COST OF REPRODUCTION IN POLEMONIUM VISCOSUM: PHENOTYPIC AND GENETIC APPROACHES

I measured the effect of early reproduction on subsequent growth and survival in the alpine perennial wildflower, Polemonium viscosum. Measurements were made over 4 yr on 34 maternal sibships under natural conditions. A significant phenotypic cost of early reproduction characterized the study population. Plants that flowered after only one year's growth had twice as many leaves and 25% more shoots than nonflowering individuals of equal age. However, early flowering decreased leaf number by 18% in the subsequent year and survivorship by 20% after two years relative to changes in leaf number and survival of nonflowering plants. For such trade-offs to shape the further evolution of reproductive schedules, flowering probability and those age-specific components of plant size that represent the energetic currency for reproductive costs must be heritable. Although families showed significant heterogeneity in the probability of early flowering, most (62%) entirely failed to flower. Moreover, phenotypic variation in vegetative size components at ages 1 and 2 had little genetic basis. Only at ages 3 and 4, after vegetative and demographic costs of early reproduction had been incurred, did vegetative size components (leaf length and number, and shoot number) vary significantly among families. Results of this study provide little evidence of a genetically based trade-off between early reproduction and subsequent survival in P. viscosum.