Abstract: The variation in corolla morphology of Pedicularis is closely related to pollinator-mediated selection, but how the related sympatric species, which shar pollinators and overlap in flowering time, maintain the interspecific divergence is still unclear. In this study, we measured the floral traits of two closely related species, Pedicularis kansuensis and Pedicularis semitorta in the east of the Tibetan Plateau, for two consecutive years. We estimated the intensity of phenotypic selection on floral traits through female fitness (seed number) and compared the difference between the two pedicularis species. The results showed that: 1) There were significant correlations among floral traits of the two species studied. For P. kansuensis, we found significant correlation between nectar depth, floral size and style length, which were consistent in different years. However, the correlation between these floral traits and inflorescence number or plant height, was low. In particular, nectar depth was not correlated with the other two traits. For P. semitorta, there was significant correlation between beak length, style length and floral size, but the correlation between beak length and other floral traits changed significantly between years. 2) The selection for inflorescence number and plant height of the two species was significant. In addition, for P. kansuensis there was significant selection for floral size, style length and nectar depth, while for P. semitorta, the phenotypic selection on floral size and style length was much less significant and in particular beak length did not affect female reproductive success. These results indicate that: 1) The evolution and function of nectar depth, floral size and style length of P. kansuensis may be highly integrated, and style length and floral size of P. semitorta may also have the same integration. 2) Increase in flower number, prolongation of the flowering period and increase in plant height are the main means to increase female fitness (seed production) of Pedicularis. Individuals of P. semitorta with larger floral size and longer styles also tend to have improved seed production. For P. semitorta, beak length may be related to pollen dispersal, and mediated by pollinators, i.e. male fitness.

Key words: sympatric species, female fitness, phenotypic selection, Pedicularis kansuensis, Pedicularis semitorta