the purple form). The basic plan of the gross anatomy based on mantle, siphons pigmentation digestive and reproductive systems is closely similar in all species. Biochemical study was made using the technique of horizontal starch gel electrophoresis. Genetic variation detected for the enzymes included Aspartate aminotransferase Alkalinem phosphatase Esterase Glucose-6phosphate dehydrogenase isocitrate dehydrogenase leucine aminopeptidase Malate dehydrogenase Malic enzyme Peptidase 6-Phosphogluconate dehydrogenase Phosphoglucose isomerase Phosphoglucomutase and Xanthine dehydrogenade. The average individual heterozygosity varies widely across species from zeroto 0.025. The occurrence of low individual heterozygosity attributed to facultative selffertilization. Neis genetic distance (D) was calculated to estimate interspecific divergence. Genetic distance average value of D < 0.01 is very low demonstrating that Thai Corbicula are almost identical to one another. Differences in ecological havitat preference were also noted in this study. In view of these data the shell characters can be used to distinguish the bivalves into various species but typically do not correlate with anatomical cnaracters and genetic data. With the support by anatomical and electrophoretic similarities a single species concept of Thai Corbicula is proposed.