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      in Environment

      Better living through multicellular life cycles

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      Cooperation is a core part of life for many organisms, ranging from microbes to complex multicellular life. It emerges when individuals share resources or partition a task in such a way that each derives a greater benefit when acting together than they could on their own. For example, birds and fish flock to evade predators, slime mold swarms to hunt for food and reproduce, and bacteria form biofilms to resist stress.

      Individuals must live in the same “neighborhood” to cooperate. For bacteria, this neighborhood can be as small as tens of microns. But in environments like the ocean, it’s rare for cells with the same genetic makeup to co-occur in the same neighborhood on their own. And this necessity poses a puzzle to scientists: In environments where survival hinges on cooperation, how do bacteria build their neighborhood?

      To study this problem, MIT professor Otto X. Cordero and colleagues took inspiration from nature: They developed a model system around a common coastal seawater bacterium that requires cooperation to eat sugars from brown algae. In the system, single cells were initially suspended in seawater too far away from other cells to cooperate. To share resources and grow, the cells had to find a mechanism of creating a neighborhood. “Surprisingly, each cell was able to divide and create its own neighborhood of clones by forming tightly packed clusters,” says Cordero, associate professor in the Department of Civil and Environmental Engineering.

      A new paper, published today in Current Biology, demonstrates how an algae-eating bacterium solves the engineering challenge of creating local cell density starting from a single-celled state.

      “A key discovery was the importance of phenotypic heterogeneity in supporting this surprising mechanism of clonal cooperation,” says Cordero, lead author of the new paper.

      Using a combination of microscopy, transcriptomics, and labeling experiments to profile a cellular metabolic state, the researchers found that cells phenotypically differentiate into a sticky “shell” population and a motile, carbon-storing “core.” The researchers propose that shell cells create the cellular neighborhood needed to sustain cooperation while core cells accumulate stores of carbon that support further clonal reproduction when the multicellular structure ruptures.

      This work addresses a key piece in the bigger challenge of understanding the bacterial processes that shape our earth, such as the cycling of carbon from dead organic matter back into food webs and the atmosphere. “Bacteria are fundamentally single cells, but often what they accomplish in nature is done through cooperation. We have much to uncover about what bacteria can accomplish together and how that differs from their capacity as individuals,” adds Cordero.

      Co-authors include Julia Schwartzman and Ali Ebrahimi, former postdocs in the Cordero Lab. Other co-authors are Gray Chadwick, a former graduate student at Caltech; Yuya Sato, a senior researcher at Japan’s National Institute of Advanced Industrial Science and Technology; Benjamin Roller, a current postdoc at the University of Vienna; and Victoria Orphan of Caltech.

      Funding was provided by the Simons Foundation. Individual authors received support from the Swiss National Science Foundation, Japan Society for the Promotion of Science, the U.S. National Science Foundation, the Kavli Institute of Theoretical Physics, and the National Institutes of Health. More

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      in Environment

      Q&A: Bettina Stoetzer on envisioning a livable future

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      In an ongoing series, MIT faculty, students, and alumni in the humanistic fields share perspectives that are significant for solving the economic, political, ethical, and cultural dimensions of climate change, as well as mitigating its myriad social and ecological impacts. Bettina Stoetzer is the Class of 1948 Career Development Associate Professor of Anthropology at MIT; her research combines perspectives on ecology and environmental change with an analysis of migration, race, and social justice. In this conversation with SHASS Communications, she shares insights from anthropology and from her forthcoming book, “Ruderal City: Ecologies of Migration and Urban Life in Berlin” (Duke University Press, 2022).Q: You research “ruderal” ecologies — those rising up like weeds in inhospitable locales such as industrial zones. What does your work reveal about the relationship between humans and the environment, particularly as climate change presents ever more challenges to human habitation?A: The term ruderal originates from the Latin word “rudus,” meaning “rubble.” In urban ecology it refers to organisms that spontaneously inhabit inhospitable environments such as rubble spaces, the cracks in sidewalks, or spaces alongside train tracks and roads. As an anthropologist, I find the ruderal to be a useful lens for examining this historical moment when environmental degradation, war, forced migration, economic inequality, and rising nationalism render much of the world inhospitable to so many beings.

      My book, “Ruderal City: Ecologies of Migration and Urban Life in Berlin,” is inspired by the insights of botany, ecology, as well as by social justice struggles. During my fieldwork in Berlin, I engaged with diverse communities — botanists, environmentalists, public officials, and other Berlin residents, such as white German nature enthusiasts, Turkish migrants who cultivate city gardens, and East African refugees who live in the forested edges of the city.The botanists I spoke with researched so-called “ruderal flora” that flourished in the city’s bombed landscapes after the end of World War II. Berlin’s rubble vegetation was abundant with plants that usually grow in much warmer climate zones, and the botanists realized that many of these plants’ seeds had arrived in the city by chance — hitching a ride via imported materials and vehicles, or the boots of refugees. At the same time, the initial appearance of these plants illustrated that Berlin had become hotter, which shed light on the early signs of climate change. But that is only part of the story. Listening to migrants, refugees, and other Berlin residents during my fieldwork, I also learned that it is important to consider the ways in which people who are often not recognized as experts relate to urban lands. White European environmental discourse often frames migrants and communities of color as having an inappropriate relation to “nature” in the city, and racializes them on that basis. For example, Turkish migrants who barbecue in Berlin’s parks are often portrayed as polluting the “green lungs” of Berlin.Yet from working with these communities, as well as with other Berliners who cultivated urban vegetable gardens, built makeshift shelters in abandoned lots, produced informal food economies in Berlin’s parks, or told stories about their experience in the forest edges of the city, I learned that people, while grappling with experiences of racism, actually carved out alternative ways of relating to urban lands that challenged white European and capitalist traditions.Engaging with these practices, I utilize the concept of the ruderal and expand it as an analytic for tracking seemingly disparate worlds — and for attending to the heterogeneous ways in which people build lives out of the ruins of European nationalism and capitalism. My goal in the book is not to equate people with plants, but rather to ask how people, plants, animals, and other living beings are intertwined in projects of capitalist extraction and in nation-making — and how they challenge and rework these projects.Q: In what ways do you think the tools and insights from anthropology can advance efforts to address climate change and its impacts?A: When tackling complex environmental challenges, climate change included, the focus is often on “the social consequences of” climate change and technological solutions to address it. What is exciting about anthropology is that it gives us tools to interrogate environmental challenges through a broader lens.Anthropologists use in-depth fieldwork to examine how people make sense of and relate to the world. Ethnographic fieldwork can help us examine how climate change affects people in their everyday lives, and it can reveal how different stakeholders approach environmental challenges. By providing a deeper understanding of the ways in which people relate to the material world, to land, and to other beings, anthropological analyses also shed light on the root causes of climate change and expand our imagination of how to live otherwise.Through these close-up analyses, ethnography can also illuminate large-scale political phenomena. For instance, by making visible the relation between climate change denial and the erosion of democratic social structures in people’s everyday lives, it can provide insights into the rise of nationalist and authoritarian movements. This is a question I explore in my new research project. (One case study in the new research focuses on the ways in which pigs, people, and viruses have co-evolved during urbanization, industrial agriculture, and the climate crisis, e.g.: the so-called African Swine Fever virus among wild boar — which proliferate in the ruins of industrial agriculture and climate changes — trigger political responses across Europe, including new border fences.)

      Through several case studies, I examine how the changing mobility patterns of wildlife (due to climate change, habitat loss, and urbanization) pose challenges for tackling the climate crisis across national borders and for developing new forms of care for nonhuman lives.Q: You teach MIT’s class 21A.407 (Gender, Race, and Environmental Justice). Broadly speaking, what are goals of this class? What lessons do you hope students will carry with them into the future?A: The key premise of this class is that the environmental challenges facing the world today cannot be adequately addressed without a deeper understanding of racial, gender, and class inequalities, as well as the legacies of colonialism. Our discussion begins with the lands on which we, at MIT, stand. We read about the colonization of New England and how it radically transformed local economies and landscapes, rearranged gender and racial relations, and led to the genocide and dispossession of Indigenous communities and their way of life.From this foundation, the goal is to expand our ideas of what it means to talk about ecology, the “environment,” and justice. There is not one way in which humans relate to land and to nonhuman beings, or one way of (re-)producing the conditions of our livelihoods (capitalism). These relations are all shaped by history, culture, and power.We read anthropological scholarship that explores how climate change, environmental pollution, and habitat destruction are also the consequences of modes of inhabiting the earth inherited from colonial relations to land that construct human and nonhuman beings as extractable “resources.” Considering these perspectives, it becomes clear that pressing environmental challenges can only be solved by also tackling racism and the legacies of colonialism.Throughout the semester, we read about environmental justice struggles that seek to stop the destruction of land, undo the harm of toxic exposures, and mitigate the effects of climate change. I hope that one of the takeaways students gain from this course is that Black, Indigenous, people-of-color, and feminist activists and scholars have been leading the way in shaping more livable futures.

      Q: In confronting an issue as formidable as global climate change, what gives you hope?A: I am really inspired by youth climate justice activists, especially from the Global South, who insist on new solutions to the climate emergency that counter market-driven perspectives, address global economic inequalities, and raise awareness about climate-driven displacement. Confronting climate change will require building more democratic structures and climate justice activists are at the forefront of this.Here at MIT, I also see a growing enthusiasm among our students to develop solutions to the climate crisis and to social injustices. I am particularly excited about Living Climate Futures, an initiative in Anthropology, History, and the Program on Science, Technology, and Society. We will be hosting a symposium at the end of April featuring environmental and climate justice leaders and youth activists from across the country. It will be a unique opportunity to explore how community leaders and research institutions such as MIT can collaborate more closely to tackle the challenges of climate change.

      Interview prepared by MIT SHASS CommunicationsSenior writer: Kathryn O’NeillSeries editor, designer: Emily Hiestand, communications director More

    • 88 Shares199 Views

      in Environment

      Predator interactions chiefly determine where Prochlorococcus thrive

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      Prochlorococcus are the smallest and most abundant photosynthesizing organisms on the planet. A single Prochlorococcus cell is dwarfed by a human red blood cell, yet globally the microbes number in the octillions and are responsible for a large fraction of the world’s oxygen production as they turn sunlight into energy.

      Prochlorococcus can be found in the ocean’s warm surface waters, and their population drops off dramatically in regions closer to the poles. Scientists have assumed that, as with many marine species, Prochlorococcus’ range is set by temperature: The colder the waters, the less likely the microbes are to live there.

      But MIT scientists have found that where the microbe lives is not determined primarily by temperature. While Prochlorococcus populations do drop off in colder waters, it’s a relationship with a shared predator, and not temperature, that sets the microbe’s range. These findings, published today in the Proceedings of the National Academy of Sciences, could help scientists predict how the microbes’ populations will shift with climate change.

      “People assume that if the ocean warms up, Prochlorococcus will move poleward. And that may be true, but not for the reason they’re predicting,” says study co-author Stephanie Dutkiewicz, senior research scientist in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS). “So, temperature is a bit of a red herring.”

      Dutkiewicz’s co-authors on the study are lead author and EAPS Research Scientist Christopher Follett, EAPS Professor Mick Follows, François Ribalet and Virginia Armbrust of the University of Washington, and Emily Zakem and David Caron of the University of Southern California at Los Angeles.

      Temperature’s collapse

      While temperature is thought to set the range of Prochloroccus and other phytoplankton in the ocean, Follett, Dutkiewicz, and their colleagues noticed a curious dissonance in data.

      The team examined observations from several research cruises that sailed through the northeast Pacific Ocean in 2003, 2016, and 2017. Each vessel traversed different latitudes, sampling waters continuously and measuring concentrations of various species of bacteria and phytoplankton, including Prochlorococcus. 

      The MIT team used the publicly archived cruise data to map out the locations where Prochlorococcus noticeably decreased or collapsed, along with each location’s ocean temperature. Surprisingly, they found that Prochlorococcus’ collapse occurred in regions of widely varying temperatures, ranging from around 13 to 18 degrees Celsius. Curiously, the upper end of this range has been shown in lab experiments to be suitable conditions for Prochlorococcus to grow and thrive.

      “Temperature itself was not able to explain where we saw these drop-offs,” Follett says.

      Follett was also working out an alternate idea related to Prochlorococcus and nutrient supply. As a byproduct of its photosynthesis, the microbe produces carbohydrate — an essential nutrient for heterotrophic bacteria, which are single-celled organisms that do not photosynthesize but live off the organic matter produced by phytoplankton.

      “Somewhere along the way, I wondered, what would happen if this food source Prochlorococcus was producing increased? What if we took that knob and spun it?” Follett says.

      In other words, how would the balance of Prochlorococcus and bacteria shift if the bacteria’s food increased as a result of, say, an increase in other carbohydrate-producing phytoplankton? The team also wondered: If the bacteria in question were about the same size as Prochlorococcus, the two would likely share a common grazer, or predator. How would the grazer’s population also shift with a change in carbohydrate supply?

      “Then we went to the whiteboard and started writing down equations and solving them for various cases, and realized that as soon as you reach an environment where other species add carbohydrates to the mix, bacteria and grazers grow up and annihilate Prochlorococcus,” Dutkiewicz says.

      Nutrient shift

      To test this idea, the researchers employed simulations of ocean circulation and marine ecosystem interactions. The team ran the MITgcm, a general circulation model that simulates, in this case, the ocean currents and regions of upwelling waters around the world. They overlaid a biogeochemistry model that simulates how nutrients are redistributed in the ocean. To all of this, they linked a complex ecosystem model that simulates the interactions between many different species of bacteria and phytoplankton, including Prochlorococcus.

      When they ran the simulations without incorporating a representation of bacteria, they found that Prochlorococcus persisted all the way to the poles, contrary to theory and observations. When they added in the equations outlining the relationship between the microbe, bacteria, and a shared predator, Prochlorococcus’ range shifted away from the poles, matching the observations of the original research cruises.

      In particular, the team observed that Prochlorococcus thrived in waters with very low nutrient levels, and where it is the dominant source of food for bacteria. These waters also happen to be warm, and Prochlorococcus and bacteria live in balance, along with their shared predator. But in more nutrient-rich enviroments, such as polar regions, where cold water and nutrients are upwelled from the deep ocean, many more species of phytoplankton can thrive. Bacteria can then feast and grow on more food sources, and in turn feed and grow more of its shared predator. Prochlorococcus, unable to keep up, is quickly decimated. 

      The results show that a relationship with a shared predator, and not temperature, sets Prochlorococcus’ range. Incorporating this mechanism into models will be crucial in predicting how the microbe — and possibly other marine species — will shift with climate change.

      “Prochlorococcus is a big harbinger of changes in the global ocean,” Dutkiewicz says. “If its range expands, that’s a canary — a sign that things have changed in the ocean by a great deal.”

      “There are reasons to believe its range will expand with a warming world,” Follett adds.” But we have to understand the physical mechanisms that set these ranges. And predictions just based on temperature will not be correct.” More