Document: SHE-3-44-6

California mainland vs. Channel Island pollination of Nicotiana glauca (Solanaceae): An invasive hummingbird-pollinated plant .

SCHUELLER, S.K.*

University of Michgian, Ann Arbor, MI 48109, USA ¹

Abstract:
Because of their unique pollinator conditions relative to the mainland, islands provide an ideal system for testing the effect of pollinators on plant reproductive success and floral evolution. Recent invasive plants provide a rare opportunity to view early establishment on islands and to investigate how plants respond to insular pollination. I studied California mainland and Channel Island populations of Nicotiana glauca (tree tobacco, Solanaceae), a widespread hummingbird-pollinated invasive that has colonized the islands within the last century. I tested the following major predictions: 1) Pollinators of island plants are a unique subset of mainland pollinators and, in response, island plants will evolve unique floral traits, 2) Visitation to island plants is less frequent than to mainland plants, and plants will evolve greater ability to self-pollinate on islands. Observations, floral measurements and hand-pollination experiments were performed across two mainland and two island (Santa Catalina and Santa Cruz) study sites in 1998 and 1999. Five hummingbird species occur on the mainland and two on the islands, but the number of pollinator species actually visiting plant populations was equivalent across sites, with a difference in the relative composition: Anna's and Black-chinned on the mainland, and Allen's and Anna's on the islands. The dominant pollinator on the islands (70-90% of total visits), the Island Allen's hummingbird, has a longer bill than mainland hummingbirds, and as predicted, island plants had significantly longer corollas (1.5 mm) than mainland plants. Although the frequency of visitation was not consistently lower on islands, the island plants did demonstrate a greater ability to self-pollinate than mainland plants. Autogamy (measured as the mean ratio of bagged to supplemental-self pollinated fruit set) was higher on both Catalina (0.49) and Cruz (0.85) than the mainland sites (both 0.13) and reflected significantly shorter anther-stigma distances (herkogamy) for island than mainland plants. These results from a recently introduced plant demonstrate how quickly plants can evolve in response to colonization and insular pollination.

Keywords: islands; hummingbirds; pollination; invasive; autogamy

This abstract is being presented at: 11:15 AM in session:
Oral Session #6: Pollination Ecology.