American Scientist

In this roundup, associate editor Nicholas Gerbis summarizes notable recent developments in scientific research, selected from reports compiled in the free electronic newsletter Sigma Xi SmartBrief.

One Queen, Two Species

Messor ibericus ant queens can clone males of another species (M. structor) as a colony survival strategy. This necessity, called xenoparity, marks the first known nonparasitic instance of one species’ eggs spreading another species’ genome (male hermaphrodite conifers and clams, for example, clone themselves by hijacking other species’ eggs). Typically, ant males come from unfertilized eggs that contain only the queen’s chromosomes. When a male mates with his queen, she stores his sperm and later fertilizes her eggs with it to produce female workers and, rarely, queens. But a team led by scientists at Montpellier Institute of Evolutionary Sciences in France believes a past genetic change has caused fertilized M. ibericus eggs to produce only queens, unbalancing the colony. To cope, the queens began mating with, then cloning, M. structor males. Now, by removing her own maternal genome from her eggs and replacing it with genetic material from an M. structor male, she can produce a male with solely M. structor genes. Eggs fertilized by that male’s sperm can produce needed female workers. Developing a way to clone the needed males in-house freed the M. ibericus from having to dwell near M. structor colonies.

Juvé, Y., et al. 2025. One mother for two species via obligate cross-species cloning in ants. Nature. Published online doi:10.1038/s41586-025-09425-w.

Dino Tooth as Climate Proxy

Scientists can now reconstruct atmospheric carbon dioxide levels from the Mesozoic Era using fossil dinosaur teeth. This approach makes ecological and atmospheric inferences by comparing the ratios of three oxygen isotopes: ¹⁶O, ¹⁷O, and ¹⁸O. Remarkably, the team led by researchers at Georg August University of Göttingen, Germany, has shown that triple-O isotope signals can persist stably in fossil teeth for hundreds of millions of years and can provide an animal-based proxy for climate in deep time. This finding matters because scientists cannot directly measure CO₂ except via ice cores, which at best go back only hundreds of thousands of years, so they must rely on proxies such as carbon isotopes in organic matter, boron isotopes in marine fossils, or the compositions of ancient leaves and soils. The triple-O method adds another arrow to that quiver, potentially improving validity and narrowing estimate ranges. The technique works because the atmospheric concentration of ¹⁷O relative to ¹⁶O and ¹⁸O varies depending on atmospheric CO₂ concentrations and plant activity in the biosphere, which affect the ¹⁷O anomaly oppositely. After animals breathe in atmospheric oxygen with this telltale ¹⁷O ratio, hard tissues such as tooth enamel preserve it.

Feng, D., T. Tütken, E. M. Griebeler, D. Herwartz, and A. Pack. 2025. Mesozoic atmospheric CO₂ concentrations reconstructed from dinosaur tooth enamel. PNAS 122:e2504324122.

Carbene Controversy Settled

In a first, researchers have confirmed that highly reactive carbon atoms called carbenes can exist in water, overturning more than half a century of controversy and confirming the 1958 hypothesis of Columbia University chemist Ronald Breslow. Intriguingly, the results suggest that, under the right conditions, cellular enzymes can protect carbene molecules and let them participate in biocatalysis, which is essential to life. Simple carbenes are structurally highly unstable and occur only as transient intermediates in chemical reactions. This instability is especially pronounced in water, which led many to argue previously that carbenes were incompatible with H₂O. Breslow proposed that the coenzyme thiamine (vitamin B₁) could provide transient carbenes that support catalytic activity by enzymes, even in a cell’s aqueous environment, by ensconcing the carbene within a protective, positively charged ring of carbon, nitrogen, and sulfur. A team led by scientists from University of California, Riverside, has now proven him right: The ring stabilizes the carbene just long enough for it to participate in useful reactions. The group has used a similar strategy to design next-generation batteries and new cancer therapies.

Raviprolu, V. T., et al. 2025. Confirmation of Breslow’s hypothesis: A carbene stable in liquid water. Science Advances 11:eadr9681.

Island Syndrome Outfoxed

The brains of most foxes occupying California’s Channel Islands (Urocyon littoralis) are not relatively smaller than the brains of their larger mainland relatives, the gray fox (U. cinereoargenteus); indeed, many are larger. This finding adds nuance to a mainstay evolutionary concept called “island syndrome,” which predicts that trait shifts such as smaller, less energy-consuming brains will be selected for once animals become isolated on islands. These changes (which can include size shifts, greater tameness, and fewer offspring) largely stem from reduced food sources, predation, and selective pressures.

When researchers from the University of Southern California and the Natural History Museum of Los Angeles County looked at island foxes on the six Channel Islands they inhabit, they found that this expected reduction in encephalization quotient (the size of an animal’s brain relative to what would typically be expected given its size) occurred only in foxes on the second smallest, most isolated island. Indeed, some foxes developed more pronounced ridges and folds in their brains to compensate for reductions in cranium size over evolutionary time. The scientists suspect that larger brains are worth their higher energy requirements because they likely provide greater spatial cognition, cognitive processing, and problem-solving. These capabilities are especially valuable for the Urocyon that dwell on the four islands with complex woodlands, where the foxes need greater spatial abilities to hunt and forage in trees.

Schoenberger, K. A., X. Wang, and S. Edmands. 2025. Increased brain size of the dwarf Channel Island fox (Urocyon littoralis) challenges “Island Syndrome” and suggests little evidence of domestication. PLOS One 20:e0328893.