A key floral scent component (β-trans-bergamotene) drives pollinator preferences independently of pollen rewards in seep monkeyflower

1) Floral odors play an important role in attracting insect pollinators. Because pollinators visit flowers to obtain pollen and nectar rewards, they should prefer floral odor profiles associated with the highest-rewarding flowers (honest signals). In previous work, bumble bees exhibited a preference for flowers from outbred over inbred Mimulus guttatus plants. Pollen is the only floral reward in M. guttatus, and pollen viability (a reliable indicator of protein content) is reduced in inbred plants. Yet, differences in pollen viability did not explain the observed preferences.
2) In this study we examined the floral volatile profiles of inbred and outbred M. guttatus to identify inbreeding effects and associations between volatile compounds and the number of viable pollen grains per flower, designated ‘PRQ’ (pollen reward quality). We also conducted pairwise choice tests with Bombus impatiens to evaluate the ability of bees to discriminate between odors of rewarding and nonrewarding flo...