ABSTRACT
Since their arrival into North America in 1991 (May and Marsden, 1992), quagga mussels (Dreissena rostriformis bugensis Andrusov, 1897) have exhibited remarkable ability to spread throughout North American waterways. As seen in Europe, the spread of quagga mussels frequently followed an initialinfestation by zebra mussels, with quagga mussels displacing the former in many locations (Mills et al., 1999; Ricciardi and Whoriskey, 2004; Brown and Stepien, 2010; Nalepa et al., 2010). The recent infestation into Lake Mead, Nevada-Arizona, marked the ‘rst occurrence of adreissenid species into the western United States and also marks an unusual situation where solely quagga mussels are present without being proceeded by zebra mussels. It is believed quagga mussels were initially introduced into Lake Mead, quickly spreading downstream of the Hoover Dam, into Lake Mojave, and then continuing onward to their current locations in the southwestern United States. It has been postulated that quagga
Introduction .............................................................................................................................................. 53 Broadcast Spawning ................................................................................................................................. 54
Environmental Cues for Spawning Induction ..................................................................................... 55 Temperature ................................................................................................................................... 56 Algal Content ................................................................................................................................. 56 Gamete-Associated Stimuli ........................................................................................................... 56 Spawning Induction ....................................................................................................................... 56
Gamete Morphology ................................................................................................................................ 57 Sperm Morphology ............................................................................................................................. 57 Egg Morphology ................................................................................................................................. 58
Events of Fertilization .............................................................................................................................. 59 Motility and Chemotaxis .................................................................................................................... 59 Acrosome Reaction ............................................................................................................................. 60 Sperm Binding and Entry into the Egg Cytoplasm ............................................................................. 60 Egg Response to Fertilization ............................................................................................................. 62 Sperm-Egg Ratios and Limitations .................................................................................................... 63
Cleavage and Early Development ............................................................................................................ 63 Larval Development ............................................................................................................................ 64
Methodology ............................................................................................................................................ 65 Collection and Spawning of Animals ................................................................................................. 65 Fertilizations ....................................................................................................................................... 66 Fixation ............................................................................................................................................... 66 Microscopy ......................................................................................................................................... 66
References ................................................................................................................................................ 66
mussels were introduced into Lake Mead via bilge water (i.e., bait or live wells) carried by a boat from the Great Lakes region (McMahon, 2011; Wong and Gerstenberger, 2011). Thus, the establishment of a reproductive population in Lake Mead has, and continues to play, acritical role in the spread of quagga mussels throughout the southwestern United States. Understanding the reproductive biology of quagga mussels and paying special attention to parameters important to environmental conditions found in the southwest will help provide better understanding of the continued spread into this region.
