125Z360 - Pleistosen Biyocoğrafyasında Başa Dönüş:

Biogeography has evolved substantially since its origins in the nineteenth century. The integration of evolutionary biology, molecular phylogenetics, and, more recently, next-generation sequencing has transformed traditional biogeography into modern phylogeography, an interdisciplinary field linking evolutionary biology, ecology, conservation, and Earth history. A central focus of contemporary phylogeography is the evolution of species' geographic ranges, particularly in relation to the climatic oscillations of the Pleistocene. The center-periphery model has become one of the principal frameworks for interpreting these patterns. In the Western Palearctic, this model was largely developed by Prof. Godfrey Hewitt using the grasshopper Pseudochorthippus parallelus as a model species. Hewitt proposed that southern refugial populations represent the rear edge, northern populations the leading edge following postglacial expansion, and intermediate populations the range center. However, these influential hypotheses were based on only two short genetic markers, providing insufficient resolution to reconstruct the species' evolutionary history. Consequently, the fundamental predictions of the Pleistocene-based center-periphery model have never been rigorously tested with genome-scale data. This project will revisit these seminal hypotheses by analysing P. parallelus populations throughout the species' distribution, from Scandinavia to the Mediterranean and from the Atlantic to Central Asia. Genome-wide SNP data generated using ddRADseq will be used to address the following questions and to test the predictions of the Pleistocene-based center-periphery model. (i) What is the geographic genetic structure of P. parallelus across the Western Palearctic? What hierarchical relationships exist among the major geographic genetic lineages? How are the populations inhabiting the southern glacial refugia (Iberia, Italy, the Balkans, Anatolia, and the Caucasus) related to one another and to the genetic lineages distributed across northern Europe and Asia? How are the sublineages within each refugium related both internally and among refugia?; (ii) What is the intraspecific phylogeny of P. parallelus? During which period did its phylogeny evolve? Where did the species originate? Does the present-day geographic genetic structure primarily reflect geographic proximity or phylogenetic relatedness?; (iii) What are the historical demographic histories and current levels of genetic differentiation of the primary and secondary genetic lineages, or of the monophyletic groups identified by the phylogeny?; (iv) How many major waves of range expansion have contributed to the current distribution of the species? How did the alternating warm and cold phases of the Pleistocene, inferred through species distribution modelling, shape the formation of the present distribution?; (v) Based on the answers to the above questions, are the principal assumptions of the Pleistocene-based center-periphery model—both in terms of the observed patterns and the evolutionary processes generating those patterns—applicable to the southern (rear-edge), central (core), and northern (leading-edge) populations of the species?; (vi) What are the patterns of hybridization among the major genetic or phylogenetic lineages? Are there additional hybrid zones beyond the two currently recognized in the Pyrenees and the Italian Alps?; (vii) Which components of the general center-periphery model are supported by the genomic evidence, and which require revision?; (viii) How many subspecies should be recognized within P. parallelus? Are the currently described subspecies taxonomically valid, and could any of them warrant recognition as distinct species?; (ix) What do the evolutionary patterns observed in P. parallelus reveal about the mechanisms and processes of speciation? The project is organized into four work packages over 36 months and will be carried out by a principal investigator, four researchers, and two consultants.