Συμβολή στη μελέτη της φυλογεωγραφίας στην Ανατολική Μεσόγειο

Abstract

Phylogeography is the scientific field that studies the geographical distribution of genealogical lineages within a species or closely related ones. Phylogenies are reconstructed and plotted geographically to display their spatial relationships and deduce the evolutionary origins and biogeographic history of populations, subspecies and species. The current study represents a phylogeographical approach of the intraspecific genealogy of the small fossorial snake Typhlops vermicularis. Typhlops vermicularis is the only extant representative of the superfamily Solecophidia and it is distributed in the eastern Mediterranean region. This area is characterized by a complex geological and climatic history that has affected or formed the phylogeny and biogeography of several organisms, and especially reptiles and amphibians which are sensitive indicators of palaeogeographic and palaeoclimatic events. The scope of the current study was to assess the phylogenetic relationships among the populations of the studied species, with the use of mitochondrial and nuclear molecular markers, and to answer questions regarding the phylogeny and biogeography of this species and the processes that affected the evolutionary and biogeographic history of animal taxa in the eastern Mediterranean. In total, 130 specimens were used, while the mitochondrial genes 12S and ND2, and the nuclear gene PRLR were chosen as markers, and were amplified via the polymerase chain reaction (PCR). Basic methods of phylogenetic analysis were followed (Neighbour-Joining, Maximum Likelihood and Bayesian Inferrence), and the genealogical relationships among the mitochondrial and nuclear haplotypes were approached through haplotype-networks with the use of the statistical parsimony algorithm. Genetic differentiation among the haplotypes of the same network was calculated with the use of Hudson’s Snn parameter. Moreover, the rapid expansion hypothesis was tested with the neutrality tests of Fu’s Fs and R2. Divergence times for the mitochondrial clades were estimated with a strict molecular-clock approach and the use of the phylogenetic split of the Cypriot lineage at the end of the Messinian Salinity Crisis (5.3 Mya) as a calibration point. Finally, a Dispersal-Vicariance analysis was performed, in order to better understand the biogeographic history of T. vermicularis. According to the results of the present study, the nuclear-marker phylogeny does not distinguish the evolutionary lineages that resulted from the phylogenetic analysis of the mitochondrial marker, except for the strongly differentiated clade A (mitochondrial DNA) or nA (nuclear DNA), which is distributed in Jordan and south Syria. This incongruence could be a result of reproduction, genealogical and dispersal factors, but also the mitochondrial-DNA inheritance and natural selection. Typhlops vermicularis includes ten mitochondrial clades, which represent ten Evolutionary Significant Units. Genetic divergence within each clade is very small, while it is significantly higher among the clades, implying one or more genetic bottleneck or founder effects. The general phylogeographical pattern agrees with Avise’s (2000) Category I, which concerns deep phylogenetic trees with the genealogical lineages in allopatry, and is observed among populations that have been isolated for a long period. In T. vermicularis, this pattern is also combined with the presence of polytomies, i.e. unresolved relationship, s a result of lack in data and possible parallel cladogenetic events. Based on the estimated times of diversification events within T. vermicularis, and the palaeogeographic and, most importantly, the palaeoclimatic events that occurred during those times in the area, it seems that, during the Late Neogene, T. vermicularis’ distribution followed many circles of expansion and shrinkage. The sudden and intense transitions from wetter to more arid conditions during that period possibly induced fragmentations in the geographic distribution of this animal and acted as a vicariant agent. During the non-favourable periods (arid and cold), several regions, especially in Anatolia, acted as biodiversity pockets for T. vermicularis, due to their geomorphological and ecological characteristics. For species, such as T. vermicularis, that present a continuous distribution throughout Anatolia, the existence of genetic “varieties” is exposed with the use of molecular markers, in areas considered as refugia. For other reptile species, geographic distributions are more confined or patchy, and coincide with the areas that acted as refugia for T. vermicularis, also acting as endemism centers. The identified T. vermicularis evolutionary lineages and the areas that played an essential role in sustaining biodiversity in the past are important in terms of management and protection. Among the T. vermicularis Evolutionary significant Units, clade A is genetically differentiated from the others (mitochondrial and nuclear DNA), while its divergence time is very old (~ 10 mya), compared to that of other recognized Typhlopidae and Leptotyphlopidae species. According to these results, this clade could represent a separate species.