Floral scent of artificial hybrids between two Schiedea species that share a moth pollinator

Premise

In flowering plants, pollinators' ability to recognize chemical displays of hybrids may erode reproductive barriers. Hybrids may produce novel or altered floral scent blends that are unattractive, or scents similar to either parent that remain attractive and promote backcrossing. We characterized the floral scent of hybrids of sympatric species with a shared pollinator and tested whether scent is sufficient for pollinator attraction.

Methods

Floral volatiles of artificial F₁ hybrids between Hawaiian Schiedea kaalae and S. hookeri (Caryophyllaceae) were characterized by dynamic headspace sampling and GC-MS. Behavioral choice tests with the native moth Pseudoschrankia brevipalpis measured the effect of adding S. kaalae scent (with flowers bagged to remove visual cues) to inflorescences of relatively unattractive wind-pollinated relatives (S. kealiae and S. globosa) from the same island.

Results

Most hybrids produced a combination of the distinct sets of floral volatiles from each parent at rates of emission that often differed from the expectation under completely additive inheritance. Floral scent did not depend on cross direction, and no novel compounds were detected in hybrids. Pseudoschrankia brevipalpis preferred inflorescences of S. globosa and S. kealiae that were augmented with the scent of hidden S. kaalae flowers.

Conclusions

Intermediate hybrid floral scent blends could potentially attract moths if they do not rely on precise compound ratios. Moth attraction to the floral scent of S. kaalae flowers indicates that moths can discriminate the floral scent of this species against a background of volatiles and visual cues from wind-pollinated relatives, showing the importance of scent variation in this genus.