THE ZEBRA MUSSEL (DREISSENA-POLYMORPHA), A NEW PEST IN NORTH-AMERICA - REPRODUCTIVE MECHANISMS AS POSSIBLE TARGETS OF CONTROL STRATEGIES

The zebra mussel (Dreissena polymorpha) has spread rapidly in temperat e fresh waters of North America since its introduction into the Great Lakes in 1985 or 1986. It attaches to hard substrates, forming layers, occluding water intakes, encrusting and killing native mussels, filte ring algae in competition with other planktivores, and possibly interf ering with fish spawning. It reproduces prolifically, suggesting that an approach to its control may be by controlling its reproduction. Pre vious literature suggests that spawning in bivalves is regulated by bo th environmental and internal chemical cues. A suggested sequence is t hat phytoplankton chemicals initially trigger spawning; chemicals asso ciated with gametes provide a species-specific pheromonal positive fee dback for spawning; and the response to environmental chemicals is med iated internally by serotonin (5-HT). The role of 5-HT in zebra mussel s is under investigation. Both males and females can be induced to spa wn by either injection or external application of 5-HT. The response c an also be activated by 8-hydroxy-2-(di-n-propylamino)-tetralin, an ag onist at 5-HT1A receptors. HPLC analysis has detected 5-HT as the majo r biogenic amine in both male and female gonads. 5-HT immunocytochemis try demonstrates nerves containing serotonergic fibers innervating gon ads of both males and females, with prominent varicosities surrounding the follicles in both sexes. A role of 5-HT in mediating spawning res ponses in zebra mussels is thus strongly supported. These studies have shown that reproductive behavior of zebra mussels can be modified by outside chemicals, a property that may be exploited for purposes of co ntrol.