PATTERNS AND CONSEQUENCES OF BENZYL ACETONE FLORAL EMISSIONS FROM NICOTIANA-ATTENUATA PLANTS

The emission of a single compound, benzyl acetone (BA, 4-phenyl-2-buta none), is barely detectable during the day in the headspace of flowers of the self-compatible disturbance species Nicotiana attenuata, but i t increases dramatically (50 x) in the evening, becoming the dominant component in the floral headspace. This striking temporal pattern of e mission may be sculpted by its potential ecological roles (e.g., synom onal and kairomonal), which we examine here. We measured the nightly B A emissions from individual flowers at six different branch positions on plants receiving either self-pollen or pollen from another genotype and calculated the nightly whole-plant emission. The first flowers pr oduced on a branch have a lower rate of emission than flowers produced later on the same branch; however, cross pollination did not influenc e the quantity of BA emitted from subsequently produced flowers. Infor med by these measures of whole-plant emission, we constructed a device that released BA at a constant rate equivalent to that of a plant wit h 240 open Flowers (an approximate 10x increase in emissions). This de vice and a control device were attached to 50 matched pairs of plants growing in a native population in Utah to estimate the fitness consequ ences of enhanced, constant BA emission. Plants with elevated BA emiss ions in the field were browsed more frequently than control plants and produced fewer capsules, so that lifetime seed production was reduced by 3.1%. However, both treatment and control plants were heavily atta cked by negro bugs (Cormelina spp.) and produced light seeds with low viabilities, representing 47% and 23% of the mass per seed and viabili ty, respectively, of unmanipulated plants, which flowered two weeks la ter in the same population. From glasshouse experiments, we estimated the consequences of out-crossing and attack by negro bugs on seed prod uction. Out-crossing did not significantly affect seed production, see d mass or viability. In contrast, negro bug infestation dramatically d ecreased seed mass and viability. We conclude that while the phenologi cal variation in attack rates might have obscured our ability to estim ate the fitness consequences of enhanced BA emission, the effects are likely to be dominated by kairomonal rather than synomonal interaction s for this self-compatible species.