Sympatric Character Convergence between Two Species of Closely Related Genera of Pholadinae (Bivalvia: Pholadidae) from the Eastern Coast of India

Biological interaction between two ecologically related species in sympatry results mostly as character divergence, which is also known as ecological character displacement. However, there are reports of character convergence in areas of overlap. Here we present a case study of sympatric convergence and allopatric divergence in form between two species, Barnea Candida (Linnaeus, 1758), and Pholas orientalis Gmelin, 1791. They are members of closely related genera of marine bivalves from the eastern coast of India. So far as we know, this is the first report of a biological interaction between marine living bivalves. These two species are mud-boring deposit feeders. All of the characters here analyzed to show character shifting have adaptive significance or are proxy data for trophic apparatus. The present study involves more than 1,200 specimens collected from three sympatric and three allopatric sites that range over 1,000 km. Statistical analyses reveal that B.candida diverges more from its allopatric position than P. orientalis in sympatry. Character displacement generally takes place in sympatry to avoid or minimize competition for similar resources. The present two species have similar reproductive and feeding strategies. They also have similar ecological requirements for food and habitat. Because of these ecological and functional constraints, Barnea Candida and Pholas orientalis could not reduce competition by resource partitioning. Instead, they compete and hence converge.