COMPARATIVE EVOLUTION INMIMULUS GUTTATUSOF THE BONNEVILLE BASIN

Abstract

In western Utah, the basin of ancient Lake Bonneville with its surrounding mountains forms an excellent natural laboratory for investigations of dispersal and speciation (Durrant, 1952; Hubbs and Miller, 1948; Vickery and Lindsay, 1961). The Pleistocene to Recent geological history of the area reveals a succession of lakes that filled the valleys, and a series of glaciers that covered portions of the encircling mountains. At present the glaciers have completely melted except for a few permanent snow fields and the huge lake has evaporated to mere remnants, Utah Lake and the Great Salt Lake. One of the successful invaders of the available new areas is Mimulus guttatus Fischer, the common yellow monkey flower. Typically, its small, geographically isolated populations differ in their morphological and physiological traits. The populations have the appearance of being in various stages of evolutionary divergence. The purpose of our study is twofold: first, to determine whether the Mimulus populations are, in fact, becoming significantly differentiated one from another and second, if they are, to estimate and compare the relative rates of such evolutionary changes by means of the natural time clock provided by the recession of the lakes and glaciers from the present habitats of the monkey flowers.