AOBPreview published online on October 12, 2007
Annals of Botany, doi:10.1093/aob/mcm254
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Ecological Context of Breeding System Variation: Sex, Size and Pollination in a (Predominantly) Gynodioecious Shrub
1 Estación Biológica de Doñana, Consejo Superior de Investigaciones Científicas (CSIC), Avenida de Maria Luisa s/n, E-41013 Sevilla, Spain
2 Department of Biology, University of Oulu, PO Box 3000, FIN-90014 Oulu, Finland
* For correspondence. E-mail conalo{at}ebd.csic.es
Received: 1 June 2007 Returned for revision: 3 August 2007 Accepted: 29 August 2007
Background and Aims: Species that exhibit among-population variation in breeding system are particularly suitable to study the importance of the ecological context for the stability and evolution of gender polymorphism. Geographical variation in breeding system and sex ratio of Daphne laureola (Thymelaeaceae) was examined and their association with environmental conditions, plant and floral display sizes, and pollination environment in a broad geographic scale was analysed.
Methods: The proportion of female and hermaphrodite individuals in 38 populations within the Iberian Peninsula was scored. Average local temperature and precipitation from these sites were obtained from interpolation models based on 30 years of data. Pollination success was estimated as stigmatic pollen loads, pollen tubes per ovule and the proportion of unfertilized flowers per individual in a sub-set of hermaphroditic and gynodioecious populations.
Key Results Daphne laureola: is predominantly gynodioecious, but hermaphroditic populations were found in northeastern and southwestern regions, characterized by higher temperatures and lower annual precipitation. In the gynodioecious populations, female plants were larger and bore more flowers than hermaphrodites. However, due to their lower pollination success, females did not consistently produce more seeds than hermaphrodites, which tends to negate a seed production advantage in D. laureola females. In the northeastern hermaphroditic populations, plants were smaller and produced 9–13 times fewer flowers than in the other Iberian regions, and thus presumably had a lower level of geitonogamous self-fertilization. However, in a few southern populations hermaphroditism was not associated with small plant size and low flower production.
Conclusions: The findings highlight that different mechanisms, including abiotic conditions and pollinator service, may account for breeding system variation within a species' distribution range and also suggest that geitonogamy may affect plant breeding system evolution.
Key words: Daphne laureola, environmental gradients, floral display, geographic variation, geitonogamy, gynodioecy, pollination success, sex ratio, Thymelaeaceae
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