Evolution of anther connective teeth in sages (Salvia, Lamiaceae) under bee and hummingbird pollination

Abstract

Salvia (Lamiaceae) is a sub-cosmopolitan genus of about 1000 species that often employ a “staminal lever mechanism” that is thought to have spurred species diversification within the genus. The function and evolution of ventral outgrowths or connective teeth, associated with the lever mechanism in some species of Salvia, is often unclear despite the wealth of pollination observations across the genus and the major role that pollinators play in driving diversification within the genus. We document the role of these teeth in pollination studies of bee-pollinated Salvia farinacea, examine connective teeth across other bee- and hummingbird-pollinated species of New World subg. Calosphace, and provide an evolutionary scenario for the connective teeth in context of the staminal lever. Our observations show that the larger teeth function as pressure points at the floral entrance and, when pressed by a pollinator, facilitate movement of the lever. Multiple shifts in pollinator within subg. Calosphace may have resulted in further modifications of the connective and possible further losses and independent origins of connective teeth in Calosphace. Other distantly related subgenera (e.g., Sclarea, Glutinaria) display morphologically and spatially different protuberances on the connective, suggesting that connective teeth only evolved near the base of subg. Calosphace.