Flower Colour Polymorphism inGeranium nepalense(Geraniaceae): Adaptation to Non-Pollinator Agents

Abstract

Flower colour polymorphism is attributed to pollinator or non-pollinator mediated selection. Geranium nepalense has common white morph and very rare pink morph. We compared pollinator visitation frequencies, temperature and soil moisture between two morphs in the mixed morph population. We also compared morph ratio and reproductive success between white and pink flower individuals. Our results indicated that no visitor groups were different between two colour morphs. But visitor groups differed in visits between two years. Halictidae preferred pink morph in the year of 2012 but showed no discrimination in 2014, whereas Syrphidae preferred white morph in 2014 but no discrimination in 2012. Overall, pink morph produced more seeds than white morph, but exhibited variation between two years. However, visitor discrimination was not the main cause of the difference in female fitness. Soil moisture was not different between two colour morphs. Temperature of white morph was lower than pink in evening but not different in morning and noon. The results indicated that non-pollinator factors may exert the selective pressure to maintain the flower colour polymorphism in this species. Although pollinators did not exert selection on the flower colour polymorphism, we suggest that they provided potential pollination environment of fluctuating selection to drive flower colour evolution if visitors were limited.