Reproductive isolation (RI) is one of the key factors for speciation and diversity maintenance, however, there are differences in formation stage, means, and strength of RI for different species. To assess the effects and the significance of reproductive isolation in Salvia species, we compared flowering, pollination, and reproduction characteristics of Salvia liguliloba and S. bowleyana, which grow sympatrically and have overlapping flowering periods in the Tianmu Mountain, Zhejiang. Furthermore, artificial hybridization between the two species were conducted to estimate and understand their genetic compatibility and reproductive isolation. Results indicated that the two Salvia species considerably differed in their flower morphological structures, inflorescence organization, and the number of flowers produced per inflorescence. Bombus trifasciatus is the sole pollinator for these two species during the overlapping flowering period. However, different visitation behavior and floral structure (P < 0.05) leads to obviously different pollination patterns between the two species. Pollen is deposited on distinctly separate areas of the pollinator’s body in a manner precluding contact with any heterospecific Salvia stigmata. Under natural condition, the two species are equally successful in reproduction (natural seed set > 87%). Artificial pollination and hybridization experiments between these two species showed that they have a higher genetic compatibility. The cross seed sets are 77.8 ± 10.7% and 78.7 ± 11.2% when the two species are reciprocally cross parents. Our research suggests that for the two Salvia species lacking genetic incompatibility systems and relying on pollinators for outcrossing, there are differences in floral structures and pollen placement sites. The mechanical isolation (a form of pre-pollination RI) prevents heterospecific pollen interference and natural hybridization of the two different species that grow sympatrically and have overlapping flowering periods, and also maintains species diversity and the constancy of species heredity.
Received: 15 February 2017
Published: 20 June 2017