Abstract
A study was carried out on freshwater planarians of the genus Dugesia from three localities in northern Tunisia: Joumine, Chiba, and Lebna. The three populations are fissiparous under field conditions and do not possess reproductive organs, except for some cases of hyperplastic ovaries in the Joumine population. After five months of breeding under laboratory conditions, with water temparature between 18 and 25 °C and under short photoperiod, 8.33 to 26% of specimens from the Joumine stream became sexualized, together with considerable increase of body length and width. For the other two populations the sexualization rate was very small. Extended period of darkness apparently played a positive role in this sexualization. The phenomenon of sexualization is discussed in the context of reproductive strategies. Histological and karyological studies of the sexualized animals allowed identification of these usually fissiparous planarians as representatives of Dugesia sicula Lepori, 1948. The species is here reported for the first time from Tunisia. The populations are restricted to permanent water basins resulting from the construction of dams in large rivers.