Evolution of ecophenotypic plasticity in Indian Oyster, Crasssostrea madrasensis (Preston) population from Ashtamudi Lake, Kerala, India

The Indian Oyster, Crassostrea madrasensis are abundant in the coastal waters of Tamil Nadu and Kerala. Since, they are benthic filter feeders, the external environmental conditions impose ceaseless effects on their shell affecting one or more of size, sculpture, anatomy pattern, shape and colour resulting in ecophenotypic plasticity. However, the identification of Oyster species is still based on phenotypic characters that are highly plastic. Therefore, this study aimed to investigate the phenotypic plasticity of the Indian Oyster, C. madrasensis population of Ashtamudi Lake with respect to certain ecological parameters. Individuals were collected from the barmouth and upper reaches of Ashtamudi Lake, Kerala and apparent variations were measured. Significant variations were found in the Shell colour and shell pattern. Accordingly, two morphotypes of C. madrasensis were recorded. Since, the two population exhibit remarkable differences in morphology, species confirmation was made possible using mitochondrial 16S rRNA gene. Even though 2.7% genetic distance observed between the two morphotypes of C. madrasensis is not enough to consider them as different species, it calls attention to the possibility of evolutionary divergence in the near future.