Speciation in the coral-boring bivalve Lithophaga purpurea: evidence from ecological, biochemical and SEM analysis

The boring mytilid Lithophaga purpurea densely inhabits the scleractinian corals Cyphastrea chalcidicum (Forskal, 1775) and Montipora erythraea Marenzeler, 1907 in the Gulf of Eilat, Red Sea. Profound differences in reproductive seasons, postlarval shell morphology and isozyme polymorphism exist between the bivalve populations inhabiting the 2 coral species which share the same reef environments. Two distinct reproductive seasons were identified in the bivalves: L. purpurea inhabiting M. erythraea reproduce in summer, while those in C. chalcidicum reproduce in late fall or early winter. SEM observations revealed distinct postlarval shell morphologies of bivalves inhabiting the 2 coral hosts. Postlarvae from C. chalcidicum are characterized by tooth-like structures on their dissoconch, as opposed to the smooth dissoconch surface of postlarvae from M. erythraea. In addition, there is d significant difference (p < 0.001) in prodissoconch height between the 2 bivalve populations. Results obtained from isozyme electrophoresis showed distinct patterns of aminopeptidase (LAP) and esterase polymorphism, indicating genetic differences between the 2 populations. These data strongly support the hypothesis that L. purpurea inhabiting the 2 coral hosts are indeed 2 distinct species. Species specificity between corals and their symbionts may therefore be more predominant than previously believed.