Colonies of aggressive, social spiders booming after a hurricane



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During the 2018 hurricane season, when a large shell landed on the gulf or Atlantic coasts and most people were trying to get out of the storm, Jonathan Pruitt was fighting to take the last flight. Once on the ground, he rented a Nissan Titan or a Ford F150 – something with at least eight inches of ground clearance – and drove to the place where he expected it to be. hurricane hits. Then he went hunting.

Megan Molteni covers the technologies of DNA, medicine and genetic privacy for WIRED.

In the days and hours leading up to the landing, he scoured the area for trees whose branches hung over a stream. Inspecting closely these members, he tried to spot a group of dead leaves hidden in a ghostly silk shroud. When he found them, he dropped a piece of paper into each strip and, using a modified electric toothbrush, made him vibrate so that he was moving around. like he was alive. Then he would count the number of spiders that had gathered to grab it.

So, what makes a man leave his comfortably landlocked home in Canada to thrill the spider colonies in the form of a cat hurricane. 5 going directly to him? The answer, of course, is science.

Spiders are usually solitary creatures. Of the more than 40,000 species of spiders in the world, only two dozen live in groups and work together to catch food and raise their translucent children. Anelosimus studiosus is one of those rare breeds, living in colonies of a few hundred females. They settle in the US states that are suffering the aftermath of the Atlantic Ocean storms every summer and every fall, and Pruitt has spent most of his career studying them. An ecologist of training evolution (his laboratory at McMaster University in Ontario is studying the formation and collapse of animal societies), he is best known to his peers as an expert on the spider's personalities – the Myers- Briggs from the world of arachnology, if you will.

Years ago he discovered that A. studiosus have two distinct personality types: they are either bold and aggressive, or shy and docile. And every spider inherits this personality trait from his parents. The audacious ones present themselves as a marauding war party to face all that is taken in their web. The timid are happy to let the trap do the work alone. If some meals escape you, so what? At least nobody was hurt.

The relative composition of bellicose or peaceful individuals determines the collective aggression of a colony, which is also transmitted from generation to generation, from parent to village. Most of the time, it does not matter much. But when resources are scarce, aggressive colonies tend to do better, sacrificing a few individuals for all others to eat. What Pruitt wanted to know is that hurricanes – tearing the leaves of trees, eliminating insects and overflowing rivers – make these spiders more aggressive?

Yeah, it looks like they can. And not just for a season, but maybe forever. This is the conclusion reached by Pruitt and his co-authors in their latest study, published today in Nature Ecology & Evolution. Last year, Pruitt did this exercise three times – before subtropical storm Alberto, Hurricane Florence and Hurricane Michael. Before each storm, he tested the aggression of dozens of colonies on the passage of the cyclone, as well as on control sites away from wind fields furthest from the storm, about 240 samples in total. Then he hid in a hotel for 48 hours, overcoming the worst of each storm, before venturing again to learn more about the results of each colony.

Navigating on flooded roads and power lines, Pruitt often relied on locals brandishing a chainsaw to make their way. "They started dismantling the fallen trees before FEMA appeared, which literally allowed me to return to my sites," he says. "Some people have not reached me because of floods. Those we think have been submerged and swept away. "

But those who survived, he raised. And, two months later, he returned to these sites two months later to count the number of eggs produced and the number of spiders hatched. What he discovered was that the colonies that had been more aggressive before the hurricane had more babies and that more and more juvenile spiders survived, following each storm. . To determine if this was a long-term trend, the Pruitt team compared 13 study sites from Louisiana to North Carolina with data valid for a century of cyclones. They found that the most aggressive settlements were in places with the highest historical exposure to cyclones.

"There is clearly some sort of selection going on here for aggressive individuals in response to these extreme weather events, and that's what's really fascinating," said George Uetz, a spider biologist. at the University of Cincinnati. Although he did not participate in the study, it was he who invented, many years ago, the method used by Pruitt to stimulate the spider web. Except that electric toothbrushes were not invented yet, so he used a vibrator. "I've had a lot of teasing for that," says Uetz.

In the wolf spiders he studies, he has observed allusions to a similar phenomenon; After a tornado hit an Ohio nature reserve, males born in blowdown areas for generations had smaller clusters of claws and less appealing, which makes them more difficult to find partners. But he has never seen anything like a storm that changes the long-term behavior of an entire species.

"On the one hand, it is not surprising that natural disasters have an impact on animal survival," he said. "But to see their impact on breeding, the way they actually lead the direction of the evolution of a species is quite rare."

Studies may be rare, but Pruitt suspects that the phenomenon is more widespread. That's why he spent the last seven weeks traveling 22,000 miles through the bayous and lowlands of the Gulf Coast, working 14 hours a day laying sticky board traps and collecting thousands of Insect flasks hanging with antifreeze with his Australian Shepherd and Border Blend, Winifred Sanderson, to keep him company.

Even as a person who grew up in a "hick part" of central Florida, Pruitt was not always prepared for what he was meeting. More than once, while driving through miles of sugarcane plantations, he says he has met armed poachers loading reptiles freshly trapped in terrarium trucks. "I tried to look as Canadian as possible," he says. "For example," Hello, I'm only collecting INSECTS! "

Its ultimate goal is to see what species are doing well after hurricanes. Do these storms allow invasive species, such as red ants, to take advantage over native animals? Or are they worse off because they have not evolved in a hurricane-affected environment? What about mosquito species that carry human diseases compared to those that are not? "The question is how important are these extreme events in maintaining the diversity of traits," says Pruitt. "Clearly, something very special is happening."

Understanding exactly how species evolve in response to extreme weather disturbances is more urgent than ever. As the planet continues to heat up, scientists predict that hurricanes will intensify, that heat waves will heat up and that droughts will continue. You probably know from Ian Malcolm's explanation of chaos theory in Jurassic Park that the flapping of the wing of a butterfly in Brazil can trigger a tornado in Texas or a hurricane in North Carolina. We now know, at least for spiders, that the relationship works both ways.


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