Divergent Pollination Systems in Sympatric Species of South American Dalechampia (Euphorbiaceae)

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Abstract
South American Dalechampia (spp.) were studied at 2 disjunct sites where they occur in 2 different combinations of sympatry. D. scandens and D. cissifolia are sympatric in parts of western Ecuador. They differ from one another in time of bract opening (which determines when the flowers are pollinated), amount of resin (the pollinator attractant) secreted and the position of the flowers relative to the gland which secretes the resin. As a consequence of these differences, D. sandens is pollinated by euglossine bees and D. cissifolia is pollinated by Hypanthidium nr. panamense (Megachilidae). In the vicinty of Manaus, Brazil, a different ecotype of D. scandens occurs sympatrically with D. affinis. Here D. scandens differs from its sympatric congener in time of bract opening, amount of resin secreted and position of flowers in the inflorescence. As a consequence, D. scandens and D. affinis are pollinated by different bees; however, near Manaus D. scandens is pollinated by H. nr. melanopterum and D. affinis is pollinated by euglossine bees. The differences in pollination systems between members of these pairs of sympatric species may reduce interspecific pollen flow and competition for pollinators. The 2 ecotypes of D. scandens differ from one another in relatively minor floral characters, yet exhibit divergent pollination relationships. These differences may have arisen as a result of disruptive selection resulting from occurrence with different congeners. These evolutionary processes may have occurred elsewhere in the genus and could account for some of the diversity of floral characters exhibited by Dalechampia spp.

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