Flower color variation: A model for the experimental study of evolution

Abstract

We review the study of flower color polymorphisms in the morning glory as a model for the analysis of adaptation. The pathway involved in the determination of flower color phenotype is traced from the molecular and genetic levels to the phenotypic level. Many of the genes that determine the enzymatic components of flavonoid biosynthesis are redundant, but, despite this complexity, it is possible to associate discrete floral phenotypes with individual genes. An important finding is that almost all of the mutations that determine phenotypic differences are the result of transposon insertions. Thus, the flower color diversity seized on by early human domesticators of this plant is a consequence of the rich variety of mobile elements that reside in the morning glory genome. We then consider a long history of research aimed at uncovering the ecological fate of these various flower phenotypes in the southeastern U.S. A large body of work has shown that insect pollinators discriminate against white phenotypes when white flowers are rare in populations. Because the plant is selfcompatible, pollinator bias causes an increase in self-fertilization in white maternal plants, which should lead to an increase in the frequency of white genes, according to modifier gene theory. Studies of geographical distributions indicate other, as yet undiscovered, disadvantages associated with the white phenotype. The ultimate goal of connecting ecology to molecular genetics through the medium of phenotype is yet to be attained, but this approach may represent a model for analyzing the translation between these two levels of biological organization.flavonoid biosynthesis ͉ transposon ͉ spatial autocorrelation ͉ pollinator behavior ͉ morning glory T he study of adaptation is a problem that intersects all disciplines of biology. The study of adaptation is also among the most difficult and challenging areas of experimental research because a complete causal analysis of adaptation involves a translation between different levels of biological organization, the ecological, the phenotypic, and the molecular level (1). In this article we review more than 20 years of research on flower color polymorphisms in the common morning glory [Ipomoea purpurea (L.) Roth] that was aimed at exploring this interface.When the morning glory research program was initiated in the late 1970s, flower color polymorphisms appeared to be a natural starting point because (i) they represented simple discrete phenotypes that were susceptible to genetic analysis; (ii) a substantial body of work existed on the biochemistry of plant secondary metabolism; (iii) flower color was known to be important in insect pollinator behavior; and (iv) selection on reproductive performance should be among the most effective forms of selection, and, as a consequence, it should be the component of selection most likely to yield to experimental analysis. Virtually nothing was known in the late 1970s about the molecular biology of the genes that determine the anthocyanin pigments responsible for...

Saci-1, -2, and -3 and Perere, Four Novel Retrotransposons with High Transcriptional Activities from the Human Parasite Schistosoma mansoni

“…Transposable elements are regarded as one of the principal forces driving the evolution of eukaryotic genomes (7), since they are associated with the generation of phenotypic diversity (8,35) and speciation (42). Although regarded as a selfish DNA with negative impact on the host (7,60), transposons have been shown to contribute significantly to gene evolution (16,24,27,39).…”

Interval mapping for loci affecting unordered categorical traits

“…Generally, the variation in colors is controlled by many loci involved in the biosynthetic pathway of pigments, including flavonoid, anthocyanin and melanin (Clegg and Durbin, 2000;Klungland and Vage, 2000;McClean et al, 2002). The underlying genetics of pigmentation is so complex that understanding the genetic factors causing phenotypic variation is still incomplete, although molecular studies are now advancing for some species.…”

“…The variations in flower colors (Clegg and Durbin, 2000), coat patterns and colors of seeds (McClean et al, 2002) and coat colors of animals (Klungland and Vage, 2000) are typical examples for unordered categorical traits. Moreover, scores obtained by the sensory test for eating qualities of fruits or meats, which are composite traits affected by many constituent biochemical attributes, cannot be described by a simple quantitative genetic model, thus, should be regarded as unordered categorical traits, although the scores may be ordered according to the evaluation of flavors, textures and so on, and have been analyzed with a method based on the conventional linear model (King et al, 2000;Causse et al, 2001Causse et al, , 2002.…”

A sex-linked allele, autosomal modifiers and temperature-dependence appear to regulate melanism in male mosquitofish (Gambusia holbrooki)

“…Some transposons are TS, alter pigmentation (Epperson and Clegg, 1987) and cause multiple changes in biochemical pathways (e.g. Clegg and Durbin, 2000). Helitrons are transposons found in the sex-determining region of the sex chromosomes of platyfish (Xiphophorus maculatus) and are posited to play a role in sex chromosome evolution (Zhou et al, 2006).…”