Fitness consequences of outcrossing in Impatiens capensis: tests of the frequency-dependent and sib-competition models

Abstract

Seedlings derived from cleistogamous (CL) and chasmogamous (CH) flowers were grown under competitive conditions while flanked by neighbors that were either related or unrelated. CH progeny sometimes expressed more phenotypic variability than CL progeny. In the greenhouse, CH progeny attained the same weight as CL progeny, and the relatedness of neighboring plants did not affect the growth of either type. In the field, CL and CH progeny performed similarly when grown with related competitors. However, CH progeny were somewhat larger when planted with nonsibs, while CL progeny were somewhat smaller under those conditions. Thus, there is no evidence that either frequency-dependent selection or the avoidance of competition among siblings favors the maintenance of outcrossing in this species. When females mate with one male (progeny are full sibs), selfed progeny are often more variable than outcrossed progeny. When females engage in both selfing and outcrossing, variation among progeny is frequently maximized at an intermediate selfing rate. The sib-competition mechanism, under a range of genetic models, is not apt to promote outcrossing, since selfed progeny are commonly more variable than outcrossed progeny. -from Authors