Observations on Fission, Maturation and Reproduction in Dugesia biblica (Turbellaria, Tricladida) from Israel

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Abstract
Laboratory studies on the normally fissiparous Dugesia biblica from Israel (3n=27+x supernumeraries) have been made in order to investigate fission rates and spontaneous maturation of four fissioning populations and one clone. Laboratory induced maturation in a sixth population of D. biblica resulted in the laying of fertile cocoons, the offspring of which were either 3n=27+x, 2n= 18+x or 2n= 18+x It is suggested that triploidy is primarily responsible for the lack of sexual reproduction in the field, and that unequal inheritance of supernumerary chromosomes during mitosis may explain the differing tendencies to undergo spontaneous maturation by individuals of a clone of D. biblica. The karyotype, habitat and reproduction of D. biblica is compared with a closely related but diploid, normally sexually reproducing Dugesia form and possible relationships between these two are discussed.