Evidence from the field that multiple processes maintain hidden adaptive capacity to a novel environment in a wild daisy
Populations often persist in novel environments despite predictions that adaptive capacity to such conditions should be limited by a lack of genetic variation. A leading hypothesis is that genetic variation for adapting to novel environments is maintained but remains hidden under native conditions. However, direct evidence for the mechanisms that maintain this adaptive potential in natural populations is scarce. Here, we integrate data from four large-scale field experiments to test whether variation in selection across life history and environments, together with genetic architecture, maintains genetic variation important for adapting to novel environments. Using a quantitative genetic breeding design, we generated families of the Sicilian daisy, Senecio chrysanthemifolius (Asteraceae), and planted seeds and cuttings across native and novel elevations on Mount Etna. We tracked fitness across elevations, life stages, seasons and generations. Genotypes with higher survival and flowering success at the novel elevation increased adaptive potential, but were only weakly selected against in the native environment where they had slightly lower fitness at a later life-history stage. A negative genetic correlation in seedling survival across seasons indicated that different genotypes were favoured across temporal variation in native environments. Crosses between genotypes with low and high fitness in the novel environment revealed that genotypes that increased adaptive potential had heritable effects on plasticity and fitness across generations, but were recessive and therefore largely hidden in heterozygotes. Together, these results provide rare field-based evidence that weak selection in native environments, temporal variation in selection and dominance effects act together to maintain cryptic adaptive potential in natural populations.