DOI: 10.5061/dryad.bg79cnp7z
title: Data from: Scented nectar and the challenge of measuring honest signals in pollination

description: 1. Nectar scents are thought to function as honest signals of reward used
 by pollinators, but this hypothesis has rarely been tested. 2. Using
 Penstemon digitalis, we examined honest signalling of the nectar volatile
 (S)-(+)-linalool and pollinator responses to linalool in both field and
 laboratory settings. Because our previous work showed that linalool
 emission was associated with higher female fitness and that nectar is
 scented with linalool, we hypothesized that linalool was an honest signal
 of nectar reward. To assess honesty, we measured linalool-nectar
 associations including nectar volume, sugar amount, concentration, and
 production rate for inflorescences and flowers in several populations. We
 also assessed whether Bombus impatiens, the main pollinator of P.
 digitalis at our sites, can use linalool as a foraging signal. We
 supplemented real or artificial flowers in the field and lab with varying
 linalool-nectar combinations to measure pollinator behavioural responses.
 3. We found that an inflorescence’s linalool emissions could be used to
 predict nectar rewards in P. digitalis, but this was driven by indirect
 associations with display size rather than directly advertising more
 profitable flowers. For flowers within inflorescences there was also no
 evidence for an association between signal and reward. Field tests of
 bumblebee behaviour were inconclusive. However, in laboratory assays
 bumblebees generally used variation in linalool emissions to choose more
 profitable flowers, demonstrating they can detect differences in linalool
 emitted by P. digitalis and associate them with reward profitability.
 These results suggest experiments that decouple display size, scent and
 reward are necessary to assess whether (and when) bees prefer higher
 linalool emissions. Bees preferred nectars with lower linalool
 concentrations when linalool flavoured the nectar solution, suggesting
 potential for conflicting pressures on scent emission in the field. 4.
 Synthesis: Our results highlight the challenges of assessing function for
 traits important to fitness and suggest that the perception of floral
 signalling honesty may depend on whether pollinators use inflorescences or
 flowers within inflorescences when making foraging decisions. We conclude
 that future research on honest signalling in flowering plants, as well as
 its connection to phenotypic selection, should explicitly consider among-
 and within-inflorescence honesty, in theoretical and experimental
 contexts.
description: Details of the data collection can be found in the main paper in
 Journal of Ecology.
description: Nectar linalool relationship: Data for Fig. 1
 Nectar volume per flower: Data for Fig 2a. uL of nectar
 calculated from wicks (details in paper) Sugar per
 flower: Data for Fig 2b. Absorbance * 0.0008 = grams of sugar
 Flower replenishment per flower: Data for Fig 2c. For uL of
 nectar per hour = (0.0051*(wickmeasure^2)+(0.2344*wickmeasure))/
 5hrs Linalool per sexual phase: Data for Fig 2d. To
 calculate ng/flower =
 ((standard.lin/1.4486)*1000)/flowers.in.sample) Field
 bee choice: Data for Fig 3a Pollen deposition: Data for
 Fig 3b Lab bee choice: Data for Fig 4