COST OF REPRODUCTION IN POLEMONIUM-VISCOSUM - PHENOTYPIC AND GENETIC APPROACHES

I measured the effect of early reproduction on subsequent growth and s urvival in the alpine perennial wildflower, Polemonium viscosum. Measu rements were made over 4 yr on 34 maternal sibships under natural cond itions. A significant phenotypic cost of early reproduction characteri zed the study population. Plants that flowered after only one year's g rowth had twice as many leaves and 25% more shoots than nonflowering i ndividuals of equal age. However, early flowering decreased leaf numbe r by 18% in the subsequent year and survivorship by 20% after two year s relative to changes in leaf number and survival of nonflowering plan ts. 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 cos ts must be heritable. Although families showed significant heterogenei ty in the probability of early flowering, most (62%) entirely failed t o 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 incur red, did vegetative size components (leaf length and number, and shoot number) vary significantly among families. Results of this study prov ide little evidence of a genetically based trade-off between early rep roduction and subsequent survival in P. viscosum.