Parthenogenesis in the parasitic and free-living forms of Strongyloides papillosus (Nematoda,Rhabdiasoidea)

Both parasitic and free-living females of a calf strain of Strongyloides papillosus have a chromosome number of 2n=4. Both forms reproduce by diploid parthenogenesis. Oocytes of parasitic females undergo only one homeotypic maturation division without homologous chromosome pairing (mitotic parthenogenesis). Oocytes of free-living females show normal pairing and disjunction of the homologous chromosomes, but only one diploid polar body is expelled (meiotic parthenogenesis). Reconstitution of the diploid chromosome number occurs by separation of the two sister chromatids of each univalent during or after anaphase I.This investigation was supported by the Consiglio Nazionale delle Ricerche (C.N.R.) of Italy.