Ecology and Evolutionary Biology

Scholar studies animals through the love in their hearts

Rachel Sauer — Tue, 29 Sep 2026 03:27:04 +0000

Scholar studies animals through the love in their hearts Rachel Sauer Mon, 09/28/2026 - 21:27

Rachel Sauer

In new book for younger readers, �鶹��Ѱ��Boulder Professor Emeritus Marc Bekoff advocates for increasing humanity’s ‘compassion footprint’

Zebras, it turns out, are bro huggers.

In Namibia’s Etosha National Park, behavioral ecologist Caitlin O’Connell observed that male zebra leaders “wrap necks, nip and sniff one another around the head and sometimes the genitals. Then they exhibit an exaggerated chewing behavior with their teeth bared and the corners of their lips drawn up as if smiling or laughing with necks extended and ears directed forward. It really looks like they are enjoying a hilarious joke together.”

And then everyone does their business on “a communal dung pile.”

Marc Bekoff is a �鶹��Ѱ�� professor emeritus of ecology and evolutionary biology.

For a long time, conventional wisdom—and even scientific observation—would have asserted that this is merely instinctual mammalian behavior, nothing more than complex evolutionary responses to environmental and inter-group stimuli. They’re animals, after all; surely they aren’t exhibiting joy, playfulness or love?

Not so, says Marc Bekoff, a �鶹��Ѱ�� professor emeritus of ecology and evolutionary biology. In his recently published book for younger readers, Love in their Hearts: A Celebration of Animal Emotions and a Guide to Compassionate Action, written with longtime collaborator Jeff Campbell, Bekoff advocates for increasing humanity’s “compassion footprint.”

“The message is to be nicer to humans, be nicer to non-humans, treat all living things with respect,” Bekoff explains. “We are never too young to hear that message and learn that lesson.”

‘Animals have thoughts and feelings’

Bekoff began learning that lesson, which became the work of his lifetime, when he felt sorry for a goldfish. Growing up in Brooklyn, New York, “everyone had the requisite goldfish in an aquarium on the kitchen counter, including my family, and I used to feel so sorry for that goldfish,” he recalls.

He also spent hours riding his tricycle around the neighborhood, talking to all the animals he saw, and rather than being worried, his parents were supportive. “I used to tell my parents I could feel the emotions of the dogs and cats and mice and birds, I would tell them that animals have thoughts and feelings, and my parents supported it because why not?” he says.

When he was 6, he and his family moved from Brooklyn to Lynbrook on Long Island, which at the time had swaths of woods to explore. Bekoff was a good athlete and a mediocre student, but he nevertheless knew that he had to at least try to get to college if he wanted to continue building a scientific foundation beneath his observations of animals.

Jane Goodall, who would become Bekoff’s dear friend and professional collaborator, “used to say it felt wrong to harm animals and it felt right to try to learn about them, so I went to college and then I got a master’s in neurobiology, then I spent two years in a PhD/MD program disliking every day of it,” Bekoff says.

It was around that time, in the late 1960s, that famed researcher and animal behaviorist Michael Fox joined the faculty at Washington University in St. Louis. Fox, a Royal Veterinary College-trained veterinarian who also held a Doctor of Science in ethology and animal behavior, was doing exactly the sort of work that Bekoff wanted to do: non-invasive, observational science focused on animal behavior.

Fox accepted Bekoff as a graduate student, and he earned a PhD in animal behavior. After a year as an assistant professor of biology at the University of Missouri in St. Louis, he came to �鶹��Ѱ��Boulder in 1974 to study behavioral ecology and carnivore behavior.

“The message is to be nicer to humans, be nicer to non-humans, treat all living things with respect,” says scientist and author Marc Bekoff.

“So, I got my job here, and down on 30th and Marine on East Campus, back when the Institute for Behavioral Genetics was one of the only buildings down there, I somehow got a grant and convinced the university to put in a chain link fence enclosure so we could study coyotes,” Bekoff says. “We had a few coyotes who had been rescued, and they became this beacon. Everybody went down there to see them, so much that we had to put up signs telling people not to play with them.”

From there, he studied Adélie penguins at Cape Crozier, Ross Island, Antarctica, then initiated a field project studying coyotes in Grand Teton National Park.

“I always was driven to know what animals were thinking and feeling, I knew there was a way to study this scientifically and I was really persistent because I knew I was right,” he says. “Back when I was starting out, the major school of thought was behaviorism—the idea that with animal behavior, everything is a stimulus response, and the brain is a black box that we can’t know anything about.

“I said no, there’s just got to be something going on in animals’ minds, particularly concerning what they’re feeling and what they’re calculating. These are wild animals who have difficult lives; I knew there had to be so much more going on.”

Complex emotional lives

A significant facet of Bekoff’s research has been to systematically and non-invasively observe animal behavior to gain insight into the “black box” of animal minds. In addition to the usual challenges of research, he says, was the resistance he initially encountered in the scientific community, many of whose members equated ethology—or the study of animal minds—with finger waggling and magical thinking.

“The science had to be irrefutable,” Bekoff says. “We didn’t have a choice. Michael Fox, my mentor at Washington University, was one of the first ethologists who practiced the science of watching—slow watching, slow looking, just going out and watching animals. We weren’t putting electrodes in their bodies or cutting out parts of their brains; it was uncontrolled.

“A group of us were just really persistent, getting grants and I published tons in refereed journals and published books, just keeping at it and putting it out there, and slowly but surely we had evidence showing that animals have extremely complex emotional lives.”

That growing body of evidence—gathered by Bekoff, Goodall and a community of scientists around the world—is, in part, what inspired Bekoff to write Love in their Hearts, for which Goodall wrote the foreword.

Bekoff gathered animal stories from colleagues around the globe, including O’Connell’s observations of zebra bro hugging, to embody “the universality of emotions.” The aim is not to prove that animals have emotions—“We know they do,” Bekoff says—but to bring those emotions to life for younger readers who may be interested in science, who may spend hours observing animals or who may simply love their pets and have a sense that their pets love them, too.

Love in Their Hearts also gives young readers actionable steps to help care for both animals and Earth—a compassionate conservation approach that children are never too young to learn, Bekoff says, and that he still teaches in Jane Goodall’s Roots and Shoots groups.

“It’s the basic principle of the One Health philosophy,” Bekoff says. “What’s good for animals is good for us, and what’s bad for them is bad for us. Let’s change the world for all its inhabitants.”

“What’s good for animals is good for us," says Marc Bekoff, "and what’s bad for them is bad for us. Let’s change the world for all its inhabitants.” (Photo: Dylan Shaw/Unsplash)

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In new book for younger readers, �鶹��Ѱ��Boulder Professor Emeritus Marc Bekoff advocates for increasing humanity’s ‘compassion footprint.’

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National monuments must be preserved in perpetuity

Rachel Sauer — Tue, 18 Aug 2026 00:47:26 +0000

National monuments must be preserved in perpetuity Rachel Sauer Mon, 08/17/2026 - 18:47

Jeff Mitton

Natural wonders that belong to all Americans should not be carved up or given away

The first humans to set foot in North America walked across the Bering Strait the last time glaciers were full. The glaciers held so much water that the sea level dropped 400 to 425 feet compared to today's levels, turning the Bering Strait to the Bering Land Bridge.

The bridge might have risen from the sea as early as 20,000 years ago, and it might have submerged as late as 11,000 years ago. Stone, bone and wooden implements can be dated to estimate when sites were occupied, such as the Lindenmeier site (14,000 years ago) in Larimer County or the Mahaffy Cache near Gregory Canyon in Boulder (13,000 years ago).

�鶹��Ѱ��Boulder Professor Emeritus Jeff Mitton in a giant alcove in Utah's Neon Canyon known as the Golden Cathedral. It has a large opening in its ceiling that becomes a waterfall after a rain. (Photo: Jeff Mitton)

The first white man to set foot in North America was Leif Erikson, a Norseman who established a colony in Newfoundland around 1,000 CE. It was abandoned 10 years later. A Spanish colony was established in St. Augustine, Florida, in 1565, and an English settlement was founded in Jamestown, Virginia, in 1607. The Pilgrims landed at Plymouth Rock in Massachusetts in 1620.

My reason for this abbreviated history is to remind people of the uncontested history of America. When the Pilgrims stepped ashore 461 years ago, the continent had already been occupied for 14,000 years by numerous (between 2 to 7 million) and diverse people organized into hundreds of Indigenous tribes. Claims that America is and has always been a white, Christian country have no basis in fact.

In the short time since the earliest European settlements, many shameful things have been done to Indigenous peoples—massacres, forced marches, confinement to reservations, children disappearing from government schools, the list is tragically long.

Two wonderful things happened recently. In September 1996, President Bill Clinton set aside 1.7 million acres in Utah as the Grand Staircase-Escalante National Monument. In December 2016, President Barack Obama set aside 1.35 million acres as the Bears Ears National Monument, also in Utah. Indigenous tribes were jubilant, for they considered these areas to be their sacred ancestral lands.

But in addition, six regional tribal entities were given advisory roles in stewardship and protectional of cultural resources for the Grand Staircase, and five regional tribal entities were given similar roles for Bears Ears. Sacred lands were protected and Indigenous tribal entities would share responsibilities for both management of the national monuments and protection of the sites and remaining artifacts, pictographs and petroglyphs.

In December 2017, President Donald Trump cut the sizes of the monuments by 85%. In October 2021, President Joe Biden re-established the monuments to their original sizes. In July 2026, President Trump hacked the national monuments a second time, by 90%.

President Trump justified his cuts to the national monuments as providing greater opportunities for energy extraction, or more precisely, mining and drilling. He also noted that this would increase the area open to cavorting about and ripping up the landscape with four-wheel drive and all-terrain vehicles and dirt bikes.

President Trump rewards the incredibly rich CEOs of mining and drilling companies while neglecting the interests of Indigenous Americans and the people who treasure wildlife and spectacular landscapes. People seeking to minimize President Trump's slashes of the monuments might point out that no one has been forbidden to go to the places, they are just being declared "multi-use."

That sounds good, but it is vacuous. Have you ever tried to share your intended camping sites or hiking trails with a mine or a cluster of drilling rigs? Can you imagine camping beside razor wire, roaring pumps and brilliant lights? Once again, broken promises from Washington dash the hopes of Indigenous tribes.

But it is not just the Indigenous who are crushed. While the elected politicians in Utah favored Trump's gift to the rich, 70% of the people in Utah wanted the monuments to remain as they were established. Americans are proud of their national parks, and they believe that they were set aside for future generations, in perpetuity. They believe the same for national monuments—I know I did.

National parks and monuments are superb places to see plants, animals and stunning landscapes as they were naturally. They belong to all the people, and one billionaire should not have the right to gift them so that they can be used for profit.

A pot abandoned in Bears Ears National Monument around 1280 CE, when people migrated southward to escape a severe and prolonged drought. (Photo: Jeff Mitton)

Bears Ears National Monument and Grand Staircase-Escalante National Monument have scenery that rivals scenery of most national parks. I have camped in Bears Ears seven times and Grand Staircase eight times, and each adventure is a treasured memory. I took a six-hour hike and climb in Bears Ears to see a pot that was abandoned in 1280 CE, when the area was abandoned due to a lingering drought. It is believed that the pot has not been moved since that time.

In the Grand Staircase, I took a hike (twice!) on slick rock into the Escalante Canyon and up into Neon Canyon to see a giant alcove known as the Golden Cathedral. It has a large opening in its ceiling that becomes a waterfall after a rain. During a dry spell, climbers lower themselves by rope through the opening.

I have no faith, so do not consider these monuments sacred, but I have the conviction that these monuments, as they were initially drawn, are so grand and unique that they must be preserved in perpetuity. It would be a national shame, a travesty, just as it would be to let Glacier, or Rocky Mountain, or Yosemite national parks to be carved up into mining claims.

The way out of this tragedy is not apparent to me. But I feel strongly that one man should not have the right to give away what should belong to all, forever. I believe that a national vote on the future of these treasures would set them aside in perpetuity.

Jeff Mitton is a professor emeritus in the Department of Ecology and Evolutionary Biology at the �鶹��Ѱ��. His column, "Natural Selections," is also printed in the Boulder Daily Camera.

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Natural wonders that belong to all Americans should not be carved up or given away.

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Top photo: The Citadel, with cliff dwellings (not visible) that were easily defended when enemies came to the Bears Ears. (Photo: Jeff Mitton)

Rebecca Safran wins American Ornithological Society Elliott Coues Award

Rachel Sauer — Tue, 18 Aug 2026 00:15:35 +0000

Rebecca Safran wins American Ornithological Society Elliott Coues Award Rachel Sauer Mon, 08/17/2026 - 18:15

The �鶹��Ѱ��Boulder ecology and evolutionary biology professor is recognized for her research on barn swallows and other avian groups, which has taken her across the world

Rebecca Safran, a professor of ecology and evolutionary biology at the �鶹��Ѱ��, has been awarded the Elliott Coues Award by the American Ornithological Society (AOS). The AOS is the world’s largest international ornithological society focused on the scientific study and conservation of birds.

The Elliott Coues Award recognizes outstanding and innovative contributions to ornithological research with no limitation to geographic area, sub-disciplines of ornithology or the time during which the work was done. The award, which consists of a medal and an honorarium, is named in honor of Elliott Coues, a pioneering ornithologist of the western United States and a founding member of the American Ornithologists Union (now AOS).

Rebecca Safran, a professor of ecology and evolutionary biology at the �鶹��Ѱ��Boulder, has been awarded the Elliott Coues Award by the American Ornithological Society.

“I am honored by this recognition of the research we do in our lab group at the �鶹��Ѱ��,” Safran said. “My first-ever scientific meeting was an AOS conference. I attend these meetings with students as often as I can for the best research updates on bird studies from around the world. There is always something new and exciting to learn. I am humbled to receive this award; past awardees are my academic heroes and have inspired much of the work many of us do today.”

In recognizing Safran, the AOS noted that she and her research group have traveled across the world to study barn swallows (Hirundo rustica) and have conducted comparative analyses on other avian groups as part of efforts to study the evolution and maintenance of population differentiation using ecological, genomics and behavioral studies.

Safran and her team established their research lab at the University of Colorado in 2008, where Safran's teaching is focused on speciation and science communication. She is the founding co-director of Inside the Greenhouse, which has a mission to find creative ways to communicate the science of climate change.

In naming Safran as an Elliott Coues Award winner, the AOS said she is passionate about the evolution and conservation of wild bird populations, interdisciplinary collaboration, art-science connections, issues related to belonging in STEM, natural history and providing learning opportunities for students at all stages of their education.

Safran is an AOS elective member (2011) and an elected board member of Environment for the Americas and the Colorado Environmental Film Festival. She is an elected fellow of the AOS (2016), the Animal Behavior Society (2024) and the American Association for the Advancement of Science (2026).

Safran previously received AOS travel grants in 1999 and 2003 and an AOU research grant in 2001. This support was key for Safran’s research and conference participation during graduate school. Safran noted she is grateful for the support the AOS now provides to members of her team for their research and conference attendance.

Safran said her work is not possible without the collaboration of students and colleagues and through funding by several entities including the AOS and National Science Foundation. Wherever she goes (and sometimes to the dismay of others walking with her), she is always on the lookout for H. rustica and their mud cup nests.

Safran earned her PhD at Cornell University, followed by a postdoctoral fellowship at Princeton University.

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The �鶹��Ѱ��Boulder ecology and evolutionary biology professor is recognized for her research on barn swallows and other avian groups, which has taken her across the world.

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What can one tiny scanner detect in Mammoth sunflowers?

Rachel Sauer — Fri, 14 Aug 2026 22:59:23 +0000

What can one tiny scanner detect in Mammoth sunflowers? Rachel Sauer Fri, 08/14/2026 - 16:59

Tiffany Plate

Researchers in �鶹��Ѱ��Boulder’s Department of Ecology and Evolutionary Biology are taking a closer look at the drought-recovery efforts of these beloved blooms

Drive down even the driest road in Colorado at the height of summer, and you’re bound to see rows of bright sunflowers lining the shoulder. And even if at the end of a long hot day those long-stemmed blooms look a little wilted, there’s a good chance that by the next morning they’re standing tall again.

That observable bounceback has led researchers to believe that sunflowers are capable of a process called “refilling,” in which the plant’s water transport capability, which can fail during intense drought stress, returns to normal after it has been rewatered. Refilling flushes drought-induced air bubbles, called embolisms, out of the plant’s water transport tubes to deliver much-needed moisture throughout the plant.

Study authors (left to right) Jared Stewart, Stephanie Polutchko and Brendan Allen found that, contrary to popular belief, sunflowers were not capable of “refilling” themselves after experiencing drought and subsequent rewatering. (Photo: Stephanie Polutchko)

But according to a recent study by researchers in the �鶹��Ѱ�� Department of Ecology and Evolutionary Biology, refilling is not the cause of sunflowers’ apparent bounceback.

“We didn't see a single convincing instance where even one of the tubes was repaired,” says Research Associate Jared Stewart. Stewart served as lead author on a recent article in the Journal of Experimental Botany documenting his team’s use of a micro-CT scanner to peek inside sunflowers at various stages of dehydration and rehydration.

The finding stands in stark contrast to the results of a study the same team performed on a weedy grass, which was published last year in the journal Proceedings from the National Academy of Sciences USA. In that instance, the grasses’ refilling capabilities were remarkable.

“There wasn't any real gray area with the two findings,” says Stewart. “This grass refilled 100% completely in every single plant, every single time. In the sunflowers, we saw zero refilling.”

So where does that leave the field of plant hydraulics? “In last year's paper we showed that this refilling process does happen,” says Stewart. “But these results suggest it’s probably not nearly as prevalent as people thought.”

Why sunflowers?

The study grew out of a conversation between Stewart and his then-postdoctoral advisor Sean Gleason, a plant physiologist with the U.S. Department of Agriculture’s Agricultural Research Service, along with �鶹��Ѱ��Boulder colleagues Stephanie Polutchko, an assistant teaching professor of ecology and evolutionary biology, and graduate student Brendan Allen. The four linked up with researchers at Colorado State University and mapped out a way they could leverage CSU’s micro-CT scanner to observe the drought processes in the plants.

Sunflower was an ideal candidate, Stewart says, because literature on plant hydraulics almost unanimously supported the idea that sunflowers were capable of refilling (in part because of the daily visual evidence of the flower wilting and then perking back up). In fact, for a long time most experts in plant hydraulics believed that refilling was a fairly universal phenomenon. The problem was that there was very little concrete evidence to back up that belief.

“Previously published evidence for this repair process has been scrutinized more and more intensely over the past decade,” says Stewart. The team thus opted for a simple experimental setup to ensure there was no confusion about the results.

A mouse-sized scanner to the rescue

An essential part of that simple design was using the micro-CT scanner that belongs to CSU’s College of Veterinary Medicine and Biomedical Sciences. The small scanner is designed to scan small, live animals and was engineered to emit as little radiation as possible—so study subjects can be scanned repeatedly without exposure to high levels of radiation.

A sunflower plant experiencing drought and one week after being rewatered (top), and micro-CT images of its stem (bottom). The white arrows indicate where the stem was scanned, and the yellow areas in the micro-CT images show air bubbles, or embolisms, in yellow. (Image courtesy of study authors)

The setup was perfect for Stewart’s team, who scanned the 11 specimens of the “Mammoth” variety of sunflowers at three different times: while under drought stress, on the morning after re-watering and after one week of recovery under well-watered conditions. The plants were able to withstand the scanning with no visible damage.

That was not true in past studies on the topic, including research that dates back more than 40 years. “Conventional ways of studying this have involved basically cutting out portions of the plant,” says Stewart. “Then you do the same procedure on a different plant that’s been rewatered.”

That process of cutting the plant has been suspected to be problematic for more than 100 years, Stewart says, since it introduces air into the incision, making it difficult to measure the embolisms that existed in the tube prior to cutting. But that method has remained one of the most commonly used in the literature and may be a cause for confusion about the topic.

Now, Stewart believes they’ve come up with a gold standard method for studying this phenomenon. “Personally, I wouldn't trust any data generated with any other published methods at this moment,” he says.

A new line of questioning

Now that the team has validated their methodology with the two different studies, they see it as a first step in designing future experiments.

“There’s a ton of different directions we’d love to go with it,” says Stewart, adding that he hopes their results might be leveraged for agricultural efforts to improve food production and food security, especially as the planet potentially faces an increase in droughts.

“I think if we got to pick another crop to study and had unlimited time and money, it'd probably be corn or rice,” says Polutchko. “We know that a grass can do it, but it's one that’s an agricultural nuisance. So, can we have a grass that we like to eat that can also do this?”

Ideally, now that the method has been laid out, other researchers with access to similar micro-CT scanners can also conduct their own research, especially on crops with agricultural significance.

As for the sunflower’s drooping and reperking routine, Stewart, Polutchko and team are still stumped. “Maybe the plant doesn’t refill those embolisms, but it has a different strategy to work around that stress. Those are great questions, and we want to know the answers.”

“In true scientist fashion, you answer one question and 10 new ones pop up!” says Polutchko.

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Researchers in �鶹��Ѱ��Boulder’s Department of Ecology and Evolutionary Biology are taking a closer look at the drought-recovery efforts of these beloved blooms.

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Top image: Unsplash

Scott Taylor elected councilor of the American Ornithological Society

Rachel Sauer — Tue, 11 Aug 2026 15:33:13 +0000

Scott Taylor elected councilor of the American Ornithological Society Rachel Sauer Tue, 08/11/2026 - 09:33

�鶹��Ѱ��Boulder researcher will serve as a member of the Society’s governing body and promote its mission to support science that advances the understanding and conservation of birds

Scott Taylor, a �鶹��Ѱ�� professor of ecology and evolutionary biology and director of the Mountain Research Station, has been elected a councilor of the American Ornithological Society (AOS).

In this three-year volunteer term, Taylor, who also is a fellow of the Institute of Arctic and Alpine Research, will serve as a member of the AOS governing body, which “establishes the direction and strategy of the AOS, makes high-level decisions about AOS’ priorities, oversees the sound financial management of AOS’ resources and ensures legal and ethical integrity of the organization,” according to the organization.

The AOS’ mission is to connect ornithologists, science and bird conservation by “supporting science that advances the understanding and conservation of birds, promoting broad access to ornithological science, supporting ornithologists throughout their career paths and fostering a welcoming, diverse, supportive and dynamic ornithological community.”

�鶹��Ѱ��Boulder scientist Scott Taylor has been elected a councilor of the American Ornithological Society.

In his councilor candidate statement, Taylor noted that he is deeply committed to the AOS “as both a scientific home and a community that has shaped my career. Having benefited from AOS through collaborations, mentorship networks and opportunities to engage with cutting-edge research, I am motivated to give back in a leadership role.”

His involvement with AOS has included serving on committees, organizing symposia and building inclusive community spaces at annual meetings

“I am particularly interested in helping the Society continue to foster a vibrant, inclusive and forward-looking ornithological community while supporting early-career scientists, strengthening connections across disciplines and engaging in effective outreach,” he noted in his candidate statement.

Taylor, who grew up in rural southern Ontario, earned his undergraduate degree in wildlife biology at the University of Guelph and his PhD at Queen’s University. He completed a postdoctoral fellowship in the Cornell Lab of Ornithology and worked as a field biologist in South America.

As principal investigator of the Taylor Lab, he leads research focused on hybridization, speciation, evolutionary ecology and population genomics, primarily of birds. He and his colleagues pursue research using natural hybrid zones and recent radiations to understand the genetic bases of traits involved in reproductive isolation, population divergence and speciation, and the impacts of anthropogenic change, including climate change, on species distributions, interactions and evolution.

Taylor also is host of the podcast “Okay, But… Birds,” which has addressed topics ranging from whether birds invented music to how wildfire smoke affects birds and a rumination on whether birdwatching is the original Pokémon with Pulitzer Prize-winning science writer Ed Yong.

“Being elected to AOS Council is an honor,” Taylor said. “I have long worked to help the AOS become a more inclusive society and am impressed by the dedication of the society to their members. In my new role, I’ll continue this work at a larger scale, supporting the next generation of ornithologists and ornithological research.”

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�鶹��Ѱ��Boulder researcher will serve as a member of the Society’s governing body and promote its mission to support science that advances the understanding and conservation of birds.

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Top image: a flock of pelicans in Peru (Photo: Scott Taylor)

The only way to make beef and dairy more climate-friendly? Stop producing it

Rachel Sauer — Tue, 28 Jul 2026 19:37:16 +0000

The only way to make beef and dairy more climate-friendly? Stop producing it Rachel Sauer Tue, 07/28/2026 - 13:37

Tiffany Plate

�鶹��Ѱ��Boulder researcher Cliff Bueno de Mesquita and colleagues are showing why microbial solutions to livestock methane emissions reductions won’t stop beef and dairy’s environmental and health problems

By nature, cows are gassy creatures. But it’s not just the stink of their manure or their belches that are troublesome. The methane gas released by ruminants like cows (or bison, sheep or goats) also causes a lot of trouble for the planet.

That’s because methane is a potent greenhouse gas with a dramatically higher global warming potential than carbon dioxide. And ruminants raised for food account for 14% of global methane emissions.

Over the last decade or so scientists have been hard at work figuring out how to infuse cows’ feedstock with additives that inhibit methane-producing microbes. The process could reduce those methane emissions and potentially produce a more “climate-friendly” beef.

Cliff Bueno de Mesquita, who studies microbial ecology of permafrost and ancient sediments in the lab of ecology and evolutionary biology Professor Noah Fierer and in the Cooperative Institute for Research in Environmental Sciences, teamed up with other microbiologists passionate about environmental issues for this perspective piece. (Photo: Cliff Bueno de Mesquita)

Sounds like a win-win, right? A new perspective piece by Cliff Bueno de Mesquita (PhDEBio'19), a research scientist in the lab of ecology and evolutionary biology Professor Noah Fierer and the Cooperative Institute for Research in Environmental Sciences (CIRES), says otherwise.

“Even if you could decrease cows’ methane emissions by 100%, cows are still worse than plant-based agriculture for their land use, water use, pollution and impacts on human health,” says Bueno de Mesquita.

In their piece in the journal Sustainable Agriculture, Bueno de Mesquita and a team of microbiologist colleagues outline all the reasons that altering cows’ rumen microbes is a misdirected use of time, money and energy. “This is basically distracting from what we really need to be doing, which is reducing the ruminant population size,” he says.

This conclusion—that reducing the numbers of ruminants raised for food is the only solution to actually reducing livestock’s impact on the planet—has already been drawn by researchers around the world.

“There are a lot of great scientists working on this topic, with strong data sets that have been assembled with all of the evidence,” says Bueno de Mesquita.

Bueno de Mesquita and his colleagues cited 98 studies, to be exact, in their peer-reviewed opinion piece that re-emphasizes the personal and planetary benefits of a shift to a plant-based diet—and lays out exactly why rumen microbes are not the answer.

The problem with microbes

Some of the literature references cited in the piece are studies that have been done on the most common feed additives that have been studied for methane inhibition: seaweed and 3-nitrooxypropanol (or Bovaer). The research shows that the demonstrated efficacy of these microbes is extremely variable, with one review reporting a range of 10–63% reduction and another review reporting a range of a 4% increase to a 97% reduction.

Bueno de Mesquita and colleagues are also concerned that altering rumen microbes may lead to unpredictable health effects for the cattle, and may even decrease immunity to pathogens that could be detrimental to human health.

Another reason for concern? This method favors intensive beef production, where cattle are fed in feedlots rather than on grass (as is more likely to be the case in small-holder production). Not to mention that seaweed harvesting has its own inherent carbon emissions and environmental impact.

But Bueno de Mesquita’s team points out that even if none of these were issues, methane reduction does nothing to address potent nitrogen emissions or other emissions from the rest of the production life cycle (e.g., land use, water use, fertilizer, crop residues, manure).

Bueno de Mesquita and colleagues created this graphic to demonstrate how many ways livestock production can impact the environment and human health—and how only one of these impacts is reduced by trying to alter the microbes in the rumen with feed additives. (Graphic: Cliff Bueno de Mesquita and Ylenia Vimercati Molano)

Shifting people’s perspectives

The authors wrote the piece to be accessible to non-scientists in hopes of reaching as wide an audience as possible. “I want the public to be aware and to be skeptical of labels coming from the beef and dairy industry that are calling those products climate friendly,” says Bueno de Mesquita.

Of course, he also hopes that people will consider simply shifting to a plant-based diet in order to make their meals more climate friendly. But he knows that’s easier said than done.

“We're basically living in a ‘carnistic’ society where eating meat is perceived to be normal, natural and necessary,” says Bueno de Mesquita. “That's sort of people's default. So when they’re met with a proposal for a minor shift that challenges that, we know there's gonna be pushback.”

Two years ago Bueno de Mesquita and his co-authors published another paper documenting a push within �鶹��Ѱ��Boulder’s Ecology and Evolutionary Biology department for more plant-based meals. “The PhD students were very hesitant to implement a dietary change, even though they know that it's going to be better for the environment.”

Even still, Bueno de Mesquita says the current perspective piece is getting a lot of traction. “I basically never get emails about my research papers,” he says. “But I've already gotten emails from multiple people saying that they agree.” He adds that even some leading microbiologists have posted it on social media.

That’s key to reaching the other audience Bueno de Mesquita and colleagues wanted to address: the microbiologists actually doing the research on rumen microbes in livestock feed, usually funded by the beef and dairy industries, he says.

“They're enabling the dairy industry to say, ‘Hey, we're doing this research. This is going to work’,” says Bueno de Mesquita. “Then the industry has an excuse to keep business as usual.”

Instead, he hopes that microbiologists and other scientists studying climate change will step up and speak with a unified voice about what needs to be done as a society. “It's very obvious,” says Bueno de Mesquita. “If you want to reduce methane from ruminants, you need to decrease the number of ruminants.”

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Can evolutionary rescue help even long-lived species from going extinct?

Rachel Sauer — Tue, 09 Jun 2026 17:44:14 +0000

Can evolutionary rescue help even long-lived species from going extinct? Rachel Sauer Tue, 06/09/2026 - 11:44

Tiffany Plate

Two �鶹��Ѱ��Boulder researchers are helping clarify how species’ populations with longer lives can still adapt to a changing climate

Our warming climate is leaving many plant and animal species with a choice: either adapt, find a new home or risk extinction. Fortunately, throughout the history of life on Earth, a concept called evolutionary rescue has stepped in to help species adapt to new environments and climates.

Evolutionary rescue is a biological process where natural selection favors the individuals of a species that carry genetics best suited to the new climate. These individuals are more likely to survive and reproduce and are therefore able to better propagate future generations to ensure survival of the species.

Scott Nordstrom (left) earned his PhD from �鶹��Ѱ��Boulder in 2023 under the advisorship of Brett Melbourne. (right), professor of ecology and evolutionary biology (Left photo from Scott Nordstrom; right photo from Brett Melbourne)

For example, a smaller bat may be better able to weather a hot summer with multiple heat waves. Or a monkeyflower that's better able to retain water in its leaves may have a better chance of surviving a megadrought. These genetic anomalies help move the population toward survival, instead of extinction.

In the face of anthropogenic climate change, however, conservationists are worried that species with the longest life spans—like giant pandas, elephants, or sequoia trees, for which new generations take years to decades—will be too slow to adapt and avoid extinction.

A mathematical model developed by Scott Nordstrom (PhDEBio’23) proved that that’s not always the case, however. As part of his doctoral dissertation, Nordstrom, in partnership with Brett Melbourne, a �鶹��Ѱ�� professor of ecology and evolutionary biology, set out to determine just how true it was that long-lived species were resigned to their fate. Their findings were published in The American Naturalist in May 2026.

Their model contributes to conversations about conservation, especially when it comes to extinction concerns. “A lot of the more endangered species or the populations that are at higher risk of extinction tend to be longer lived,” says Nordstrom. “So, it's especially relevant for thinking about conservation.”

Shifting focus: From flour beetles to tortoises

Before taking on this project, Nordstrom and Melbourne had been working with colleagues at Colorado State University to understand the evolutionary rescue patterns of flour beetles, which live for about a month before a new generation is birthed.

“We found that genetic diversity of the population is really critical for allowing rapid adaptation to occur,” says Melbourne. “And that got us thinking about how things could be really different for longer-lived species.”

Large tree species, like the Giant Sequoia, can live for thousands of years, but are now more endangered than ever due to increased wildfire activity in the American West. (Photo: Pexels)

The researchers set out to try to understand how relevant their findings were to species with longer lives.

Experimental work tracking the genetic variations in generations of long-lived species was not possible, however, so the pair created the next best thing: A flexible mathematical model and computer simulations that would allow them to map out potential evolutionary patterns of these species.

For each simulation, they input a sample population into the model, using “good” environmental factors (i.e., the climate that they were already adapted to). Then they switched those factors to “bad” (i.e., a climate with warmer temperatures or less water).

“Each individual’s survival depended on how well it was adapted to its environment, so when the environment shifted from good to bad, survival was low and the populations started shrinking,” says Nordstrom.

“But because there was genetic variation within the populations, some individuals were slightly better adapted to the bad environment, and those individuals were more likely to survive and pass on their genes, allowing the population to adapt,” he adds.

When nurture beats nature

Through their simulations, Nordstrom and Melbourne were also surprised to find that long-lived species can experience a complicated evolutionary dynamic in which a population’s traits seem to decouple from their genetics. In these cases, some random environmental event has affected an organism's trait in a way that turns out to be an advantage in the changed environment.

For example, an American alligator might be genetically predisposed to weigh 600 pounds but actually weighs 400 pounds because environmental factors impeded its growth in early development. Perhaps the alligator was born in a drought year, when typical prey like fish and turtles were scarce.

Ultimately, that smaller alligator may be able to survive heat extremes better in a hotter climate, thus slowing the rate of population decline. And because they are long-lived (up to 50 years), there is a good chance that there will be multiple small alligators in a population at once, thus changing the composition of that population in a way that slows the rate of population decline, allowing adaptation time to catch up and prevent extinction, the researchers speculate.

Researchers have long thought that species like the American alligator, which can live up to 50 years, are less likely to benefit from evolutionary rescue to help them adapt to changes in the climate of their habitats. (Photo: Unsplash)

Interestingly, those chances are much less likely to occur to short-lived species like flour beetles. Nordstrom says that’s because their short life spans don’t allow for their non-genetic phenotypic variation (like that seen in the undersized alligators) to remain in the population as time progresses; instead, only their genes are passed on to their offspring, and their offspring will thus not inherit their size advantage.

“The flour beetles just mate once and pass their genes forward,” says Nordstrom. “Next generation, repeat.”

That means that natural selection occurring within a generation can be important for evolutionary rescue in long-lived species. Previously, it was speculated that only evolution between generations determined whether populations could adapt to new conditions in time.

“This process of rescue is one part evolution and one part demography,” says Nordstrom. “In the race of evolution versus demography, this definitely helps the demography because it slows down population decline.”

He adds that this will be surprising to researchers who have up to this point only considered the evolutionary component here. “But we showed that the demography is actually super important, too.”

While Nordstrom and Melbourne can’t say that all long-lived species will benefit from their demography, Nordstrom says it’s important for future researchers and conservation managers to know that evolutionary rescue is not out of the question for endangered species like pandas and bison.

“Maybe it's a little bit more complicated than we thought,” says Nordstrom. “But this is the first major study finding that it’s not necessarily true that slower generational turnover guarantees that adaptation and evolution will be slower.”

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Two �鶹��Ѱ��Boulder researchers are helping clarify how species’ populations with longer lives can still adapt to a changing climate.

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Scholars apply economic analysis to ecological research

Rachel Sauer — Wed, 20 May 2026 21:25:35 +0000

Scholars apply economic analysis to ecological research Rachel Sauer Wed, 05/20/2026 - 15:25

“If you’re studying a natural area, you could get a permit and go sample all over, but you can’t do that in a city. Even if you get a permit, you can’t just go into people’s backyards,” explains �鶹��Ѱ��Boulder scientist Asia Kaiser about the challenges of ecological research in urban areas. (Photo: Sandy Millar/Unsplash)

Rachel Sauer

In research published today, recent PhD graduate Asia Kaiser details how synthetic control methods estimated significant declines in bee observations when traditional analyses didn’t

Since it launched in 2008 as a UC Berkeley student’s master's project, the iNaturalist platform has been a source of both fascination and frustration for researchers.

The hundreds of millions of observations about the natural world logged by both professional and citizen scientists around the globe are a treasure trove of information about biodiversity. But is that data usable in research? The prevailing sentiment has veered toward doubt, skepticism or an outright “no.”

“I think the feeling has been, ‘Oh, because this data is just being collected opportunistically by nature enthusiasts and not in a standardized, rigorous way, it can’t be used in scientific research,’” says Asia Kaiser, who earlier this month earned her PhD in the �鶹��Ѱ�� Department of Ecology and Evolutionary Biology. “If you haven’t planned out data collection in advance, a lot of researchers hesitate to use it.”

Recent PhD graduate Asia Kaiser studied how synthetic control methods estimated significant declines in bee observations when traditional analyses didn’t.

There had to be a way, Kaiser thought, to tap into the vast cache of information logged into iNaturalist without sacrificing scientific rigor, especially data collected in urban environments. The answer, it turned out, lay in economics.

In research published today, Kaiser and co-authors Julian Resasco and Laura Dee, both associate professors of ecology and evolutionary biology, detail how combining iNaturalist records with synthetic control methods, originally used in economics, estimated a significant decline in bee observations in Philadelphia during the two years following Hurricane Ida in 2021, while conventional ecological analyses didn’t detect the decline.

“Basically, the inspiration for this project was thinking about causal inference in ecology,” Kaiser explains. “When we have observational data, can we actually use that to ask questions about drivers of biodiversity?”

‘You can’t just go into people’s backyards’

These questions dovetailed neatly with Kaiser’s research focus, which is bees—specifically, how human land use affects different insect groups and, consequently, the ecosystem services they provide in coupled human-natural systems. Among her research aims is understanding biodiversity in urban environments, improving the resilience of urban agroecosystems, increasing equitable access to fresh produce and promoting environmental justice in cities.

However, monitoring biodiversity and evaluating drivers of change in urban environments is confounded by several issues: “Cities are mosaics of land-use types, including parks, private properties, buildings, roads and industrial zones,” Kaiser writes in the paper. “As a result, sampling efforts can be complicated by permission and safety issues, and leaving unattended sampling equipment in the field brings a higher risk of theft, tampering and vandalism in cities.

“Given these challenges, measuring biodiversity in cities requires different tools and data streams than those used in natural ecosystems. Participatory science data is a promising solution for monitoring biodiversity in cities; cities are the land use type with some of the highest upload volumes of data to participatory science platforms, largely because upload frequency is strongly influenced by population density.”

Despite the abundance of participatory science data in platforms like iNaturalist, researchers have hesitated to draw from it, relying instead on randomized, controlled and replicable experiments to identify and estimate causal relationships. That kind of science, Kaiser says, becomes more difficult in urban environments due to sampling challenges and historical legacies that shape different neighborhoods, among other reasons.

“If you’re studying a natural area, you could get a permit and go sample all over, but you can’t do that in a city,” Kaiser says. “Even if you get a permit, you can’t just go into people’s backyards.”

The idea of how to bridge the gap between the abundance of iNaturalist data logged in urban areas and the rigor expected in scientific research came to Kaiser when she was assigned to watch a lecture given by a Nobel laureate in economics. The lecture topic was synthetic control methods, which originated in economics as a way to create a nonexistent control group that allows for comparisons between real-world groups before and after an event or intervention.

One of the most famous uses of synthetic control methods in economics was in estimating the impact of Germany’s reunification after the fall of the Berlin Wall on the gross domestic product (GDP) of western Germany. Economists created a “synthetic” Germany from economic data to study GDP with and without reunification.

Though synthetic control methods hadn’t been widely used in ecology research, “I thought it could be adopted with iNaturalist data,” Kaiser explains. She was further interested in studying the effects of Hurricane Ida on her home city of Philadelphia, which included significant flooding.

“Even though it didn’t have a huge impact on people per se, the effects of the hurricane were really dramatic. Looking at the water levels, the stream gauges had their highest values ever in the 100 years that they’ve been measuring. My feeling was that would have a pretty big impact on bees, because if you look at bee biodiversity, bees are pretty sensitive to precipitation and water. The ones that nest in the ground are really affected by huge flooding events.”

Declines following a hurricane

To apply synthetic control methods to ecological research, Kaiser and her colleagues drew data from the Global Biodiversity Information Facility, which collects research-grade iNaturalist data—that which includes, among other points, latitude and longitude, collection date and time and correct identification—as a proxy for bee abundance in Philadelphia.

They analyzed for bee population declines and, in addition to synthetic control methods, also performed the more traditional methods of interrupted time series regression, before-after control impact regression and before-after regression.

Kaiser and her colleagues found that synthetic control estimated a 15.5%—20.9% decline in bee observations in the two years following Hurricane Ida. In contrast, the three more common ecological analyses didn’t detect this decline.

“That was an amazing moment, seeing this decline in the data and better understanding how iNaturalist data may be able to help us look at the impact of unusual climate events—things that are happening more and more these days, like huge fires, huge floods, abnormally warm winters,” Kaiser says. “Unless you were already collecting data in a region before, you can’t really see the impact before the event, but synthetic control methods might be able to help us in those situations.”

Kaiser adds that this method also might be useful for looking at the effect of policy interventions. For example, the city of Boulder is establishing pollinator corridors, and Kaiser sees potential in using this method to draw from iNaturalist data in studying the outcomes of these corridors.

Scientists who reviewed the paper expressed excitement and skepticism about using synthetic control methods in ecological research, Kaiser says: “They asked questions about whether or not the decline I’m seeing is a true thing that’s happening or an artifact of the way data has been collected. iNaturalist is very sensitive to observers—wealthy neighborhoods have higher uploads, areas around research universities have higher uploads—but this statistical method can help control for those things.”

Thanks to the professional and citizen scientists gathering data and sharing it on iNaturalist, Kaiser says she sees potential to apply synthetic control methods to a range of ecological research. For example, “using the bee biodiversity that’s collected on iNaturalist, does that correlate with how well flowers are being pollinated? I think that’s something we’ll be able to study.”

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In research published today, recent PhD graduate Asia Kaiser details how synthetic control methods estimated significant declines in bee observations when traditional analyses didn’t.

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Fly agaric has a long association with fairies and humans

Rachel Sauer — Wed, 20 May 2026 19:01:01 +0000

Fly agaric has a long association with fairies and humans Rachel Sauer Wed, 05/20/2026 - 13:01

A red cap dotted with the dried crumbles of the egg sac make fly agaric easy to find and identify. (Photo: Jeff Mitton)

Jeff Mitton

Since the Renaissance, fly agaric has appeared in art and literature, frequently associated with fairies, trolls, wizards, witches and other mystical creatures

The most iconic and easily identified mushroom in the world is Amanita muscaria, or fly agaric. It grows around the world at northern latitudes in association with spruces, pines, birches and aspens, with its roots forming mutually beneficial mycorrhizal associations to exchange water and nutrients. It is easy to recognize, for it has a bright red cap, and all else white: stipe (stem), gills (underside of cap) and crumbles of the egg sac on the cap. These bright, contrasting colors make it easy to find and identify in a forest.

Fly agaric's bright, contrasting colors evolved to advertise their molecular defenses, muscimol and ibotenic acid. Unless an herbivore has evolved a way to combat activities of these compounds, these defenses are toxic and hallucinogenic, triggering severe and prolonged vomiting and loss of coordination and balance.

These colorful mushrooms and their psychoactive compounds have been associated with mankind for about 10,000 years. The association started with shamans in northern Europe and Siberia, who used the mushrooms during religious ceremonies to imagine communication with gods, ancestors and spirits. Similarly, they could be an ecstatic inebriant to enliven celebrations of winter solstice and the return of sunlight.

From the 13th through the 19th centuries, fly agaric was commonly used to kill flies in European homes and buildings. Flies were abundant before the invention of screens on windows and doors, and they were dreaded, thanks to a rumor that they get into the head and cause insanity. The practice came about after it was discovered that dried crumbs of fly agaric dropped into milk attracted flies, and when the flies sipped the milk, the ibotenic acid paralyzed and ultimately killed them. The common name fly agaric stems from this practice—agaric is the name for the familiar toadstool-shaped mushroom. Its formal name is Amanita muscaria: Amanita is the genus of mushrooms, and muscaria is a reference to the common housefly, Musca domestica.

Since the Renaissance, fly agaric has appeared in art and literature, frequently associated with fairies, trolls, wizards, witches and other mystical creatures in fairy tales and books for children. Recent examples will be most familiar. Dancing red-and-white mushrooms appear in Fantasia. In Alice's Adventures in Wonderland, Alice converses with a hookah-smoking caterpillar sitting on a gigantic red-and-white mushroom. Fly agaric also appears in Snow White and the Seven Dwarf. Smurfs are small, blue, humanoid creatures living in red-and-white, hollowed-out mushrooms.

Laplanders, who use reindeer as work animals, saw their reindeer eat fly agaric and subsequently romp and stagger. Laplander herdsmen believed that reindeer sought fly agaric for its psychoactive reward. The Laplanders also used fly agaric to achieve an ecstatic and imaginative state, and it is possible that they were at the root of the Christmas story of flying reindeer led by a jolly man dressed in the colors of the mushroom who enters a dwelling via its chimney. Perhaps this entry recalled shamans who would enter a dwelling through the smoke hole in the roof, delivering sacks of colorful mushrooms to fuel a celebration. The Christmas Story appeared in 1823 in a poem referred to as "A Visit from St. Nicholas” by Clement Clarke Moore.

A red cap dotted with the dried crumbles of the egg sac make fly agaric easy to find and identify. (Photo: Jeff Mitton)

More than 600 described species in the genus Amanita occupy the full range from deadly (death cap, A. phalloides; destroying angel, A. bisporigera) to delicious (blusher, A. rubescens; Caesar's mushroom, A. caesarea). With so many species and such dire consequences for a mistaken identification, you should be trained before collecting fly agarics from the forest for personal use.

While hiking at the University of Colorado's Mountain Research Station, I came across a cluster of fly agaric mushrooms. I was surprised to find several divots in the cap—something small, the size of a bird or chipmunk, had taken bites. Who was eating fly agaric?

Reindeer have four chambered stomachs with microbial fermentation, which allows them to digest the cellulose in plant cell walls. All ruminants—including cattle, sheep, goats and bison, eat fly agaric without discomfort.

Another group of animals that can enjoy fly agaric with impunity is squirrels (family Sciuridae), and every squirrel species that I checked (pine, grey, fox, golden mantled ground squirrel, rocks squirrels, chipmunks) eat fly agaric and use a unique method to safely pass the toxin. Squirrels have a novel glycoprotein lining in their intestines that immediately binds the toxins, inactivating them, and escorting them the rest of the way through the digestive tract.

Photographers have amply documented foxes gulping down hunks of fly agaric, but they suffer the agony of severe, prolonged vomiting and staggering that omnivores generally experience. Foxes may be sly, but not when it comes to choosing ingredients for a salad.

Meanwhile, turkeys, grouse, crows, ravens and jays eat fly agaric without distress, but many birds suffer both gastrointestinal distress and severe neurological symptoms.

It is thought provoking to discover an area here in Colorado where the bright mushrooms are popping up, for the association of humans and fly agaric has multiple facets and reaches far back into time. Aposematic coloration reliably warns of the defensive substances (muscimol and ibotenic acid), foreshadowing gastrointestinal misery and eruption for some species. Like all other molecular defenses, one or more species have evolved a way around the defenses and evolved to use them either as food or as an intoxicant.

Ten thousand years ago shamans used the same molecules to produce altered states in their followers for ceremonies and celebrations. Artists and writers brought back inspiration from altered states, and today we have enchanting fairy tales and numerous imaginary creatures to entertain and stimulate imaginations. Each year, families drape festive lights and children listen for the sound of hooves on the roof and a cheerful voice encouraging his reindeer.

For scientists, the chemistries of muscimol and ibotenic acid provide insight into chemical ecology of natural populations and enhance the pleasures of a walk in the woods.

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Top photo: A cluster of fly agaric mushrooms show variation of size, shape and color (Photo: Jeff Mitton)

Hot ponds can help amphibians fight infection—or make things worse

Rachel Sauer — Thu, 07 May 2026 16:35:45 +0000

Hot ponds can help amphibians fight infection—or make things worse Rachel Sauer Thu, 05/07/2026 - 10:35

Blake Puscher

New research from �鶹��Ѱ��Boulder finds that temperature differences between ponds can influence the severity of chytridiomycosis, a deadly fungal disease linked to global amphibian declines

Amphibian populations, including frogs, toads, salamanders and newts, have been declining globally since the 1980s. Many species have even gone extinct.

There are several potential causes for this decline, but one contributor is disease. For example, infection by parasitic flatworms can cause frogs to grow extra limbs, making it harder for them to evade predators. Another prominent amphibian disease called chytridiomycosis has been specifically linked to amphibian declines. It is caused by the fungus Batrachochytrium dendrobatidis, or Bd.

In a study comparing the temperatures of ponds to their level of infection over time, researchers Brendan Hobart and Valerie McKenzie, a �鶹��Ѱ�� professor of ecology and evolutionary biology, discovered that Bd thrives on hosts within a specific range of temperatures and level of temperature variability, above or below which infections are not as severe. This relationship was found to be driven primarily by differences between ponds rather than seasonal differences.

Valerie McKenzie, a �鶹��Ѱ�� professor of ecology and evolutionary biology, worked with PhD graduate Brendan Hobart and other research colleagues to study how temperature affects amphibians' susceptibility to fungal infections.

Hobart worked on the study as a PhD student at �鶹��Ѱ��Boulder and has since completed his PhD and moved on to a research scientist position at the University of Wisconsin. Another �鶹��Ѱ��PhD student, Timothy Korpita, was also involved, along with several people from the National Wildlife Health Center. McKenzie is the principal investigator of the McKenzie Lab.

What makes Bd unique?

Fungi grow on substrates, which are surfaces that provide them with the nutrients they need to develop their reproductive structures and release spores. Some of these spores will end up in new substrates, beginning the next generation. Instead of growing on decaying biological material or living plants like many other species of fungi, Bd’s substrate is the skin of a living animal, specifically an amphibian. Additionally, rather than releasing spores that float through the air, Bd propagates using zoospores, which can swim short distances through the water using their whip-like tails.

“They are microscopic,” McKenzie says, “and they will attach themselves to a skin cell, then penetrate and go inside. They use amphibian skin cells as a place to replicate themselves, rupture that skin cell and let out more zoospores that can go on to infect nearby skin cells or go in the water and infect other individuals.”

Bd’s ability to spread from one pond to another is still something of a mystery, however.

“We still do not understand all the mechanisms by which it is getting spread,” McKenzie says. “People have made guesses that it could be birds that land in the pond water picking up some of these zoospores in their feathers and then fly off and land in another pond.” Even their ability to infect different hosts is surprising, considering that the zoospores can swim only one or two centimeters, but they are able to chemically target molecules found on amphibian skin to make the most of this short range.

Regardless of how the fungus gets around, its strategy is clearly effective, as it has infected a large number of diverse amphibians. According to McKenzie, there are something like 8,000 species of amphibians, which is only slightly fewer than the number of mammalian species.

“This one fungal pathogen is causing declines, or is predicted to cause declines, in maybe a third of amphibians. Imagine if COVID, for example, was causing massive die-offs of not only humans, but all kinds of mammals, like squirrels, whales, wolves, cats, dogs. That is sort of what is happening to amphibians with this fungus. It is unprecedented for what one pathogen can do.”

Bd is dangerous for amphibians because it targets their skin, which they rely on for many purposes, like balancing hydration. According to McKenzie, disruption to the skin can result in secondary organ failure. The disease can be more or less severe for different species, but there are many species that have been seriously affected worldwide. Bd is currently most prominent in the Americas—particularly the Central and South American tropics—eastern Australia and east Africa, but may spread to other parts of the world over time.

How temperature influences infections

Previous research into Bd has singled out thermal conditions, meaning the temperature of the habitats that hosts live in, as key drivers of host outcomes. Particularly, the variability of temperatures and the mean (average) temperature are important variables. “Temperature is the ultimate determinant of most or all biological processes,” Hobart says.

“It is especially relevant to ectotherms”—cold-blooded animals do not produce their own heat—"and their pathogens because their body temperature largely fluctuates with the environment,” Hobart says.

Salamander populations, along with other amphibian populations, have been in decline since the 1980s. Among the causes for these declines is the fungus Batrachochytrium dendrobatidis, or Bd. (Photo: Iuliu Illes/Unsplash)

This study is directed toward exploring the relationship between temperature and infections further, particularly by separating changes in temperature into seasonal and among-site components. To do this, the researchers measured temperatures and Bd infections of eastern newt populations across 20 ponds in Wisconsin over the course of two years.

“All of these ponds were within a few miles,” Hobart says. “From a broad scale perspective, they all have the same climate. If you were to look up a weather forecast on an app, it would be the same for all the ponds, but the actual conditions are very different depending on things like how much tree cover there is over the pond, how clear the water is, how much stuff is floating on the surface, all these different biotic and abiotic factors.”

These differences lead to significant variation in pond-to-pond water temperature, and they are what the study covered rather than gradients in temperature within a given pond.

When the researchers looked at the temperature variability and average temperature, they found that both changed at the same time, or in other words, covaried. According to Hobart, this is because the ponds with the most variable temperature also tended to be the warmest. For this reason, the two variables were combined into a thermal mean and variability index (MVI), which ranged from cool and stable to hot and variable temperatures. When combined with infection data obtained by capturing, swabbing and releasing newts, this index was shown to have a non-linear relationship with infection load (meaning not only whether the fungal disease was present but also how much was on the animals’ skin).

Considering thermal variation both over time and between ponds, infection load was highest at middling MVI values, declining similarly when the index either increased or decreased from there.

“It is this primary hump-shaped relationship,” Hobart says. When the variations over time and space were separated out, the spatial variation resembled the overall relationship very closely, while the temporal variation looked different. “That is what produced this finding that variation from site to site was driving the overall pattern.”

“This one fungal pathogen is causing declines, or is predicted to cause declines, in maybe a third of amphibians ... It is unprecedented for what one pathogen can do.”

Implications for conservation

Considering how severe the effect of Bd has been on amphibian populations, anything people can do to reduce infections is of interest. The results from this study suggest that changing the temperature of a pond could be an effective way of doing this, but it is not as simple as it sounds.

Like many fungi, Bd does best within a limited range of temperatures, which is about 23–28 degrees Celsius or 73–82 Fahrenheit, according to the researchers. At middling MVI values, the temperature is right for Bd, and there is even some evidence that Bd handles temperature variability better than its hosts, giving it an additional advantage.

However, once the temperature increases out of Bd’s ideal range, the benefits of variability cannot counteract the unfavorable heat, especially because amphibian immune responses often increase in strength at these temperatures. On the other hand, when the temperature is low, Bd does not get any advantage from variability and is also outside of its ideal temperature range.

This means that, depending on the starting conditions, the severity of Bd infections in a pond might be diminished by either increasing or decreasing the temperature, but in some cases, changing the temperature would only make things worse.

“It has been suggested,” Hobart says, “that one could cut down trees around a pond to let more light in and make that pond hot. In principle, that seems like a fine idea.” However, “if you did not know where you were on that index, and you cut down a bunch of trees, you could inadvertently increase infection.”

In other words, if a pond’s temperature is middling, increasing it could help with infections, but if the pond is cooler to begin with, it could bring the thermal MVI into the range where Bd thrives.

“There have been a lot of studies looking at the relationship between temperature and this amphibian pathogen,” McKenzie says. For example, there was recently a study that involved building masonry brick “saunas” that frogs can crawl into to heat up and kill off the Bd. “I think what this study shows is that what works for one site may not be applicable for another site, even if that site is relatively close and similar.”

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