Sending private messages: Floral ultraviolet signals are correlated with pollination syndromes in Erica

The presence of ultraviolet (UV, wavelengths between 300-400 nm) reflectance in insect-pollinated flowers has been linked to pollination efficiency and pollination shifts, but little is known about its prevalence and function in other pollination systems and African species. We chose the genus Erica for studying the prevalence of UV because of its extreme radiation (c. 680 species) in the Cape, South Africa, with a diversity of pollination syndromes. This study quantified the prevalence and brightness of UV reflectance for five Erica pollination syndromes and tested pollinator preferences for UV reflectance in the two groups with the highest prevalence: sunbirds and long-proboscid flies. Our results show that UV colouration is absent or rare in Erica species pollinated by unclassified insects, rodents or wind. About 17 % of bird-pollinated species reflected UV but choice experiments revealed that free-ranging sunbirds showed no preference for UV signals. All sampled long-proboscid fly-pollinated species reflected UV and its experimental removal decreased seed set drastically, suggesting that long-proboscid flies in the Cape strongly prefer or depend on UV and thereby contributed to selecting for the evolution of this signal.