Evolutionary Modification in Clarkia. I. Selection for Hairlessness

Abstract

Plants of Clarkia unguiculata with moderate numbers of long hairs on the ovary and calyx were selected for relative “hairlessness” through 11 generations. Inbreeding depression, manifested as a high degree of sterility, necessitated co-selection for fertility. The proportion of fertile plants among families ranged from 0–50% in the 5th selected generation and increased to a range of 53–100% in the 10th selected generation. At the same time, the mean number of hairs on the ovary decreased from a range of 0.0–1.1 to a range of 0.0–0.2; and the mean number of hairs per sepal from 0.5–16.0 to 0.1–2.2. The percentage of plants per family with no hairs on the ovary and no hairs on the calyx increased from a range of 0–63 in the 5th selected generation to a range of 4–88 in the 10th selected generation. Nonselected progenies have long hairs on both ovary (mean 10–17) and sepals (mean 46–50) in all plants. The demonstrated response to selection has important implications regarding catastrophic selecion and the evolution of Clarkia species in marginal habitats.