Activation of spawning in zebra mussels by algae-, cryptomonad-, and gamete-associated factors

Abstract

In zebra mussels (Dreissena polymorpha) simultaneous release of gametes and peaks in larval densities at particular locations suggest that spawning is triggered by synchronizing stimuli. Furthermore, spawning tends to occur only after an adequate environmental temperature is reached. To test the hypothesis that phytoplankton and gamete-associated chemicals initiate spawning in zebra mussels and that the responsiveness to such chemicals is affected by ambient temperature, the spawning response of zebra mussels to extracts from algae, a cryptomonad, and a cyanobacterium and to water associated with released gametes was assayed in animals acclimated to 12 ^C and 17 ^C. For animals held at 12 ^C, only serotonin, a known activator of bivalve spawning used as a positive control, stimulated spawning. However, for animals acclimated to 17 ^C, extracts made from a diatom (Phaeodactylum), a brown alga (Fucus), and a cryptomonad (Rhodomonas) stimulated spawning in both sexes; extracts from green algae (Platymonas and Dunaliella) and a cyanobacterium (Oscillatoria) did not cause spawning. Water associated with either released sperm or eggs elicited spawning in both females and males. Positive controls, stimulated with serotonin, spawned at a high (>90%) rate, whereas no negative control spawned. Thus, phytoplankton chemicals and gamete-associated factors may have a role in synchronizing spawning in zebra mussels once adequate ambient temperature is reached.