Polyploidy and Novelty in Flowering Plants

The role of polyploidy per se in the development of evolutionary novelty remains one of the outstanding questions in flowering plant evolution. Since chromosome doubling usually is associated with hybridization, the effects of doubling are difficult to uncouple from those of hybridity and recombination. Synthetic polyploids in crops typically are inferior to their diploid counterparts under conditions to which the diploids are adapted. This observation has suggested to many that chromosome doubling is a hindrance to progressive evolution. Evidence is presented herein from biochemical, physiological, developmental, and genetical sources which indicates that the nucleotypic effects of chromosome doubling are not necessarily negative. Indeed chromosome doubling may "propel" a population in to a new adaptive sphere, and render it capable of occupying habitats beyond the limits of its diploid progenitor. This postulate is consistent with what we know of the ecological tolerances of diploids and related polyploids. As the establishment of a polyploid subpopulation may occur within a short time span, chromosome doubling may bring about abrupt, transgressive, and conspicuous changes in the adaptive gestalt of populations within microevolutionary time.