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Welcome back to the Abstract! What a week it has been for news that happened 66 million years ago. It was the best of times (for ants and fungus!) and the worst of times (for almost everything else!). In addition to asteroidal death-bringers, the week also produced new views of the Sun and a quiet little study about a quiet little rodent. Enjoy. How Ant Agriculture Rose from the Ashes of Dinosaurs “The coevolution of fungus-ant agriculture,” Schultz et al, Science Generally speaking, you don’t want a massive asteroid slamming into your home world. When this happened 66 million years ago, Earth was instantly transformed into a nightmare planet consumed by heat, mega-tsunamis, intense wildfires, and noxious particles that fell from the sky. It was a death sentence for almost all large animals, in seas and on land. But for ants? It was a farm-to-table feast. That’s the conclusion of a new study this week that traced the origins of ant agriculture back to the Chicxulub impact, the cataclysmic event that summarily executed all dinosaurs (except birds), ammonites, mosasaurs, and a whole lot of other life-forms that were just minding their own business.
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In the years following the impact, dust clouds blotted out most sunlight, ushering in a cool and dark period that killed off a host of sun-starved plants and any surviving animals that relied on them. Then, as now, fungi stepped up to eat the dead, rapidly spreading through the same leaf litter environments occupied by dinosaur-era ants. The sudden bounty sparked an agricultural revolution that has been passed down, across tens of millions of years, to many ant colonies today. “We found that fungus-ant agriculture originated ~66 million years ago when the end-of-Cretaceous asteroid impact temporarily interrupted photosynthesis, causing global mass extinctions but favoring the proliferation of fungi,” said Ted Schultz of the Smithsonian National Museum of Natural History and colleagues. “This would have allowed both partners to persist and coevolve through a period of mass extinctions and, ultimately, to radiate into an entirely restructured Neotropical rain forest ecosystem ~59 to 59.5 million years ago,” the team said. In other words, the successful cultivation of fungus by ants was a mutually beneficial arrangement that kept farmer ants fed, while also introducing fungi species to new ranges and niches. Schultz and his colleagues were able to pinpoint the origin of this coevolution back to the Chicxulub impact by building an evolutionary tree using genetic data from hundreds of fungal cultivars, as well as the ants that farm them. In addition to illuminating the dawn of ant-riculture in the ashes of the old world, the approach revealed another farming revolution that occurred 27 million years ago, as dry habitats began to encroach on rainforest biomes of South America. Ants at this time domesticated fungal cultivars and brought them into more arid habitats, like grasslands and savannah, where the fungi became completely dependent on their insect overlords. “As some species of wet forest–dwelling, fungus-farming ants adapted to dry or seasonally dry habitats and transported their forest-adapted fungal cultivars into those habitats, cultivar species became isolated from their extended, free-living ancestral populations,” Schultz and his colleagues said. “As in many examples from human agriculture in which cultivars were carried beyond their ancestral ranges, transport into seasonally dry habitats by ants would have facilitated the process of fungal cultivar domestication and the observed dependence of extant higher cultivars on their ant farmers for propagation and survival.” The dinosaur-killing asteroid has always fascinated me because it was a dual purveyor of apocalyptic oblivion and supercharged evolutionary creativity. Most mammals, including humans, directly owe our existence to that One Bad Day. Now, scientists have shown that this colossal impact also provided the conditions for ants to pioneer agriculture, the same innovation that has fueled the modern human domination of the planet. So while farming in ants was an outcome of the last extinction event, farming in humans may be the precipitating event for the next one, driven by our own activity. The Other Other Dinosaur-Era Impact “3D anatomy of the Cretaceous–Paleogene age Nadir Crater,” Nicholson et al, Communications Earth & Environment What’s worse than one asteroid careening into Earth and triggering mass death? A possible answer is many asteroids hitting our world with varying degrees of annihilatory excess. While the cosmic sequence of events that led up to Dino-Doomsday is still mysterious, some scientists have suggested that the main killer asteroid, which impacted in Mexico’s Yucatan region, was just the largest of several rocks that careened into the inner solar system after the breakup of a parent body. This hypothesis was bolstered by the recent discovery of Nadir Crater, a five-mile-wide depression located in the Atlantic Ocean off the coast of West Africa, which also dates back 66 million years. This week, scientists confirmed that this crater was formed by an asteroid, though the rock would have been only about a quarter mile in scale, much smaller than the roughly 10-mile Chicxulub impactor that slammed into what is now the Yucatan region of Mexico. “Here we present 3D seismic data that image this crater in exceptional detail, unique for any such structure, which demonstrates beyond reasonable doubt that the crater-forming mechanism was a hypervelocity impact,” said Uisdean Nicholson of Heriot-Watt University and colleagues. “The 3D seismic data across the Nadir Crater provides an exceptional opportunity to test the impact crater hypothesis, develop new models of crater formation in an oblique marine impact and to understand the environmental consequences of such an event.” All Hail the Pumpkin Sun Magnet “Observing the evolution of the Sun’s global coronal magnetic field over eight months,” Yang et al, Science Once again, we must salute the almighty Sun. In a first-of-its-kind study, scientists conducted long-term observations of the global coronal magnetic field, the part of the Sun’s magnetic mojo that shapes its outermost layer and is responsible for solar storms. While this magnetic activity has been studied in snapshots before, the new results capture observations over eight months by the Upgraded Coronal Multi-channel Polarimeter on the Mauna Loa Solar Observatory in Hawaii. The data confirms models of solar magnetism and provide new insights into the emergence of solar storms. Most importantly, however, we got some mesmerizing new pictures of the Sun as a Jack-o-Lantern. Solitary Living with the Bush Karoo Rat “Tolerant mothers: aggression does not explain solitary living in the bush Karoo rat,” Makuya et al, Proceedings of the Royal Society B Just because you don’t want to play doesn’t necessarily make you a hater. That’s the conclusion of a new study that probes the mechanisms behind solitary living in mammals by observing the bush Karoo rat, an incredibly adorable rodent that weighs 100 grams and lives in South Africa.  Bush Karoo rat, contemplating life. Image: Bernard Dupont “Many mammal species are thought to adopt solitary living owing to mothers becoming intolerant of adult offspring and the occurrence of social intolerance between adults,” said Lindelani Makuya of the University of the Witwatersrand and colleagues. “However, field studies on how solitary mammals interact are rare.” To rectify this observation gap, the team observed dozens of mama rats with their pups, which revealed virtually no aggression and lots of cute cuddling. As adults, the rats simply prefer to chill out solo, but they don’t typically enforce that inclination by getting violent toward their fellow rats. Instead, everyone just kind of respects each other’s space, suggesting that aggression is not a prerequisite for independent life. “Here we show that solitary living can occur without social intolerance,” the team concluded, offering a sentence that should be an inspiration to introverts of all clades. Thanks for reading! See you next week.
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