Neither vegetative nor reproductive advantages account for high frequency of male-steriles in southern Spanish gynodioecious Daphne laureola (Thymelaeaceae).
In gynodioecious species, male-steriles (termed "females" hereafter) usually exhibit some reproductive advantage over hermaphrodites that allow them to compensate for the loss of male reproductive function. This compensation can result from higher fecundity, vegetative outperformance, and/or lower inbreeding depression. In this study we compared vegetative and reproductive parameters of female and hermaphrodite Daphne laureola individuals in two southeastern Spanish populations and estimated the magnitude of inbreeding depression up to the seedling emergence stage by conducting controlled pollinations and experimental sowings of seed progenies in the field. Reproductive shrubs of both sexes did not differ significantly in size, leaf production, leaf size, leaf growth, nutrient allocation to leaves, and production of flowers and fruits. Seed set and seed size of cross- and self-pollinated flowers of hermaphrodites and cross-pollinated females were also similar. Seedling emergence rates of self- and cross-pollinated seeds from hermaphrodites under natural field conditions were similar, suggesting a minor role of inbreeding depression up to that reproductive stage. Seeds from females produced more seedlings than selfed seeds from hermaphrodites. In 21 populations surveyed in the study region over a broad geographical and elevational gradient, the proportion of females ranged between 20.6 and 56.1% and was inversely related to elevation. The establishment and maintenance of females in southeastern Spanish populations of D. laureola seem to be mainly mediated by ecological factors.
Alonso
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Estación Biológica de Doñana, Consejo Superior de Investigaciones Científicas, Apartado 1056, E-41080 Sevilla, Spain.
Herrera
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