Parthenogenetic oogenesis varies among and even within species. Based on cytological mechanisms, it can largely be divided into apomixis (ameiotic parthenogenesis) producing genetically identical progeny, and automixis (meiotic parthenogenesis) producing genetically non-identical progeny. Polyploidy is common in parthenogenetic species, although the association between parthenogenesis and polyploidy throughout evolution is poorly understood. Marmorkrebs, or the marbled crayfish, was first identified as a parthenogenetic decapod and was tentatively named as Procambarus fallax f. virginalis. Previous studies revealed that Marmorkrebs is triploid and produces genetically identical offspring, suggesting that apomixis occurs during parthenogenetic oogenesis. However, the behavior of chromosomes during the process of oogenesis is still not well characterized. In this study, we observed parthenogenetic oogenesis around the time of ovulation in P. fallax f. virginalis by histology and immunohistochemistry. During oogenesis, the chromosomes were separated into two groups and behaved independently from each other, and one complete division corresponding to mitosis (the second meiosis-like division) was observed. This suggests that parthenogenetic oogenesis in Marmorkrebs exhibits gonomery, a phenomenon commonly found in apomictic parthenogenesis in polyploid animals.
Keywords: parthenogenesis • apomixis • chromosome behavior • oogenesis • Marmorkrebs • gonomery