Fruit flies force their young to drink alcohol -- for their own good

The fruit fly study adds to the evidence "that using toxins in the environment to medicate offspring may be common across the animal kingdom," says biologist Todd Schlenke. 

By Carol Clark

When fruit flies sense parasitic wasps in their vicinity, they lay their eggs in an alcohol-soaked environment, essentially forcing their larvae to consume booze as a drug to combat the deadly wasps.

The discovery by biologists at Emory University is published in the journal Science.

“The adult flies actually anticipate an infection risk to their children, and then they medicate them by depositing them in alcohol,” says Todd Schlenke, the evolutionary geneticist whose lab did the research. “We found that this medicating behavior was shared by diverse fly species, adding to the evidence that using toxins in the environment to medicate offspring may be common across the animal kingdom.”

Adult fruit flies detect the wasps by sight, and appear to have much better vision than previously realized, he adds. “Our data indicate that the flies can visually distinguish the relatively small morphological differences between male and female wasps, and between different species of wasps.” 

The experiments were led by Balint Zacsoh, who recently graduated from Emory with a degree in biology and still works in the Schlenke lab. The team also included Emory graduate student Zachary Lynch and postdoc Nathan Mortimer.


Adult wasps are about to emerge from fruit fly pupae, above, after eating the fruit fly larvae from the inside out. Photo by Todd Schlenke.

The larvae of the common fruit fly, Drosophila melanogaster, eat the rot, or fungi and bacteria, that grows on overripe, fermenting fruit. They have evolved a certain amount of resistance to the toxic effects of the alcohol levels in their natural habitat, which can range up to 15 percent.

Tiny, endoparasitoid wasps are major killers of fruit flies. The wasps inject their eggs inside the fruit fly larvae, along with venom that aims to suppress their hosts’ cellular immune response. If the flies fail to kill the wasp egg, a wasp larva hatches inside the fruit fly larva and begins to eat its host from the inside out.

Last year, the Schlenke lab published a study showing how fruit fly larvae infected with wasps prefer to eat food high in alcohol. This behavior greatly improves the survival rate of the fruit flies because they have evolved high tolerance of the toxic effects of the alcohol, but the wasps have not.

“The fruit fly larvae raise their blood alcohol levels, so that the wasps living in their blood will suffer,” Schlenke says. “When you think of an immune system, you usually think of blood cells and immune proteins, but behavior can also be a big part of an organism’s immune defense.”


A female parasitic wasp, on the prowl for fruit fly larvae to inject with her eggs.

For the latest study, the researchers asked whether the fruit fly parents could sense when their children were at risk for infection, and whether they then sought out alcohol to prophylactically medicate them. 

Adult female fruit flies were released in one mesh cage with parasitic wasps and another mesh cage with no wasps. Both cages had two petri dishes containing yeast, the nourishment for lab-raised fruit flies and their larvae. The yeast in one of the petri dishes was mixed with 6 percent alcohol, while the yeast in the other dish was alcohol free. After 24 hours, the petri dishes were removed and the researchers counted the eggs that the fruit flies had laid.

The results were dramatic. In the mesh cage with parasitic wasps, 90 percent of the eggs laid were in the dish containing alcohol. In the cage with no wasps, only 40 percent of the eggs were in the alcohol dish.

“The fruit flies clearly change their reproductive behavior when the wasps are present,“ Schlenke says. “The alcohol is slightly toxic to the fruit flies as well, but the wasps are a bigger danger than the alcohol.”

The fly strains used in the experiments have been bred in the lab for decades. “The flies that we work with have not seen wasps in their lives before, and neither have their ancestors going back hundreds of generations,” Schlenke says. “And yet, the flies still recognize these wasps as a danger when they are put in a cage with them.”

Experiments showed that the flies are extremely discerning about differences in the wasps. They preferred to lay their eggs in alcohol when female wasps were present, but not if only male wasps were in the cage.


The adult female fruit flies only react to the presence of female wasps that infect fruit-fly larvae, above, and not to male wasps, or to other species of wasps that do not infect their larvae.

Theorizing that the flies were reacting to pheromones, the researchers conducted experiments using two groups of mutated fruit flies. One group lacked the ability to smell, and another group lacked sight. The flies unable to smell, however, still preferred to lay their eggs in alcohol when female wasps were present. The blind flies did not make the distinction, choosing the non-alcohol food for their offspring, even in the presence of female wasps.

“This result was a surprise to me,” Schlenke says. “I thought the flies were probably using olfaction to sense the female wasps. The small, compound eyes of flies are believed to be more geared to detecting motion than high-resolution images.”

The only obvious visual differences between the female and male wasps, he adds, is that the males have longer antennae, slightly smaller bodies, and lack an ovipositor.

The compound eye of a fruit fly. 

Further experimentation showed that the fruit flies can distinguish different species of wasps, and will only choose the alcohol food in response to wasp species that infect larvae, not fly pupae. “Fly larvae usually leave the food before they pupate,” Schlenke explains, “so there is likely little benefit to laying eggs at alcoholic sites when pupal parasites are present.”

The researchers also connected the exposure to female parasitic wasps to changes in a fruit fly neuropeptide.

Stress, and the resulting reduced level of neuropeptide F, or NPF, has previously been associated with alcohol-seeking behavior in fruit flies. Similarly, levels of a homologous neuropeptide in humans, NPY, is associated with alcoholism.

“We found that when a fruit fly is exposed to female parasitic wasps, this exposure reduces the level of NPF in the fly brain, causing the fly to seek out alcoholic sites for oviposition,” Schlenke says. “Furthermore, the alcohol-seeking behavior appears to remain for the duration of the fly’s life, even when the parasitic wasps are no longer present, an example of long-term memory.”

Finally, Drosophila melanogaster is not unique in using this offspring medication behavior. “We tested a number of fly species,” Schlenke says, “and found that each fly species that uses rotting fruit for food mounts this immune behavior against parasitic wasps. Medication may be far more common in nature than we previously thought.”

Related:
Fruit flies use alcohol as a drug to kill parasites
Monarch butterflies use drugs
What aphids can teach us about immunity


Photo of fruit fly eye by Bbski, Wikipedia Commons.

A social catalyst for science outreach

By Carol Clark

In January, Kristopher Hite moved from Colorado to join Emory as a post-doc in the biology lab of Roger Deal. Hite hit the ground running, fueled by his love of good science communications, along with his passion for science itself.

“If we could get more science educators to teach everyone, and not just the people in their classes, then the world would be a better place,” says Hite, who thinks of the World Wide Web as a virtual classroom.

SciOctopus, the ScienceOnline mascot.

Hite recently attended ScienceOnline, an annual event in Raleigh, North Carolina, that brings together scientists, writers, educators, programmers and others using the Web to change how science is done, taught and communicated.

“You bring what you know to ScienceOnline, and you receive an immense amount in return,” Hite says. He compares it to teachers learning from their students. “The wider the audience of people that you interact with, the more you can potentially learn,” he says.

While at Science Online, he heard about a Twitter event started by Adam Taylor, a high school science teacher in Nashville. Called #scistuchat, it unites high school students and leading scientists for virtual conversations.

Last week, he participated with three other scientists in a #scistuchat about cloning, using his Twitter handle @thorsonofodin. “It was so cool!” he says. “There was an explosion of tweets from high school students from all over the country, asking relevant questions.”

A ScienceOnline talk by Frasier Cain of Universe Today also inspired Hite. Cain explained how the Virtual Star Party was created through Google Hangouts, a free service that facilitates video-conferences that can be live-streamed to the world. Every Sunday, viewers can look through powerful telescopes from points around the globe for stunning live footage of beautiful objects in deep space.

"I had so much fun at ScienceOnline, so many new friends made and ideas hatched," says Hite. Photo by Russ Creech.

“Frasier Cain took the time to sit down with me individually, and taught me how to share what you’re seeing on Google Hangouts,” Hite says. “We have some cool microscopes here in our lab at Emory, and if I can find a few other people from other parts of the world who are interested, I’d like to start a Microscope Hangout.” People who ordinarily would not have access to a science lab could peer through microscopes and hear scientists explain what they are seeing.

Hite and other attendees from Atlanta wanted to keep the conversations going that started at ScienceOnline in Raleigh. He took the lead in launching a local ScienceOnline get-together. The inaugural Atlanta Science TweetUp, #ATLSciTweetUp, will meet from 8 to 11:30 pm on Friday, March 1 at the Thinking Man Tavern in Decatur. Everyone interested in community and collaborations at the intersection of science and the web is welcome.

“I had so much fun at ScienceOnline, so many new friends made and ideas hatched, I just want to help pass that on,” Hite says. “We’re holding it in a pub so it’s casual and organic, people can float in and out. Maybe we’ll even draw in people from the pub who didn’t come there for the science.”

Those that can’t make it in person can follow the conversation on Twitter at #ATLSciTweetUp, or at the Facebook page: http://www.facebook.com/ATLScitweetup.

And check out Hite's photo journal from ScienceOnline at his blog, tompainesghost.com.

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Evolutionary biologists urged to adapt their research methods

Synthesizing ancestral molecules can give a clearer view of genetic evolution, says Shozo Yokoyama. Photo of olive baboon by Nivet Dilmen, via Wikipedia Commons.

By Carol Clark

To truly understand the mechanisms of natural selection, evolutionary biologists need to shift their focus from present-day molecules to synthesized, ancestral ones, says Shozo Yokoyama, a biologist at Emory University.

Yokoyama presented evidence for why evolutionary biology needs to make this shift on Friday, February 15, during the American Academy of Arts and Sciences (AAAS) annual meeting in Boston.

“This is not just an evolutionary biology problem, it’s a science problem,” says Yokoyama, a leading expert in the natural selection of color vision. “If you want to understand the mechanisms of an adaptive phenotype, the function of a gene and how that function changes, you have to look back in time. That is the secret. Studying ancestral molecules will give us a better understanding of genes that could be applied to medicine and other areas of science.”

For years, positive Darwinian selection has been studied almost exclusively using comparative sequence analysis of present-day molecules, Yokoyama notes. This approach has been fueled by increasingly fast and cheap genome sequencing techniques. But the faster, easier route, he says, is not necessarily the best one if you want to arrive at a true, quantitative result.

“If you only study present-day molecules, you’re only getting part of the picture, and that picture is often wrong,” he says.

Fish provide clues for how environmental factors can lead to vision changes. Photo of scorpionfish by Andrew David, NOAA's Fisheries Collection.

Yokoyama has spent two decades teasing out secrets of the adaptive evolution of vision in fish and other vertebrates.

Five classes of opsin genes encode visual pigments and are responsible for dim-light and color vision. Fish provide clues for how environmental factors can lead to vision changes, since the available light at various ocean depths is well quantified. The common vertebrate ancestor, for example, possessed ultraviolet vision, which is suited to both shallow water and land.

“As the environment of a species sinks deeper in the ocean, or rises closer to the surface and moves to land, bits and pieces of the opsin genes change and vision adapts,” Yokoyama says. “I’m interested in exactly how that happens at the molecular level.”

Molecular biologists can take DNA from an animal, isolate and clone its opsin genes, then use in vitro assays to construct a specific visual pigment. The pigment can be manipulated by changing the positions of the amino acids, in order to study the regulation of the gene’s function.

In 1990, for example, Yokoyama identified the three specific amino acid changes that switch the human red pigment into a green pigment.

A few years later, another group of researchers confirmed Yokoyama’s findings, but found that the three changes only worked in one direction. In order to reverse the process, and turn the green pigment back to red, it took seven changes.

“They discovered this weird quirk that didn’t make sense,” Yokoyama says. “Why wouldn’t it take the same number of changes to go in either direction? That question was interesting to me.”

Unlike many other animals, most primates, including humans, have both a red and a green pigment, enabling them to distinguish red from green and vice-versa. Photo by Richard Ruggiero, U.S. Fish and Wildlife Service.

He spent 10 years researching and pondering the question before he realized the key problem: The experiments were conducted on present-day molecules.

When the earliest mammalian ancestors appeared 100 million years ago, they had only the red pigment. Around 30 million years ago, the gene for the red pigment duplicated itself in some primates. One of these duplicated red pigments then acquired sensitivity to the color green, turning into a green pigment.

“At the point that the three changes in amino acids occurred in this pigment, other mutations were happening as well,” Yokoyama says. “You have to understand the original interactions of all of the amino acids in the pigment, which means you have to look at the ancestral molecules. That’s the trick.”

In other words, just as changes in an animal’s external environment drive natural selection, so do changes in the animal’s molecular environment.

Statistical analysis allows Yokoyama and his collaborators to travel back in time and estimate the sequences for ancestral molecules. “It’s a lot of work,” he says. “We don’t have a clear picture of every intermediate species. We have to do a step-by-step retracing, screening for noise in the results at each step, before we can construct a reliable evolutionary tree.”

In 2008, Yokoyama led an effort to construct the most extensive evolutionary tree for dim-light vision, including animals from eels to humans. At key branches of the tree, Yokoyama’s lab engineered ancestral gene functions, in order to connect changes in the living environment to the molecular changes.

The lengthy process of synthesizing ancestral proteins and pigments and conducting experiments on them combines microbiology with painstaking techniques of theoretical computation, biophysics, quantum chemistry and genetic engineering.

This multi-dimensional approach allowed Yokoyama’s lab in 2009 to identify the scabbardfish as the first fish known to have switched from ultraviolet vision to violet vision. And Yokoyama pinpointed exactly how the scabbardfish made the switch, by deleting an amino acid molecule at site 86 in the chain of amino acids in the opsin gene.

“Experimenting on ancestral molecules is the key to getting a correct answer to problems of natural selection, but there are very few examples of that being done in evolutionary biology,” Yokoyama says.

Related:
Fish vision makes waves in natural selection

Objects of our afflictions

A hand-drawn arrow shows the trajectory of the bullet that passed through Private Ludwig Kohn in this detail of a Civil War surgical card. These cards, from the Army Medical Museum, Surgeon General's Office, document Union army doctors’ most interesting cases.

By Mary Loftus, Emory Magazine

The US National Library of Medicine in Bethesda, Maryland, began in 1836 as a shelf of books in the Office of the Surgeon General and evolved to become the largest biomedical library in the world, concurrently housing millions of physical items and serving electronic data to millions of online users around the world.

An x-ray of Hitler's skull.

“My fantasy holiday,” writer Mary Roach, author of the books "Stiff," "Spook" and "Bonk" has said, “is a week spent locked in the archives of the National Library of Medicine.”

Jeff Reznick, who received his PhD in history from Emory in 1999, is chief of the library’s History of Medicine division. He serves as a steward of some of the medical library’s rarest, oldest, and yes, quirkiest items – from palmistry guides to Civil War surgical cards to the first published illustration of Watson and Crick’s double helix.

“We’re not a lending library in the traditional sense,” Reznick explains, “but a contemporary research institution that is home to an amazing historical collection as well as an extensive exhibition program.”

The collections contain medieval manuscripts, rare first editions, silent films, paintings, photographs, postcards, lantern slides, original drawings, hospital records, and laboratory notebooks—17 million artifacts that range from the famous to the obscure, the sublime to the repulsive.

A cuttlefish, valued for its "bone," which could be ground up to make a tooth powder, from the pages of "Materia Medica Animalia" a rare 1853 book.

A selection of the library’s most captivating artifacts is highlighted in the newly published "Hidden Treasure," edited by Reznick’s colleague and library historian Michael Sappol. The coffee-table book is filled with 450 vivid illustrations and essays. Within its pages are sketches of conjoined twins, Hitler’s x-rays, autopsy illustrations, midwife dolls, Darwin’s sketches, a grand atlas of skin diseases, public health warning cards, and malaria pinup calendars. "Hidden Treasure" is available free as a downloadable e-copy at http://collections.nlm.nih.gov/HiddenTreasure, or as a hardbound book.

A review in The Lancet reads, “Each selection is truly intriguing and informative, reminding us that medicine is inherently connected to the human experience and all of its attendant complexities. As the images show, there are few, if any, areas of life that medicine does not affect.”

A young boy displaying Hirsutism, increased growth of facial hair, from the 1856 "Atlas of Skin Diseases."

The book’s introduction, cowritten by Reznick, notes: “These are things that are not entirely reducible to ‘information,’ that are only partly susceptible to digitization. They have a feel and texture and smell and color; they are strong or brittle, clean or dusty; they have been taken from place to place, bought or sold or bartered or stolen or issued or given away as gifts. They have been treasured or neglected, defaced or mended, added to or pruned back. Each object has lived a ‘social life,’ sometimes several lives.”

A 19th-century lantern slide.

Emory Professor of English Benjamin Reiss, author of "Theaters of Madness: Insane Asylums and Nineteenth-Century American Culture," says the library contains “an extraordinary collection and is underused as a scholarly resource.”

Reiss was invited to contribute an essay for "Hidden Treasure" on a set of magic lantern slides that were exhibited to mental patients in a 19th-century insane asylum. “The assignment led me on a really interesting historical detective mission, trying to figure out who made the slides, what the exhibits were like, and what role the exhibits played in the treatment of patients,” he says.

He found that many of the slides were part of patients’ “moral treatment,” meant to impress rational, orderly imagery—such as snowflakes—upon their minds, while others, such as a giant flea attacking a man in a chair, were for entertainment.

“Given that many patients were delusional and/or medicated with dream-inducing opiates, one wonders about the wisdom of serving up these ready-made hallucinations, magnified to terrifying proportions,” Reiss writes.

Related:
The rare book that changed medicine

Bonobos comfort friends in distress

The consolation behavior of young bonobos is a sign of sensitivity to the emotions of others and the ability to take the perspective of another. Photo courtesy of Zanna Clay.

By Lisa Newbern, Woodruff Health Sciences Center

Comforting a friend or relative in distress may be a more hard-wired behavior than previously thought, according to a new study of bonobos, which are great apes known for their empathy and close relation to humans and chimpanzees. The study provides key evolutionary insight into how critical social skills may develop in humans. The results were published by the journal PLOS

One.

Researchers from Emory's Yerkes National Primate Research Center observed juvenile bonobos at the Lola ya Bonobo sanctuary in the Democratic Republic of Congo engaging in consolation behavior more than their adult counterparts. Juvenile bonobos (three-to-seven years old) are equivalent in age to preschool or elementary school-aged children.

Emory psychologists Zanna Clay and Frans de Waal, director of the Living Links Center at Yerkes, led the study.

"Our findings suggest that for bonobos, sensitivity to the emotions of others emerges early and does not require advanced thought processes that develop only in adults," Clay says.

Starting at around age two, human children usually display consolation behavior, a sign of sensitivity to the emotions of others and the ability to take the perspective of another. Consolation has been observed in humans, bonobos, chimpanzees and other animals, including dogs, elephants and some types of birds, but has not been seen in monkeys.

At the Lola ya Bonobo sanctuary, most bonobos come as juvenile or infant orphans because their parents are killed for meat or captured as pets. A minority of bonobos in the sanctuary is second generation and raised by their biological mothers. The researchers found bonobos raised by their own mothers were more likely to comfort others compared to orphaned bonobos. This may indicate early life stress interferes with development of consolation behavior, while a stable parental relationship encourages it, Clay says.

Clay observed more than 350 conflicts between bonobos at the sanctuary during several months. Some conflicts involved violence, such as hitting, pushing or grabbing, while others only involved threats or chasing. Consolation occurred when a third bonobo — usually one that was close to the scene of conflict — comforted one of the parties in the conflict.

Consolation behavior includes hugs, grooming and sometimes sexual behavior. Consolation appears to lower stress in the recipient, based on a reduction in the recipient’s rates of self-scratching and self-grooming, the authors write.

"We found strong effects of friendship and kinship, with bonobos being more likely to comfort those they are emotionally close to," Clay says. "This is consistent with the idea that empathy and emotional sensitivity contribute to consolation behavior."

In future research, Clay plans to take a closer look at the emergence of consolation behavior in bonobos at early ages. A process that may facilitate development of consolation behavior is when older bonobos use younger ones as teddy bears; their passive participation may get the younger bonobos used to the idea, she says.

Related:
Are hugs the new drugs?
Chimps, bonobos yield clues to social brain
Hugs go way back in evolution

The physics of icicles and our lumpy universe

Everyone knows that no two snowflakes are alike, but what about icicles? Physicist Stephen Morris built an icicle-making machine in his University of Toronto lab to tackle this question by systematically studying the shape of icicles and how they grow. (See video above). His research is not just fascinating physics. It could also have implications for preventing dangerous ice formations on airplane wings or power lines.

And icicles are just the tip of the problem. The entire universe is not uniform, instead it’s “a kind of foam or lumpy mass,” Morris says.

Morris is in Atlanta this week, where he will be giving talks about pattern formations in nature, going back to the lumps that developed in the primordial soup of early Earth. You can catch him in a public lecture tonight, Feb. 4 at 6 pm at Georgia Tech, and in an Emory physics colloquia tomorrow, Feb. 5 at 2:30 pm.

Related:
Physicists crack another piece of the glass puzzle
Crystal-liquid interface made visible for the first time