Selfing facilitates reproductive isolation among three sympatric species of Pitcairnia (Bromeliaceae)

The reproductive biology of three sympatric species Pitcairnia flammea, P. corcovadensis and P. albiflos (Bromeliaceae) was studied on Corcovado Mountain in the city of Rio de Janeiro, Brazil. Controlled pollination experiments were also conducted using plants transplanted to a greenhouse. The three species are self-compatible and interspecifically cross compatible, Pitcairnia corcovadensis was principally an autonomous self-pollinator, having scarce pollinator activity, anthers and stigmas at the same level, and absence of nectar. In P. flammea, many flowers opened per day. the stigma and anther were close to each other, and its nectar was regularly consumed by hummingbirds, all factors that promote geitonogamy in this species. Although fully self-compatible. P. albiflos always opened a few flowers per days showing an adaptation to cross-pollination. Observations during two flowering seasons showed that despite different times for peak flowering, blooming of these three species overlapped in April. They grow in mixed clumps that may facilitate promiscuous pollination between them but no intermediate forms were observed under natural conditions. The absence of temporal isolation, geographic isolation and isolation via post-pollination reproduction suggests that evolution toward selfing was important to avoid hybridization between these sympatric species.