Floral trait variation in Spergularia marina (Caryophyllaceae): ontogenetic, maternal family, and population effects

Abstract

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, Spergulana 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.

Pollination mode and life form strongly affect the relation between mating system and pollen to ovule ratios

“…Both P : O ratios and outcrossing rates can show large intraspecific variability (e.g. Schoen, 1977; Affre et al ., 1995; Mazer & Delesalle, 1996; Sherry & Lord, 1996; Koelewijn, 2004). However, for both P : O ratios and outcrossing rates, the intraspecific variability seems relatively low when compared with the variability among species.…”

Phenotypic plasticity in the expression of self-incompatibility in Campanula rapunculoides

“…Under conditions of high fruit‐set early in the season, later‐developing flowers would exhibit a ‘position’ effect, not by virtue of their position on the raceme, but by the presence of prior fruits. As Mazer & Delesalle (1996) point out, positional or developmental effects must be experimentally separated from effects caused by seasonal or resource environments if sources of variation in phenotypically plastic traits are to be resolved.…”

“…Basically, the analysis of the potential sources of variation in the expression of self‐incompatibility is a study of phenotypic plasticity where the total phenotypic variation observed in a population with respect to some trait is attributed to variation among genotypes (genetic determination or heritability), and/or variation induced by the environment ( Schlichting, 1986). Developmental differences among flowers on an inflorescence (ontogenetic plasticity) may also contribute to phenotypic variation ( Mazer & Delesalle, 1996) and there may be interactions between sources of variation, such as genotype‐by‐environment interactions, where the response to changing environmental conditions is not uniform among genotypes ( de Jong, 1990). Phenotypic plasticity has been of continuing interest to evolutionary biologists for decades as a potential explanation for how organisms adapt to heterogeneous environments (reviewed in Schlichting, 1986).…”

Evolution of the self‐pollinating flower in Clarkia xantiana (Onagraceae). I. Size and development of floral organs

“…There are now quite a few studies of genetic variation and covariation in floral form (Shore and Barrett, 1990;Meagher, 1992;Conner and Via, 1993;Mitchell and Shaw, 1993;O'Neil and Schmitt, 1993;Carr and Fenster, 1994;Robertson, Diaz, and MacNair, 1994;Stanton and Young, 1994;Young et al, 1994;Bradshaw et al, 1995;Andersson, 1996Andersson, , 1997Campbell, 1996;Galen, 1996;Mazer and Delesalle, 1996). While the verdict is still out on the relative strengths of constraint vs. selection in shaping the genetic and developmental architecture of floral form, it is clear that developmental constraints are not so large as to prevent the independent evolution of floral characters under the appropriate selective regime (Stanton and Delph, Galloway, and Stanton, 1996;.…”