The theory of facilitated variation

ArticleinProceedings of the National Academy of Sciences 104 Suppl 1(Suppl 1):8582-9 · June 2007with14 Reads
DOI: 10.1073/pnas.0701035104 · Source: PubMed
This theory concerns the means by which animals generate phenotypic variation from genetic change. Most anatomical and physiological traits that have evolved since the Cambrian are, we propose, the result of regulatory changes in the usage of various members of a large set of conserved core components that function in development and physiology. Genetic change of the DNA sequences for regulatory elements of DNA, RNAs, and proteins leads to heritable regulatory change, which specifies new combinations of core components, operating in new amounts and states at new times and places in the animal. These new configurations of components comprise new traits. The number and kinds of regulatory changes needed for viable phenotypic variation are determined by the properties of the developmental and physiological processes in which core components serve, in particular by the processes' modularity, robustness, adaptability, capacity to engage in weak regulatory linkage, and exploratory behavior. These properties reduce the number of regulatory changes needed to generate viable selectable phenotypic variation, increase the variety of regulatory targets, reduce the lethality of genetic change, and increase the amount of genetic variation retained by a population. By such reductions and increases, the conserved core processes facilitate the generation of phenotypic variation, which selection thereafter converts to evolutionary and genetic change in the population. Thus, we call it a theory of facilitated phenotypic variation.
    • "Further characterization of the precise regulation of wing patterning by Wnt signaling is necessary to elucidate potential links between wing shape and pigmentation. Both modularity and plasticity have been theorized to promote morphological diversification [4,[51][52][53]. Our findings suggest that wing patterns are highly robust and are therefore likely to exhibit limited variability in nature. "
    [Show abstract] [Hide abstract] ABSTRACT: Background: Organisms develop and evolve in a modular fashion, but how individual modules interact with the environment remains poorly understood. Phenotypically plastic traits are often under selection, and studies are needed to address how traits respond to the environment in a modular fashion. In this study, tissue-specific plasticity of melanic spots was examined in the large milkweed bug, Oncopeltus fasciatus. Results: Although the size of the abdominal melanic bands varied according to rearing temperatures, wing melanic bands were more robust. To explore the regulation of abdominal pigmentation plasticity, candidate genes involved in abdominal melanic spot patterning and biosynthesis of melanin were analyzed. While the knockdown of dopa decarboxylase (Ddc) led to lighter pigmentation in both the wings and the abdomen, the shape of the melanic elements remained unaffected. Although the knockdown of Abdominal-B (Abd-B) partially phenocopied the low-temperature phenotype, the abdominal bands were still sensitive to temperature shifts. These observations suggest that regulators downstream of Abd-B but upstream of DDC are responsible for the temperature response of the abdomen. Ablation of wings led to the regeneration of a smaller wing with reduced melanic bands that were shifted proximally. In addition, the knockdown of the Wnt signaling nuclear effector genes, armadillo 1 and armadillo 2, altered both the melanic bands and the wing shape. Thus, the pleiotropic effects of Wnt signaling may constrain the amount of plasticity in wing melanic bands. Conclusions: We propose that when traits are regulated by distinct pre-patterning mechanisms, they can respond to the environment in a modular fashion, whereas when the environment impacts developmental regulators that are shared between different modules, phenotypic plasticity can manifest as a developmentally integrated system.
    Full-text · Article · Dec 2016
    • "Only a small proportion of theoretically possible changes seemed to be realized in phenotypic evolution and diversification , with some outcomes appearing recurrently whereas others are seemingly forbidden [1][2][3][4][5] . Such determinism and predictability of phenotypic outcomes is surprising considering the dimensionality of the genome, the proteome, and the developmental dynamics linking them and point to the existence of constraints in phenotypic variation. "
    [Show abstract] [Hide abstract] ABSTRACT: Background Recurrence and predictability of evolution are thought to reflect the correspondence between genomic and phenotypic dimensions of organisms, and the connectivity in deterministic networks within these dimensions. Direct examination of the correspondence between opportunities for diversification imbedded in such networks and realized diversity is illuminating, but is empirically challenging because both the deterministic networks and phenotypic diversity are modified in the course of evolution. Here we overcome this problem by directly comparing the structure of a “global” carotenoid network – comprising of all known enzymatic reactions among naturally occurring carotenoids – with the patterns of evolutionary diversification in carotenoid-producing metabolic networks utilized by birds. ResultsWe found that phenotypic diversification in carotenoid networks across 250 species was closely associated with enzymatic connectivity of the underlying biochemical network – compounds with greater connectivity occurred the most frequently across species and were the hotspots of metabolic pathway diversification. In contrast, we found no evidence for diversification along the metabolic pathways, corroborating findings that the utilization of the global carotenoid network was not strongly influenced by history in avian evolution. Conclusions The finding that the diversification in species-specific carotenoid networks is qualitatively predictable from the connectivity of the underlying enzymatic network points to significant structural determinism in phenotypic evolution.
    Full-text · Article · Aug 2016
    • "Mangold discovered this phenomenon in 1924. In embryonic induction, " a small group of cells, the " organizer, " induces the development of the central nervous system in nearby cells of the rest of the vertebrate embryo " (Kirschner and Gerhart, 2007). It was thought at first that the organizer provided " detailed instructions " to the responding cells, but later it was found that a variety of agents could, in fact, induce development. "
    [Show abstract] [Hide abstract] ABSTRACT: These narratives accompany the PowerPoint presentation titled "E. E. Just's Broad (and Hidden) Influence on the Development of Modern Biology," given on June 17, 2016, in Woods Hole, Massachusetts.
    Full-text · Dataset · Jul 2016 · BMC Evolutionary Biology
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