The Baldwin Effect and Genetic Assimilation: Revisiting Two Mechanisms of Evolutionary Change Mediated by Phenotypic Plasticity

Abstract

Two different, but related, evolutionary theories pertaining to phenotypic plasticity were proposed by James Mark Baldwin and Conrad Hal Waddington. Unfortunately, these theories are often confused with one another. Baldwin's notion of organic selection posits that plasticity influences whether an individual will survive in a new environment, thus dictating the course of future evolution. Heritable variations can then be selected upon to direct phenotypic evolution (i.e., "orthoplasy"). The combination of these two processes (organic selection and orthoplasy) is now commonly referred to as the "Baldwin effect." Alternately, Waddington's genetic assimilation is a process whereby an environmentally induced phenotype, or "acquired character," becomes canalized through selection acting upon the developmental system. Genetic accommodation is a modern term used to describe the process of heritable changes that occur in response to a novel induction. Genetic accommodation is a key component of the Baldwin effect, and genetic assimilation is a type of genetic accommodation. I here define both the Baldwin effect and genetic assimilation in terms of genetic accommodation, describe cases in which either should occur in nature, and propose that each could play a role in evolutionary diversification.

Evolved pesticide tolerance influences susceptibility to parasites in amphibians

“…Theory suggests that the evolution of pesticide tolerance can be achieved via two mechanisms: selection for constitutive tolerance over multiple generations or by inducing tolerance within a single generation via phenotypic plasticity (Cothran et al., 2013; Hua et al., 2015; Jansen et al., 2011). The evolution of constitutive tolerance is more likely when populations are in close proximity to agriculture (<200 m) and consistently exposed to pesticides (Crispo, 2007; Declerck et al., 2006). In contrast, inducible tolerance is more likely when populations are far from agriculture, infrequently exposed to pesticides, and there are costs of maintaining pesticide tolerance when pesticides are not present (i.e., phenotypic trade‐off; Crispo, 2007; Crispo et al., 2010).…”

“…The evolution of constitutive tolerance is more likely when populations are in close proximity to agriculture (<200 m) and consistently exposed to pesticides (Crispo, 2007; Declerck et al., 2006). In contrast, inducible tolerance is more likely when populations are far from agriculture, infrequently exposed to pesticides, and there are costs of maintaining pesticide tolerance when pesticides are not present (i.e., phenotypic trade‐off; Crispo, 2007; Crispo et al., 2010). While constitutive and inducible pesticide tolerance can improve survival following pesticide exposure, both mechanisms can alter how organisms interact with other community members (i.e., competition, predator–prey, host–parasite interactions; Gotthard & Nylin, 1995; Hanazato, 1995; McCarroll & Hemingway, 2002; Raberg, 2014).…”

Costly plastic morphological responses to predator specific odour cues in three-spined sticklebacks (Gasterosteus aculeatus)

“…Phenotypic plasticity, i.e., the ability of a single genotype to produce different phenotypes in response to environmental variation (see West-Eberhard 1989 for a review), may enable individuals to cope with new environmental challenges and thus might facilitate colonisation of new habitats and persistence under alternative ecological frameworks (Price et al 2003;Wund et al 2008). Phenotypic plasticity increases variability, on which selection can operate, possibly resulting in genetic assimilation, i.e., genetic changes in the same direction (Waddington 1942;Crispo 2007), eventually further reinforcing phenotypic differentiation (Pfennig et al 2010). Thus, plasticity might be an important prerequisite for genetic evolution: not only it represents a new source of variability, but it can be, itself, exposed to selection (Scheiner 1993;Schlichting and Pigliucci 1998;.…”

Epigenomic plasticity within populations: its evolutionary significance and potential

“…The extent and type of epigenetic variation determines how a trait will evolve . Generally, plasticity has been understood to facilitate phenotypic evolution, first by the simple means of allowing populations to survive long enough to adapt (the Baldwin effect (Crispo, 2007)), and second by canalisation, in which facultative plastic responses become obligate stages of development. Canalisation does not necessarily require any epigenetics in the modern sense, and could realistically be achieved solely through changes at the DNA sequence level, such as, for example, an alteration to a promoter sequence causing the constitutive expression of a previously developmentally regulated protein.…”