In newly published research in the journal Ecology, Vannette noted that floral nectar is produced by many plants to reward pollinators, but this sugary secretion often contains chemical compounds that are bitter tasting or toxic, and can deter pollinators. Plants including citrus (Citrus), tobacco (Nicotiana), milkweed (Asclepias), turtlehead (Chelone), Catalpa, and others produce nectar containing bioactive compounds, including deterrent or toxic compounds.
“This poses a paradox of toxic nectar: why are deterrent or harmful compounds present in a resource intended to attract pollinators?” she asked. “One hypothesis is that these compounds reduce microbial growth, which could otherwise spoil the nectar resource.”
Vannette, an assistant professor in the UC Davis Department of Entomology and Nematology, and her colleague Tadashi Fukami, associate professor at Stanford University, tested this hypothesis by growing yeasts and bacteria in sugar solutions spiked with a chemical compounds that are found in nectar.
“We examined effects on the growth of microbes isolated from nectar and non-nectar sources. Contrary to expectations, chemical compounds only weakly inhibited microbial growth in most cases. Interestingly, some microorganisms even grew better in the presence of plant compounds, like nicotine. But most surprising, we found that microbial growth in nectar reduced nectar toxicity, decreasing the concentration of chemical compounds in some nectar solutions.”
Microbial effects on nectar, in turn, increased consumption of nectar containing chemical compounds by honey bee pollinators, she said. “We found that microorganisms in nectar can both reduce the concentration of some plant compounds in nectar and increase consumption of nectar that does contain these compounds. This indicates that although ‘toxic nectar' does not strongly inhibit microbial growth in nectar, microbes modify the palatability of nectar to pollinators, which can change foraging behaviors and may reduce selection on this trait in nectar.”
The paper, exploring the effects of nectar-inhabiting microbes on chemical compounds found in nectar and nectar consumption by pollinators, “demonstrates that the compounds in nectar—such as on citrus blossoms--do not inhibit microbial growth, Vannette said. “However, yeasts and bacteria that grow in nectar can modify the effects of plant chemical compounds on pollinator foraging and nectar consumption..”
In her abstract, Vannette wrote “Secondary metabolites that are present in floral nectar have been hypothesized to enhance specificity in plant-pollinator mutualism by reducing larceny by non-pollinators, including microorganisms that colonize nectar. However, few studies have tested this hypothesis. Using synthetic nectar, we conducted laboratory and field experiments to examine the effects of five chemical compounds found in nectar on the growth and metabolism of nectar-colonizing yeasts and bacteria, and the interactive effects of these compounds and nectar microbes on the consumption of nectar by pollinators.”
“In most cases, focal compounds inhibited microbial growth, but the extent of these effects depended on compound identity, concentration, and microbial species. Moreover, most compounds did not substantially decrease sugar metabolism by microbes, and microbes reduced the concentration of some compounds in nectar. Using artificial flowers in the field, we also found that the common nectar yeast Metschnikowia reukaufii altered nectar consumption by small floral visitors, but only in nectar containing catalpol. This effect was likely mediated by a mechanism independent of catalpol metabolism. Despite strong compound-specific effects on microbial growth, our results suggest that the secondary metabolites tested here are unlikely to be an effective general defense mechanism for preserving nectar sugars for pollinators. Instead, our results indicate that microbial colonization of nectar could reduce the concentration of secondary compounds in nectar and, in some cases, reduce deterrence to pollinators.”
The research, “Nectar Microbes Can Reduce Secondary Metabolites in Nectar and Alter Effects on Nectar Consumption by Pollinators,” appears on the Ecology website, http://onlinelibrary.wiley.com/doi/10.1890/15-0858.1/full
The research was funded by the Gordon and Betty Moore Foundation, the National Science Foundation, and Stanford University.
Future work will examine how microbial modification of nectar traits influences floral attractiveness, how microbial growth may modify the specificity of plant-pollinator interactions, and if microbial effects vary among plant species.
Vannette, a former postdoctoral fellow at Stanford University, joined the UC Davis Department of Entomology and Nematology in September 2015. “I am interested in understanding and predicting how microbial communities influence interactions between plants and insects,” she said. “In the Vannette lab (in Briggs Hall), we use tools and concepts from microbial ecology, chemical ecology, and community ecology to better understand the ecology and evolution of interactions among plants, microbes and insects."
Ecology journal research paper
Williams will receive an award of $25,000 to be used in support of his research, teaching and public service activities. He will serve as a Chancellor's Fellow until July 1, 2020, Katehi said.
The program, established in 2000 to honor the achievements of outstanding faculty members early in their careers, is funded in part by the Davis Chancellor's Club and the Annual Fund of UC Davis.
His research focuses on the ecology and evolution of bees and other pollinator insects and their interactions with flowering plants, especially in light of changing landscapes. His work is particularly timely given concern over the global decline in bees and other pollinators.
Colleagues praise him for being a gifted scientist doing groundbreaking fundamental research and as an effective communicator of research findings to California agriculture, especially the almond industry.
Williams joined the UC Davis faculty in 2009 and received tenure as an associate professor in 2013. He received his doctorate in evolution and ecology from State University of New York, Stony Brook.
More information on the Fellows, from Dateline
So says ecologist Richard Karban, professor of entomology in the UC Davis Department of Entomology and Nematology, in his newly published book, Plant Sensing and Communication (University of Chicago Press).
The 240-page book is a “landmark in its field,” said Graeme Ruxton of the University of St. Andrews, UK, co-author of Experimental Design for the Life Sciences and Plant-Animal Communication.
The book is “the first comprehensive overview of what is known about how plants perceive their environments, communicate those perceptions, and learn,” according to the publisher. “Facing many of the same challenges as animals, plants have developed many similar capabilities: they sense light, chemicals, mechanical stimulation, temperature, electricity, and sound. Moreover, prior experiences have lasting impacts on sensitivity and response to cues; plants, in essence, have memory."
Added the publisher: “Nor are their senses limited to the processes of an individual plant: plants eavesdrop on the cues and behaviors of neighbors and—for example, through flowers and fruits—exchange information with other types of organisms. Far from inanimate organisms limited by their stationary existence, plants, this book makes unquestionably clear, are in constant and lively discourse.”
What are 10 things to know about plant sensing and communication? According to Karban:
- Plants sense their environments and respond.
- Although they lack central nervous systems, they process information and appear to "behave intelligently."
- They sense the position of competitors and "forage" for light.
- They sense the availability of water and nutrients in the soil and "forage" for these resources.
- Their decisions are influenced by past experiences, akin to memory.
- The respond to reliable cues that predict future events, allowing them to "anticipate."
- Plants respond differently to cues that they themselves produce, allowing them to distinguish self from non-self.
- They respond differently to close relatives and strangers.
- Plants that are prevented from sensing or responding experience reduced fitness.
- By understanding the "language" of plant responses, we can grow healthier and more productive plants.
Karban has researched plant communication in sagebrush (Artemisia tridentata) on the east side of the Sierra since 1995. His groundbreaking research on plant communication among kin, published in February 2013 in the Proceedings of the Royal Society B: Biological Sciences, drew international attention. In that study, Karban and his co-researchers found that kin have distinct advantages when it comes to plant communication, just as “the ability of many animals to recognize kin has allowed them to evolve diverse cooperative behaviors.”
“Plants responded more effectively to volatile cues from close relatives than from distant relatives in all four experiments and communication reduced levels of leaf damage experienced over the three growing seasons,” they wrote.
In other words, if you're a sagebrush and your nearby kin is being eaten by a grasshopper, deer, jackrabbit, caterpillar or other predator, communication is more effective if you're closely related. Through volatile cues, your kin will inform you of the danger so you can adjust your defenses.
Karban likened this kind of plant communication to eavesdropping.” Plants “hear” the volatile cues of their neighbors as predators damage them.
The most basic form of communication? When a plant is being shaded, it senses the diminished light quality caused by a competitor and responds by moving away, Karban says.
“Plants are smart,” wrote Adrian Barnett of New Scientist in reviewing the book. “But to notice we have to overcome our ingrained cultural biases. . . . Clearly, we will never play chess with a rose, nor ask the orchid on our windowsill for advice. But that is the point: humans are guilty of serious parochialism, of defining intelligence in terms of a nervous system and muscle-based speed that enables things to be done fast…Plants are highly responsive, attuned to gravity, grains of sand, sunlight, starlight, the footfalls of tiny insects, and to slow rhythms outside our range. They are subtle, aware, strategic beings whose lives involve an environmental sensitivity very distant from the simple flower and seed factories of popular imagination.”
Barnett praised Karban's book as a “timely, highly accessible summary of fast-developing fields.”
Karban is a fellow of the American Association for the Advancement of Science (AAAS) and has published more than 100 journal articles and now, three books.
Karban is featured in the Dec. 23-30, 2013 edition of The New Yorker in Michael Pollan's piece, “The Intelligent Plant: Scientists Debate a New Way of Understanding Plants."
DAVIS--Evolutionary-ecologist Nancy Moran of Yale University will present a "Major issues in Modern Biology" seminar, sponsored by the Storer Endowment in Life Sciences, on Wednesday afternoon, June 5 in the Genome Center Lecture Hall.
Her seminar, titled “Two Sides of Symbiosis in the Ecology and Evolution of Insect Hosts” is at 4:10 and will be followed by a reception in the executive meeting room of the Hyatt Hotel.
Graduate student Leslie Saul-Gershenz of the Neal Williams lab, UC Davis Department of Entomology, will host and introduce her.
Moran’s research involves the evolution of bacterial genomes and of symbiotic associations. She has shown that intimate symbiotic associations date to the origins of major groups of organisms, and she has used genomic and experimental work to show that these associations provide hosts with essential molecules and defenses. She also works on general principles involving the evolution of genomes in bacteria.
“The central role of microbial partners in animal ecology and evolution is more and more evident, but the consequences of associating with beneficial microbes can be mixed,” Moran says in her abstract. “Some of the best examples of how symbiosis affects host evolution and diversification are in insects. Members of this immense, diverse group use a great variety of ecological niches, and encounter many challenges, including nutritional limitations, threats from pathogens and predators, and thermal stress. Bacteria possess genes and pathways that can help insects to overcome these challenges, so it's not surprising that mutualistic associations between insects and bacteria are ubiquitous.
“Symbiont acquisition underlies the success and diversification of some major insect groups. Genomic approaches have elucidated details of these associations in sap-feeding insects such as aphids, revealing mechanisms by which bacterial symbionts assist with host nutrition or with defense against natural enemies. Some insects, such as cicadas and sharpshooters, depend on a small consortium of unrelated bacterial symbionts, and this dependence requires elaborate mechanisms for transferring and packaging the symbionts within the host body.
“But symbiosis has another side, as long-term dependence on symbionts can limit host tolerances, due to degenerative evolution of domesticated symbiotic partners. Obligate symbionts often exhibit signs of genomic degradation and reduction; indeed, the tiniest known bacterial genomes are those of insect symbionts. Insect hosts often are dependent on partners that are increasingly incapable of performing. One evolutionary solution is replacement of ancient symbionts with newly acquired ones, as seen in grain weevils and spittlebugs. Whether symbionts undergo this degenerative evolution depends on whether mechanisms for inter-host transmission impose strict clonality in symbiont populations. “
Moran joined the Yale faculty in 2010 as the William H. Fleming Professor in Ecology and Evolutionary Biology. She obtained her bachelor of arts degree from the University of Texas in 1976 and a Ph.D. in zoology from the University of Michigan in 1982.
From 1986 to 2010, Moran served on the faculty of the University of Arizona, where she was a Regents’ professor. She was awarded a MacArthur Fellowship in 1997, and was elected to membership in the National Academy of Sciences in 2004, the American Academy of Arts and Sciences in 2004, the American Academy of Microbiology in 2004, and the American Association for the Advancement of Science in 2007. In 2010, she was awarded the International Prize for Biology by the Japan Society for the Promotion of Science. She has published more than 190 scientific papers.
The Tracy and Ruth Storer Endowment in the Life Sciences funds the major issues in the Modern Biology Lecture series. This lecture series is designed to bring to Davis eminent biologists whose current work represents the cutting edge of their fields of inquiry. The lectures are open to the entire campus and other interested persons.
Feb. 13, 2013
If you're not closely related, communication won't be as effective.
Newly published research in today's Proceedings of the Royal Society B: Biological Sciences shows that kin have distinct advantages when it comes to plant communication, just as “the ability of many animals to recognize kin has allowed them to evolve diverse cooperative behaviors,” says lead researcher and ecologist Richard Karban, a professor in the UC Davis Department of Entomology.
For example, fire ants can recognize kin. “Ants will destroy queens that are not relatives but protect those who are,” Karban said.
That ability is less well studied for plants, until now.
“When sagebrush plants are damaged by their herbivores, they emit volatiles that cause their neighbors to adjust their defenses,” Karban said. “These adjustments reduce rates of damage and increase growth and survival of the neighbors.”
The research, “Kin Recognition Affects Plant Communication and Defense,” is co-authored by two scientists from Japan and two from UC Davis: Kaori Shiojiri of the Hakubi Center for Advanced Research, Kyoto University, and Satomi Ishizaki of the Graduate School of Science and Technology, Niigata University; and William Wetzel of the UC Davis Center for Population Biology, and Richard Evans of the UC Davis Department of Plant Science.
To simulate predator damage, the researchers “wounded” the plants by clipping them and then studied the responses to the volatile cues. They found that the plants that received cues from experimentally clipped close relatives experienced less leaf damage over the growing season that those that received cues from clipped neighbors that were more distantly related.
“More effective defense adds to a growing list of favorable consequences of kin recognition for plants,” they wrote.
The researchers performed their field work on sagebrush (Artemisia tridentata) at Taylor Meadow, UC Sagehen Creek Field Station, near Truckee. They conducted four field experiments over three years “that compared the proportion of leaves that were damaged by herbivores over the growing season when plants were provided with volatile cues clipped from a close relative versus cues from a distant relative,” the scientists wrote.
For closely related kin, they snipped stem cuttings (clones), potted them, and then returned the pots to the field. They determined relatedness “by using microsatellites that varied among individual sagebrush clones.”
The result: “Plants responded more effectively to volatile cues from close relatives than from distant relatives in all four experiments and communication reduced levels of leaf damage experienced over the three growing seasons,” they wrote. “This result was unlikely to be caused by volatiles repelling or poisoning insect herbivores.”
Karban, who has studied plant communication among the sagebrush at the site since 1999, likened the plant communication to neighbors “eavesdropping.” They “hear” the volatile cues of their neighbors as predators damage them.
Plants do communicate, Karban said. A basic form of plant communication occurs when it is being shaded and it responds by moving away.
“Some definitions of communication require that both the sender and receiver benefit by engaging in the behavior,” the researchers wrote. “Sagebrush is a long-lived perennial, making estimates of the costs and benefits of communication difficult although plants that responded to volatile cues from damaged neighbors experienced greater survival at the seedling stage and greater production of new branches and inflorescences over 12 years.”
Karban said that the volatiles released by “experimentally damaged plants are highly variable among individuals.”
“In the future we plan to examine this chemical variability to determine which chemicals are active as signals and why they exhibit so much variability,” Karban said. “Ultimately, we would like to be able to understand the chemical nature of the volatile cues, how plants use them to communicate, and whether as agriculturalists, we can control host plant resistance to herbivores.”
The work was supported by grants from the Japan Society for the Promotion of Science (JSPS) and the U.S. Department of Agriculture.
Rick Karban's Lab Research