关键词: Delphinium caeruleum, 具黄色髯毛的退化雄蕊, 雄性适合度, 雌性适合度, 青藏高原

Abstract

Nectar guides are special floral structures that are assumed to attract and/or direct pollinators towards a concealed nectar reward. Nectar guides are commonly found in many angiosperm plants, especially entomophilous flowers, but their functional significance and impacts on the reproductive success of plants are poorly understood. For example, Delphinium caeruleum of the family Ranunculaceae possesses two barbate staminodes, between which is the nectar entrance. To test the effects of these barbs on male and female fitness, we experimentally investigated the effects of barb removal on seed production and pollen exportation of D. caeruleum at the Haibei Station of Qinghai Province. Our results showed that flowers of D. caeruleum were dichogamous and herkogamous, which prevented autonomous selfing in this species. The mating system of D. caeruleum belongs to obligate xenogamy and thus pollinators are necessary for the successful pollination. Compared to control flowers, the number of pollen grains exported was reduced significantly after removing the barbs, but fruit set and seed number was not affected. Our primary results indicate that the barbs on the staminode act as nectar guides, which improve the male fitness of D. caeruleum, but have little effect on female fitness. Our results suggest that selection through male fitness might have played an important role in the floral evolution of D. caeruleum at our study site. These results need to be further investigated at a larger number of sites to evaluate selection mechanisms on floral traits of D. caeruleum.

Key words: Delphinium caeruleum, the barbate staminodes, male fitness, female fitness, the Qinghai-Tibet Plateau