Experimental Sympatric Populations of Clarkia

Abstract

Clarkia lingulata is a tetrasomic derivative of C. biloba. The two species grow in adjacent colonies at the margin of distribution of the parental species. To compare their relative adaptedness when growing sympatrically, a mixture of seeds of the two species was sown in various natural habitats outside of the natural range. Populations in the driest sites died out rapidly whereas others persisted and reproduced. C. lingulata consistently matured about 2 weeks earlier than C. biloba. suggesting adaptation to a shorter growing season. This is in agreement with the recent expansion of the natural range of C. lingulata. C. lingulata was not more successful than C. biloba in the experimental populations because the initial frequency favored C. biloba. As a consequence of smaller numbers, the loss of effective gametes through formation of sterile hybrids was greater for C. lingulata than for C. biloba. The elimination of C. lingulata from experimental populations indicates that it must have been spatially isolated from C. biloba at its time of origin. The two species will not be able to grow in mixed color-nies, except temporarily, unless barriers to hybridization develop.