The ghost of spur evolution past: Match and mismatch in the pollination mechanisms of highly specialized long-spurred orchids

AMORIM, F.W.; MORÉ, M.; BENITEZ-VIEYRA, S.; SAZIMA, M; COCUCCI, A.A.

Bonito, Mato Grosso do Sul

Encuentro; 49th Annual Meeting Association for Tropical Biology and Conservation; 2012

Association for Tropical Biology and Conservation

Long-spurred orchids rely on highly specialized pollination mechanisms by which reproductivesuccess is achieved through a close association with long-tongued hawkmoths. In Habenariaspecies, pollination success depends on the attachment of pollinaria onto the heads ofhawkmoths with very long proboscises. However, in the Neotropical region these moths areless abundant than their shorter-tongued relatives and prone to population fluctuations thatmay give rise to differences in pollinator-mediated selection on floral traits through timeand space. For three South American Habenaria species we characterized their hawkmothassemblages and estimated phenotypic selection gradients on orchid spur lengths. Weexamined the match between pollinator proboscis and flower spur lengths to determinewhether actual pollinators may act as selective agents on flower morphology. The orchidspecies studied are terrestrial herbs growing generally in grasslands with swampy soils andon the margins of streams and ponds. Habenaria gourlieana population was studied at ElDurazno, Córdoba – Argentina, while H. johannensis and H. paulistana populations werestudied at the Atlantic Rain Forest in the São Paulo state, Southeastern Brazil. The threespecies develop long inflorescences with a variable number of large flowers (3 up to 30), whichare greenish-white in color, emit scent after dusk and spurs can reach until 16 cm. We foundsignificant directional selection on spur length only in the Argentinian population, where mostpollinators had proboscises longer than the mean of orchid spur length. The two Atlantic RainForest populations had a strong spur-proboscis mismatch, where pollinators had proboscisesshorter than the mean of the spur lengths of both orchid species. Since phenotypic selectionis dependent on the mutual match between pollinator and flower morphologies, our findingsindicate that pollinator-mediated selection may vary through time and space according to localvariations in pollinator assemblages.