Phenotypic plasticity in development and evolution: facts and concepts. Introduction

Abstract

This theme issue pursues an exploration of the potential of taking into account the environmental sensitivity of development to explaining the evolution of metazoan life cycles, with special focus on complex life cycles and the role of developmental plasticity. The evolution of switches between alternative phenotypes as a response to different environmental cues and the evolution of the control of the temporal expression of alternative phenotypes within an organism's life cycle are here treated together as different dimensions of the complex relationships between genotype and phenotype, fostering the emergence of a more general and comprehensive picture of phenotypic evolution through a quite diverse sample of case studies. This introductory article reviews fundamental facts and concepts about phenotypic plasticity, adopting the most authoritative terminology in use in the current literature. The main topics are types and components of phenotypic variation, the evolution of organismal traits through plasticity, the origin and evolution of phenotypic plasticity and its adaptive value.

Figure 1.

Schematic representation of the reaction norms for three characters (A–C): A and B are plastic (plastic reaction norm), whereas C is a non-plastic character (non-plastic reaction norm). A is a polyphenic character, while C is monophenic.

Figure 2.

Schematic representation of possible direction of evolutionary change in phenotypic variation with respect to environmental sensitivity. Lines represent the reaction norms of target phenotypes (see text) and circles show the variation around the target phenotype. With respect to the central panel, the left panel depicts a situation with a higher developmental homeostasis, while the right panel depicts a situation with a higher environmental canalization (modified from Nijhout & Davidowitz 2003).