A Cytophotometric Study of Parthenogenesis in Themiste Lageniformis (Sipuncula)
Abstract:This study examines the cytogenetics of reproduction and development of Themiste lageniformis, a parthenogenic sipunculan. It tests the hypothesis that parthenogenesis is of the diploid type and that parthenoproduced offspring develop from eggs that have had their diploid condition restored by automixis. Cytophotometry of Feulgen-stained cells was conducted to determine the relative amounts of DNA in gametes, early embryos, larvae, and adults. The nuclei examined were from adult male and female somatic tissue, spawned sperm, and from zygogenic and parthenogenic embryos fixed at 15 min, 55 min, 105 min, and 12 days after activation. The data indicate that the DNA content is related geometrically (doubles) between sperm and somatic cells and between the polar body and the zygote, early embryos and larvae. Apomixis and automixis are discussed as possible explanations for the data and automixis emerges as the best candidate. Additional data and observations are necessary to clarify certain details of the process.
Document Type: Research Article
Publication date: 1989-09-01
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