Different Morphs of Heterostylous Plant (Tirpitzia Sinensis) Associated With Floral Characters Have Various Adaptation Strategies to Pollinator to Ensure Reproductive Success

Abstract Background: Heterostylous plants are commonly associated with pollinators promoting disassortative pollination. How different morphs adapt to pollinators to ensure reproductive success and whether floral characters (such as pistil, stamen and nectar traits) are relevant to this process remain unclear. Results: Tirpitzia sinensis is distylous flowers. Its floral characters were measured. Field observation of effective pollinator and pollination efficiency to different morphs was conducted, and breeding systems were examined by hand pollination treatments. Our results showed that L-morph produced more but smaller pollen grains per anther than S-morph. T. sinensis secreted more nectar at night as a possible adaptation to hawkmoths (Macroglossum spp.) active at dusk. L-morph produced much nectar due to its large secretion volume at night. The nectar was rich in sucrose. The sucrose/hexose ratio was higher in the nectar of S-morph than in that of L-morph. S-morph had higher visit rate but lower pollination efficiency of hawkmoths compared with L-morph. T. sinensis was self-incompatible. Seed sets in nature did not differ between morphs. Conclusions: Our findings suggest that L-morph increases its pollination efficiency through outstanding stigma, many pollen grains per anther, and high amount of nectar. S-morph attracts many hawkmoths to pollinate due to its high sucrose/hexose ratio in its nectar.