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After Eons Of Isolation, These Desert Fish Flub Social Cues

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Getting out into society after a long isolation gets awkward. Ask the Pahrump poolfish, loners in a desert for some 10,000 years.

This hold-in-your-hand-size fish (Empetrichthys latos) has a chubby, torpedo shape and a mouth that looks as if it’s almost smiling. Until the 1950s, this species had three forms, each evolving in its own spring. Now only one survives, which developed in a spring-fed oasis in the Mojave Desert’s Pahrump Valley, about an hour’s drive west of Las Vegas.

Fish in a desert are not that weird when you take the long view (SN: 1/26/16). In a former life, some desert valleys were ancient lakes. As the region’s lakes dried up, fish got stuck in the remaining puddles. Various stranded species over time adapted to quirks of their private microlakes, and a desert-fish version of the Galapagos Islands’ diverse finches arose.

“We like to say that Darwin, if he had a different travel agent, could have come to the same conclusions just from the desert,” says evolutionary biologist Craig Stockwell of North Dakota State University in Fargo.

The desert “island” where E. latos evolved was Manse Spring on a private ranch. From a distance, the spring looked “just like a little clump of trees,” remembers ecologist Shawn Goodchild, who is now based in Lake Park, Minn. The spot of desert greenery surrounded the Pahrump poolfish’s entire native range, about the length of an Olympic swimming pool.

By the 1960s, biologists feared the fish were doomed. The spring’s flow rate had dropped some 70 percent as irrigation for farms in the desert sucked away water. And disastrous predators arrived: a kid’s discarded goldfish. Conservation managers fought back, but neither poison nor dynamite wiped out the newcomers. And then in August of 1975, Manse Spring dried up.

Conservation managers had moved some poolfish to other springs, but the long-isolated species just didn’t seem to get the dangers of living with other kinds of fishes. The poolfish were easily picked off by predators in their new home.

Lab tests of fake fish-murder scenes may help explain why. For instance, researchers tainted aquarium water with pureed fish bits. In an expected reaction, fathead minnows (Pimephales promelas) freaked at traces of dead minnow drifting through the water and huddled low in the tank. The Pahrump poolfish in water tainted with blender-whizzed skin of their kind just kept swimming around the upper waters as if corpse taint were no scarier than tap water. Literally. Stockwell and colleagues can say that because they ran a fear test with nonscary dechlorinated tap water. Poolfish didn’t huddle then either, the team reports in the Aug. 31 Proceedings of the Royal Society B.

Then, however, Stockwell and a colleague were musing about some rescued poolfish in cattle tanks when nearby dragonflies caught the researchers’ attention.

Before dragonflies mature into shimmering aerial marvels, the young prowl underwater as violent predators. In moves worthy of scary aliens in a sci-fi movie, many dragonfly nymphs can shoot their jaws out from their head to scoop up prey, including fish eggs and fish larvae. With young dragonflies prowling a pool’s bottom and plants, poolfish moving up the water column “would be a good way to reduce their risk,” Stockwell says. Testing of that idea has begun.

Fish that people thought were foolishly naïve may just be savvy in a different way. Especially after isolation in a desert with dragons.

Animals

Honeybees Order Numbers From Left To Right, A Study Claims

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Like many humans, honeybees seem to prefer their numbers ordered from left to right.

Honeybees trained to recognize a specific number tend to fly left when given two side-by-side options of a smaller number and right when the options represent a larger number, a new study claims. The finding suggests that honeybees have a “mental number line” and that this association has biological roots, researchers report October 17 in the Proceedings of the National Academy of Sciences.

While some scientists agree that the study makes a compelling case for a mental number line in honeybees, others argue that the new work is an oversimplification of complex human behavior.

Many humans have a mental number line that often puts smaller numbers on the left and bigger numbers on the right — if asked to organize several bunches of grapes by size, you’d likely line them up by increasing number of grapes from left to right. Whether this association is present at birth or learned later in life has long been a subject of debate.

Previous work has shown that honeybees can count, and that they even understand the concept of zero (SN: 6/7/18). “When you realize all these facts, an obvious question [is whether honeybees have] the so-called mental number line,” says Martin Giurfa, a biologist at the Université Paul Sabatier in Toulouse, France. Working from home during COVID-19 lockdowns, Giurfa tested 134 honeybees (Apis mellifera) on their number-ordering abilities using a design developed with researchers who had done similar experiments with chicks and human babies (SN: 1/29/15).

First, Giurfa had to teach his bee pupils to recognize numbers. Using sugar water, he lured honeybees into a testing chamber built from a repurposed wine box. For each bee, he hung a panel on the back of the box with a certain number of symbols on it — one, three or five — and fed them the sugar water so they’d learn to associate the number with food. By varying what the symbols looked like between visits, he ensured the bees were learning the number itself and not certain shapes or arrangements.

After 30 trips to the box, it was time for a test: Giurfa removed the training panel and set up two, mirror-image panels, one on the left wall of the box and one on the right. These new panels either had the same number of symbols as the training panel, fewer symbols or more.

Which panel did the bees fly to — left or right? “It depends on your reference number,” Giurfa says. Of the bees trained on “one,” 72 percent flew to the “three” panel to the right, but of the bees trained on “five,” 73 percent went to the “three” panel to the left. “That’s exactly the concept of the mental number line,” Giurfa says. “You align numbers based on your reference.” If the test number was the same as the training number, the bees showed no preference for left or right.

These experiments “make a very compelling case” for a mental number line in honeybees, says Felicity Muth, a biologist at the University of Texas at Austin who was not involved with the study. “They have a number of controls that really rule out any of the alternative explanations I can think of.”

Giurfa believes these results show that mental number lines, or at least some component of them, are present across the animal kingdom. However, not everyone is convinced.

“The oversimplification of complex human concepts, such as that of ‘number line,’ must be avoided, since they severely distort the reality of the phenomena that make them possible,” says Rafael Núñez, a cognitive scientist at the University of California, San Diego.

Núñez, who coauthored an article critical of the earlier chick study, thinks animal research should address why bees and chicks would have inborn mental number lines while some human groups, like those he’s studied in Papua New Guinea, don’t. Giurfa acknowledges that culture plays a role in explaining why not every adult naturally orders numbers from left to right, but feels that the proof is there for a biological underpinning (SN: 8/23/21).  

This study stops short of explaining why the brains of bees, chicks and babies have all converged on the same left-to-right number ordering but does offer a possible answer — their asymmetrical brains. All three have brains that process information differently on the left and right sides. “It might be an inherent property to these lateralized brain systems,” Giurfa says.

A shared system for organizing numbers, if truly widespread, would highlight how surprisingly similar animal minds can be to our own. Though some cognitive powers seem to be uniquely human, Giurfa thinks there is danger in dismissing the abilities of animals. “We are different from animals in some aspects,” he says, “but we are very similar in others. Denying this similarity is not what will help us understand what we are.”

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Some Seabirds Survive Typhoons By Flying Into Them

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Some seabirds don’t just survive storms. They ride them.

Streaked shearwaters nesting on islands off Japan sometimes head straight toward passing typhoons, where they fly near the eye of the storm for hours at a time, researchers report in the Oct. 11 Proceedings of the National Academy of Sciences. This strange behavior — not reported in any other bird species — might help streaked shearwaters (Calonectris leucomelas) survive strong storms.

Birds and other animals living in areas with hurricanes and typhoons have adopted strategies to weather these deadly storms (SN: 10/2/15).  In recent years, a few studies using GPS trackers have revealed that some ocean-dwelling birds — such as the frigatebird (Fregata minor) — will take massive detours to avoid cyclones.

This is an understandable strategy for birds that spend most of their time at sea where “there is literally nowhere to hide,” says Emily Shepard, a behavior ecologist at Swansea University in Wales. To find out whether shearwaters also avoid storms, she and her colleagues used 11 years of tracking data from GPS locators attached to the wings of 75 birds nesting on Awashima Island in Japan.

By combining this information with data on wind speeds during typhoons, the researchers discovered that shearwaters that were caught out in the open ocean when a storm blew in would ride tailwinds around the edges of the storm. However, others that found themselves sandwiched between land and the eye of a strong cyclone would sometimes veer off their usual flight patterns and head toward the center of the storm.

Of the 75 monitored shearwaters, 13 flew to within 60 kilometers of the eye — an area Shepherd calls the “eye socket,” where the winds were strongest — for up to eight hours, tracking the cyclone as it headed northward. “It was one of those moments where we couldn’t believe what we were seeing,” Shepard says. “We had a few predictions for how they might behave, but this was not one of them.”

The shearwaters were more likely to head for the eye during stronger storms, soaring on winds as swift as 75 kilometers per hour. This suggest that the birds might be following the eye to avoid being blown inland, where they risk crashing onto land or being hit by flying debris, Shepard says.

While this is the first time this behavior has been spotted in any bird species, flying with the winds could be a common tactic for preserving energy during cyclones, says Andrew Farnsworth, an ornithologist at Cornell University who was not involved in the study. “It might seem counterintuitive,” he says. “But from the perspective of bird behavior, it makes a lot of sense.”

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Not All Camouflage Is Equal. Here Are Prey Animals' Best Options

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From crabs to caterpillars, a wide range of animals successfully use camouflage to hamper detection by hungry predators. But some concealment strategies are more effective than others, a new study suggests.

The analysis compiles and synthesizes data from scores of studies on animal camouflage. Comparisons between different camouflaging methods show that masquerading as specific objects in the environment is the best way to go unseen, scientists report September 14 in Proceedings B of the Royal Society

Behavioral and sensory ecologist João Vitor de Alcantara Viana had been studying animal camouflage for his doctoral research when he realized a comprehensive comparison of different camouflage strategies had never been done. 

“There was a big gap in the literature on this topic,” says de Alcantara Viana, of the State University of Campinas in São Paulo, Brazil.

So, de Alcantara Viana and colleagues searched scientific publication databases for studies on animal camouflage dated from 1900 through July 2022. The team zeroed in on 84 studies that experimentally tested at least one camouflage strategy, and reported either how long predators took to find camouflaged prey or how often predators attacked. The team also limited their analysis to studies that compared camouflaged prey with noncamouflaged, often artificial, versions.

Next, the team grouped the data from these studies by the types of predators and prey analyzed and the variety of camouflage strategies examined. Camouflage tactics included “background matching,” where the animal matches the color and patterning of the environment, and “masquerading,” where prey mimics a particular object uninteresting to predators, like a twig, a leaf, a bird dropping or even a shed tarantula skin (SN: 12/10/13; SN: 6/6/14).

Camouflage is generally effective at making the hunt difficult for predators, increasing their search time by more than 62 percent and dropping the rate they attack prey by more than 27 percent across the board, the team found. 

But the type of prey mattered. Caterpillars got more benefit from camouflage than their winged adult forms, for example. This may be because moths and butterflies can fly and have other antipredator adaptations available to them, de Alcantara Viana says.

The masquerade strategy was especially effective at helping prey elude predators, increasing search time by nearly 300 percent. One of the most striking examples of this, says de Alcantara Viana, are caterpillars that disguise themselves as twigs. A study on brimstone moth caterpillars (Opisthograptis luteolata) and chickens showed that the birds take longer to attack masquerading caterpillars after being recently exposed to twigs. 

Masquerading as the most effective camouflage strategy is intriguing, says Anna Hughes, a sensory ecologist at the University of Essex in England who was not involved with this research. “If this is indeed the case, it will be interesting to further investigate the constraints — size, movement requirements — that mean that not all animals evolve this strategy,” she says. The researchers note that masquerading is probably more likely to evolve if the animal is a similar size as the object it’s mimicking. This could limit what species can benefit from this super camo.

de Alcantara Viana and his colleagues think masquerading is so effective because it’s so specialized, with animals impersonating specific objects, compared with other strategies based on blending in against an irregular background. Prey that masquerade benefit from the predator misidentifying them as real objects in the environment, not just failing to detect the prey. 

The quality of the new work is excellent, Hughes says. Still, it’s not quite clear if the noncamouflaged controls, which she says vary quite widely from one study to another, have inherently different effects on predator reactions. This could make the tested camouflage seem more or less effective than it is in nature.

Another notable finding from the new analysis is that most studies have been conducted in the Northern Hemisphere, Hughes says. “I think it is clear that our understanding of the evolution of camouflage strategies is going to be, by definition, incomplete unless more studies are carried out in the Southern Hemisphere.”

Much of recent camouflage research has also tried to understand precisely how specific defenses protect prey from attacks, says Tom Sherratt, an evolutionary ecologist at Carleton University in Ottawa, Canada, also not involved with this study.

“We are now at a point where we can begin to compare among these defenses,” Sherratt says, which can help researchers figure out why species use particular camouflage strategies.

de Alcantara Viana says he and his colleagues are working on another analysis to understand “the other side of the coin,” how camouflaged predators benefit from concealing themselves from prey.

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