Systematics and historical biogeography of the genus Dugesia (platyhelminthes, Tricladida)

Dugesia is a genus of free-living flatworms which species inhabit freshwater bodies across a wide distribution range that includes Africa, Madagascar, Eurasia and Australasia. They do not survive in salt water or under desiccation conditions. All Dugesia species have a characteristic triangular-shaped head with two eyes and an elongated and dorsoventrally flattened body. This general shape makes them recognizable to non-experts that also know them because of their regeneration capabilities. The two first works of this thesis are focused on the Dugesia historical biogeography. In first place we studied its species on Greece, because of its complex and well-known geological history and the high diversity of species known on the area. The results showed interesting evidences of the diversification of the genus on the area driven by its history of geological breakage since the Neogene, by the contact and severing of ancient freshwater bodies, and probably by changes in the sea level of the Mediterranean. We also observed patterns of dispersion in the Greek mainland and the Peloponnese. In a second work we included the whole Dugesia distribution range. The aim was to test the previous hypotheses on the antiquity and dispersal routes of the genus to its present geographical distribution. The last hypothesis proposed an African origin in a Gondwanan scenario during the Mesozoic period followed by a dispersion in Eurasia through the impact of the Indian subcontinent or through the impact of the Arabian plate. Our results suggest an older origin, being the genus already present on Pangaea before its breakage. Taking into account this old origin and the internal and external homogeneity of the Dugesia genus species, this is probably a case of long-term or extreme morphological stasis. The copulatory apparatus is essential for Dugesia species description and identification. However, fissiparous specimens do not have this organ, making impossible to know which species are we dealing with. In other cases the inner morphology is very similar or identical among different species, hindering the species identification. In these cases the use of molecular species delimitation methods are of major interest in order to try to overcome these morphology associated drawbacks. In a third work we used one of these methods called General Mixed Yule-Coalescent (GMYC) together with morphological data in an integrative taxonomy framework in order to describe new species from Greece and to give more support to those already described. We formally described four new Dugesia species and the new genus Recurva containing two species and a putative third one. For those clades delimited by the GMYC method for which we did not have any or incomplete morphological data we proposed two different categories: Unconfirmed or Confirmed Candidate Species. The use of molecular species delimitation methods seems to be very convenient when dealing with freshwater flatworms. At the beginning of this thesis we aimed to obtain more molecular markers by the obtention of complete mitogenomes from different triclad species. Unfortunately, this work was delayed and finally we did not succeed in the obtention of a Dugesia mitogenome but of Crenobia alpina (Planariidae) and Obama sp. (Geoplanidae). We took advantatge of these new free-living flatworm mitogenomes and we carried out an evolutionary analysis comparing them with those of parasitic flatworms in order to test if, as previously thought, the different lifecycles have had a selective effect on the nucleotide composition of the mitogenomes. Surprisingly, our results showed a more relaxed selection in the Geoplanoidea species (Dugesia, Obama and Schmidtea) in comparison with the parasitic platihelminths and Crenobia.