Sexual and reproductive traits of Hypania invalida (Polychaeta, Ampharetidae): a remarkable invasive species in Central European waterways

SUMMARY 1. The Ponto-Caspian polychaete Hypania invalida (Archiv fur Naturgeschichte, 1860, 26, 109) is undergoing rapid range expansion in the Rhine and other central European waterways. We examined its reproductive traits in an attempt to account for its remarkable invasive success. 2. For the first time in this species, we found males, dioecy (gonochorism) and an exclusively sexual mode of reproduction; no indication for hermaphroditism or (unisexual) partheno- genesis, that could explain the rapid range expansion of H. invalida, was found. 3. Our experimental evidence shows that H. invalida reproduces by males discharging their sperm into the water column while eggs are retained and fer…