Animals World

18/12/2021

The American West’s changing climate might mean more plague-carrying critters

Every year, a handful of Americans catch plague. The disease, caused by the bacteria Yersinia pestis, was introduced to North America during the early 1900s and stuck around in rodents in Arizona, New Mexico, and Colorado. When treated with antibiotics, it’s no longer deadly to humans—prairie dogs aren’t so lucky.

According to recent research, between 1950 and 2017, swaths of the Mountain West became 30 to 40 percent more suitable for the bacteria because of climate change. That’s a hint at how future warming might affect the transmission of animal-borne diseases in general.

“There’s this conventional wisdom that the biggest impacts are going to be from heat and disasters, and I just don’t think that’s a sure thing,” Colin Carlson, the study’s lead author, told Gizmodo. “I think it’s just harder to reconstruct the climate signal for infectious diseases.”

Plague can infect a wide range of species, but it establishes long-term reservoirs in rodent populations. In Central Asia, it appears to hang around in gerbils, while in North America, prairie dogs seem to play a key role. The bacteria spreads from animal to animal via several species of flea, or in some cases when a predator like a cat or coyote eats an infected critter. There’s some evidence that Y. pestis can also form a symbiotic relationship with amoeba, and even lives in the soil itself if conditions are right.

That complexity makes modelling plague reservoirs, let alone predicting the extent of possible outbreaks, very tricky. Different rodents may live in different size populations as the climate changes, while certain species of tick are better at spreading the bacteria at specific temperatures.

So the researchers set out to map out the distribution of plague in the past, as a way of understanding what factors might move it around in the future.

To do so, they overlaid data on human infections—which averaged 7.7 per year between 1950 and 2000—with the weather conditions at the time patients got sick. They also mapped data from wildlife surveys from 2000 to 2017, which recorded 5,000 plague cases out of 41,000 tested animals, almost entirely in coyotes. (Coyotes catch and spread the bacteria without getting sick, so the evidence comes from plague antibodies in their blood.)

Between 1950 and 2017, plague risk was highest in “rodent biodiversity hotspots,” which could be because there are more rodents to infect, or because those hotspots are more likely to have some ideal host that scientists haven’t yet pinpointed. It also appears that the bacteria form reservoirs only at high-altitude, likely because of some combination of soil conditions and the rodents that live there.

Long-term warming appears to have created more suitable conditions for reservoirs, as rodents expand into more high-altitude locations. It’s also possible that reservoirs have developed, undetected, in parts of Canada, Mexico, and California’s Central Valley.

The model also supports a relationship between climate events and pandemic plague. Plague was most abundant in animals during unseasonably warm years, but there was a higher risk of human infection in cold, wet years. The researchers think that that’s because hotter years allow a buildup of rodents and fleas, and so the overall amount of disease grows. When it gets cold, those rodents die off—and as the fleas jump ship, plague clusters in the survivors. Other fleas forge off in search of new hosts, which brings them into contact with humans.

Previous research by one of the new study’s coauthors focused on the most famous plague pandemic, the Black Death, which upended feudal Europe and set the stage for the modern world. It found that the bacteria left Central Asia in response to a fluctuating climate. Waves of the Black Death in Europe were preceded by a series of cold years in Mongolia, which the researchers believe sent plague-infested insects west.

This doesn’t mean that more people will begin dying of the disease as the country warms. The substantial increase in risk for animals has only raised instances of human spillover by a fraction of a percent, and those cases are still treatable.

But, the authors write, plague happens to be a good model for understanding the interplay between climate, ecosystems, and disease, because it’s so closely monitored in the US. The same process is taking place with other pathogens, from yellow fever, to lyme disease, to the flesh-eating leishmaniasis—but those shifts are even harder to track.

18/12/2021

A newfound South American dinosaur had a tail like a war club

A new species of armored dinosaur from subantarctic Chile boasted a large tail weapon that looked dramatically different from those found on its relatives, and may shed light on a mysterious phase in the group’s evolution.

Scientists found the mostly-complete skeleton in 2018 in the Río de las Chinas Valley of Chilean Patagonia and determined it to be roughly 71.7 to 74.9 million years old, dating it to the late Cretaceous. When they further examined the skeleton, the researchers found a baffling mixture of features typically seen in ankylosaurs and stegosaurs. However, its “bizarre” tail didn’t seem to match with the tails seen in either of these famous groups; rather than the traditional spikes or clubs, the newly-named Stegouros elengassen had seven pairs of bony deposits encasing half the tail in a flattened frond-like structure, the researchers reported on December 1 in Nature.

Still, an analysis of the armored dinosaur family tree revealed that the fossil belonged to an ankylosaur, suggesting that different branches of the group flourished in the northern and southern hemispheres after the supercontinent Pangaea broke up.

“This is the first time scientists get a good look at what a South American ankylosaur is like,” says Alexander Vargas, a paleontologist at the University of Chile in Santiago and coauthor of the study. Stegouros’s tail weapon, he adds, is “absolutely unlike anything we have seen before.”

A number of present-day mammals and reptiles, including porcupines and alligators, use their tails as whips or lashes to defend themselves from predators or rivals. But southern African girdled lizards go a step farther: Their tails are equipped with bony spines. More elaborate versions of these tail armaments were once wielded by extinct relatives of turtles and armadillos.

“But the champions of them all are the armored dinosaurs,” Vargas says. In addition to the bony plates and spines along their backs, some members of this group developed specialized tail weapons. These included the tail spikes seen in stegosaurs such as Stegosaurus and rounded tail clubs belonging to ankylosaurs such as Ankylosaurus.

A newfound South American dinosaur had a tail like a war club
Paleontologist Sergio Soto examines the ankylosaur fossils found in southern Chile.
The ankylosaurs generally had broad backs and thick limbs. While ankylosaur fossils are plentiful in North America and Asia, Vargas says, until now only fragmented bones and teeth have been found of their more southern cousins.

“These scraps and pieces were often interpreted as a sign that ankylosaurs, which in North America were very abundant and diverse, somehow managed to cross into South America, to migrate,” he says.

The specimen that he and his colleagues discovered in 2018 at the southern tip of South America changes this picture, Vargas says. When the team began to excavate the fossil, they first noticed its slender limbs and speculated that the specimen might have been a bipedal herbivore. Next came the tail with its “astonishing weapon,” Vargas says, which indicated that the skeleton actually represented some kind of armored dinosaur.

“We thought we might have a stegosaur when we uncovered the hips,” he says. “They were identical to a stegosaur.” The fossil’s upper arm and right hand also resembled those of stegosaurs. Yet when the team reached the skull, they found that the upper jaw and palate looked distinctly ankylosaurian.

[Related: An overlooked fossil turned out to be a new herbivorous dinosaur with an oddly shaped nose]

To find out which group the puzzling species belonged to, the researchers analyzed hundreds of different traits from dozens of dinosaur species and ultimately identified Stegouros as an ankylosaur. What’s more, its ancestors split off from the rest of the ankylosaurs some 167 million years ago in the mid-Jurassic.

“It’s an evolutionary link between the ankylosaurs…and other armored dinosaurs like the stegosaurs,” Vargas says.

This could explain why Stegouros bears so little resemblance to most ankylosaurs, with its agile limbs, narrow feet, light armor, and a hawk-like beak. The petite ankylosaur was only about 2 meters (6.6 feet) long and had a shorter tail than other armored dinosaurs. The weapon’s flattened shape might have made it easier for Stegouros to avoid dragging its tail and “being able to wield it for defense,” Vargas says. He and his colleagues named the structure after an Aztec war club, or macuahuitl, which resembles a wooden sword with obsidian blades protruding from either side. The researchers determined that Stegouros is closely related to two other ankylosaurs from Australia and Antarctica. The latter, which is known as Antarctopelta, features “enigmatic” bony plates that have perplexed scientists but which might be part of the same kind of macuahuitl used by Stegouros, Vargas says.

The findings suggest that Stegouros “is not an invader from the north,” he says. “It is actually a lineage that has roots so deep in time it’s [from] when all continents were together.”

As Pangaea finished separating into Laurasia (present-day North America and Eurasia) and Gondwana (which would become South America and the remaining continents) in the late Jurassic, the more familiar ankylosaurs would come to dominate the northern continent while Stegouros and its relatives laid claim to the south.