Two pathways for spermatogenesis in Sinanodonta woodiana (Lea, 1834) (Bivalvia: Unionidae)

Abstract

Abstract The Chinese pond mussel, Sinanodonta woodiana, an invasive species indigenous to Asia, naturally colonizes new locations as a glochidium that parasitizes fish. Human activity has facilitated a continental-scale spread of S. woodiana in Europe, where it is found in artificial reservoirs and has begun to invade natural habitats. This study aimed to investigate the reproductive activity of males in a female-biased population of S. woodiana that lives in a riverine channel linked to a power plant with a cooling water system in NW Poland. Cells formed during spermatogenesis and morphological changes in reproductive follicles (acini) were analysed over a 2-year period using light microscopy. Typical and atypical spermatogenic pathways were identified. The atypical spermatozoa were released from multinucleated cysts and had significantly shorter heads than typical spermatozoa. Spermatozoa formed in the typical way occurred consistently in all months over the study period, while the atypical spermatozoa were recorded occasionally in the first year of the study and more frequently in the second study. The highest proportion of males with spent gonads was found in late summer and early autumn. Our data show that mussels produce spermatozoa year-round, but that the levels of typical and atypical spermatogenesis varied. The two pathways of spermatogenesis in S. woodiana provide an important insight into potential mechanisms underlying the evolution of doubly uniparental inheritance of mitochondrial DNA, a phenomenon observed in S. woodiana. Additionally, a detailed understanding of the reproductive cycle of this non-native species can help to understand its reproductive potential and predict the likely direction of population change in a newly colonized area. The breeding population of S. woodiana studied by us inhabits a tributary of the Odra River, one of Poland’s largest rivers, and thus poses a threat to the natural environment. Riverine habitats like our study site are local heat islands and the mussels reproducing in them over time may colonize natural waters and expand the range of their distribution.