GENETIC DIFFERENTIATION BETWEEN POPULATIONS OF PLANTAGO-LANCEOLATA .1. LOCAL ADAPTATION IN 3 CONTRASTING HABITATS

(1) Reciprocal-transplant experiments were used to study genetic differentiation and adaptation to local conditions in populations of Plantago lanceolata at three different grassland sites. At two sites survival of the 'native' population was significantly better than that of one of the 'alien' populations. (2) Plant growth and morphology varied in response to the different environmental conditions at the three habitats. Nevertheless, the three populations consistently differed in vegetative growth, growth habit, number of seeds when ripe spikes were produced, and onset of flowering at all sites. (3) Plants from an early-mown hayfield flowered earlier than plants from a late-mown hayfield; plants from a pasture population flowered last. Seed yield of all alien populations was reduced in relation to the native population by 40-95%. (4) Fitness differences between native and alien populations after taking variation in reproductive traits into account were much higher than differences due to survival in juvenile or adult stage alone. (5) Although the phenotype of P. lanceolata is highly plastic, as exemplified by large differences between sites, it appears that genetically determined differences in plant development are maintained and have a great impact on lifetime seed yield.