The study of wild populations will benefit of increasing integration of ecological, molecular, genetic, and evolutionary approaches. The Glanville fritillary butterfly has a classic metapopulation in a network of 4,000 habitat patches in the Åland Islands, Finland, within an area of 50 by 70 km, across which population surveys have been conducted since 1993. Taking advantage of the opportunity to sample a few larvae from full-sib groups of gregarious larvae in hundreds of local populations, this project involves large-scale phenotyping and genotyping of individuals across the large metapopulation. The aim is to advance our general understanding of the genetic basis of variation in individual performance and life-time reproductive success (fitness), and the role of ongoing natural selection in population dynamics of species living in fragmented landscapes. For genotyping, we select ~1,000 SNPs from annotated genes in the recently sequenced transcriptome of this species. The same SNPs will be used to construct a pedigree for the entire metapopulation for 4 years. Two broad questions will be addressed: (1) Genetic basis of variation in dispersal, related life-history traits, and life-time reproductive success. This will be studied with association analyses, correlating individual phenotypes and genotypes to identify molecular variation with consequences for individual performance and fitness; and with pedigree analyses of natural populations, relating life-time reproductive success of individual larval groups to their phenotypic and genotypic composition. (2) Spatio-temporal population dynamics, the role of ongoing natural selection and consequences for regional adaptation. The purpose is to investigate the causes and consequences of spatio-temporal variation in population dynamics, including the role of ongoing natural selection. Mathematical modelling will be used to investigate the coupling of ecological and evolutionary dynamics in the spatial context.