Chapter 33 : The Evolution of Diversity and the Emergence of Rules Governing Phenotypic Evolution

Abstract:

Adaptive radiations are in fact commonplace; indeed, the vast majority of life’s diversity appears to have arisen through successive adaptive radiations, the most famous perhaps being the radiation that took place approximately 530 million years ago during the Cambrian period (the Cambrian radiation) and from which arose the major groups of complex animals. The author’s own interest in the emergence of diversity began with the common plant- and soil-colonizing bacterium Pseudomonas fluorescens and its propagation in unshaken test tubes (microcosms). Necessary to bring the study of evolution into line with advances in genetics and molecular biology is knowledge of the mutational origins of new phenotypes, and, critically, understanding of the connection between genotype and phenotype in sufficient detail so as to explain precisely why natural selection favors one type over another. Recent discovery of repeated molecular evolution—not just in laboratory populations of microbes but also in natural populations of insects and plants—has brought renewed interest to this possibility, but mechanistic insight of the hard-proof variety has been lacking. Indeed, the author’s recent work on the genetics of wrinkly spreader diversity provides evidence that genetic architecture does indeed contribute to the repeatability of evolution by biasing the molecular variation presented to selection. Among the most exciting of contemporary issues is genetic architecture—the genotype-to-phenotype map—and its influence on the evolution of populations. With the emergence of improved understanding of this map-its definition, its formulation, and the constraints it imposes-rules by which the outcome of phenotypic evolution might be predicted may just arise.