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Title Μελέτη της Φυλογεωγραφίας του Mediodactylus kotschyi (Sauria: Gekkonidae) στο αρχιπέλαγος του Αιγαίου και τις γειτονικές περιοχές
Alternative Title Study of the phylogeography of Mediodactylus kotschyi (Sauria: Gekkonidae) in the Aegean archipelago and the adjacent mainland
Author Κασαπίδης, Παναγιώτης
Thesis advisor Ζούρος, Ελευθέριος
Abstract The Aegean archipelago is an area with complicated and turbulent geological history, great biodiversity, where intense evolutionary processes have taken place, but which had little attracted the scientific interest of the evolutionary biologists. The aim of the present study was to elucidate the phylogeographical patterns of the gecko Mediodactylus kotschyi and to interrelate them with the paleogeographic history of the area. M. kotschyi was considered as an ideal model organism for such a study because of its wide distribution on the Aegean islands and the adjacent mainland and its great morphological differentiation with at least 25 different described subspecies. In order to study the phylogeography of the species, I sequenced a part of the first subunit of the cytochrome oxidase mitochondrial gene, from 105 individuals, representing 43 different populations. The results showed that populations of M. kotschyi exhibit a great genetic differentiation and are separated with very big genetic distances, which in some cases exceed 30%. Different methods of phylogenetic analysis point to one topology, which consists of 10 main monophyletic clades supported by high bootstrap values (>90%), and are clearly structured in a geographical scale. These clades are the following: 1) ?Crete and satellite islets?, 2) ?Kasos-Karpathos complex?: includes the haplotypes from Kasos, Karpathos, Prasonisi (which form a monophyletic group) and the islets of Sofrano, Tria Nisia and Astakida (monophyletic group), 3) ?Central and south Cyclades complex?, 4) ?Continental Greece complex?:includes the haplotypes from Peloponnese, Aigina and Tinos (?Peloponnese clade?), North Greece and Sporades (?N. Greece clade?), Kythira and Antikythira clade , 5) ?N. Dodecanese clade?, 6) ?Gavdos-Kastelorizo-Akschehir clade?, 7) ?Cyprus clade?, 8) ?Adana clade?, 9) ?Israel clade?, 10) ?Silifke clade?. The geographic distribution of the main clades of the gene tree, correspond to previously recognized biogeographical regions of a wide spectrum of organisms. These regions, with the present knowledge of the paleogeographical history, have been separated by sea barriers following the breaking of the unite land of ?Aegeais?, which once occupied the area of the present Aegean archipelago. The sequence of these separations fits well with the separations of the populations according to the gene tree of M. kotschyi. This fact clearly indicates that the differentiation of the species? populations is due to vicarianism. However, some phylogeographic patterns (such as the connection of Gavdos haplotypes with those of Asia Minor) can be attributed to dispersal events. If we focus on the intrapopulation divergence, there is a positive correlation with the island size. Smaller islands have zero polymorphism , while for the larger ones (like Cyprus and Peloponnese) genetic divergence reaches up to 10%. By combining molecular data with a general knowledge of the present demographic structure of the populations, we can hypothesize that in the bigger islands and the continental areas, M. kotschyi has a demographic pattern of isolated demes with low genetic flow, that permits different old separated genalogical mitochondrial lineages to persist in the present day populations. On the contrary, in the small islands, zero polymorphism is due to genetic drift. Although the calibration of a molecular clock is a difficult and controversial subject, in this case, not only showed good agreement between molecular and paleogeographical data, but also permitted to check two different scenarios for the paleogegraphical events that caused the separation of the M. kotschyi populations. The first scenario assumes that the divergence of the populations of the species started about 10 Mya, when ?Aegeais? started to break apart, while the second assumes that this happened at 5,3 Mya when the Messinian salinity crisis ended. Finally, I concluded that molecular data fit better with the sequence of paleogeographical events that followed the separation of Crete from ?Aegeais? 10 Mya. Based on this assumption , the separations of the main clades of the tree (which form a basal polytomy in the consensus tree) are placed between 10 to 6 Mya, while the separation of the mass of Central-South Cyclades from mainland Greece and the isolation of Peloponnese fron N. Greece and Kythira-Antikythira are placed 5 to 3 mya (during the lower-middle Pleiocene. The separation of Karpathos from Rhodes must have happened at the end of Pleiocene ? beginning of Pleistocene. The comparison with the molecular data from other organisms distributed in the same region (the genus of land snails Albinaria, the Podarcis erhardii complex and the Rana ridibunda complex) and have similar patterns of vicarian differentiation, showed that correspondent phylogeographic separations are not always due to the same paleogeographic event. The genus Albinaria has as similar history of differentiation in the Aegean with that of M. kotschyi, where the breaking of ?Aegeais? during the upper Meiocene caused the major phylogeographic separations. For the frogs of the genus Rana and the Podarcis erhardii complex, their differentiation in the Aegean seems to have been initiated after the end of the Messinian salinity crisis. The correspondence of the gene tree clades with the morphological subspecies of M. kotschyi is generally good, although in some cases there are subspecies which do not have monophyletic origin. The inclusion of the subspecies into groups of subspecies by Beutler (1981) seems to be phylogenetically more robust. In any case, a revision of the taxonomic status of the present subspecies based on the molecular findings of this study is absolutely necessary. Relevant to the taxonomic problems is the question whether some populations of M. kotschyi can be assigned a full species status, because of the extremely large genetic distances and the consequent long times that seperate them. Genetic distances based on mitochondrial DNA are not a safe criterion for determine different species. So, other genetic markers, morphological studies or even experimental crosses are needed before someone decides to determine different phylogenetic groups as species. From the point of view of conservation genetics, the main phylogenetic clades can be obviously treated as Evolutionary Significant Units (ESUs). Some of these ESUs could be threatened and in need for conservation because of their small population size and their geographically restricted populations (e.g populations of Crete and satellite islets). Under a conservational frame, it has to be checked whether a further expansion of the gecko Tarentola mauritanica in the Aegean (which seems that has been imported to Greece by humans) may affect in the near future the survival of the populations of M. kotschyi through competition or predation.
Language Greek
Subject Φυλογεωγραφία; Αιγαίο; Νησιά; Μοριακό ρολόι; DNA, Μιτοχονδριακό (M+DNA)
Issue date 2002-02-04
Collection   School/Department--School of Sciences and Engineering--Department of Biology--Doctoral theses
  Type of Work--Doctoral theses
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