Is pollen removal or seed set favoured by flower longevity in a hummingbird-pollinated Salvia species?
OBJECTIVE
The period between the beginning of anthesis and flower senescence modulates the transport of pollen by pollinators among conspecific flowers, and its length may therefore influence reproductive success. This study evaluated whether floral longevity favours pollen removal from the anthers over fecundity (seed set) in an ornithophilous species that does not undergo pollen limitation.


METHODS
Field investigations were conducted on floral longevity, nectar production, pollinator behaviour, and variations in fruit set (FS), mean number of seeds per fruit (MSF) and pollen removal by hummingbirds (PR) during the anthesis of Salvia sellowiana in south-east Brazil.


RESULTS
Anthesis of flowers exposed to pollinators lasted 4 d, as well as on flowers with pollen removed from the anthers or deposited on the stigma. The longevity of bagged flowers was significantly higher (approx. 9 d). FS and PR reached 87.2 and 90 %, respectively, in natural conditions. PR increased gradually over the period of anthesis; however, FS and MSF reached their maxima in the first hours of anthesis. Nectar production was continuous, but the secretion rate was reduced after pollination. The removal of nectar from non-pollinated flowers stimulated its production.


CONCLUSIONS
The longevity of anthesis in S. sellowiana seems to be related to the mechanism of gradual dispensing of pollen, resulting in greater male reproductive success. This is in agreement with the pollen-donation hypothesis. The small number of ovules (four) of S. sellowiana and the high frequency and the foraging mode of its pollinators may favour the selection for floral longevity driven by male fitness in this system.
Aximoff
Izar Araujo
IA
Instituto de Pesquisas Jardim Botânico do Rio de Janeiro, Rua Pacheco Leão 915, Rio de Janeiro - RJ, Brazil.
Freitas
Leandro
L
D000818:Animals; D001717:Birds / Q000502:physiology*; D035264:Flowers; D011058:Pollen; D027544:Salvia / Q000196:embryology / Q000502:physiology*; D012639:Seeds