Abstract:

The reproduction of plants is generally pollen-limited in natural populations. The theory of phenotypic selection suggests that pollinator-mediated selection occurs when the degree of pollen limitation varies among individuals within a plant population. In this study， we explored aspects of floral adaptation and selection mechanisms in Salvia digitaloides by comparing the differences in reproductive success and selection of floral traits under different pollination conditions. The main results were as follows： 1） The reproductive efficiency of plants （i.e.， fruit set and number of seeds set per flower） was significantly negatively correlated with the height of the stigma in flowers under open pollination （P<0.05）， but significantly negatively correlated with flower production under supplementary hand pollination. The number of seeds set per flower was negatively correlated with style exsertion under supplementary hand pollination （P=0.031）. 2） The extent of the decrease in the number of seeds set per flower due to pollen limitation under open pollination was negatively correlated with both flower production and style exsertion （P=0.006， 0.041）. 3） Under both open and supplementary hand pollination， flower production was subject to significant directional selection， but the selection intensity was much lower under supplementary hand pollination than under open pollination. There was significant negative directional selection for stigma height under open pollination， and for style exsertion under supplementary hand pollination. There was positive correlational selection for the combination of corolla entrance size and style exsertion. Together， the results show that the floral traits of S. digitaloides are subject to significant pollinator-mediated selection， with the floral structural traits showing a trend of functional integration for the improvement of pollination efficiency.

Key words: Salvia, fitness, pollination, phenotypic selection, pollen limitation