Speciation is the major process creating diversity of life on Earth. The proposed study will focus on the genomics of ecological speciation. Little is known about constraints on ecological speciation and the effects that the shift in the spatial arrangement of habitats has on the differentiation process. Goal of this project is to discover how past environmental changes effected differentiation in the genome of Murella muralis, a land snail that has an impressive shell shape diversity displayed on a small geographical scale. Using a genotyping-by-sequencing approach based on a Illumina next-generation sequencing, the project will survey genome-wide patterns of divergence across the genome of M. muralis and allow conducting population genomics analyses on the resulting single nucleotide polymorphisms (SNPs). Three specific objectives will be addressed. (1) The demographic history will be tested to infer the “history of gene flow” and disentangle different models of divergence. (2) The fine palaeogeographical and past climatic knowledge of the study area will allow defining the effects of environmental changes on genomic variation in the course of time. This is a general key point in the study of speciation (geography and time-course of speciation). (3) Do shell traits map in regions of strong divergence? Two methods (i. estimate peculiar patterns of introgression in admixed populations; ii. crossing experiments, QTL mapping approach) will be used to test if highly differentiated regions are in regions of reduced introgression and separate differentiated regions under selection, linked to shell traits, from random population divergence.The key novel aspect of the project is that I will have the unique opportunity to search in detail genomic constrains on differentiation over multiple spatial-temporal scales in nature for a non model organism.