Understanding how eco-evolutionary processes and environmental variation shape different dimensions of biodiversity is a major goal in evolutionary biology and ecology, and essential for the successful protection of biological variation. In this thesis, I used fritillary butterflies as model organisms to explore and further understand the origin and dynamics of genetic and phenotypic variation at different hierarchical levels of organisation and across different spatial scales.

A combination of mark-release-recapture, morphological, and genomic analyses indicated that a complex interaction of eco-evolutionary processes has contributed to the observed patterns of variation within and between the studied fritillary species. Results implied that mechanisms influencing gene flow seem to have played a crucial role in shaping genetic and phenotypic large-scale variation. Geographic distance and landscape elements, which might hinder dispersal, were identified as important drivers of population divergence in all studied species. Although some parallel patterns were evident, such as shared genetic clusters in former glacial refugia from which apparent northward dispersal took place, and similar responses to selective pressures regarding wing melanisation, most associations of environmental factors with the genetic and phenotypic variation were species-specific.

Spatial heterogeneity of ecological environments was also important for population differentiation. For example, small-scaled phenotypic and genetic divergence documented between two colour morphs in Fabriciana adippe might be explained by adaptation to distinct microhabitats within the same landscape. On a large scale, the phenotypic variation in F. adippe and Speyeria aglaja (but not F. niobe) was linked to similar environmental variables as their genetic structure, hinting at a genetic underpinning of the morphological variation due to local adaption. Besides deterministic processes such as divergent selection, stochastic processes such as genetic drift and founder events might have contributed to the patterns of variation in these species.

This thesis illustrates that even closely related species and populations in sympatry may respond differently to shared environments, possibly due to differences in dispersal abilities and ecological niche breadth. As the relative importance of eco-evolutionary processes may vary between species, my thesis thereby highlights the importance of comparative studies of variation to understand and protect biodiversity.