Study on the breeding system and floral color change of four Lonicera species in the Qinling mountains

We examined the floral biology, mating system, flower color change, and pollination process of Lonicera chrysantha Turcz., L. japonica Thunb., L. ferdinandii Franch. and L. maackii (Rupr.) Maxim. from the Qinling mountains via field observation, artificial pollination experiments, and artificial experimental patches. Pollen limitations and some differences in single-flower flowering and floral traits were observed among the species, which were all self-incompatible plants. Except for L. ferdinandii, all species changed their corolla color with decreasing pollen/nectar rewards and lost both male and female reproductive abilities. The nectar reward in L. ferdinandii did not alter significantly, and it retained strong female reproductive function. The retention of post-color change flowers might be a reproductive strategy of plants, in which an increase in floral display enhanced attractiveness to pollinators. The artificial control experiments showed that most pollinators preferred to visit the white flowers (pre-change flowers), and the amount of reward and number of yellow flowers (post-change flowers) significantly impacted pollinators' access frequency. That is, access frequency decreased with nectar reduction or increase in yellow flowers. These results indicate that flower color changes might increase plant attractiveness to distant pollinators, or have a certain influence on nearby pollinators. The post-change flowers might play a role in signaling to pollinators during their approach that the reward of nectar or pollen had changed, thus re-directing the insects to the sufficiently rewarded white flowers of homophyletic or heterologous plants. This could improve both the foraging efficiency of pollinators and reduce the chance of geitonogamy, which has important implications for the Lonicera species and their pollinators. These results show the reaction of plants and pollinators to long-term mutual adaptation.