Programmed cell death in hyperplasic ovaries of ex‐fissiparous planarian Dugesia arabica

Abstract

Planarians can reproduce exclusively sexually or/and asexually by fissiparity. Among fissiparous populations individuals can sexualize and develop ovaries of remarkable size called hyperplasic ovaries (Gremigni and Banchetti, 1972). Nevertheless, it has been reported that individuals that become sexual are usually sterile because they usually lay infertile cocoons (Grasso and Beanzzi, 1973).The aim of this study is to demonstrate, through ultrastructural and TdT‐mediated dUTP nick end‐labeling (TUNEL assay) in intact sections of hyperplasic ovaries the cause of infertility of ex‐fissiparous planarians. Our study has been carried out on Dugesia arabica collected from Yemen (Harrath et al., 2013) that reproduce asexually in the field. After having been kept for few months in the laboratory, some of the specimens had been sexualized.Ultratsructural and TUNEL assay investigations demonstrate that oogonia and young oocytes still develop normally compared to previous studies describing oogenesis in other Dugesia species. At the later stage, very few fertile oocytes of a hyperplasic ovary may succeed in completing their growth whereas the majority at the diplotene stage undergoes a progressive degeneration through programmed cell death. The latter leads to the self‐destruction of oocytes and may represent the most important cause of infertility of ex‐fissiparous planarians. This process should be correlated with polyploidization or genomic variations.