• Massimo Pigliucci

      Articles written in Journal of Genetics

    • Modelling phenotypic plasticity. I. Linear and higher-order effects of dominance, drift, environmental frequency and selection on a one-locus, two-allele model

      Massimo Pigliucci

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      The evolutionary dynamics of dominance, drift, selection and probability of environmental change is explored in the case of a single-locus two-allele model for the genetic control of phenotypic plasticity. The model represents a situation similar to the real case of the pennant/vestigial phenotype inDrosophila melanogaster. The aim of the simulation is to analyse the contribution of the four factors, of their quadratic effects, and of the two-way interactions on the equilibrium frequencies of the two alleles and on the genotypic constitution of the population. Selection turned out to be the only factor whose linear component significantly affects the system (73% of the variance explained); on the other hand, the cumulative effect of the nonlinear terms is strong (20% of the variance), and most of the interactions are highly significant. Some counter-intuitive effects of the interaction between selection and dominance or selection and frequency of the two environments are shown by means of contour plots from a multidimensional regression surface analysis. An interesting outcome is that plasticity can be favoured in a homogeneous environment, and it is selected against in one particular case of environmental heterogeneity: when two environments are equally likely to occur.

    • Mutational effects on constraints on character evolution and phenotypic plasticity inArabidopsis thaliana

      Massimo Pigliucci Gaines A. Tyler Carl D. Schlichting

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      Although the concept of genetic constraints plays an important role in our understanding of the evolution of natural populations, there are still few empirical investigations probing the nature and limits of constraints in plant and animal species, aside from some studies inDrosophila. In the work reported here, we use an induced mutation - artificial selection protocol to analyse constraints on character means and phenotypic plasticity to nutrients inArabidopsis thaliana, an annual crucifer. We induced point mutations in a highly inbred line characterized by an extreme phenotype (very fast life cycle, early flowering, reduced leaf production) and little plasticity. We then selected individuals with increased leaf numbers. The goals were to determine if: (i) it is possible to increase leaf production; (ii) this has an effect on reproductive fitness; (iii) a mutation-selection process simultaneously alters the environmental insensitivity of the plant, thereby allowing phenotypic plasticity; and (iv) changes in the target trait affect other characters or their plasticities. The results demonstrate that: (a) mutations do increase leaf number; (b) this yields a much higher reproductive fitness, owing to the extension of the very short life cycle of the base inbred line; (c) there are no changes in plasticity of leaf number or of any other trait, possibly because few loci are involved in the control of plasticity; (d) changes in leaf number are related to alterations in three other traits comprising a strong set of covarying characters inA. thaliana. Two uncorrelated traits are capable of independent evolution from the constrained set. We therefore suggest that environmentally insensitive ecotypes of A.thaliana can quickly evolve to form ecologically specialized, relatively environmentally invariant genotypes.

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