Pollination in the desert: Adaptation to bees and birds in salvia rhombifolia

All rights reserved. Premise of research. Along the western coast of South America, the Peruvian and the Atacama Deserts extend over a length of 3500 km. For a short period in the year, the desert is affected by a dense fog formed under the influence of the Humboldt Current that gives rise to an ephemeral plant community called the “Lomas.” Salvia rhombifolia Ruiz & Pavon is an endemic annual component of the Lomas. Previous observations indicated bee and bird visitors at the plant; however, no detailed studies were performed. Here, we test the hypothesis that both bees and birds are pollinators and thus increase the chance of pollination in the extreme habitat of the plant. Methodology. Fieldwork was conducted with three large populations of S. rhombifolia in the fog season of 2015. We combined morphometric analyses with corolla color, nectar volume, and sugar concentration to characterize the floral syndrome of this species. Data on pollinators, including frequency of visits, behavior, and mor-phometry, were analyzed statistically and compared with the floral traits to identify the best fit between flowers and pollinators. Pollinator efficiency was tested with single-visit experiments comparing the seed set after controlled bird and bee pollination. Pivotal results. Salvia rhombifolia exhibits small blue flowers (!1.5 cm). Nectar volume was low (ca. 1 µL) and sugar concentration moderate (22.8%). Pollinators were bees (six species) and hummingbirds (two species). Morphometric analyses of pollinators and flowers underlined their close mechanical fit. The fruit set under controlled conditions indicated that birds (100%) and bees (82%) were likely effective pollinators. Conclusions. The results clearly show that S. rhombifolia is not specialized for bees but an “intermediate” species that also attracts birds. The flexible use of pollinators appears to be triggered by the extreme abiotic conditions and the need to reproduce sexually.