Pollination ecology, specialization, and genetic isolation in sympatric bee pollinated Salvia (Lamiaceae)

Premise of research. Previous pollination ecology studies in Salvia have shown that there is low specialization to certain subgroups of bees and that pollinator number varies with species and locality. We studied twelve Salvia species (three clades with different corolla morphologies and staminal lever mechanisms) which in part co-occur and co-flower to examine pre-zygotic isolation mechanisms and the degree of specialization vs. generalization in pollination ecology.

Methodology. Pollinators were identified using field observations, photos, and related literature across three sites in Turkey. Video documentation of the visitation rate and the site of pollen placement on the pollinator body, morphometric measurements between flowers and pollinators, flowering time, flower color, handling time, and stigma contact ratio were analyzed. Plant-pollinator networks were constructed.

Pivotal results. Mechanical, phenological, and ethological isolation occur among sympatric Salvia species. Morphological fit is evident between flower tube length and proboscis length of main pollinators. Pollinator networks indicate that most species are ecological generalists but only few are specialists.

Conclusions. The twelve Salvia species, though phenotypically and functionally specialized due to their zygomorphic-bilabiate flowers and bee pollination syndrome, differ in the degree of ecological specialization. Most of the sympatric Salvia species tend to be ecologically generalized with two or more main pollinators and a few additional secondary pollinators, while a few Salvia species are clearly specialized. Some floral traits (e.g., flower color, morphology, size, corolla tube length and width of corolla tube entrance, type and size of the staminal lever mechanism, small numbers of flowers in the inflorescence), short flowering time, and small population size appear correlated to the degree of ecological specialization.