Floral biology of Pilosocereus tuberculatus (Werderm.) Byles & Rowley: a bat pollinated cactus endemic from the “Caatinga” in northeastern Brazil1

Brazil is the third major centre of diversity for the family Cactaceae, with approximately ¾ of the species found in the country being endemic, and a total of 162 native species, including around 20 belonging to Pilosocereus. This family is exclusively pollinated by animals, varying widely between beetles, bees, butterflies, moths, hummingbirds and bats. Pilosocereus tuberculatus is a tree-like cactus with candelabriform branching, with a relict distribution restricted to a few localities in the states of Pernambuco, Bahia, Sergipe and probably southern Piauí. The present work reports observations of bat-pollination in natural populations of the species in an area of dryland woody vegetation (‘caatinga’) in the municipality of Buíque, state of Pernambuco, Brazil. The slightly zygomorphic flowers have olive-green outer perianth-segments and white inner perianth-segments with purplish spots, and a straight, almost cylindric flower tube 3.5–4.0 cm long. Nocturnal anthesis, a strong smell and internally white flowers with abundant nectar (23–309µl) of relatively low sugar content (9.5–17.0%) are characteristic of the bat-pollination syndrome. Pollen is available and the stigma is functional during anthesis as a whole, from between 18:00–18:20h and 8:20–8:50h the following morning. Visits were recorded during the day by bees (Apis mellifera, Trigona spinipes and Xylocopa grisescens) and a hummingbird (Heliomaster squamosus) and during the night by bats (Glossophaga soricina and Lonchophylla mordax). The bats were observed at intervals varying between 5 seconds and 55 minutes, during 18 nights (i.e. 270 hours of observation). In P. tuberculatus spontaneous self-pollination did not produce fruits. The ratio of fruits formed by cross-pollination (69%) compared with manual self-pollination (0%) indicates that the predominant reproductive system in P. tuberculatus is allogamy, and that its reproduction depends on the efficiency of the pollen-vectors. Based on behaviour displayed during bat, bee and hummingbird visits, and the ratio of natural fruit formation, P. tuberculatus depends mostly on its nocturnal visitors for pollination. Bat-pollination, which is predominant for the genus Pilosocereus, has been interpreted as a mechanism of parallel evolution between cacti and bats, and it is possible to consider P. tuberculatus as an example of this close relationship, including a the new record of the glossophagine bat L. mordax as a cactophilic bat.