FLORAL TRAIT VARIATION IN SPERGULARIA MARINA (CARYOPHYLLACEAE) - ONTOGENETIC, MATERNAL FAMILY, AND POPULATION EFFECTS

摘要

Traits expressed by modular organisms present difficulties when estimating the genetic component to their variation if their phenotype changes as an individual ages, confounding ontogenetic and genetic sources of phenotypic variation. For such traits, it is necessary to control for ontogenetic effects in order to estimate accurately the degree of genetic variation in a trait. To measure the magnitude of ontogenetic change in floral traits and to determine whether it may obscure underlying genetic sources of floral trait variation in the autogamous annual, Spergularia marina (Caryophyllaceae), we monitored the expression of floral traits over a five-week period in greenhouse-raised plants from four California wild populations. From 130 individuals representing 8-10 maternal families per population, we sampled one flower per week to record the number of ovules, normal anthers (the number of which is positively correlated with pollen production per flower), abnormal anthers (those that grade phenotypically into petals), and petals; and the areas of a single petal and the entire corolla. All traits except the number of abnormal anthers exhibited strong temporal changes in phenotype, although the direction and magnitude of the change differed among traits. To determine whether populations appear to be evolving independently, we examined differences among them in floral trait means, in the magnitude of-among-family variation, and in the degree to which they show temporal change in floral trait means. There were significant differences among population means for all traits except the number of ovules and petals per flower. In addition, populations differ in those traits that exhibit significant differences among maternal family means. For most traits, populations also differ in the magnitude of week-to-week changes in mean phenotype, suggesting the presence of genetic variation among populations in the expression of temporal change in floral traits. Finally, for most traits, the magnitude and significance of differences among populations and among maternal family means changed over time. Consequently, broad-sense heritability estimates, predictions of the response to selection, and measures of interpopulation divergence for floral traits are sensitive to the time of flower sampling in S. marina. The role of natural selection in moulding ontogenetic variation in floral traits has not been extensively studied in any species, but the presence of genetic variation among populations observed here suggests that this character is open to evolutionary change.