Geographical variation in floral traits and pollination adaptation of floral color diversity of Primulina heterotricha (Gesneriaceae), an endemic species of Hainan Island, China

Hainan Island, as one of the global biodiversity hotspots, has its biodiversity concentrated in National Park of Hainan Tropical Rainforest. Primulina heterotricha, an endemic plant of Hainan Island, has a widespread distribution and consists of two floral color morphs: yellow-flowered and purple-flowered individuals. First, to clarify the differentiation pattern of floral traits among different geographical populations, we measured key floral traits including flower size, floral mouth width, and corolla tube length across various geographical populations, and analyzed the potential driving effect of geographical isolation on the differentiation of these floral traits. Second, focusing on the differentiation of two floral color morphs and the differences in pollination mechanisms, we comparatively analyzed the flowering dynamics of yellow-flowered and purple-flowered individuals, as well as flower-visiting insects and their visiting behaviors, to reveal the possible differences in pollination mechanisms between populations with different flower colors. A multivariate analysis of variance (MANOVA) revealed significant differences in floral traits among different geographical populations (P < 0.05), but geographical distance and altitude had no significant effect on floral traits. Populations with different floral colors also did not show significant difference in floral traits (P > 0.05). Moreover, at different flowering stages, there were no significant differences in stamen length, pistil length and herkogamy degree between the two floral color populations (P > 0.05), but the stigma gradually elongated and exceeded the position of the anthers as the flowering period progressed. Observations on flower-visiting insects indicated that the main flower-visiting insects of yellow-flowered populations were Amegilla leptocoma and A. yunnanensis, while the main flower-visiting insect of the purple-flowered populations was A. leptocoma. Thus, yellow-flowered individuals have a more generalized assemblage of flower visitors, whereas purple-flowered individuals exhibit a more specialized pollination system. This study investigated the differentiation pattern of floral traits among different geographical populations, floral color diversity and pollination adaptation process of P. heterotricha, and provides a scientific basis for biodiversity conservation and pollination service function assessment in National Park of Hainan Tropical Rainforest.