On Tre Appearance of Female Asynapsis and Polyploidy in a Population of Tre Diploid Synaptic Biotype of Dugesia Benazzii: First Steps of Tre Evolution towards Tre Pol Yploid Biotypes

The planarian Dugesia benazzii presents a diploid biotype which is synaptic and amphimictic and two polyploid biotypes which are characterized either i) by asynapsis in the female line or ii) by chromosome set doubling in the synaptic oocytes. Asynapsis and chromosome set doubling are characters controlled by multifactorial mechanisms. It has been suggested that these factors are also present in the diploid biotype, but in a very low number so that their phenotipic expression is extremely rare. The present research confirms that the diploid biotype is heterozygous for these factors . This is evidenced by the appearance of asynaptic oocytes (which are either diploid or tetraploid) and of sinaptic polyploid oocytes. According to the A. these manifestations represent the first steps of the evolution towards polyploid biotypes.