Abstract

To gain a full understanding of the mechanisms underlying fitness and adaptation, it is crucial to consider the ecological conditions that shape evolutionary dynamics in nature. The extent of environmental heterogeneity plays a key role in these dynamics and influences genetic and phenotypic variation in wild populations. Using the well-studied Glanville fritillary butterfly metapopulation of the Åland Islands in Finland, we measured life history traits and female host plant preference of wild butterflies in large outdoor population cages and associated trait variation with SNPs in candidate genes. We discovered a strong association between a genetic polymorphism in a gene of the Cytochrome P450 family and lifetime reproductive output of the butterflies, the key component of fitness. The specific Cyp gene plays an important role in the detoxification of host plant chemicals (allelochemicals) in butterflies and other species. Previous research has shown that the Glanville fritillary Åland population exhibits spatial variation in host plant adaptation involving two plant species, Plantago lanceolata and Veronica spicata, which show differences in allelochemical levels. We show here that the Cyp genotype is associated with host plant preference and that there is a strong correlation between Cyp allele frequencies and host plant preference across the Åland Islands. Our results suggest that the spatial heterogeneity of the habitat may contribute to the maintenance of genetic variation in Cyp through local adaptation.