Science news in brief: From bats babbling like babies to a fossilised brain

And other stories from around the world

Thursday 26 August 2021 00:01
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<p>The young bats’ songs are not sung at the high frequencies their elders use for echolocation</p>

The young bats’ songs are not sung at the high frequencies their elders use for echolocation

Some bat pups babble just like human babies

Greater sac-winged bats are a field biologist’s dream. They hunt insects at dawn and dusk, stay awake much of the day and rest at night.

“They like fairly well-lit places,” says Dr Mirjam Knörnschild, a behavioural ecologist at the Museum of Natural History in Berlin who studies the bats, which roost on trees or the sides of buildings rather than in gloomy, guano-filled caves.

And the bats, about 2 inches long, keep enough distance between themselves to tell one from another. “We mark them with coloured plastic rings on their forearms,” Dr Knörnschild says. “We can also use a directional microphone and record the vocalisations of individual bats.”

That’s important because these bats are the only mammals other than humans that are known to babble like human babies. The babbling of bat pups includes adult syllables and sounds that only the young make, and the nature of the babbling changes over time as the bats learn territorial and courting songs. Also, their songs are not sung at the high-frequencies that bats use for echolocation.

“It instantly reminds you of infants,” says Dr Ahana A Fernandez, also at the museum, who conducted a recent analysis of the babbling with Dr Knörnschild and other colleagues.

They analysed recordings of 216 “babbling bouts” of 20 bat pups from two colonies in Costa Rica and Panama. The researchers found that the sounds the pups make are similar to human infants in their repetition of syllables, the rhythmic nature of the babbling and the universality of babbling behaviour.

Prof Kimbrough Oller at The University of Memphis, who has studied the vocal development of human infants for decades, says “there are some remarkable parallels” with human babbling and also bird song in the extensive observations and analysis of the bat pups, one of which was just “the quantity of babbling that’s going on”.

No other mammals are known to do this sort of babbling, although it is common in songbirds.

Males compete intensely with their bat-song to attract a harem of females. The females choose which male they prefer, and the males are constantly courting them, in a kind of ongoing talent competition.

“Female choice seems to play an extraordinarily strong role” in mating behaviour, Dr Knörnschild says. “The males are somewhat smaller than the females and they cannot physically force them to do anything.”

— James Gorman

The Western diamondback rattlesnake’s acoustic warnings are like a car’s backup beeper

This rattlesnake dares you to call its bluff

The Western diamondback rattlesnake is a master of nonverbal communication. It need only shake the rattle on its tail to send a crystal clear message: “Hey. I’m sitting here. Don’t step on me because I’m going to bite you,” says Prof Boris Chagnaud, a biologist at the University of Graz in Austria.

But the rattlesnake has another, wilier trick up its tail. As it perceives a potential threat coming closer, the rattlesnake will sharply increase the speed of its rattle, accelerating from da … da … da … to dadada. Prof Chagnaud compares the acoustic warnings to a car’s backup beeper, which will beep more as the back of your car approaches an object. This uptick tricks unsuspecting humans into believing the snake is closer than it actually is, according to a paper by Prof Chagnaud and colleagues published in the journal Current Biology.

Scientists knew that rattlesnakes often change their rattling noises, but no one quite knew why. Prof Matthew Rowe, a biologist at the University of Oklahoma who was not involved with the research, says he had witnessed this rattling trick hundreds of times but never questioned what the signal might be communicating to the snake’s enemies. “That’s embarrassing for me,” he says.

The research began when Prof Chagnaud, who studies the vibrating vocalisations of toadfish, wanted to compare the fish to rattlesnakes, which use similar muscles to rattle their tails. In 2018, he visited the resident rattlesnakes in the lab of Dr Tobias Kohl, a researcher at the Technical University of Munich in Germany and an author on the paper. In Dr Kohl’s lab, Prof Chagnaud noticed the snakes would abruptly increase the frequency of their rattling as he drew near.

The researchers placed the snakes on a table across from a sheet with a projection of a black disc. They were able to make the disc increase in size, mimicking an object coming closer.

As the black disc got bigger, the snakes increased their rattling rate up to 40 hertz and then abruptly shot up their rattling frequency to 100 hertz.

The researchers propose that this sudden jump in frequency is an evolved behaviour that rattlesnakes use to fool the listener about their actual distance to the snake. “The shift in rattling is subterfuge on the part of the snake,” says Prof Bruce Young, an anatomist at the Kirksville College of Osteopathic Medicine in Missouri, who reviewed the paper.

— Sabrina Imbler

Capsicum spp originated in Central and South America

How peppers proliferated around the planet

Peppers are cosmopolitan, a vegetable that comes in far more varieties than there are nations in the world. One day you can slice a mild orange bell pepper to dip in hummus. Another you may roast red peppers and blend them into a dip or a sauce of their own, like ajvar or romesco. Poblano peppers can add some heat to a dish, or even become a meal like chile relleno. But watch out for those carolina reaper peppers.

All of these dishes have in common the humble pepper plant, or Capsicum spp. The plant originated in Central and South America and eventually crossed the oceans in the hands of traders, says Dr Pasquale Tripodi of the CREA Research Centre for Vegetable and Ornamental Crops in Italy. In a paper published in The Proceedings of the National Academy of Sciences, Dr Tripodi and European colleagues shared the results of their studies of the genetics of more than 10,000 samples of peppers from around the world.

Their findings reveal intriguing details about the plant’s global travels, such as how one colonial power’s trading networks may have spread peppers far and wide, and how some of the plants ended up sweet and crisp while others gained their fiery edge.

Dr Tripodi and his colleagues focused on the most widely consumed pepper group, Capsicum annuum, the species that is grown into bell peppers of all colours, cayenne peppers and jalapenos. The researchers found that Europe and Asia shared a variety of types, suggesting that peppers moved along trade routes between east and west. There were also links between eastern European peppers and those in the Middle East, perhaps reflecting Ottoman trade routes. The team speculates that Portuguese traders, who in the 16th century moved between South America, Europe, Africa and Asia, may have transported some peppers along with them, helping to explain similarities between African peppers and those on either end of this long axis.

Once peppers gained admirers in a new location, farmers seem to have made their own selections over the years; peppers in Eastern Europe were sweeter and less pungent, while east Asian peppers were small and fiery. The researchers uncovered genes associated with these traits and others, which may be of use to breeders in the future.

— Veronique Greenwood

The extinct penny-size horseshoe crab was buried more than 300 million years ago in what was once a shallow, brackish marine basin

Brain remains intact in 310 million-year-old fossil

Brain tissue is innately squishy. Unlike bones, shells or teeth, it is rich in fat and rots quickly, seldom making an appearance in the fossil record.

So when Dr Russell Bicknell, an invertebrate palaeontologist at the University of New England in Australia, noticed a pop of white near the front of a fossilised horseshoe crab body where the animal’s brain would have been, he was surprised. A closer look revealed an exceptional imprint of the brain along with other bits of the creature’s nervous system.

Unearthed from the Mazon Creek deposit in northeastern Illinois, and dating back 310 million years, it’s the first fossilised horseshoe crab brain ever found. Dr Bicknell and his colleagues reported the find in the journal Geology.

“These kinds of fossils are so rare that if you happen to stumble upon one, you’d generally be in shock,” he says. “We’re talking a needle-in-a-haystack level of wow.”

The find helps fill a gap in the evolution of arthropod brains and also shows how little they have changed over hundreds of millions of years.

Soft-tissue preservation requires special conditions. Scientists have found brains encased in fossilised tree resin, better known as amber, that were under 66 million years old. They have also found brains preserved as flattened carbon films, sometimes replaced or overlaid by minerals in shale deposits that are more than 500 million years old.

However, the fossilised brain of Euproops danae, which is kept in a collection at the Yale Peabody Museum of Natural History, required a different set of conditions to be preserved.

The extinct penny-size horseshoe crab was buried more than 300 million years ago in what was once a shallow, brackish marine basin. Siderite, an iron carbonate mineral, accumulated rapidly around the dead creature’s body, forming a mould. With time, as the soft tissue decayed, a white-coloured clay mineral called kaolinite filled the void left by the brain. It was this white cast on a dark-grey rock that helped Dr Bicknell spot the uniquely preserved brain impression.

“This is a completely different mode of brain preservation,” said Prof Nicholas Strausfeld, a neuroanatomist at the University of Arizona who was among the first to report a fossilised arthropod brain in 2012 but wasn’t involved in this study. “It’s remarkable.”

— Priyanka Runwal

This article originally appeared in The New York Times

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