Sex-ratio variation in the gynodioecious shrub Gnidia wikstroemiana (Thymelaeaceae)

Abstract: The determination of sex-ratio variation is a useful guide for identifying models of sex-ratio evolution in gynodioecious species. This study counted the numbers of female and hermaphrodite plants in five populations of the gynodioecious shrub Gnidia wikstroemiana distributed over 2.3° of latitude in dry, highland shrublands and grasslands of South Africa. Population sizes ranged from 71 to 435 plants with populations occurring on diverse rocky terrains along a 422-m altitudinal gradient. Female frequencies varied from 35 to 47% but sex-ratios did not differ significantly among the five populations. However, sex-ratios in three populations occurring on ridge slopes deviated significantly from the 1:1 ratio while those populations located on the crests of mountains did not. These results suggest that both nuclear gynodioecy and subdioecy are involved in the sex-ratio evolution of this species. [Copyright &y& Elsevier]