Floral Traits And Pollination Adaptation In Species Of Epimedium (Berberidaceae)

China is the modern geographical distribution center of Epimedium and hosts approximately80%of species in this genus. Few interspecific differences and many intraspecies varation make it particularly difficult in taxonomy and phylogeny. It is necessary to use better methods in analyses the system and evolution of Epimedium. Some floral traits obviously varied among species, which provided an ideal study system to explore the adaptation of floral traits in Epimedium. We aimed at several important and typical floral traits combined with pollination systems and reproductive success, and used a comparative study in several related species to investigate the evolutionary adaptation of floral traits.To explore the difference of floral traits and pollinator types among species, we conducted measurement of floral traits and pollination observation in seven Epimedium species. Results showed that these species had similar flower morphology, and also some difference in floral traits among species. The species were pollinated by bumblebees and honyebes. Except for E. sutchuenense, bumblebees were the main effective pollinators in other six species. The interspecies difference in pollinator types mainly depended on whether honeybees were as pollinators. So it is necessary to comprehensively explore the cause of pollinator difference among plant species. We observed that there was a positive relationship between pollen number and ovule number among species. The experiments of artificial pollination and pollen tube competition showed that all species were high self-incompatibility, and there was an obvious barrier in the growth of self-pollen tubes in each species.Pollen presentation theory (PPT) predicts that plant species typically pollinated by frequent and wasteful pollinators ought to be much more parsimonious and only gradually release pollen compared to plant species pollinated by infrequent pollinators that are efficient at delivering the pollen they remove. To test PPT, we compare the pollen presentation schedules and pollination systems in three related Epimedium species, having different pollinators. Results showed that differences in anther dehiscence and flowering traits resulted in different pollen packaging schedules. For E. sutchuenense and E. franchetii, a special’roll-up’movement of the anther wall during anther dehiscence increased pollen removal compared to the dehiscence pattern in E. mikinorii, which lacked the’roll-up’movement. Investigations revealed that honeybees had a higher pollen removal rate and lower stigmatic pollen load compared to bumblebees. In accordance with PPT, E. sulchuenense presents pollen sequentially and slowly for the frequent and wasteful honeybees. In comparison to E. sutchuenense, E. franchelii had a faster presentation rate and was adapted to the efficient and infrequent bumblebees. However, E. mikinorii was pollinated by both bumblebees and honeybees at high frequency and had the fastest pollen presentation. This pattern could reduce pollen wastage by honeybees and might be an adaptation to its short flower longevity (less than1day), to increase the chances of pollen deposition on stigmas. The study revealed the evolutionary and ecological adaptation of pollen presentation schedules in the three Epimedium species. And also indicates that pollen presentation schedules can be a consequence of interactions among anther dehiscence, flowering traits and pollination environments for a given species.Self-interference is one of the most important selective forces in shaping floral evolution. Herkogamy and dichogamy can both achieve reductions in the extent of self-interference, but they may have different roles in minimizing self-interference in a single species. Varying degrees of herkogamy and dichogamy can be commonly observed in Epimedium with self-incompatibility in the field. Four Epimedium species endemic to China were selected to explore the roles of herkogamy and dichogamy in avoiding self-interference. We sought to test the hypothesis that in the genus, herkogamy and dichogamy might be separated and become selected preferentially. We observed that two species (E.franchetii and E. mikinorii) expressed strong herkogamy and weak protogyny (adichogamy) while another two species (E. sutchuenense and E. leptorrhizum) expressed slight herkogamy and partial protandry. Field investigations indicated that there was no physical self-interference between male function and female function regarding pollen removal and pollen deposition in all species. Self-pollination (autonomous or facilitated) was greater in species with slight herkogamy than those with strong herkogamy. Artificial pollination treatments revealed that self-pollination could reduce out-crossed female fertility in all species, and we found evidence that self-interference reduced seed set in E. sutchuenense and E. leptorrhizum in the field, but not in E. franchetii and E. mikinorii. These results indicate that well-developed herkogamy is more effective compared to dichogamy in avoiding self-interference in the four species. In genus Epimedium, herkogamy instead of dichogamy should be selected preferentially and evolved as an effective mechanism of avoiding self-interference and might not need to evolve linked with dichogamy. Our field surveys and pollination observation of two sympatry Epimedium species showed that all populations of E. sutchuenense were exclusively pollinated by honeybee, and one population of E. franchetii was pollinated by bumblebee, but honeybees were the main pollinators in another population of E. franchetii which was near many introduced honey hives. We selected three pupolations of E. sutchuenense and the two distinct populations of E. franchetii as our objects. We comprehensively compared the floral characteristics, pollination frequency, pollination efficiency and reproductive success to explore the effect of honeybee on the pollination ecology in the two Epimedium species. Our results showed that there was no difference of floral characteristics amony species and populations. Considering the habitat of pupolations, we infered that human beekeeping very likely had affected pollination system of the two Epimedium species. Honeybees were low-efficiency pollinators of E. sutchuenense, but in E. franchetii, honeybees had nearly equal efficiency with bumblebees. The different pollination efficiency of honeybees between the two Epimedium species was due to the distinct extent of herkogamy. A larger extent of herkogamy in E. franchetii could reduce pollen removal and increase pollen deposition on stigmas during one visit by honeybees. Although honeybees with high pollination frequency and efficiency could be as effective pollinators compared to bumblebees, honeybees reduced reproductive success probably owing to geitonogamy. Moreover, E. sutchuenense had lower reproductive success and expressed pollen limitation in all populations. We inferred that abundant pollen wasted by honeybees caused pollen quantity limitation, moreover, slight herkogamy would increase self-pollen deposition thus reduced female fitness. Pollination behavior of honeybees combined with some floral traits (e.g. herkogamy or/and dichogamy) is important to explore the ecological impact of honeybees on pollination system and reproductive success in plant species.