Restriction of pollinator assemblage through flower length and width in three long-tongued hawkmoth pollinated species of Mandevilla (Apocynaceae, Apocynoideae)

MORÉ, M.; SÉRSIC, A.N.; COCUCCI, A.A.

ANNALS OF THE MISSOURI BOTANICAL GARDEN

MISSOURI BOTANICAL GARDEN

Año: 2007 vol. 94 p. 485 - 504

0026-6493

ABSTRAC TApocynaceae have a precise pollination mechanism. However, broad pollinator assemblages, including several insectorders, have often been recorded. We test how the corolla tube length and operative width required for effective release of thepollination mechanism could restrict the pollinator assemblage in putatively hawkmoth-pollinated Apocynaceae that differ inflower depth. If corolla tube length were effective in filtering pollinators, a broader pollen vector assemblage would beexpected in short-flowered species. For this to occur, the operative width of the pollinating apparatus would be additionallyexpected not to be specific to any particular pollinator. Alternatively, if the pollination mechanism were to have any effect inthe exclusion of pollinators, access to short flowers would be expected to be limited by proboscis width rather than length.Pollination of three species in the Apocynaceae was studied in seven populations through direct observations andpalynological analysis of hawkmoths. Proboscis widths of hawkmoths carrying and not carrying pollen were compared withoperative floral width as measured by proboscis analogues of different diameters that could successfully release the pollinationmechanism. Species studied were exclusively hawkmoth pollinated. Pollen was always attached to pollinator proboscides,either near the base or on the apical half. The long-tongued hawkmoth species Manduca sexta (L.) was the major pollinator ofMandevilla longiflora (Desf.) Pichon and Mandevilla petraea (A. St.-Hil.) Pichon. Surprisingly, another long-tongued species,Manduca tucumana (Rothschild & Jordan), was the main pollinator of the short-flowered Mandevilla laxa (Ruiz & Pav.)Woodson. Here, the operative flower width was a decisive factor restricting the pollinator spectrum to hawkmoths withproboscides narrow enough to release the pollination apparatus. Short-tongued hawkmoths, which also have wider proboscides,cannot release the pollination mechanism. In M. petraea, the operative length, and not the operative width, restricts thepollinator assemblage. Thus, two different plant strategies were observed to restrict the pollinator spectrum: floral tube lengthand the operative width of the pollination mechanism.Key words: Apocynaceae, long-tongued pollinators, Mandevilla, Manduca, operative flower width, plant-pollinatorinteraction, specialization, Sphingidae.