Abstract:
Based on its native distribution and temperature constraints, the invasive zebra mussel (Dreissena polymorpha) was not expected to colonize southern portions of the U.S., but it has now spread from the Great Lakes to the Gulf of Mexico. Temperature is critical in zebra mussel reproduction, yet no studies have compared gametogenesis in the cool north vs. the warm south.
I studied zebra mussel seasonal gametogenesis in Marion Reservoir, Kansas, histologically in 2011-12, examining monthly gonad development and categorizing mussels into one of five stages: resting, early development, late development, spawning, or reabsorbing. I also histologically examined multiple size classes to determine size at maturity, and measured colonizers on artificial substrates in the reservoir to determine time to maturity.
Adults spawned March–August (at 7.8–34.6°C), compared to mid-June–September (at 18–24°C) in the Great Lakes. Sixty percent of zebra mussels were mature at 5 mm; 100% were mature at 7 mm, compared to 7.5–10 mm in the northern U.S. and 5–12 mm in Europe. Zebra mussels reached maturity within 4 weeks compared to 5 weeks in the Great Lakes and Europe.
I conclude that zebra mussels in Kansas mature faster, at a smaller size, and that spawning season is longer than farther north, possibly contributing to greater annual fecundity.
