Dugesia sicula Lepori, 1948

Dugesia sicula was first reported for Sardinia on the basis of fissiparous populations, in which a certain percentage of individuals underwent a sexualization process, from 12 Sardinian localities, including 2 small nearby islets (spring and wells on the Tavolara Island Protected Area and watercourses on the S. Antioco Island) (Pala et al., 1995) (Fig. 1). After several years other fissiparous populations were found in two other watercourses, one in the northwestern Asinara Island National Park (Rio d’Auteri reservoir) (Stocchino, 2003) and another in southeastern Sardinia (Fiume Quirra) (M. Pala, pers. comm.) (Fig. 1). All Sardinian populations showed a coastal distribution with a high degree of tolerance to variations in environmental factors, especially temperature and watercourses hydrological regime e.g. temporary water (Pala et al., 1995; G.A. Stocchino, pers. obs.).

Dugesia sicula has a pan-Mediterranean geographic range where it is mostly represented by fissiparous populations with only a few sexual populations being present in Mallorca, Algeria, Tunisia and Israel. Two mixed populations, including both sexual and fissiparous individuals, were reported from Sicily (Stocchino & Manconi 2013 and references therein). A recent reassessment of the taxonomic status of D. biblica Benazzi & Banchetti, 1973 from Israel and Turkey, based on morphological and molecular studies, considered this species to be a junior synonym of D. sicula (Solà et al., 2015).

As for karyology, numerous studies confirmed a diploid condition for sexual populations with a chromosome complement of 2n = 18; n = 9, and a triploid condition for fissiparous populations with a chromosome complement of 3n = 27; n = 9 + 1-5 B-chromosomes (see Stocchino et al., 2012 and references therein).

Among Dugesia species, the haploid complement of nine chromosomes of D. sicula is shared with only five other species: D. maghrebiana Stocchino et al., 2009, from North Africa; D. arabica Harrath & Sluys, 2013 from Yemen; D. aethiopica Stocchino et al., 2002 and D. afromontana Stocchino & Sluys, 2012 from the Afrotropical region; D. bifida Stocchino & Sluys, 2014 from Madagascar (Stocchino et al., 2002, 2004, 2009, 2012, 2014; Harrath et al., 2013).

Although D. sicula is extremely widespread, a molecular analyses on many fissiparous populations from its entire distributional range revealed a remarkable pattern of low interpopulation genetic variability, which was interpreted as the result of recent anthropochore colonizations after triploidization of sexual diploid populations (Lazaro et al., 2009).