Long considered loners, many marsupials may have complex social lives

Marsupials may have richer social lives than previously thought.

Generally considered loners, the pouched animals have a wide diversity of social relationships that have gone unrecognized, a new analysis published October 26 in Proceedings of the Royal Society B suggests. The findings could have implications for how scientists think about the lifestyles of early mammals.

“These findings are helpful to move us away from a linear thinking that used to exist in some parts of evolutionary theory, that species develop from supposedly simple into more complex forms,” says Dieter Lukas, an evolutionary ecologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who was not involved with the study.

Mammals run the gamut of social organization systems, ranging from loose, ephemeral interactions like aggregations of jaguars in the South American wetlands to the antlike subterranean societies of naked mole-rats (SN: 10/13/21; SN: 10/20/20).

But marsupials — a subgroup of mammals that give birth to relatively underdeveloped young reared in pouches — have traditionally been considered largely solitary. Some kangaroo species were known to form transient or permanent groups of dozens of individuals. But among marsupials, long-term bonds between males and females were thought rare and there were no known examples of group members cooperating to raise young. Previous work on patterns of mammalian social evolution regarded about 90 percent of examined marsupial species to be solitary.

“If you look at other [studies] about some specific species, you will see [the researchers] tend to assume that the marsupials are solitary,” says Jingyu Qiu, a behavioral ecologist at CNRS in Strasbourg, France.

Sorting social lives
Qiu and her colleagues developed a database of field studies that illuminated marsupial social organization, taking into account how populations vary within a species and delving into the evolutionary history of marsupial social lives. The researchers compiled data from 120 studies on 149 populations of 65 marsupial species, categorizing each population as solitary, living in pairs — such as one male and one female — or falling into four kinds of group living, including one male and multiple females (or vice versa), multiple males and females, or single sex groups.

While 19 species, or 31 percent of those studied, appear to go strictly solo, nearly half of the species always live in pairs or groups. The team also found lots of variation within species; 27 of the 65 species — more than 40 percent — fell into multiple social organization classifications.
When the researchers looked at this social variation against climatic conditions in Australia, they found that social variability was more common in drier environments with less predictable rainfall. It’s possible that being able to switch between solitary and group living acts as a buffer against resource unpredictability.

The researchers’ focus on social flexibility “highlights that there is nothing simple even about a supposedly solitary species,” Lukas says.

Implications for the earliest mammals
Qiu and her colleagues also ran computer analyses comparing the evolutionary relationships of the marsupials with how they form social relationships. This let the team predict the social organization of the earliest marsupials, which split from placental mammals about 160 million years ago. Because modern marsupials have been considered solitary, the marsupial ancestors — and the earliest mammals on the whole — have generally been assumed to be solitary as well.

The team found that solitary was the most likely social category of the ancestral marsupials, a 35 percent probability. But Qiu points out that the varied combinations where pair and group living are possible options make up the other 65 percent. So “it is more likely that the ancestor was also non-solitary,” she says. The findings also give insights into the range of possible lifestyles experienced by the earliest mammals, she says.

But Robert Voss, a mammalogist at the American Museum of Natural History in New York City, questions the analyses’ insights about a potentially social ancestral marsupial. The uncertainty about the solitary alternative, he says, is largely due to the researchers’ benchmarks for what does and what doesn’t constitute social behavior — thresholds that Voss views as too permissive. For example, Voss disagrees with the team’s characterization of opossum social organization.

“Anecdotal observations of [members of the same species] occasionally denning together is not compelling evidence for social behavior,” says Voss. “None of the cited studies suggest that opossums are anything other than solitary.”

Future work, Qiu says, will involve gathering data on a larger subset of mammals outside of marsupials to get a clearer picture of how social traits have evolved among mammals.

A spider monkey’s remains tell a story of ancient diplomacy in the Americas

A sacrificed spider monkey is shedding new light on an ancient Mesoamerican relationship.

The remains of a 1,700-year-old monkey found in the ancient city of Teotihuacan outside modern-day Mexico City suggest the primate was a diplomatic gift from the Maya. The find is the earliest evidence of a primate held in captivity in the Americas, researchers report November 21 in Proceedings of the National Academy of Sciences.

Unearthed in 2018 at the base of a pyramid in Teotihuacan, the monkey’s skeleton lay beside the corpses of other animals — including an eagle and several rattlesnakes — in an area of the city where visiting Maya elites may have resided.

Evidence of animal sacrifices, including of predators like jaguars, have been found in the city before. But “up to that point, we did not have any instances of sacrificed primates in Teotihuacan,” says Nawa Sugiyama, an anthropological archaeologist at the University of California, Riverside.

Chemical analysis of the spider monkey’s bones and teeth showed that the female had likely been captured in a humid environment at a young age sometime in the third century. The monkey then lived in captivity for a few years before meeting her end between the years 250 and 300.

The highlands around Mexico City are a long way from the natural habitat of spider monkeys (Ateles geoffroy), which require wet tropical forests to thrive. This fact, along with the presence of Maya murals and vessels, suggests to Sugiyama and her colleagues that the spider monkey was a gift from elite Mayas to the people of Teotihuacan.

The find is an example of diplomatic relations between two cultures that sometimes had violent interactions. Maya hieroglyphs indicated that military forces from Teotihuacan invaded the Maya city of Tikal in 378, marking the start of a roughly 70-year period in which Teotihuacan meddled in Maya politics (SN: 10/22/21).

The “striking” discovery of the monkey shows that relationship between these two cultures far predates the invasion, says David Stuart, an archaeologist and epigraphist at the University of Texas at Austin who was not involved in the study.

“The war of 378 had a long history leading up to it,” he says. “The monkey is a really compelling illustration of this long relationship.”

Josep Cornella breaks boundaries to make new and better catalysts

Josep Cornella doesn’t deal in absolutes. While chemists typically draw rigid lines between organic and inorganic chemistry, Cornella, a researcher at Max-Planck-Institut für Kohlenforschung in Mülheim an der Ruhr, Germany, believes in just the opposite.

“You have to be open to cross boundaries,” he says, “and learn from it.” The fringes are “where the rich new things are.”

Cornella is an organic chemist by industry standards; he synthesizes molecules that contain carbon. But he’s put together a team from a wide range of backgrounds: inorganic chemists, physical organic chemists, computational chemists. Together, the team brainstorms novel approaches to designing new catalysts, so that chemical reactions essential to pharmaceuticals and agriculture can be made more efficient and friendly for the environment. Along the way, Cornella has unlocked mysteries that stumped chemists for years.

“He has told us about catalysts … that we didn’t have before, and which were just pipe dreams,” says Hosea Nelson, a chemist at Caltech who has not worked with Cornella.
Bold idea
When Cornella heard a speaker at a 2014 conference say that bismuth was nontoxic, he was sure it was a mistake. Bismuth is a heavy metal that sits between toxic lead and polonium on the periodic table. But it is indeed relatively nontoxic — it’s even used in the over-the-counter nausea medicine Pepto-Bismol.

Still, bismuth remains poorly understood. That’s one reason it attracted him. “It was a rather forgotten element of the periodic table,” Cornella says. But, “it’s there for a reason.”

Cornella started wondering if an element like bismuth could be trained for use as a catalyst. For the last century, scientists have been using transition metals, like palladium and iron, as the main catalysts in industrial synthesis. “Could we actually train [bismuth] to do what these guys do so well?” he asked. It was a conceptual question that “was completely naïve, or maybe stupid.”

Far from stupid: His team successfully used bismuth as a catalyst to make a carbon-fluorine bond. And bismuth didn’t just mimic a transition metal’s role — it worked better. Only a small amount of bismuth was required, much less than the amount of transition metal needed to complete the same task.

“A lot of people, including myself and other [researchers] around the world, have spent a lot of time thinking about how to make bismuth reactions catalytic,” Nelson says. “He’s the guy who cracked that nut.”

Standout research
While the bismuth research is “weird” and “exciting,” Cornella says, it remains a proof of concept. Bismuth, though cheap, is not as abundant as he had hoped, so it’s not a very sustainable option for industry.

But other Cornella team findings are already being used in the real world. In 2019, the group figured out how to make an alternative to Ni(COD)2, a finicky catalyst commonly used by chemists in the lab. If it’s not kept at freezing temperatures and protected from oxygen by a layer of inert gases, the nickel complex falls apart.

The alternative complex, developed by Lukas Nattmann, a Ph.D. student in Cornella’s lab at the time, stays stable in oxygen at room temperature. It’s a game changer: It saves energy and materials, and it’s universal. “You can basically take all those reactions that were developed for 60 years of Ni(COD)2 and basically replace all of them with our catalyst, and it works just fine,” Cornella says.
Cornella’s lab is also developing new reagents, substances that transform one material into another. The researchers are looking to transform atoms in functional groups — specific groupings of atoms that behave in specific ways regardless of the molecules they are found in — into other atoms in a single step. Doing these reactions in one step could cut preparation time from two weeks to a day, which would be very useful in the pharmaceutical industry

Taking risks
It’s the success that gets attention, but failure is “our daily basis,” Cornella says. “It’s a lot of failure.” As a student, when he couldn’t get a reaction to work, he’d set up a simple reaction called a TBS protection — the kind of reaction that’s impossible to get wrong — to remind himself that he wasn’t “completely useless.”

Today he runs a lab that champions taking risks. He encourages students to learn from one another about areas they know nothing about. For instance, a pure organic chemist could come into Cornella’s lab and leave with a good understanding of organometallic chemistry after spending long days working alongside a colleague who is an expert in that area.

To Cornella, this sharing of knowledge is crucial. “If you tackle a problem from just one unique perspective,” he says, “maybe you’re missing some stuff.”

While Cornella might not like absolutes, Phil Baran, who advised Cornella during his postdoctoral work at Scripps Research in San Diego, sees Cornella as fitting into one of two distinct categories: “There are chemists who do chemistry in order to eat, like it’s a job. And there are chemists who eat in order to do chemistry,” Baran says. Cornella fits into the latter group. “It’s his oxygen.”

Marcos Simões-Costa asks how cells in the embryo get their identities

Growing up in Brazil, Marcos Simões-Costa often visited his grandparents’ farm in the Amazon. That immersion in nature — squawking toucans and all — sparked his fascination with science and evolution. But a video of a developing embryo, shown in his middle school science class, cemented his desire to become a developmental biologist.

“It’s such a beautiful process,” he says. “I was always into drawing and art, and it was very visual — the shapes of the embryo changing, the fact that you start with one cell and the complexity is increasing. I just got lost in that video.”

Today, Simões-Costa, of Harvard Medical School and Boston Children’s Hospital, is honoring his younger self by demystifying how the embryo develops. He studies the embryos and stem cells of birds and mice to learn how networks of genes and the elements that control them influence the identity of cells. The work could lead to new treatments for various diseases, including cancer.

“The embryo is our best teacher,” he says.
Standout research
Simões-Costa focuses on the embryo’s neural crest cells, a population of stem cells that form in the developing central nervous system. The cells migrate to other parts of the embryo and give rise to many different cell types, from the bone cells of the face to muscle cells to brain and nerve cells.

Scientists have wondered for years why, despite being so similar, neural crest cells in the cranial region of the embryo can form bone and cartilage, while those in the trunk region can’t form either. While a postdoc at Caltech, Simões-Costa studied the cascade of molecules that govern how genes are expressed in each cell type. With his adviser, developmental biologist Marianne Bronner, he identified transcription factors — proteins that can turn genes on and off — that were present only in cranial cells. Transplanting the genes for those proteins into trunk cells endowed the cells with the ability to create cartilage and bone.

Now in his own lab, he continues to piece together just how this vast regulatory network influences the specialization of cells. His team reconstructed how neural crest cells’ full set of genetic instructions, or the genome, folds into a compact, 3-D shape. The researchers identified short DNA sequences, called enhancers, that are located in faraway regions of the genome, but end up close to key genes when the genome folds. These enhancers work with transcription factors and other regulatory elements to control gene activity.

Simões-Costa is also using neural crest cells to elucidate a strange behavior shared by cancer cells and some embryonic cells. These cells produce energy anaerobically, without oxygen, even when oxygen is present. Called the Warburg effect, this metabolic process has been studied extensively in cancer cells, but its function remained unclear.

Colored tracks representing cell movements..
Through experiments manipulating the metabolism of neural crest cells, Simões-Costa’s team found that the Warburg effect is necessary for the cells to move around during early development. The mechanism, which should stay turned off in nonembryonic cells, somehow “gets reactivated in adult cells in the context of cancer, leading those cells to become more migratory and more invasive,” Simões-Costa says.

“He’s one of the few people who’s really looked at [this process in neural crest cells] at a molecular level and done a deep dive into the mechanisms underlying it,” says Bronner.

Cleverly combining classical embryological methods with the latest genomic technologies to address fundamental questions in developmental biology is what makes Simões-Costa special, says Kelly Liu, a developmental biologist at Cornell University. He wants to understand not only what individual genes do, but how they work at a systems level, she says.

What’s next
How does the genetic blueprint tell cells where they are in the embryo, and what they should be doing? How do cancer cells hijack the Warburg effect, and could understanding of that process lead to new treatments? These are some of the questions Simões-Costa wants to tackle next.

“It’s been 20 years since the Human Genome Project came to a conclusion,” he says, referring to the massive effort to read the human genetic instruction book. “But there’s still so much mystery in the genetic code.”

Those mysteries, plus a deep passion for lab work, fuel Simões-Costa’s research. “Being at the bench is when I’m the happiest,” he says. He likens the delicate craft of performing precise surgeries on tissues and cells to meditation. “It does not get old.”