Last Updated: November 2, 2005

 

Introduction:

Phenotypic Plasticity can be defined as the property of a genotype to produce different phenotypes when exposed to different environments. Phenotypic Plasticity can occur in the morphology and behavior of organisms.1

Phenotype can be defined as the actual physical characteristics of an organism. Ie. Color, behavior, shape, etc.

Genotype can be defined as all of the genetic material inside an organism’s genome.

Phenotypic Evolution: A Reaction Norm Perspective

Carl D. Schlichting, University of Connecticut, and Massimo Pigliucci, SUNY-Stony Brook
Publication Date: 1998
340 pages, 180 illustrations
paper

About This Title:

" Understanding the process of adaptive evolution of phenotypes is a fundamental problem in evolutionary biology. It has been approached from the point of view of population and quantitative genetics, optimality theory, or developmental biology. In the last decade, there has been an explosion of research on phenotypic plasticity (the environmentally induced production of different phenotypes by a single genotype) as well as on the molecular details of development, reflecting the increased recognition of their importance in shaping phenotypic evolution. However, the “hardening” of the neodarwinian synthesis in the ’40s led to the largely independent investigation of genetic, developmental and environmental bases of phenotypic expression. As a result, these different perspectives have not been integrated into a satisfying cohesive view of phenotypic evolution.

Phenotypic Evolution explicitly recognizes organisms as complex genetic-epigenetic systems developing in response to changing internal and external environments. As a key to a better understanding of how phenotypes evolve, the authors have developed a framework that centers on the concept of the Developmental Reaction Norm. This encompasses their views: (1) that organisms are better considered as integrated units than as disconnected parts (allometry and phenotypic integration); (2) that an understanding of ontogeny is vital for evaluating evolution of adult forms (ontogenetic trajectories, epigenetics, and constraints); and (3) that environmental heterogeneity is ubiquitous and must be acknowledged for its pervasive role in phenotypic expression."

Significance of Phenotypic Plasticity:

Dr. Lee Spetner wrote:

• “A change in phenotype in the fossil record is recognized as evolution. There is no way to tell from the fossils whether the observed changes in continuous records were caused by variation appearing in the genotype or only in the phenotype” (NBC:196).

In other words, it is impossible to deduce whether or not apparent transitional features of a fossil are truly the results of changes in the genotype (i.e. random mutations) or are merely the results of specific organisms adapting to their different environments as a result of phenotypic plasticity.

Also, the phenomenon of phenotypic plasticity is what one would expect to find if an intelligent Creator were responsible for the existence of life on earth.

Examples of Phenotypic Plasticity:

1. Induced defenses in response to an invading crab predator: An explanation of historical and geographic phenotypic change

Vol. 97, Issue 5, 2123-2127, February 29, 2000

Evolution

Geoffrey C. Trussell*, and L. David Smith
* School of Marine Science, College of William and Mary, Gloucester Point, VA 23062; and Marine Science Center, Northeastern University, Nahant, MA 01908
Edited by Robert T. Paine, University of Washington, Seattle, WA, and approved December 22, 1999 (received for review October 1, 1999)

Abstract:

“The expression of defensive morphologies in prey often is correlated with predator abundance or diversity over a range of temporal and spatial scales. These patterns are assumed to reflect natural selection via differential predation on genetically determined, fixed phenotypes. Phenotypic variation, however, also can reflect within-generation developmental responses to environmental cues (phenotypic plasticity). For example, water-borne effluents from predators can induce the production of defensive morphologies in many prey taxa. This phenomenon, however, has been examined only on narrow scales. Here, we demonstrate adaptive phenotypic plasticity in prey from geographically separated populations that were reared in the presence of an introduced predator. Marine snails exposed to predatory crab effluent in the field increased shell thickness rapidly compared with controls. Induced changes were comparable to (i) historical transitions in thickness previously attributed to selection by the invading predator and (ii) present-day clinal variation predicted from water temperature differences. Thus, predator-induced phenotypic plasticity may explain broad-scale geographic and temporal phenotypic variation. If inducible defenses are heritable, then selection on the reaction norm may influence coevolution between predator and prey. Trade-offs may explain why inducible rather than constitutive defenses have evolved in several gastropod species.”

 

2. Phenotypic Plasticity in the lower pharyngeal jaw dentition of astaoreochromis allaudi (teleostei cichlidae)

A. Huysseune

Instituut voor Dierkunde, Universiteit Gent, Ledeganckstraat 35, B-9000, Gent, Belgium

Accepted 13 June 1995. ; Available online 10 March 2000.