Abstract
The coexistence of different color morphs is often attributed to variable selection pressures across space, time, morph frequencies, or selection agents, but the routes by which each morph is favored are rarely identified. In this study we investigated factors that influence floral color polymorphisms on a local scale in Protea, within which approximately 40% of species are polymorphic. Previous work shows that seed predators and reproductive differences likely contribute to maintaining polymorphism in four Protea species. We explored whether selection acts directly or indirectly on floral color in two populations of Protea aurea, using path analysis of pollinator behavior, nectar production, seed predation, color, morphology, and maternal fecundity fitness components. We found that avian pollinators spent more time on white morphs, likely due to nectar differences, but that this had no apparent consequences for fecundity. Instead, the number of flowers per inflorescence underpinned many of the reproductively important differences between color morphs. White morphs had more flowers per inflorescence, which itself was positively correlated with nectar production, seed predator occurrence, and total long-term seed production. The number of seeds per plant to survive predation, in contrast, was not directly associated with color or any other floral trait. Thus, although color differences may be associated with conflicting selection pressures, the selection appears to be associated with the number of flowers per inflorescence and its unmeasured correlates, rather than with inflorescence color itself.
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Acknowledgments
We thank C. Adams for assistance in the field and G. Anderson for editorial comments. T. Rebelo and L. Nurrish provided advice and logistical support in South Africa. This work was funded by National Science Foundation Grants DEB-0716622 and DEB-1046328. Data were collected under Cape Nature permits AAA005-00125-0028 and AAA005-00214-0028. The experiments reported comply with the current laws of the country in which they were performed. The authors declare that they have no conflict of interest.
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Carlson, J.E., Holsinger, K.E. Direct and indirect selection on floral pigmentation by pollinators and seed predators in a color polymorphic South African shrub. Oecologia 171, 905–919 (2013). https://doi.org/10.1007/s00442-012-2453-2
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DOI: https://doi.org/10.1007/s00442-012-2453-2