Evolutionary response of staminal lever mechanism of different species in Salvia to spatial variation in pollinators

Abstract

Aims Floral diversification in animal-pollinated species was widely believed to be driven by pollinator-mediated natural selection in response to the geographical mosaic of pollinators. Our objective was to explore the evolutionary response of staminal lever mechanism in Salvia to variation in pollinator assemblage in a spatial context. Methods We employed three species (four populations) and conducted comparative studies on pollinator-flower interactions in different populations through investigating pollinator assemblage and measuring floral traits and body size of pollinators. Important findings Floral traits investigated, including corolla length, staminal lever length and other structural traits, exhibited distinct differences among populations. These corresponded with variations in composition of pollinators and the main pollinator and its body size in each population. The two types of pollination modes in each population were ventral pollination and dorsal pollination, which was the effective one. The main pollinator’s body length was significantly positively correlated with staminal lever length and negatively correlated with corolla length in spatial context. Both corolla entrance height and stigma height were related to variation in body thickness of the main pollinator among populations. In conclusion, the vulnerability of lever-like stamens and other relevant floral traits to the geographical mosaic of pollinators implies the key role that the staminal lever plays in pollination, and its high evolutionary plasticity might have contributed to adaptive radiation of species in Salvia.