Abstract: Empirical studies comparing mating systems and pollination mechanisms in closely related species within one genus will help us to better understand the evolution of plant mating system. In the present study, we performed field experiments on Anisodus luridus and A. carniolicoides, attempting to explore the evolution of self- compatibility and pollinator shift in the genus Anisodus. Our results showed that both A. luridus and A. carniolicoides were fully self-compatible, but the seed number and fruit set of the netted flowers without emasculation were significantly lower than the intact control flowers subjected to open pollination, indicating the two species only had a weak ability of autonomous selfing. Seed production with supplemental pollen was greatly enhanced compared with natural flowers , suggesting pollen limitation in both species. Vespula rufarufa and Dolichovespula saxonica . were the most frequent pollinators of A. luridus and A. carniolicoides, respectively. While other floral visitors , including bumblebees, flies and ants, accounted for the minority of visitation in the two species. The number of pollen grains deposited on stigmas of intact flowers within one day was significantly higher than
emasculated flowers in A. carniolicoides, but not in A. luridus . Therefore, visitations of D. saxonica to A. carniolicoides was speculated to result in selfing within flower , i . e . facilitated selfing , whereas V. rufarufa could facilitate outcrossing among flowers in A. luridus . Compared with the pollination mechanism of A. tanguticus, the putatively primitive species in Anisodus, we found self- compatibility occurred in the derived species , indicating the evolutionary transition from self-incompatibility to self- compatibility and pollinator shift during the speciation in this genus. Moreover, the unpredictable and frequent rain in alpine environment might depress pollinator activity , which could be the principal reason for pollen limitation in A. luridus and A. carniolicoides.

Key words: Mating system