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

AMORIM FELIPE W; MORÉ MARCELA; BENITEZ-VIEYRA SANTIAGO M; SAZIMA MARLIES; COCUCCI, ANDREA A.

Bonito, Mato Grosso do Sul

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

Association for Tropical Biology and Conservation

The ghost of spur evolution past: Match and mismatch in the pollination mechanisms of highly specialized long-spurred orchids Amorim FW1, Moré M2, Vieyra SB2, Sazima M1, Cocucci A2 1Universidade Estadual de Campinas - UNICAMP - Biologia Vegetal, 2Universidad Nacional de Córdoba - CONICET - Laboratorio de Ecología Evolutiva - Biología Floral, Instituto Multidisciplinario de Biología Vegetal. Long-spurred orchids rely on highly specialized pollination mechanisms by which reproductive success is achieved through a close association with long-tongued hawkmoths. In Habenaria species, pollination success depends on the attachment of pollinaria onto the heads of hawkmoths with very long proboscises. However, in the Neotropical region these moths are less abundant than their shorter-tongued relatives and prone to population fluctuations that may give rise to differences in pollinator-mediated selection on floral traits through time and space. For three South American Habenaria species we characterized their hawkmoth assemblages and estimated phenotypic selection gradients on orchid spur lengths. We examined the match between pollinator proboscis and flower spur lengths to determine whether actual pollinators may act as selective agents on flower morphology. The orchid species studied are terrestrial herbs growing generally in grasslands with swampy soils and on the margins of streams and ponds. Habenaria gourlieana population was studied at El Durazno, Córdoba – Argentina, while H. johannensis and H. paulistana populations were studied at the Atlantic Rain Forest in the São Paulo state, Southeastern Brazil. The three species develop long inflorescences with a variable number of large flowers (3 up to 30), which are greenish-white in color, emit scent after dusk and spurs can reach until 16 cm. We found significant directional selection on spur length only in the Argentinian population, where most pollinators had proboscises longer than the mean of orchid spur length. The two Atlantic Rain Forest populations had a strong spur-proboscis mismatch, where pollinators had proboscises shorter than the mean of the spur lengths of both orchid species. Since phenotypic selection is dependent on the mutual match between pollinator and flower morphologies, our findings indicate that pollinator-mediated selection may vary through time and space according to local variations in pollinator assemblages.