Metabolic Integration of Spectral and Chemical Cues Mediating Plant Responses to Competitors and Herbivores

Light quality and chemicals in a plant’s environment can provide crucial information about the presence and nature of antagonists, such as competitors and herbivores. Here, we evaluate the roles of three sources of information—shifts in the red:far red (R:FR) ratio of light reflected off of potentially competing neighbors, induced metabolic changes to damage by insect herbivores, and induced changes to volatile organic compounds emitted from herbivore-damaged neighboring plants—to affect metabolic responses in the tall goldenrod, Solidago altissima. We address the hypothesis that plants integrate the information available about competitors and herbivory to optimize metabolic responses to interacting stressors by exposing plants to the different types of environmental information in isolation and combination. We found strong interactions between the exposure to decreased R:FR light ratios and damage on the induction of secondary metabolites (volatile and non-volatile) in plants. Similarly, the perception of VOCs emitted from neighboring plants was altered by the simultaneous exposure to spectral cues from neighbors. These results suggest that plants integrate spectral and chemical environmental cues to change the production and perception of volatile and non-volatile compounds and highlight the role of plant context-dependent metabolic responses in mediating population and community dynamics

DEFENSIVE FUNCTIONS AND POTENTIAL ECOLOGICAL CONFLICTS OF FLORAL STICKINESS

This dataset includes results from HPLC and GC-MS analyses on the non-volatile and volatile secondary metabolites of B. resinosa. The data are raw signal intensity and signal intensity of each compound relative to an internal standard. The data were the basis for the analyses in the original publication and can be used for subsequent analyses after informing the original authors.Stickiness of vegetative tissues has evolved multiple times in different plant families but is rare and understudied in flowers. While stickiness in general is thought to function primarily as a defense against herbivores, it can compromise mutualistic interactions (such as those with pollinators) in reproductive tissues. Here, we test the hypothesis that stickiness on flower petals of the High-Andean plant, Bejaria resinosa (Ericaceae), functions as a defense against florivores. We address ecological consequences and discuss potential trade-offs associated with a repellant trait expressed in flowers that mediate mutualistic interactions. In surveys and manipulative experiments, we assess florivory and resulting fitness effects on plants with sticky and non-sticky flowers in different native populations of B. resinosa in Colombia. In addition, we analyze the volatile and non-volatile components in sticky and non-sticky flower morphs to understand the chemical information context within which stickiness is expressed. We demonstrate that fruit set is strongly affected by floral stickiness but also varies with population. While identifying floral stickiness as a major defensive function, our data also suggest that the context-dependency of chemical defense functionality likely arises from differential availability of primary pollinators and potential trade-offs between chemical defense with different modes of action.The research was funded by a grant to AC by Fundación CEIBA (Centro de Estudios Interdisciplinarios Básicos y Aplicados) and a grant from the New Phytologist Foundation to AK

nectar

To establish if foliar herbivory causes changes in floral rewards that could alter floral visitation, we selected another 30 pairs of plants (15 pin and 15 thrum) of P. angustifolia. On each pair, we selected branches with inflorescences at the bud stage to serve as locally-induced, systemically-induced, and control branches and applied grasshopper herbivory treatments as described above. After 3 days, grasshoppers and bags were removed. From a subset of the same inflorescences (5 pin and 6 thrum), we also collected nectar on one randomly chosen flower. Nectar volume was measured using 2µL microcapillary pipettes (Drummond Scientific Company, Broomall, PA). The sugar concentration was estimated using a handheld refractometer (Reichert Digital Brix/RI-Chek). Due to low nectar volumes, all samples were diluted in 0.1 mL distilled water prior to taking concentration measurements. The concentration of the floral nectar was then calculated as the measured solution concentration multiplied by the ratio of the final solution volume to the collected nectar volume. The first column shows the flower morph: pin (P) and thrum (T). The second column is the volume in microliters of nectar present in the flower. The third column is the concentration of the nectar in each flower. The fourth column is the treatment of each branch: C control, S systemic induction and L local induction. The fifth column is the block of each pair of plants

Mean number of visitors (+/-SE) to <i>Palicourea angustifolia</i> plants that have been locally or systemically exposed to herbivory by <i>Zeromastax selenesii</i> and non-exposed (control plants).

<p>Data are summed across all pollinator species. Treatments with a common letter are not significantly different (Tukey test, P > 0.05).</p

totalvisits_summed

To determine if foliar herbivory affected pollinator visitation, we monitored pollinator visits to 26 pairs of plants from the experiment described above. Plant pairs used for the observations were always located within approximately 2 m of each other to allow simultaneous pollinator observations. On each pair of plants, we recorded floral visitors in a series of one to three separate 30-minute continuous observations conducted after the removal of grasshoppers from the leaves. Just prior to each observation, we counted the number of open flowers on inflorescences from each of the three branches. The locally-induced, systemically induced, and control branches from a single plant pair were then observed simultaneously to record the identity of the floral visitors and the number of flowers visited by each individual visitor. The first column shows the name of the pollinator. the second column is the number for each couple of plants. the third column is the treatment of each branch: L local herbivory, S systemic herbivory, and C control. The fourth column is the number of visits of each pollinator. the fifth column is the number of individuals that made that visit and the sixth column is the average of opened flowers at the moment of the observation

Nectar volume (A) and nectar concentration (B) (+/- SE) of <i>Palicourea angustifolia</i> plants that have been locally or systemically exposed to herbivory by <i>Zeromastax selenesii</i> and non-exposed (control plants).

<p>Treatments with a common letter are not significantly different (Tukey test, P > 0.05).</p

Output of the generalized linear mixed models analyzing the effects of foliar herbivory treatment (local induction, systemic induction and control), number of open flowers and their interaction on the total number of visits to flowers, the total number of visitors, and the visits of individual species.

<p>Output of the generalized linear mixed models analyzing the effects of foliar herbivory treatment (local induction, systemic induction and control), number of open flowers and their interaction on the total number of visits to flowers, the total number of visitors, and the visits of individual species.</p

Mean number of visits of pollinators (+/-SE) to <i>Palicourea angustifolia</i> plants that have been locally or systemically exposed to herbivory by <i>Zeromastax selenesii</i> and non-exposed (control plants).

<p><b>A.</b> All pollinator species combined <b>B.</b> <i>Ocreatus underwoodii</i>, <b>C.</b> <i>Colibri thalassinus</i>, <b>D.</b> <i>Trigona fulviventris</i> and <b>E.</b> <i>Paratrigona</i> sp. Treatments with a common letter are not significantly different (Tukey test, P > 0.05).</p

Percentage of fruit set on <i>Palicourea angustifolia</i> plants that have been locally or systemically exposed to herbivory by <i>Zeromastax selenesii</i> and non-exposed (control plants).

<p>Treatments with same letter are not significantly different (Tukey test, P > 0.05).</p