In a study published Jan. 26 in Cancer Discovery, a journal of the American Association for Cancer Research, the investigators reported that this biologic process could help explain why cancers so often recur after treatment. The research was done in both organoids and mouse models made from patients’ samples of acute myeloid leukemia (AML) tumors. The findings were also verified by looking at samples from AML patients that were collected throughout the course of treatment and relapse.

“Acute myeloid leukemia can be put into remission with chemotherapy, but it almost always comes back, and when it does it’s incurable,” said senior author Dr. Ari M. Melnick, the Gebroe Family Professor of Hematology and Medical Oncology and a member of the Sandra and Edward Meyer Cancer Center at Weill Cornell Medicine. “A longstanding question in the field has been, ‘Why can’t you get rid of all the cancer cells?’ A similar question can be posed for many other types of aggressive cancer in addition to AML.”

For years, cancer researchers have studied how tumors are able to rebound after they appear to be completely wiped out by chemotherapy. One theory has been that because not all cells within a tumor are the same at the genetic level — a condition called tumor heterogeneity — a small subset of cells are able to resist treatment and begin growing again. Another theory involves the idea of tumor stem cells — that some of the cells within a tumor have special properties that allow them to re-form a tumor after chemotherapy has been given.

The idea that senescence is involved does not replace these other theories. In fact, it could provide new insight into explaining these other processes, Dr. Melnick said.

In the study, the researchers found that when AML cells were exposed to chemotherapy, a subset of the cells went into a state of hibernation, or senescence, while at the same time assuming a condition that looked very much like inflammation. They looked similar to cells that have undergone an injury and need to promote wound healing — shutting down the majority of their functions while recruiting immune cells to nurse them back to health.

“These characteristics are also commonly seen in developing embryos that temporarily shut down their growth due to lack of nutrition, a state called embryonic diapause,” Dr. Melnick explained. “It’s not a special process, but normal biological activity that’s playing out in the context of tumors.”

Further research revealed that this inflammatory senescent state was induced by a protein called ATR, suggesting that blocking ATR could be a way to prevent cancer cells from adopting this condition. The investigators tested this hypothesis in the lab and confirmed that giving leukemia cells an ATR inhibitor before chemotherapy prevented them from entering senescence, thereby allowing chemotherapy to kill all of the cells.

Importantly, studies published at the same time from two other groups reported that the role of senescence is important not just for AML, but for recurrent cases of breast cancer, prostate cancer and gastrointestinal cancers as well. Dr. Melnick was a contributor to one of those other studies.

Dr. Melnick and his colleagues are now working with companies that make ATR inhibitors to find a way to translate these findings to the clinic. However, much more research is needed, because many questions remain about when and how ATR inhibitors would need to be given.

“Timing will be very critical,” he said. “We still have a lot to work out in the laboratory before we can study this in patients.”

Dr. Cihangir Duy, a former postdoctoral fellow in Dr. Melnick’s lab, was the study’s first author. Dr. Duy now leads his own lab at Fox Chase Cancer Center in Philadelphia.

Dr. Ari Melnick has been a paid consultant for KDAC Therapeutics, Epizyme, and Constellation Pharmaceuticals.

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The study, published in the journal Science Advances, yields information on a important period in our planet’s formation, when a deep sea of incandescent magma stretched across Earth’s surface and extended hundreds of kilometres into its interior.

It is the gradual cooling and crystallisation of this ‘magma ocean’ that set the chemistry of Earth’s interior — a defining stage in the assembly of our planet’s structure and the formation of our early atmosphere.

Scientists know that catastrophic impacts during the formation of the Earth and Moon would have generated enough energy to melt our planet’s interior. But we don’t know much about this distant and fiery phase of Earth’s history because tectonic processes have recycled almost all rocks older than 4 billion years.

Now researchers have found the chemical remnants of the magma ocean in 3.6-billion-year-old rocks from southwestern Greenland.

The findings support the long-held theory that Earth was once almost entirely molten and provide a window into a time when the planet started to solidify and develop the chemistry that now governs its internal structure. The research suggests that other rocks on Earth’s surface may also preserve evidence of ancient magma oceans.

“There are few opportunities to get geological constraints on the events in the first billion years of Earth’s history. It’s astonishing that we can even hold these rocks in our hands — let alone get so much detail about the early history of our planet,” said lead author Dr Helen Williams, from Cambridge’s Department of Earth Sciences.

The study brings forensic chemical analysis together with thermodynamic modelling in search of the primeval origins of the Greenland rocks, and how they got to the surface.

At first glance, the rocks that make up Greenland’s Isua supracrustal belt look just like any modern basalt you’d find on the sea floor. But this outcrop, which was first described in the 1960s, is the oldest exposure of rocks on Earth. It is known to contain the earliest evidence of microbial life and plate tectonics.

The new research shows that the Isua rocks also preserve rare evidence which even predates plate tectonics — the residues of some of the crystals left behind as that magma ocean cooled.

“It was a combination of some new chemical analyses we did and the previously published data that flagged to us that the Isua rocks might contain traces of ancient material. The hafnium and neodymium isotopes were really tantalizing, because those isotope systems are very hard to modify — so we had to look at their chemistry in more detail,” said co-author Dr Hanika Rizo, from Carleton University.

Iron isotopic systematics confirmed to Williams and the team that the Isua rocks were derived from parts of the Earth’s interior that formed as a consequence of magma ocean crystallisation.

Most of this primeval rock has been mixed up by convection in the mantle, but scientists think that some isolated zones deep at the mantle-core boundary — ancient crystal graveyards — may have remained undisturbed for billions of years.

It’s the relics of these crystal graveyards that Williams and her colleagues observed in the Isua rock chemistry. “Those samples with the iron fingerprint also have a tungsten anomaly — a signature of Earth’s formation — which makes us think that their origin can be traced back to these primeval crystals,” said Williams.

But how did these signals from the deep mantle find their way up to the surface? Their isotopic makeup shows they were not just funnelled up from melting at the core-mantle boundary. Their journey was more circuitous, involving several stages of crystallization and remelting — a kind of distillation process. The mix of ancient crystals and magma would have first migrated to the upper mantle, where it was churned up to create a ‘marble cake’ of rocks from different depths. Later melting of that hybrid of rocks is what produced the magma which fed this part of Greenland.

The team’s findings suggest that modern hotspot volcanoes, which are thought to have formed relatively recently, may actually be influenced by ancient processes.

“The geochemical signals we report in the Greenland rocks bear similarities to rocks erupted from hotspot volcanoes like Hawaii — something we are interested in is whether they might also be tapping into the depths and accessing regions of the interior usually beyond our reach,” said Dr Oliver Shorttle, who is jointly based at Cambridge’s Department of Earth Sciences and Institute of Astronomy.

The team’s findings came out of a project funded by Deep Volatiles, a NERC-funded 5-year research programme. They now plan to continue their quest to understand the magma ocean by widening their search for clues in ancient rocks and experimentally modelling isotopic fractionation in the lower mantle.

“We’ve been able to unpick what one part of our planet’s interior was doing billions of years ago, but to fill in the picture further we must keep searching for more chemical clues in ancient rocks,” said co-author Dr Simon Matthews from the University of Iceland.

Scientists have often been reluctant to look for chemical evidence of these ancient events. “The evidence is often altered by the course of time. But the fact we found what we did suggests that the chemistry of other ancient rocks may yield further insights into the Earth’s formation and evolution — and that’s immensely exciting,” said Williams.

A research team led by Alexander Groos, Heinz Veit (both from the Institute of Geography) and Naki Akçar (Institute of Geological Sciences) at the University of Bern, in collaboration with colleagues from ETH Zurich, the University of Marburg and the University of Ankara, used the Ethiopian Highlands as a test site to investigate the extent and impact of regional cooling on tropical mountains during the last glacial period. The results have been published in the scientific journals Science Advances and Earth Surface Dynamics.

Formation of plateau and valley glaciers

“The Ethiopian Highlands are currently not covered by ice, despite its elevation of over 4,000 m,” explains Groos, who studied the glacial, climatic and landscape history of the Bale and Arsi Mountains in the southern highlands as part of his dissertation. “Moraines and other land forms, however, attest to the fact that these mountains were glaciated during the last cold period,” he continues.

Moraine boulders in the Bale and Arsi Mountains were mapped and sampled in the field and later dated using the chlorine isotope “36Cl” to accurately determine the extent and timing of past glaciations. The researchers were in for a surprise: “Our results show that glaciers in the southern Ethiopian Highlands reached their maximum extent between 40,000 and 30,000 years ago,” says Groos, “several thousand years earlier than in other mountainous regions in Eastern Africa and worldwide.” In total, the glaciers in the southern highlands covered an area of more than 350 km² during their maximum. In addition to the cooling of at least 4 to 6 °C, the extensive volcanic plateaus above 4,000 m favored the development of glaciation in this magnitude.

The researchers gained important insights by comparing the specially reconstructed glacier fluctuations in the Ethiopian Highlands with those of the highest East African mountains and climate archives from the Great African Rift Valley. “The cross-comparisons show that the tropical mountains in Eastern Africa have experienced a more pronounced cooling than the surrounding lowlands,” Groos concludes. “Furthermore, the results suggest a nonuniform response by East African glaciers and ice caps to climate changes during the last cold period, which can be attributed to regional differences in precipitation distribution and mountain relief, among other factors,” he continues.

The enigma of the stone stripes

During their fieldwork on the central Sanetti Plateau in the Bale Mountains, the researchers also came across gigantic stone stripes (up to 1,000 m long, 15 m wide and 2 m deep) outside the area of the former ice cap. “The existence of these stone stripes on a tropical plateau surprised us, as so-called periglacial landforms of this magnitude were previously only known from the temperate zone and polar regions and are associated with ground temperatures around freezing point,” Groos said. However, the average ground temperature on the Sanetti Plateau is currently about 11 °C.

The large boulders and basalt columns that make up the stone stripes originally came from heavily eroded rock formations and volcanic plugs. As things stand, the researchers assume that the stone stripes were formed during the last glacial period through natural sorting of the previously chaotically distributed rocks in the course of the periodic freezing and thawing of the ground near the former ice cap. However, locally this would have required a drop in the mean ground temperature of at least 11 °C and in the mean air temperature of at least 7 °C. Whether this unprecedented cooling is a regional phenomenon or exemplary for the cooling of tropical high mountains during the last glacial period must be shown by future studies from other tropical mountain regions.

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The study is a collaboration between researchers in the UK, US and Belgium. The lead authors Prof David L Robertson (at the MRC-University of Glasgow Centre for Virus Research, Scotland) and Prof Sergei Pond (at the Institute for Genomics and Evolutionary Medicine, Temple University, Philadelphia) were able to turn their experience of analysing data from HIV and other viruses to SARS-CoV-2. Pond’s state-of-the-art analytical framework, HyPhy, was instrumental in teasing out the signatures of evolution embedded in the virus genomes and rests on decades of theoretical knowledge on molecular evolutionary processes.

First author Dr Oscar MacLean explains, “This does not mean no changes have occurred, mutations of no evolutionary significance accumulate and ‘surf’ along the millions of transmission events, like they do in all viruses.” Some changes can have an effect; for example, the Spike replacement D614G which has been found to enhance transmissibility and certain other tweaks of virus biology scattered over its genome. On the whole, though, ‘neutral’ evolutionary processes have dominated. MacLean adds, “This stasis can be attributed to the highly susceptible nature of the human population to this new pathogen, with limited pressure from population immunity, and lack of containment, leading to exponential growth making almost every virus a winner.”

Pond comments, “what’s been so surprising is just how transmissible SARS-CoV-2 has been from the outset. Usually viruses that jump to a new host species take some time to acquire adaptations to be as capable as SARS-CoV-2 at spreading, and most never make it past that stage, resulting in dead-end spillovers or localised outbreaks.”

Studying the mutational processes of SARS-CoV-2 and related sarbecoviruses (the group of viruses SARS-CoV-2 belongs to from bats and pangolins), the authors find evidence of fairly significant change, but all before the emergence of SARS-CoV-2 in humans. This means that the ‘generalist’ nature of many coronaviruses and their apparent facility to jump between hosts, imbued SARS-CoV-2 with ready-made ability to infect humans and other mammals, but those properties most have probably evolved in bats prior to spillover to humans.

Joint first author and PhD student Spyros Lytras adds, “Interestingly, one of the closer bat viruses, RmYN02, has an intriguing genome structure made up of both SARS-CoV-2-like and bat-virus-like segments. Its genetic material carries both distinct composition signatures (associated with the action of host anti-viral immunity), supporting this change of evolutionary pace occurred in bats without the need for an intermediate animal species.”

Robertson comments, “the reason for the ‘shifting of gears’ of SARS-CoV-2 in terms of its increased rate of evolution at the end of 2020, associated with more heavily mutated lineages, is because the immunological profile of the human population has changed.” The virus towards the end of 2020 was increasingly coming into contact with existing host immunity as numbers of previously infected people are now high. This will select for variants that can dodge some of the host response. Coupled with the evasion of immunity in longer-term infections in chronic cases (e.g., in immunocompromised patients), these new selective pressures are increasing the number of important virus mutants.

It’s important to appreciate SARS-CoV-2 still remains an acute virus, cleared by the immune response in the vast majority of infections. However, it’s now moving away faster from the January 2020 variant used in all of the current vaccines to raise protective immunity. The current vaccines will continue to work against most of the circulating variants but the more time that passes, and the bigger the differential between vaccinated and not-vaccinated numbers of people, the more opportunity there will be for vaccine escape. Robertson adds, “The first race was to develop a vaccine. The race now is to get the global population vaccinated as quickly as possible.”

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“There are only about 300 known RV Tauri variables in the Milky Way galaxy,” said Laura Vega, a recent doctoral recipient at Vanderbilt University in Nashville, Tennessee. “We focused our study on the second brightest, named U Monocerotis, which is now the first of these systems from which X-rays have been detected.”

A paper describing the findings, led by Vega, was published in The Astrophysical Journal.

The system, called U Mon for short, lies around 3,600 light-years away in the constellation Monoceros. Its two stars circle each other about every six and a half years on an orbit tipped about 75 degrees from our perspective.

The primary star, an elderly yellow supergiant, has around twice the Sun’s mass but has billowed to 100 times the Sun’s size. A tug of war between pressure and temperature in its atmosphere causes it to regularly expand and contract, and these pulsations create predictable brightness changes with alternating deep and shallow dips in light — a hallmark of RV Tauri systems. Scientists know less about the companion star, but they think it’s of similar mass and much younger than the primary.

The cool disk around both stars is composed of gas and dust ejected by the primary star as it evolved. Using radio observations from the Submillimeter Array on Maunakea, Hawai’i, Vega’s team estimated that the disk is around 51 billion miles (82 billion kilometers) across. The binary orbits inside a central gap that the scientists think is comparable to the distance between the two stars at their maximum separation, when they’re about 540 million miles (870 million kilometers) apart.

When the stars are farthest from each other, they’re roughly aligned with our line of sight. The disk partially obscures the primary and creates another predictable fluctuation in the system’s light. Vega and her colleagues think this is when one or both stars interact with the disk’s inner edge, siphoning off streams of gas and dust. They suggest that the companion star funnels the gas into its own disk, which heats up and generates an X-ray-emitting outflow of gas. This model could explain X-rays detected in 2016 by the European Space Agency’s XMM-Newton satellite.

“The XMM observations make U Mon the first RV Tauri variable detected in X-rays,” said Kim Weaver, the XMM U.S. project scientist and an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It’s exciting to see ground- and space-based multiwavelength measurements come together to give us new insights into a long-studied system.”

In their analysis of U Mon, Vega’s team also incorporated 130 years of visible light observations.

The earliest available measurement of the system, collected on Dec. 25, 1888, came from the archives of the American Association of Variable Star Observers (AAVSO), an international network of amateur and professional astronomers headquartered in Cambridge, Massachusetts. AAVSO provided additional historical measurements ranging from the mid-1940s to the present.

The researchers also used archived images cataloged by the Digital Access to a Sky Century @ Harvard (DASCH), a program at the Harvard College Observatory in Cambridge dedicated to digitizing astronomical images from glass photographic plates made by ground-based telescopes between the 1880s and 1990s.

U Mon’s light varies both because the primary star pulsates and because the disk partially obscures it every 6.5 years or so. The combined AAVSO and DASCH data allowed Vega and her colleagues to spot an even longer cycle, where the system’s brightness rises and falls about every 60 years. They think a warp or clump in the disk, located about as far from the binary as Neptune is from the Sun, causes this extra variation as it orbits.

Vega completed her analysis of the U Mon system as a NASA Harriett G. Jenkins Predoctoral Fellow, a program funded by the NASA Office of STEM Engagement’s Minority University Research and Education Project.

“For her doctoral dissertation, Laura used this historical dataset to detect a characteristic that would otherwise appear only once in an astronomer’s career,” said co-author Rodolfo Montez Jr., an astrophysicist at the Center for Astrophysics | Harvard & Smithsonian, also in Cambridge. “It’s a testament to how our knowledge of the universe builds over time.”

Co-author Keivan Stassun, an expert in star formation and Vega’s doctoral advisor at Vanderbilt, notes that this evolved system has many features and behaviors in common with newly formed binaries. Both are embedded in disks of gas and dust, pull material from those disks, and produce outflows of gas. And in both cases, the disks can form warps or clumps. In young binaries, those might signal the beginnings of planet formation.

“We still have questions about the feature in U Mon’s disk, which may be answered by future radio observations,” Stassun said. “But otherwise, many of the same characteristics are there. It’s fascinating how closely these two binary life stages mirror each other.”

This squirrel-sized primate lives in the forests of Madagascar, where it spends up to seven months each year mostly motionless and chilling, using the minimum energy necessary to withstand the winter. While zonked, it lives off of fat stored in its tail.

Animals that hibernate in the wild rarely do so in zoos and sanctuaries, with their climate controls and year-round access to food. But now our closest hibernating relative has gone into true, deep hibernation in captivity for the first time at the Duke Lemur Center.

“They did not disappoint,” said research scientist Marina Blanco, who led the project. “Indeed, our dwarf lemurs hibernated just like their wild kin do in western Madagascar.”

The researchers say recreating some of the seasonal fluctuations of the lemurs’ native habitat might be good for the well-being of a species hardwired for hibernation, and also may yield insights into metabolic disorders in humans.

“Hibernation is literally in their DNA,” Blanco said.

Blanco has studied dwarf lemurs for 15 years in Madagascar, fitting them with tracking collars to locate them when they are hibernating in their tree holes or underground burrows. But what she and others observed in the wild didn’t square with how the animals behaved when cared for in captivity.

Captive dwarf lemurs are fed extra during the summer so they can bulk up like they do in the wild, and then they’ll hunker down and let their heart rate and temperature drop for short bouts — a physiological condition known as torpor. But they rarely stay in this suspended state for longer than 24 hours. Which got Blanco to wondering: After years in captivity, do dwarf lemurs still have what it takes to survive seasonal swings like their wild counterparts do? And what can these animals teach us about how to safely put the human body on pause too, slowing the body’s processes long enough for, say, life-saving surgery or even space travel?

To find out, Duke Lemur Center staff teamed up to build fake tree hollows out of wooden boxes and placed them in the dwarf lemurs’ indoor enclosures, as a haven for them to wait out the winter. To mimic the seasonal changes the lemurs experience over the course of the year in Madagascar, the team also gradually adjusted the lights from 12 hours a day to a more “winter-like” 9.5 hours, and lowered the thermostat from 77 degrees Fahrenheit to the low 50s.

The animals were offered food if they were awake and active, and weighed every two weeks, but otherwise they were left to lie.

It worked. In the March 11 issue of the journal Scientific Reports, the researchers show for the first time that fat-tailed dwarf lemurs can hibernate quite well in captivity.

For four months, the eight lemurs in the study spent some 70% of their time in metabolic slow-motion: curled up, cool to the touch, barely moving or breathing for up to 11 days at a stretch, showing little interest in food — akin to their wild counterparts.

Now that spring is afoot in North Carolina and the temperatures are warming, the lemurs are waking up. Their first physical exams after they emerged showed them to be 22% to 35% lighter than they were at the start but otherwise healthy. Their heart rates are back up from just eight beats per minute to about 200, and their appetites have returned.

“We’ve been able to replicate their wild conditions well enough to get them to replicate their natural patterns,” said Erin Ehmke, who directs research at the center.

Females were the hibernation champs, out-stuporing the males and maintaining more of their winter weight. They need what’s left of their fat stores for the months of pregnancy and lactation that typically follow after they wake up, Blanco said.

Study co-author Lydia Greene says the next step is to use non-invasive research techniques such as metabolite analysis and sensors in their enclosures to better understand what dwarf lemurs do to prepare their bodies and eventually bounce back from months of standby mode — work that could lead to new treatments for heart attacks, strokes, and other life-threatening conditions in humans.

Blanco suspects the impressive energy-saving capabilities of these lemurs may also relate to another trait they possess: longevity. The oldest dwarf lemur on record, Jonas, died at the Duke Lemur Center at the age of 29. The fact that dwarf lemurs live longer than non-hibernating species their size suggests that something intrinsic to their biological machinery may protect against aging.

“But until now, if you wanted to study hibernation in these primates, you needed to go to Madagascar to find them in the act,” Blanco said. “Now we can study hibernation here and do more close monitoring.”

The research provides some of the strongest evidence to date for the idea of evasive mimicry, a strategy in which animals protect themselves from predators by matching the colors or patterns of agile relatives. First proposed more than 60 years ago, the hypothesis has been a challenge to test.

But in an experimental setting, researchers found that wild birds learned and remembered the wing patterns of artificial butterflies that evaded their attacks, as well as those that had a foul flavor, equally spurning both in follow-up tests and often ignoring lookalikes with similar color patterns. Unexpectedly, the birds learned to avoid evasive butterflies faster than distasteful ones.

The results suggest that being hard to catch may deter predators at least as effectively as chemical defenses.

“There’s a common idea that being distasteful is one of the best kinds of defense to have, but at least in this experiment, that didn’t prove to be the case,” said study co-author Keith Willmott, curator and director of the Florida Museum of Natural History’s McGuire Center for Lepidoptera and Biodiversity.

Most research on warning coloration has focused on species with chemical defenses and those that mimic them. Monarch butterflies, for example, sport bright wing patterns of black lines on a field of orange, indicating they contain bad-tasting toxins. A predator that eats one will likely avoid both monarchs and the similar-looking viceroy butterfly in the future.

But a growing number of studies suggest a flashy exterior can mean something entirely different: that an animal is quick. Predators learn to associate these kinds of patterns with a futile chase that leaves them hungry, and species that evolve imitations of these “racing stripes” can capitalize on a defensive strategy while reinforcing the visual message.

“When many species share the same color pattern, they’re better able to educate predators to avoid them,” Willmott said. “The more species that share it, the better.”

During his Ph.D. studies, Willmott worked on the classification of a group of fast-flying tropical butterflies known as Adelpha. At first, he found them nearly impossible to identify. It seemed the genus either contained only a few species with slight variations in wing pattern or dozens of species that looked virtually the same. The latter turned out to be the case, with more than 90 species making up the group. Like some researchers before him, Willmott began to wonder whether evasive mimicry could explain why so many species of Adelpha looked alike.

“It was always mysterious to me,” he said. “Species whose upper wings looked incredibly similar were distantly related, and we started to see cases where even subspecies of multiple species suddenly developed very unique color patterns. Really, the only way you can explain that is through mimicry.”

While other researchers suggested some Adelpha must have hidden chemical defenses, the explanation didn’t quite satisfy Willmott. Toxic butterflies are usually slow fliers with long wings and a propensity for playing dead when caught. Adelpha butterflies, however, don’t display these traits, having instead a short, stout thorax and smaller, triangular wings — characteristics that enable fast, erratic flight and sharp turns.

But he wasn’t sure how to test this hypothesis until a conversation with fellow researchers at a 2018 conference in India: Johanna Mappes was an expert at developing predator-prey experiments with wild birds; Pável Matos-Maraví was interested in the evasive behavior of skipper butterflies; and Marianne Elias and her Ph.D. student Erika Páez were eager to study what drove the evolution of wing color patterns in the genus Adelpha, including the possible effects of predators.

Simulating how evasive mimicry might play out in the wild appealed to the group. The ability of prey to escape predators’ attacks has been “virtually unstudied,” said Elias, a research group leader at the Institute of Systematics, Evolution, Biodiversity at the National Museum of Natural History in France.

Previous work had shown birds can identify the visual cues of evasive prey. Together, the team designed an experiment to test whether potential examples of evasive mimicry in Adelpha could be the result of natural selection.

At a special facility in Finland, the researchers collaborated with Janne Valkonen of the University of Jyväskylä to capture wild blue tits, birds that would never have encountered tropical Adelpha butterflies, and train them to catch a paper butterfly with an almond treat attached to its underside. Then, the birds were presented with a plain brown paper butterfly as a control and a paper butterfly with one of three common Adelpha wing patterns: a vertical white band on black forewings, a vertical orange band on black forewings or a combination of orange-striped forewings with white-striped hindwings.

The paper Adelpha butterfly either concealed an almond soaked in a bitter substance — a proxy for chemical defense — or evaded the bird’s attack by gliding away on a rail. The birds learned to connect a particular wing pattern with the negative experience of distastefulness or escape, eventually avoiding this butterfly and striking the control instead. In a final test, they were given four butterflies at the same time: the plain brown butterfly and all three Adelpha butterflies, including one with the pattern they had seen before.

They strongly avoided the butterfly they had learned to associate with the bitter almond or fast flight and often avoided butterflies that shared a similar color or pattern.

Birds were 1.6 times more likely to attack the distasteful butterfly than evasive ones, perhaps because they had varying levels of tolerance for the bad-tasting almond, said Páez, who co-led the study with Valkonen. After all, even a bitter morsel of food is better than nothing.

“Bad-tasting prey could provide a nutritive meal whereas missing prey completely cannot,” she said.

While birds tend to avoid colorful prey by default, the study provides evidence of learned behavior, Willmott said.

“This potentially explains many cases of apparent mimicry that lacked evidence of chemical defense.”

Matos-Maraví of the Biology Centre, Czech Academy of Sciences, and Mappes of the University of Jyväskylä and the University of Helsinki also co-authored the study.