Primula alpicola is a typical distylous perennial herb and a good material to study floral adaptation and evolution. Different natural selection patterns on floral traits have been documented between tow morphs of Primula poissonii. However, the roles of pollinators and predators in natural selection have not been tested in distylous species. In addition, seasonal change of pollinators and predators may affect the natural selection on flowering phenology.
Researchers from XIshuangbanna Tropical Botanical Garden (XTBG) experimentally assessed phenotypic selection on floral traits mediated by pollinators in distylous P. alpicola in the Eastern Himalayan region. They quantified phenotypic selection on traits, including flowering phenology and aspects of floral display via female fitness.
The researchers also compared the phenotypic selection gradients in open-pollinated and hand-pollinated plants, in order to determine the role of pollinators in generating selection effects on floral traits。
The study population is located in the Sejila (Sygera) Mountains in a typical valley on the northwestern side of the Yarlung Zangbo River (the upper, Tibetan, section of the Brahmaputra).
The study demonstrates that the pollinators contribute to selection via female fitness on flowering phenology and floral display in the inter-morph pollination distylous perennial herb P. alpicola.
Pollinators mediated directional selection favors late flowering, and correlational selection favors many flowers combined with short scape, that maybe attribute to stronger pollen limitation in the early season and resource tradeoff between pollinators’ attraction and flower production.
They used path analysis and structural equation modeling (SEM) to examine how herbivores affected the relationship between floral traits and female fitness, but no significant selection was caused by seed predators.
The results suggest pollinators, not herbivores maybe the significant agent of selection on flora traits.