Reproductive biology of columnar cacti: are bats the only protagonists in the pollination of Pilosocereus, a typical chiropterophilous genus?

The Cactaceae display a wide array of pollination systems, with many different animals already confirmed as pollinators. Pilosocereus is one of the most conspicuous bat-pollinated genera characteristic of the tropical dry forests of Brazil, known as Caatinga. The role of bats, hawkmoths and bees as pollinators in natural populations was investigated for four Pilosocereus species (P. catingicola, P. chrysostele, P. gounellei and P. pachycladus). Earlier results obtained with P. tuberculatus were also included in the comparative discussion. These species depend mainly upon nocturnal visitors; however, Xylocopa grisescens bees also play a secondary role in the fruit set. Although chiropterophily is predominant in Pilosocereus, P. gounellei was visited and pollinated at night exclusively by sphingids. All species are described as presenting a chiropterophilous syndrome based on their nocturnal anthesis, strong and unpleasant flower scent, pale, white or cream inner perianth, compact and abundant flower parts, and large volume of nectar with low sugar concentration. Pollen is available and the stigma is receptive throughout anthesis. With the exception of P. gounellei, there was no fruit set from spontaneous or manual self-pollination, indicating that allogamy is the predominant reproductive system in all the species studied. These species thus rely on animals that function as efficient pollen vectors for their sexual reproduction. The Pilosocereus species present different levels of dependence on bats, from the participation of secondary pollinators to not being visited by bats at all. Dependence levels are associated with the species floral attributes, which, although subdued, can determine different pollination systems.