Discrimination of field-collected juveniles of two introduced dreissenids (Dreissena polymorpha and Dreissena bugensis) using mitochondrial DNA and shell morphology

We developed molecular markers to distinguish two species of exotic bivalves, the zebra mussel (Dreissena polymorpha) and the quagga mussel (Dreissena bugensis sensu late). Restriction analysis of a 710 base pair fragment of the COI mitochondrial gene showed a single restriction pattern for zebra mussels and a single restriction pattern for quagga mussels for each of the enzymes ScrfI, Csp6I, and Sau96I. This molecular analysis also confirmed that there were no sex-specific restriction patterns for either species. We then used our molecular markers to confirm the species identity of postmetamorphic and early juvenile stages (greater than or equal to 300 mu m shell length) of zebra and quagga mussels from Lake Erie and the Rideau River (Ottawa, Ont.). Useful shell characteristics to discriminate between postmetamorphic and early juvenile stages (greater than or equal to 300 mu m shell length) of zebra and quagga mussel included (i) overlap of valves at the posterior region, (ii) position of the dorsal point of curvature, (iii) angle of shell at the dorso-anterior region (hinge), and (iv) level of flatness of the ventral region (>2 mm shell length). Juveniles of approximately 300-700 mu m shell length can be identified using the valve overlap criterion alone.