Botany | Ecology and Evolutionary Biology | Evolution
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 untangle the interactions and trait pleiotropisms that influence floral color polymorphisms on a local scale in Protea, within which ~40% of species are polymorphic. Previous work shows that seed predators and reproductive differences likely influence polymorphism maintenance in four Protea species. Here, we explore whether selection acts on floral color directly or indirectly in Protea aurea, using path analysis of pollinator behavior, nectar production, seed predation, color, morphology, and fitness measures. We found that avian pollinators spent more time on white morphs, likely due to nectar differences, but this had no apparent consequences for fecundity. Instead, a single continuous trait underpinned many of the reproductively-important differences between color morphs: the number of flowers per flowerhead. This trait differed between color morphs (white had more), and it was also positively correlated with nectar, seed predation, and fecundity independent of predation. Realized fecundity, in contrast, was not directly associated with color or any other floral trait, although it covaried with leaf chlorophyll content, which was higher in white morphs. Thus, although conflicting selection via predation and higher reproductive potential may promote color polymorphism in Protea aurea, the phenotypes targeted by selection are more strongly associated with the number of flowers per head, leaf chlorophyll content, and their unmeasured correlates, rather than with flowerhead color itself.
Carlson, Jane E. and Holsinger, Kent E., "Direct and indirect selection on floral pigmentation by pollinators and seed predators in a color polymorphic South African shrub" (2013). EEB Articles. 31.