XVI International Botanical Congess

We used two species of Nicotiana, N. alata and N. forgetiana, and their hybrids to test scenarios of speciation under natural conditions. Nicotiana alata is strictly pollinated by hawkmoths while hummingbirds primarily pollinate N. forgetiana. The species are loosely sympatric and hybrids are vigorous but are not produced in nature. Three experiments were set up in Rio Grande do Sul, Brasil, within the range of both species: 1) mixed populations of each species, 2) mixed populations of each species plus f1 hybrids, and 3) populations of polymorphic f2 hybrids. In experiment 1, pollinators showed strong fidelity to each species with few Amistakes@ being made by hawkmoths. In experiment 2, pollinators preferred their suited species but also visited f1 hybrids with similar frequency. In experiment 3, hawkmoths preferred longer tubed flowers regardless of color while hummingbirds preferred shorter tubed, reddish flowers. These results indicate that discriminant pollinators can be effective reproductive barriers between species and can be effective selective agents causing divergence of floral traits and perhaps speciation.