Habitat fragmentation affects climate adaptation in a forest herb

Abstract: Climate change and increased drought frequencies are expected to have a major impact on forest herb persistence. The adaptive capacity of forest herbs will depend on their long standing imprints of local adaptation and phenotypic plasticity. To evaluate how local adaptation to habitat fragmentation affects climate adaptation we quantified a wide range of traits in a common garden experiment of Primula elatior. Specifically, we disentangled the relative contribution of climate, habitat fragmentation, and drought stress on trait variation of the germination lag time, germination rate, growth rate, root:shoot ratio, specific leaf area, stomatal density, glandular trichome density, flower phenology and flower investment. To further evaluate mating shifts we quantified flower colour adaptations, herkogamy, and self-incompatibility. Local adaptations in P. elatior displayed strong alignment with climate along its range. Northern populations displayed a reduced establishment and competitive potential, while southern populations displayed a high sensitivity to increased drought stress under climate change. Habitat fragmentation resulted in the evolutionary breakdown of reciprocal herkogamy, and a biochemical self-compatibility in S morphs. Furthermore, a significant differentiation of the flower colour attraction patterns and a strongly reduced flowering investment was observed in the south of the range. Fragmented populations also displayed a strategic developmental focus on survival and stress resistance. The interaction between local adaptation to climate and habitat fragmentation could have far reaching effects on (meta-)population dynamics under climate change and could limit the successful application of assisted migration strategies.