Pollinator extinctions alter structure of ecological networks

On the wings of National Pollinator Week, a new study by Emory biologist Berry Brosi gives insights into the dynamics of plant-pollinator interactions.

By Carol Clark

The absence of a single dominant bumblebee species from an ecosystem disrupts foraging patterns among a broad range of remaining pollinators in the system — from other bees to butterflies, beetles and more, field experiments show.

Biology Letters published the research, which may have implications for the survival of both rare wild plants and major food crops as many pollinator species are in decline.

“We see an ecological cascade of effects across the whole pollinator community, fundamentally changing the structure of plant-pollinator interaction networks,” says Berry Brosi, a biologist at Emory University and lead author of the study. “We can see this shift in who visits which plant even in pollinators that are not closely related to the bumblebee species that we remove from the system.” 

If a single, dominant species of bumblebee mainly visits an alpine sunflower, for instance, other pollinators — including other species of bumblebees — are less likely to visit alpine sunflowers. If the dominant bumblebee is removed, however, the dynamic changes.

“When the sunflowers became less crowded and more available, a broader range of pollinators chose to visit them,” Brosi says.

The field experiments, based in the Colorado Rockies, also showed that the removal of a dominant bumblebee species led to fewer plant species being visited on average.

“That was a surprise,” Brosi says. “If a nectar resource is abundant and highly rewarding, more types of pollinators will go for it, leaving out some of the rarer plants that some of the other pollinator species normally specialize in.”

The findings are important since most flowering plants and food crops need pollinators to produce seeds.

“Basically, for almost every pollinator group that we have good data for, we’ve seen declines in those pollinators,” Brosi says. “The results of our field experiments suggest that losses of pollinator species — at a local population level or on a global, true extinction scale — are likely to have bigger impacts on plant populations than previously predicted by simulation models.”

The experiments were done at the Rocky Mountain Biological Laboratory near Crested Butte, Colorado. Located at 9,500 feet, the facility’s subalpine meadows are too high for honeybees, but they are filled with a variety of bumblebees and other pollinators.

The study included a series of 20-meter-square wildflower plots. Each was evaluated in a control state, left in its natural condition, and in a manipulated state, in which bumblebees of just one species had been removed using nets. The bumblebees were later released unharmed when the experiments were over.

The work built on 2013 research led by Brosi that focused on bumblebees and one target plant species, alpine larkspur. That study showed how removing a bumblebee species disrupted floral fidelity, or specialization, among the remaining bees in the system, leading to less successful plant reproduction.

For the current paper, the researchers looked at a system of more than 30 species of pollinators and their interactions with 43 plants species.

“There’s been a lot of observational research done on plant-pollinator networks,” Brosi said. “One of the general findings is that they have a really consistent structure. That tends to hold true almost irrespective of ecosystem and geographic area, from the northeastern coast of Greenland to tropical rainforests.”

Mathematical simulation models have suggested that plant-pollinator networks would have good resiliency if there is an extinction in the system, based on the assumption that the network structure would remain consistent.

“Our experiments show that this assumption is not tenable,” Brosi says. “These networks are dynamic and when a pollinator species is missing, we’re going to see both qualitative and quantitative changes. Future simulation models need to incorporate ecological processes like competition that can shape which pollinators interact with which plants.”

Co-authors of the study are Kyle Niezgoda, who worked on the project as an undergraduate in Emory’s Department of Environmental Sciences, and Heather Briggs of the University of California, Santa Cruz.

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Mutant mosquitos make insecticide-resistance monitoring key to controlling Zika

"You can't stop evolution," Emory disease ecologist Gonzalo Vazquez-Prokopec says, explaining that it is a natural process for mosquitos to mutate in response to insecticides. (CDC photo by James Gathany)

By Carol Clark

One of the most common insecticides used in the battle against the Aedes aegypti mosquito has no measurable impact when applied in communities where the mosquito has built up resistance to it, a study led by Emory University finds.

The study is the first to show how vital insecticide-resistance monitoring is to control the Aedes mosquito — which carries the viruses that cause Zika, dengue fever and yellow fever.

The journal PLoS Neglected Tropical Diseases published the research.

“The results are striking,” says Gonzalo Vazquez-Prokopec, a disease ecologist at Emory and first author of the study. “If you use the insecticide deltamethrin in an area with high-deltamethrin resistance, it’s the same as if you didn’t spray at all. It does not kill the Aedes aegypti mosquitos. The efficacy is not different to a control.”

The results of the randomized, controlled trial are important because some public health departments in places where Zika and dengue viruses are endemic do not necessarily monitor for insecticide resistance.

“The recent epidemic of the Zika virus has raised awareness that we need to focus on what really works when it comes to mosquito control,” Vazquez-Prokopec says. “The data from our study makes a bold statement: Any mosquito-control program involving spraying insecticides needs to be based on knowledge of the current levels of insecticide-resistance of the local mosquitos.”

It is not difficult to determine levels of insecticide resistance, he adds. Public health workers can use standardized bioassays to coat a bottle with an insecticide in a specific dose. They can then introduce mosquitos from the area to be monitored into the bottles and observe the number of them killed after 24 hours.

The current study — conducted in three neighborhoods of Merida, Mexico — measured the efficacy of indoor residual spraying against adult Aedes aegypti mosquitos in houses treated with either deltamethrin (to which the local mosquitos expressed a high degree of resistance) or bendiocarb (another insecticide to which the mosquitos were fully susceptible), as compared to untreated control houses.

The bediocarb-treated areas showed a 60-percent kill rate for Aedes aegypti mosquitos during a three-month period, while the deltamethrin-treated areas and the control areas showed no detectable impact on the mosquitos.

A research technician sprays the ceiling and walls of a home in Merida, Mexico, as part of the first study to show how vital insecticide-resistance monitoring is to control a mosquito that can spread the Zika virus. (Photo by Nsa Dada)

It’s a natural biological process for mosquitos to mutate in response to insecticide exposure, Vazquez-Prokopec says. These mutations can occur at the molecular level, preventing the insecticide from binding to an enzymatic target site. They can also happen at the metabolic level — when a mosquito’s metabolism “up regulates” the production of enzymes that can neutralize the toxic effects of an insecticide.

“Both mechanisms can occur in the same mosquito,” Vazquez-Prokopec says, “making insecticide resistance a challenging and fascinating problem.”

Even more worrying are so-called “super bug” mosquitos, that show resistance to more than one insecticide.

“You can’t stop evolution,” Vazquez-Prokopec says. “That’s why it’s important for countries to have resistance-monitoring systems at both local and national levels to help manage the use of insecticides more efficiently and effectively.”

For the past 20 years, there has been a rise in resistance to insecticides in mosquitos, particularly in the Anopheles genus, some of which transmit the malaria parasite. Anopheles mosquitos only bite between dusk and dawn, so the use of bed nets in areas where malaria is endemic have long been a method to reduce the opportunity for mosquitos to transmit malaria.

More than a decade ago, bed nets treated with pyretheroids — a class of pesticides that includes deltamethrin — were rolled out in Africa in a big way to fight malaria. Pyretheroids are commonly used because they are odorless, cheap, long-lasting and have low mammalian toxicity.

The widespread use of insecticide-treated bed nets eventually led to a rise in resistance to pyretheroids by the Anopheles mosquito. The nets, however, still provide a physical barrier between people and mosquitos so they retain some benefit.

A similar rise in resistance is being seen in the Aedes mosquito in some areas. But the Aedes mosquitos bite during the day, making bed nets ineffective and insecticide spraying campaigns more critical to their control.

Previous research led by Vazquez-Prokopec showed that contact tracing of human cases of dengue fever, combined with indoor residual spraying for Aedes mosquitos in homes, provided a significant reduction in the transmission of dengue during an outbreak.

The insecticide-resistance study adds to the growing body of knowledge of what works — and what doesn’t — to control the Aedes mosquito in order to lessen the impact of a mosquito-borne disease outbreak, or to prevent one altogether.

“We’re always going to be chasing the problem of insecticide resistance in mosquitos, but the more data that we have — and the more tools we have in our arsenal — the more time we can buy,” Vazquez-Prokopec says.

Co-authors of the study include scientists from Mexico’s Autonomous University of Yucatán, where Emory has a long-standing collaboration. The work was funded by the Emory Global Health Institute and Marcus Foundation, the Centers for Disease Control and Prevention, Mexico’s CONACYT and the National Health Medical Research Council.

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To boldly go where public health hasn't gone before

"Hopefully, Emory will make a mark in NASA history," says Yang Liu, associate professor of environmental health. (NASA photo)

From Rollins Magazine

Rollins School of Public Health researchers will soon take their research into orbit, partnering with the National Aeronautics and Space Administration (NASA) in a new satellite mission to study air pollution.

NASA chose Rollins as a joint recipient of its $100 million award — $2.3 million of which will come to Rollins — to study the effects of air pollution on the population through a satellite mission, according to Yang Liu, associate professor of environmental health. He noted that this is the first time a NASA space mission has incorporated a public health component.

"We're the scientific guinea pig," Liu said.

The Rollins research group, led by Liu, co-created the project idea with NASA's Jet Propulsion Laboratory (JPL). The mission will construct and use a Multi-Angle Imager for Aerosols (MAIA) device to record airborne particulate matter, which will collect data on the effects of pollution on public health from at least 10 locations with major metropolitan areas.

Once constructed by JPL, the MAIA device will be mounted on a compatible Earth-orbiting satellite. "Even though it's a small mission, it's actually the first ever in which we get to work with NASA engineers to build public health into the DNA of this instrument," Liu said.

The Rollins team will analyze the data to make predictions about public health issues such as birth outcomes and cardiovascular disease. The team will also serve as the public health liaison between JPL and other institutions in the complete research group. Recruited by Liu, the complete group has teams at University of California, Los Angeles, Harvard University, University of British Columbia, and University of Dalhousie.

Because the device will orbit via satellite, it will provide a more holistic view of air pollution data than the commonly used ground monitors.

"It's very difficult to cross to a completely different scientific community and convince them that this mission is not only worthwhile but also feasible," Liu said. "Hopefully, Emory will make a mark in NASA history."

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A disarming comedian interviews an Emory psychologist loaded with facts about the brain

Comedian Jordan Klepper, center, takes a break from filming in the Emory psychology department. He interviewed Emory psychologist Stephan Hamann, left, about the brain science involved in trying to understand the U.S. political divide and culture wars. (Photo by Carol Clark)

By Carol Clark

Why do some people have a liberal mindset while others seem set on conservatism? And what makes it so difficult to find common ground? Those are some of the questions explored in a one-hour special, “Jordan Klepper Solves Guns,” which aired recently on Comedy Central.

Comedian Jordan Klepper and a camera crew came to the Emory campus last October to film part of the program in the Department of Psychology. Klepper interviewed psychologist Stephan Hamann about his research into how the brain may influence whether people are on one end of the political spectrum or the other, and how we might use this knowledge to better understand one another. 

“People develop their beliefs over a lifetime,” Hamann explains, “and when you tell them something that they feel challenges those core beliefs, they can have a threat response and just shut down. Brain research shows how they stop processing information on a rational level and begin operating on a more emotional level. Of course, that’s the exact opposite of what you want them to do.”

The best way to try to discuss an idea that counters someone’s convictions is to go slow and lay the ground work, he adds. “You have to be as empathetic and compassionate as possible. That’s the first step. You have to earn someone’s trust before you jump to the argument.”

Klepper also underwent an fMRI scan of his own brain in Emory’s Facility for Education and Research in Neuroscience (FERN).

“The program did a good job of conveying a little bit of the science involved in brain imaging,” Hamann says. “These are challenging times, so it’s gratifying to be part of something aiming 5o help Americans find common ground. I like the way the program ended on a positive note, trying to get people to connect up with the political process.”

If you missed the broadcast, you can watch it on Klepper’s web site, JordanKlepperSolves.com.

The neuroscience of learning across borders

Brains without borders: Emory Laney Graduate School student Charlie Ferris, from psychologist Stephan Hamann's lab, poses with a brain sculpture at the Institute of Neurobiology in Querétaro, Mexico, during the recent Binational Mechanisms of Learning Forum. (Photo by COMEXUS) 

By Carol Clark

Jessica Dugan sits at a computer in the Emory University psychology department in Atlanta, training a rhesus monkey in a lab at a university in Querétaro, Mexico, on the concept of transitive inference. 

She watches the monkey in real-time on her screen. With a few clicks on her keyboard she can present the monkey with random images on a computer attached to its cage and see which image it chooses. The monkey is automatically rewarded with food pellets for correct choices. Eventually, the monkey begins to grasp that the computer “game” is based on a concept of transitive inference — the idea of a hierarchy based on a shared property.

“It’s pretty cool,” Dugan says. “As long as there’s a wi-fi connection, we can remotely put a monkey on task and conduct a training exercise or an experiment. Technology can make collaboration across countries a lot easier.”

The joint project between Emory and the National Autonomous University of Mexico (UNAM) Institute for Neurobiology is just one more in a series of doors opening for Dugan, leading to new ways of learning science and conducting research.

She entered Emory’s Laney Graduate School under the mentorship of psychologist Patricia Bauer, who focuses on human development of memory from infancy through childhood. Dugan is particularly passionate about designing and conducting experiments with children to get at some of the key questions surrounding metacognition — introspection about thought processes.

“Basically, I’m interested in how someone thinking about thinking may be able to improve their ability to learn new information,” she explains. “Self-generation of new knowledge is something that we use every day. It’s a process that’s critical to success in education and beyond.”

Dugan is simultaneously working with rhesus monkeys in the lab of Emory psychologist Robert Hampton. “Studying the cognition of the relatives of our earliest ancestors may help us understand if there was some evolutionary demand that led to us being able to perform certain cognitive tasks,” she says.

And now she’s broadened her horizons by working across countries through the UNAM collaboration.

In May, Dugan was part of a group of 15 Emory graduate students who traveled to Mexico for the UNAM Binational Mechanisms of Learning Forum. The forum was the capstone of a year-long graduate seminar held at both Emory and UNAM called “Mechanisms of Learning Across Species and Development.”

Emory psychologist Patricia Bauer, left, listens as Maria Jose Olvera, a graduate student from the Institute of Neurobiology, explains her research. (Photo by COMEXUS)

“It was an amazing experience,” Dugan says of the nearly week-long forum. “The neuroscience they are doing in Mexico is impressive. It makes me wonder why in the United States we tend to mainly focus on science done here or in Europe. It was as though I was watching a documentary about the cosmos and someone started describing our place on Earth and the camera zoomed out so you realized how small that we are. The Mexico forum gave me a much more universal perspective.”

“We want our students to have an international appreciation for science, so they’re not so America-centric,” Bauer says. “There are lots of things to learn from other parts of the world.”

Bauer co-taught the Mechanisms of Learning seminar in Atlanta this year with Emory psychologist Joseph Manns, and both also traveled to Mexico to participate in the forum. 

Meanwhile, Hampton co-taught the seminar to graduate students in Mexico with UNAM neuroscientist Hugo Merchant, who also researches rhesus monkeys. Hampton is on sabbatical from Emory and has been living in Querétaro and working at the Institute of Neurobiology for the past academic year, funded by the Fulbright Scholars Program.

“The idea is not just to exchange information that makes our science stronger,” Hampton says. “Mexico is a country with a huge border with the United States. We need to have more contact with one another so that we understand each other better and reduce the potential for conflicts between our two countries.”

Emory graduate student Kelly Chong, a member of the lab of biologist Robert Liu, discusses her research with Arturo Gonzalez Isla, a graduate student at the Institute of Neurobiology in Mexico. (Photo by COMEXUS)

UNAM, based in Mexico City, is one of the largest universities in the world, with nearly 400,000 students and faculty. Its Institute for Neurobiology is about three hours north in Querétaro, a small but growing city in the highlands of central Mexico.

“The air is a little bit thinner and the sun’s a bit stronger than in Atlanta,” Hampton says. “It’s ‘tranquillo’ — a calm place — with a high quality of life.”

The institute “is doing the full spectrum of neuroscience,” he adds, “from high-level primate cognition work to molecular biology, neuroanatomy, neurodevelopment and more.”

While most classes are taught in Spanish, the Mexican students are required to both read and publish scientific papers in English.

Emory has hosted the Mechanisms of Learning Forum for the past three years as a capstone to the graduate seminar and as part of a training program co-directed by Bauer and Hampton, funded by the National Institutes of Health.

This year, with Hampton based in Mexico, the decision was made to hold the forum in Querétaro, with funding from the Institute of Neurobiology and Emory's Halle Institute, Department of Psychology and Emory College. The U.S. Embassy in Mexico, Mexico’s National Association of Universities and Institutions of Higher Education (ANUIES), and COMEXUS — the Fulbright Scholars Program supporting Hampton’s sabbatical — also pitched in to support the event.

Thirty-three graduate students from the U.S. and Mexico came together with nine faculty guest speakers from institutions in both countries to discuss their work. The speakers covered topics ranging from human language learning, avian song learning, rodent motor learning and the electrophysiology of memory in adult humans.

“It was a phenomenal opportunity,” says Emory graduate student Emily Brown, who had never been to Mexico. “The best part of the experience for me was meeting the other graduate students and expanding my scientific network to another country. It was neat to see that they are facing similar challenges as graduate students in the United States, and doing similar research.”

A central part of the forum is an open-ended hypothesis-generating exercise. “You get together with people from different backgrounds whom you don’t normally get to bounce ideas off,” Brown explains. “It’s a chance to play with ideas across boundaries and disciplines. The aim is to be creative and to not reject something that may sound a little crazy at first. Instead, you brainstorm about possible techniques or strategies that might make it work. It’s expansive thinking that you don’t necessarily get to do on a day-to-day basis.”

“It’s a great exercise,” Dugan adds, “because as a graduate student you spend a lot of time cranking out things that have to be immediately useful. You can get stuck in a mindset of what won’t work. It’s beneficial to get together with people who have different passions and just think creatively.”

Emory graduate student Emily Brown in the Advanced Facility for Avian Research in Ontario with one of her research subjects — a black-capped chickadee. "The people more likely to make the big discoveries are those willing to talk to each other across labs, institutions and countries," Brown says.

Creative thinking has already led Brown into unexpected places. She began her graduate school career studying memory systems of rhesus monkeys in the Hampton lab, and thought she would stick to that path. Then she began hearing about memory work with wild birds and proposed a research project in collaboration with Hampton and Emory psychologist Donna Maney, who is focused on how genes, hormones and the environment affects the brains of birds.

One of the guest speakers at the 2014 Mechanisms of Learning Forum was David Sherry, an expert on bird cognition from the University of Western Ontario’s Advanced Facility for Avian Research in London, Ontario. Brown was inspired by his talk and ultimately able to expand her collaboration to include Sherry. She is now continuing as a graduate student at Emory while in the Sherry lab in Canada.

“It’s one of the top avian research facilities in the world,” Brown says. “I’m developing a technique to study memory and cognition in wild, free-living birds. Right now, I’m working with black-capped chickadees, which are known for taking bits of food, hiding them for later, and then using their memory to locate them. Ideally, the techniques I’m developing could be used with any small songbirds that you see coming to a feeder in your yard.”

Birds make a good model species because they are so widespread and their behavior in the wild is well-documented, she says. “You have some bird species that are closely related living in dramatically different ecosystems and those that are not closely related at all operating in similar ecosystems. So you can compare which cognitive functions of species might be more driven by the environment and the pressures that they’re facing there.”

Adding Mexico to the mix of her graduate school experiences seemed like a natural progression to Brown. “Scientists are doing science everywhere and we shouldn’t be closed off to each other because of some borders on a map,” she says. “Science is advanced by communication. The people more likely to make the big discoveries are those willing to talk to each other across labs, institutions and countries.”

And the talk doesn’t always have to be about work.

A highlight for Brown in Mexico was a social outing — a hike through a wildlife preserve with the host students. “I had a chance to see a lot of the local flora and fauna,” she says. “It’s a really different ecosystem than Atlanta or Ontario. It’s dry, full of cactuses and vermillion flycatchers. They’re very pretty birds.”

Dugan agrees that breaking down barriers is important to the future of science. “The science community is all over the world,” she says. “Science in general is in jeopardy right now but we’re stronger together. People around the world are benefitting from — and contributing to — scientific progress.”

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