Pollination systems and nectar rewards in four Andean species of Salvia (Lamiaceae)

Abstract

Adaptation to the most effective pollinator is often conceived as the primary explanation of widespread convergence in flower phenotypes. However, specialization does not exclude the presence of other floral visitors, which may contribute to plant reproduction. Here we combined observations about pollinators visitation rates and effectiveness with nectar secretion dynamics and sugar composition in four Andean Salvia species from Bolivia. The study revealed a wider diversity than expected both in pollination systems and in nectar strategies. While S. haenkei and S. stachydifolia were almost exclusively pollinated by either hummingbirds or bees, respectively, mixed pollination was found in S. orbignaei, a species previously described as hummingbird-pollinated. Salvia personata was exclusively pollinated by syrphid flies. Differences in nectar volume and sugar concentration were found between insect-pollinated species and mixed- or hummingbird-pollinated species. However, the four Salvia species displayed different strategies regarding nectar sugar composition, with sucrose-rich nectar in S. orbignaei, glucose-rich nectar in S. haenkei and S. stachydifolia, and glucose-rich nectar lacking fructose in S. personata, suggesting an adaptation to syrphid fly pollination. Our results provide a clearer picture of floral trait evolution in Salvia and highlight the contribution of some pollinators different from those expected according to the floral syndromes.