Reply from M. Pigliucci and J. Kaplan.
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Journal Article↗
Biomedical subjects
M Pigliucci
Publications and source records attributed to M Pigliucci.
Developmental phenotypic plasticity: where internal programming meets the external environment.
Developmental plasticity has long been the focus of research in both evolutionary ecology and molecular genetics. Recently, the concept of ontogenetic contingency has been proposed to indicate the dependence of plastic responses on the timing and sequence of developmental events. Also, the idea of the developmental reaction norm has been put forward to indicate the complex interactions among development, phenotypic plasticity, and allometry of different structures. Finally, for the first time, studies ranging from the ecological to the molecular aspects of the same plastic response are available on insect and flowering plant model systems.
Biological Evolution↗
Developmental phenotypic plasticity: where ecology and evolution meet molecular biology.
The plastic response of phenotypic traits to environmental change is a common research focus in several disciplines-from ecology and evolutionary biology to physiology and molecular genetics. The use of model systems such as the flowering plant Arabidopsis thaliana has facilitated a dialogue between developmental biologists asking how plasticity is controlled (proximate causes) and organismal biologists asking why plasticity exists (ultimate causes). Researchers studying ultimate causes and consequences are increasingly compelled to reject simplistic, 'black box' models, while those studying proximate causes and mechanisms are increasingly obliged to subject their interpretations to ecological 'reality checks.' We review the successful multidisciplinary efforts to understand the phytochrome-mediated shade-avoidance and light-seeking responses of flowering plants as a pertinent example of convergence between evolutionary and molecular biology. In this example, the two-way exchange between reductionist and holist camps has been essential to rapid and sustained progress. This should serve as a model for future collaborative efforts towards understanding the responses of organisms to their constantly changing environments.
Arabidopsis↗
Modelling phenotypic plasticity. II. Do genetic correlations matter?
Predictions of the evolutionary trajectory of reaction norms and interpretation of empirical results are usually based on two mathematically equivalent ways of partitioning phenotypic variance into its genetic, environmental, and interaction components: the genotype by environment interaction estimated by means of an analysis of variance, or the interenvironment genetic correlation (i.e. the genetic correlation between the expressions of the same trait in two environments). Both these quantities are supposed to indicate the amount of genetic variability for plasticity in natural population. I point out that not only are the qualitative predictions based on these statistical methods sometimes in conflict with each other, but that both may fail to predict rates of evolution and equilibria under some circumstances, because they ignore the details of the genetic machinery. It is shown that, ultimately, the only way to predict reliably the evolution of plasticity is actually to know its specific genetic basis and the genotypic constitution of the population, however inconvenient this may be from both theoretical and empirical standpoints. The discussion is framed in terms of a simple one-locus two-allele model that mimics the real case of the pennant/vestigial system describing plasticity of wing length to temperature in Drosophila melanogaster.
Alleles↗
Reaction norms of Arabidopsis IV. Relationships between plasticity and fitness.
The study of the association between fitness and reaction norms is of primary importance given the hypothesized role for phenotypic plasticity in shaping evolutionary patterns: in microevolution, as one of mechanism for maintaining genetic variation, and in macroevolution, as a means of generating phenotypic novelties. In a glasshouse experiment, we investigated variation in reaction norms to nutrient availability in populations of Arabidopsis thaliana, and the relationship between this variation and reproductive fitness. We found evidence for across-treatment directional selection on the means for leaf number, flowering time, plant height, branching and growth rate; across-treatment stabilizing selection was detected for growth rate; and across-treatment disruptive selection was significant for leaf number. We also uncovered selection on the plasticity of some traits: directional for the plasticity of branching, and stabilizing for the plasticity of both branching and growth rate. When the two environments were considered separately, directional selection for height was detected under low nutrients; under high nutrients, we found evidence for directional selection on leaf number and height, and for disruptive selection on flowering time. The genetic correlation between a trait's expression in one environment and its expression in the alternate environment was positive and highly significant only for flowering time and growth rate. A principle components analysis revealed possible constraints on future selection responses, because of correlations among character means and among character plasticities.
Analysis of Variance↗
Geographical patterns of karyotype polymorphism in Italian populations of Ornithogalum montanum (Liliaceae).
The geographical patterns of quinacrine banding polymorphism at 20 sites, and of numbers of accessory (B) chromosomes, were studied in nine Italian populations of Ornithogalum montanum Cyr. ex Ten. (Liliaceae). Eight banding sites appear monomorphic. The standardized gene frequency variance, Fst, is heterogeneous among the remaining 12 sites; variation is greatest for four polymorphisms whose frequency is correlated with the winter temperature of the localities studied. A strong negative association is apparent between numbers of B chromosomes and Q bands. Spatial autocorrelation shows three distinct modes of geographical variation: (i) random distributions; (ii) patterns with positive short-range autocorrelation; (iii) patterns with negative intermediate-range autocorrelation. Some microevolutionary implications of these findings are discussed.
Biological Evolution↗