Growth in Artificial Climates‐‐An Indication of Mimulus' Ability to Invade New Habitats

Abstract

Minulus guttatus and its related species have adaptable genotypes that enabled each plant to grow in a wide range of climates. The growth of the clone members of the plants differed significantly from group to partially—overlapping group of climates. The group of optimal climates had moderate day temperatures with cool nights, high illumination, and long day photoperiods of 16 hr. Overall the plants grow optimally in a wide range of moderate climates, suboptimally in both cooler and warmer climates, and least well or not at all in the most extreme climates. A few variant plants (some 12%) flourished in the more extreme climates. Thus, at least some of the populations have enough variability as to the climates producing optimal or near—optimal growth that some of their members could invade new areas. Secondary peaks of optimal growth were produced by one—third of the plants. These optima occurred in climates significantly different from the ones in which the plants produced their primary peaks. In effect, some of the populations have members that are preadapted to invade new habitats. Interpopulation hybridization produced a high proportion of vigorous even heterotic F2 recombinants, of which many (25%) reproduced in more climates than either parent. Thus, interpopulation hybridization, were it to occur in nature, could substantially increase the amount of variability useful to the plants in invading regons with different climates. Many individual Minulus plants not only are variable but have, intrinsic to their genotype, wide climatic tolerance, often with additional growth optima that endow them with the capability of growing in new habitats already. The estimates of the ability to invade new habitats for populations made up of such individuals must be high. This evaluation is borne out by their success in invading three continents in the last century or so.