104.1 Saturday, Jan. 7 Specific floral odorants contribute to differential pollinator attraction in monkeyflowers (Mimulus) BYERS, KJRP*; BRADSHAW, HD; RIFFELL, JA; University of Washington; University of Washington; University of Washington email@example.com
Floral diversity is immense, with more than 250,000 species of angiosperms known. The number of phylogenetically diverse floral species that share common characteristics implies a background pattern of selection acting on floral traits. Unique combinations of these floral traits, or "pollination syndromes," are hypothesized to reflect selective pressure imposed by certain classes of pollinators. One flower character in particular, scent, has been hypothesized to operate as an unseen signal to attract certain pollinators, particularly when combined with other signals such as color and shape. However, the contribution of scent in pollinator-mediated selection between sister taxa has nearly always been inferred and rarely directly tested. The genus Mimulus (Phyrmaceae) forms a developing model system for studying floral diversity and speciation using a combination of genetics and field ecology. Two sister species of Mimulus, Mimulus cardinalis and Mimulus lewisii, are pollinated by hummingbirds and bumblebees respectively, and in combination with readily available genetic tools present a unique system in which to examine the sensory mechanisms and signals that mediate pollinator-driven speciation. Using a combination of headspace collection, gas chromatograph-coupled multi-unit recording, and behavioral experimentation, we investigated the role of multiple Mimulus volatiles on bumblebees (Bombus occidentalis). Several key compounds are found at different concentrations in the two species, with notable effects on electrophysiology and behavioral responses by bumblebees. Together, these results suggest that scent alone may be a sufficient force to drive differential pollinator attraction to sister species, providing a mechanism for speciation and maintenance of reproductive isolation in angiosperm taxa.