Pollination biology of Echinopsis leucantha (Cactaceae): passerine birds and exotic bees as effective pollinators

Cactus flowers have traditionally been considered to be specialized to certain pollination guilds, but pollination studies reveal that most species are actually generalists. This suggests that floral traits are not always predictive of the animal visitors that pollinate cactus flowers. Here, we studied the pollination of Echinopsis leucantha (Gillies ex Salm-Dyck) Walp., an endemic cactus of Argentina, whose floral traits would suggest that it is pollinated by moths. The floral lifespan and flower availability throughout the reproductive period were evaluated. Field experiments were carried out to study the reproductive system and the identity and effectiveness of floral visitors. Echinopsis leucantha flowers had a nocturnal anthesis time that extended into the following morning. The species was self-incompatible. Floral visitors included moths, bees, and passerine birds. However, diurnal visitors were more effective as pollinators than nocturnal ones. The flowers of E. leucantha were phenotypically specialized (sphingophily); however, the pollination system was functionally and ecologically generalized. The results confirm that generalized pollination systems are widespread among species of the Echinopsis genus with nocturnal flowers, for which diurnal pollinators seem to have a key role in fruit and seed production. Our study constitutes the first record of passerine bird pollination in the Cactaceae for mainland South America. Keywords: Cactaceae, Echinopsis, floral syndrome, passerine, pollination. Les fleurs de cactus ont traditionnellement ete considerees comme specialisees envers certaines guildes de pollinisateurs, mais les etudes de pollinisation revelent que la plupart des especes sont en fait generalistes. Cela suggere que les traits floraux ne sont pas toujours predicteurs des visiteurs animaux qui pollinisent les fleurs de cactus. Les auteurs ont etudie ici la pollinisation d'Echinopsis leucantha (Gillies ex Salm-Dyck) Walp., un cactus endemique de l'Argentine, dont les traits floraux pourraient suggerer qu'il est pollinise par des papillons nocturnes. La duree de vie et la disponibilite des fleurs a travers toute la periode de reproduction ont ete evaluees. Des experiences sur le terrain ont ete realisees afin d'etudier le systeme reproducteur et l'identite et l'efficacite des visiteurs floraux. Les fleurs d'E. leucantha avaient une periode d'anthese nocturne qui s'etendait durant la matinee suivante. L'espece etait auto-incompatible. Les visiteurs floraux comprenaient les papillons nocturnes, les abeilles et les passereaux. Cependant, les visiteurs diurnes etaient des pollinisateurs plus efficaces que les visiteurs nocturnes. Les fleurs d'E. leucantha etaient specialisees phenotypiquement (sphingophilie); cependant, le systeme pollinisateur etait fonctionnellement et ecologiquement generaliste. Les resultats confirment que les systemes de pollinisation generalistes sont repandus chez les especes du genre Echinopsis possedant des fleurs nocturnes, pour lesquelles les pollinisateurs diurnes semblent jouer un role cle dans la production de fruits et de graines. Leur etude est la premiere a rapporter une pollinisation par des passereaux chez des Cactaceae du continent sudamericain. [Traduit par la Redaction] Mots-cles : Cactaceae, Echinopsis, syndrome floral, passereau, pollinisation.
Introduction Most angiosperms have been found to have generalist pollination systems, and specialization is now believed to be less common than once supposed (Waser et al. 1996; Ollerton et al. [...]