How fish may see colour in the deep ocean’s darkness
The silver spinyfin, or little dori, inhabits a layer of the deep sea, where the twilight zone’s blue fades to black, often half a mile below the surface. Down there, they may see the world like no other animal known to science.
Scientists have generally understood that colour vision wasn’t necessary in the deep sea. It’s too far for sunbeams to penetrate, and so there’s no light to give way to colour. But in a study published in Science, researchers interested in the evolution of colour vision analysed the genomes of 101 different fishes. They discovered that one, the silver spinyfin, has more genes for discriminating dull light than any other vertebrate on the planet. These genes make it possible to see the whole range of residual daylight and the full spectrum of bioluminescence in the deep sea. Other fishes may have this ability to detect colour in the deep sea, too.
“In vertebrate fishes, nothing has been seen like this before,” says Megan Porter, who studies how vision evolves at the University of Hawaii at Manoa and was not involved in the research. “This goes against what we understood as how visual systems evolved in the deep sea, which means we have to question how visual systems work and function in the dim light.”
The basics of vision start when light hits our retinas, which contain photoreceptor cells called rods and cones that are sensitive to particular wavelengths. Inside these cells, photopigments, or proteins called visual opsins, help translate light into signals our bodies can understand.
Typically, vertebrates have up to four cone photoreceptors and one rod photoreceptor. Most humans, for instance, see colour input from three cones – red, green and blue. Cones help us see colours in bright light, but in dim light, we’re generally colour blind and see only intensity based on input from a single rod.
But some deep sea fish appear to see their world in a very different way.
Zuzana Musilová, an evolutionary biologist at Charles University in Prague who led the study and her team, first noticed these fish had lost the genes other fish had for making cone cells and opsins that could detect red and ultraviolet parts of the spectrum. This wasn’t surprising: these wavelengths don’t penetrate the deep sea. But then they found some deep sea fishes had extra copies of genes to make rods.
“We were quite, let’s say, astonished by this finding itself because that’s very unique,” Musilová says.
Dinosaur with bat wings was more than legend
Imagine an animal that looks like a dinosaur, and you probably will not imagine a bat. But that may change. A team of palaeontologists in China have announced the discovery of a dinosaur that sported the same kinds of fleshy wings bats use to flit through the air.
The dinosaur, Ambopteryx longibrachium, lived about 163 million years ago. When Min Wang, a vertebrate palaeontologist at the Chinese Academy of Sciences, first saw the fossil, which he and his team pulled out of Jurassic-age rocks in Liaoning province in China, “I thought it was a bird,” he says.
Birds evolved from dinosaurs, and so the two groups share many features. Wang assumed Ambopteryx was a bird because the animal sported relatively long forelimbs, just as modern birds do. But as his team carefully chipped away the rock surrounding the fossil over the course of about a year, distinctly dinosaurian features began to emerge. Ambopteryx, for one thing, had long fingers, a trait that birds lack.
Wang’s team was also surprised to find the remains of soft tissue around the dinosaur’s arms and torso. This tissue, in life, formed flaps of skin that probably resembled bat-like wings, Wang says.
The new find, published in the journal Nature, follows a report in Nature in 2015 – by a team including authors of the new paper – that described the only other known bat-like dinosaur. That animal, called Yi qi, was the first of its kind, and other palaeontologists were sceptical. The doubts arose because Yi qi was so bizarre.
“I think that if you had asked a palaeontologist to just draw up some kind of fantasy dinosaur, you know, a lot of us never would have come up with something that was that weird,” says Stephen Brusatte, a vertebrate palaeontologist at the University of Edinburgh, who was not involved in the new research. But the discovery of Ambopteryx, which is a close cousin of Yi qi, “pretty much seals the deal that there was this group of dinosaurs with bat-like wings”, he says.
So bat-like dinosaurs definitely existed. But exactly how Ambopteryx flew through the air remains unclear. The team’s best guess is that the animal’s flying style was “halfway between a flying squirrel and a bat”, says Jingmai O’Connor, a co-author and a vertebrate palaeontologist at the Chinese Academy of Sciences.
Despite this lingering mystery, Brusatte says, the discovery of Ambopteryx underscores that on the dinosaur family tree, there were several branches – not just the one that led to birds – that gave rise to flying dinosaurs. And, he adds, it is unsurprising that dinosaurs may have evolved to fill the kinds of ecological roles filled today by mammals such as flying squirrels.
Seeking life in Antarctica? Look for the penguins’ outhouse
We tend to appreciate penguins for their cuteness. But to the natural world, it’s their poo that matters.
According to research, published in the journal Current Biology, penguin and elephant seal excrement fosters biodiversity across Antarctica.
Despite the cold, dry weather, the nitrogen in the animals’ waste provides nutrients that are otherwise unavailable in this stark setting, says Stef Bokhorst, the paper’s lead author and a polar ecologist with the Vrije Universiteit Amsterdam in the Netherlands.
“If you put more poo in the system, the Antarctic wildlife like that,” he says.
Because it’s so consistently cold, Antarctica is challenging to study and it’s been difficult to predict patterns of biodiversity. But Bokhorst and his colleagues managed to find a direct connection between areas of biodiversity – filled with lichens, mosses, microscopic animals and small creatures – and the nitrogen left behind when penguins and elephant seals defecate.
The larger the penguin colony, the further its footprint spread, the study shows.
The team looked at nitrogen because its various isotopes make it relatively easy to trace it from the sea to mosses and lichen that grow on land, and to the animals that feed on them. The penguins and elephant seals were the conduits ferrying that nitrogen from water to land, the study shows.
“We know that nutrient content of your food has a big impact on abundance and diversity of consumers, but for whatever reasons, no one’s looked at that in such a cold place as the Antarctic,” Dr Bokhorst says.
The continent, he says, is the “ideal experimental lab” for studying how nutrients relate to an ecosystem’s biodiversity because its food web is relatively simple. In a more habitable place, there are so many interacting factors that it’s often difficult to figure out what’s driving what – whether predation or more nutrients are leading to changes, for instance, Bokhorst says. In the new study, it was not hard to trace the path of the nitrogen from penguin and elephant seal to lichen and moss and then to mites and worms.
Wasps passed this logic test. Can you?
Here’s a pop quiz for you. Tom is taller than Dick. Dick is taller than Harry. Who’s taller, Harry or Tom?
If you said Tom, congratulations. You just demonstrated what’s called “transitive inference” – the ability to compare things indirectly based on previous juxtapositions. But before you pat yourself on the back too much, you should know that this skill was recently demonstrated by another creature: the humble paper wasp that might be living in your garden right now.
In summer 2017, researchers at the University of Michigan put two species of paper wasps through a transitive inference test. A statistically significant portion of the time, the wasps passed. Other animals – including rats, geese and cichlid fish – have also exhibited this capacity. But this study, which was published in Biology Letters, is the first to successfully showcase it in an invertebrate (honeybees failed a similar test in 2004).
Paper wasps are found on every continent except Antarctica. You might be near some right now. “They tend to nest in the eaves of houses or inside barbecue grills,” says Elizabeth Tibbetts, the study’s lead author.
In a previous study, Tibbetts showed that individual female wasps can identify one another by their distinct facial patterns, which resemble Rorschach ink blots. “When two wasps meet, they learn, ‘Oh, that’s what Suzy looks like,’” she says. “And the next time they meet, they remember who Suzy is.”
In the spring, the females spend a lot of time brawling, getting in each other’s faces and trading slaps with their appendages. These matchups look like schoolyard tussles. “Some wasps will be fighting; some wasps will be watching the fights,” Tibbetts says. “It’s a very exciting time.” The wasps remember the winners and losers and use them to establish a social hierarchy: the strongest reproduce, while the weaker ones do all the work.
Colin Allen, a cognitive philosopher at the University of Pittsburgh, cautions against over-interpreting the study, saying the simplicity of the test makes it “hard to judge what processes are operating in these wasps”. But he calls it “an important reminder” that just because bees can’t do something, doesn’t necessarily mean that no insects can.
It fits well with another of the study’s lessons: just because humans can do something, doesn’t necessarily mean that all insects can’t.
You will never smell my world the way I do
The scent of lily of the valley cannot be easily bottled. For decades companies that make soap, lotions and perfumes have relied on a chemical called bourgeonal to imbue their products with the sweet smell of the little white flowers. A tiny drop can be extraordinarily intense.
If you can smell it at all, that is. For a small percentage of people, it fails to register as anything.
Similarly, the earthy compound 2-ethylfenchol, present in beets, is so powerful for some people that a small chunk of the root vegetable smells like a heap of dirt. For others, that same compound is as undetectable as the scent of bottled water.
These – and dozens of other differences in scent perception – are detailed in a new study, published last week in the journal PNAS. The work provides new evidence of how extraordinarily different one person’s “smellscape” may be from another’s. It’s not that some people are generally better smellers, like someone else may have better eyesight, it’s that any one person might experience certain scents more intensely than their peers.
“We’re all smelling things a little bit differently,” says Steven Munger, director of the Centre for Smell and Taste at the University of Florida, who was not involved in the study.
The scientists who conducted the study looked for patterns in subjects’ genetic code that could explain these olfactory differences. They were surprised to find that a single genetic mutation was linked to differences in perception of the lily of the valley scent, beet’s earthiness, the intensity of whiskey’s smokiness along with dozens of other scents.
“I think it’s a very important finding,” says Stavros Lomvardas, a neuroscientist at Columbia University’s Zuckerman Institute, who was not involved in the research either.
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