NATURAL SELECTION ON GENETICALLY CORRELATED PHENOLOGICAL CHARACTERS INLYTHRUM SALICARIAL. (LYTHRACEAE)

Abstract

The seasonal timing of life-history events such as flowering can be critical to plant reproductive success (Rathcke and Lacey 1985). There is considerable evidence for a relationship between the timing of flowering and fecundity (Schemske 1977;Augspurger 1981;Roach 1986;Mazer 1987), and for selection on timing of initial flowering (Schemske 1984; Stewart and Schoen 1987;Campbell 1989 Campbell , 1991Kelly 1992a). However, the prevalence of phenotypic (Mazer 1987; Dorn and Mitchell-aids 1991; Kelly 1992a,b) and genetic correlations (Dorn and Mitchell-aids 1991; but see Kelly 1993) between the timing of flowering and other life-history events or other quantitative traits makes it difficult to predict how populations might respond to selection acting on flowering time. Many of the traits that can be correlated with the timing of flowering such as plant size, duration of flowering, and the number of flowers produced, are traits that could be subject to selection themselves. A high degree of intercorrelation among characters can make it difficult to disentangle the effects of direct selection from the effects of selection on correlated traits, especially if correlated traits are not included in the selection analysis.Many of the potential problems associated with the interpretation of selection on correlated characters can be ameliorated if the genetic variance-covariance structure of the traits in the population subject to selection is known. Unfortunately, few studies have simultaneously assayed selection gradients, heritabilities, and genetic correlations (but see Kelly 1992aKelly , 1993Campbell et al. 1994). Knowledge of heritabilities allows a prediction of whether the population will respond to selection. Moreover, low additive genetic coefficients of variation (Houle 1992) for characters that are subject to strong phenotypic selection can be interpreted as evidence that selection has eroded genetic variation. The existence of genetic correlations can explain the presence of significant additive genetic variance in the face of strong selection if they act as evolutionary constraints. Knowing both the pattern of phenotypic selection and genetic correlations can allow a much more insightful interpretation of the potential for an evolutionary response to indirect selection via selection on a genetically correlated trait (see Campbell et al. 1994).The study of life-history characters such as flowering time provides an ideal system to understand how selection acts on phenotypically and genetically correlated characters. The degree of flowering synchrony among individuals within a plant population could influence reproductive success by enhancing the ability of individual plants to attract pollinators if attraction is density dependent (Augspurger 1980(Augspurger , 1981Thomson 1980; but see Schemske 1980;Zimmerman 1980;Melampy 1987;Rodriguez-Robles et al. 1992). Plants flowering in synchrony will also have a greater number of potential mates. Thus, stabilizing selection should favor individuals exhibiting flowe...

Quantifying Evolutionary Genetic Constraints in the Ivyleaf Morning Glory,Ipomoea hederacea

“…Our study indicates that flowering time is an important trait in determining plant fitness: there was strong directional selection to flower early in both competition treatments, which is consistent with numerous other studies that have measured selection on flowering time (e.g., Schemske 1977;Zimmerman and Gross 1984;Stewart and Schoen 1987;Campbell 1991;O'Neil 1997). The likely mechanism behind this selection for early flowering is that we grew plants collected from North Carolina north of their range limit, where season-ending frosts are more common early in the season and at longer day lengths.…”

Adaptive Value of Phenological Traits in Stressful Environments: Predictions Based on Seed Production and Laboratory Natural Selection

“…In contrast to pre-anthesis traits, the adaptive value of post-anthesis traits has received less empirical attention [30], [31], [37], [58]. Differences in selection on post-anthesis traits in A. thaliana were detected between the two environmental stresses simulated in this study.…”

“…Natural variation for flowering has also been observed in selfing species suggesting that ecological factors, such as herbivory [32], pre-dispersal seed predation [31], [33], or seasonal variation in the likelihood of seed dispersion [23], may be selective agents that act on flowering. Often referred to as seed-fill duration in crop species [34], [35], [36], the duration of the reproductive period, i.e., the time elapsed from anthesis to the maturity of all fruits, is related to the number and quality of seeds [36], [37], [38], [39]. Seed number is often used as a proxy for female fitness and seed quality is known to influence seedling establishment [33], [40].…”

Whole Genome Duplication Affects Evolvability of Flowering Time in an Autotetraploid Plant

“…First, base populations were formed, comprising two individuals from each of 113 diploid maternal families collected in from field, 105 tetraploid maternal families collected in the field and 29 pairs of neotetraploid maternal families generated by crossing diploids that were converted to tetraploidy using colchicine (table 1). We choose to select for earlier flowering time because of the geographic distribution of cytotypes indicates the trait is ecologically relevant, because flowering time has be used in other work on autopolyploids [54], [55], and because it is practical for a selection experiment of this size. Selection early flowering time was chosen over selection for late flowering as late flowering is more likely to result from developmental abnormalities (i.e.…”