Three-eyed distant relative of insects and crustaceans reveals amazing detail of early animal evolution

A team from the University of Leicester, Yunnan Key Laboratory for Palaeobiology and the Institute of Palaeontology at Yunnan University, Chengjiang Fossil Museum, and the Natural History Museum in London, have redescribed a unique fossil animal from rocks nearly 520 million years old that fills in a gap in our understanding of the evolution of animals known as arthropods.

The animal, which has the scientific name Kylinxia, was imaged using a CT scanner which revealed its soft anatomy buried in the rock. The size of a large shrimp, its surprising features include three eyes on the head and a pair of fearsome limbs presumably used to catch prey.

The study is published this week in the high impact journal Current Biology.

Fossils of many kinds of marine animals first appear in rocks from about half a billion years ago and signal a time when complex ecosystems were developing in the world's oceans. One of the key localities for such fossils is the area around the town of Chengjiang in southern China, where the fossils in this study were collected by the Chinese team. The fossils were recovered from the Cambrian Chengjiang biota of China's Yunnan Province, from which over 250 species of exceptionally preserved fossil organisms have been described.

The new find is important for deciphering the history of arthropods. These are animals whose bodies are divided into segments, most of which bear a paired of jointed limbs, like crabs, lobsters, insects, and spiders.

Although there are plenty of arthropods in the fossil record -- most famously the trilobites -- the vast majority only preserve their hard skeletons. Because the new Chinese material is preserved nearly complete, the team were able to image the head of Kylinxia, identifying six segments: the front one bearing eyes, the second with a pair of large grasping limbs, and the other four each bearing a pair of jointed limbs.

Lead author of the study Robert O'Flynn, a PhD student at the University of Leicester School of Geography, Geology and the Environment, said: "The preservation of the fossil animal is amazing. After CT-scanning we can digitally turn it around and literally stare into the face of something that was alive over 500 million years ago. As we spun the animal around, we could see that its head possesses six segments, just as in many living arthropods."

Professor Mark Williams, Robert's primary supervisor at the University of Leicester, said: "Kylinxia, and the Chengjiang biota whence it came, are instrumental to building our understanding of early euarthropod evolution. I like to think that similar discoveries will continue to be made by Robert."

Professor Yu Liu from the Yunnan Key Laboratory for Palaeobiology said: "Robert and I were examining the micro-CT data as part of his doctoral thesis in the hope of refining and correcting previous interpretation of head structures in this genus, Kylinxia. Amazingly, we found that its head is composed of six segments, as in, e.g., insects."

Dr Greg Edgecombe from the Natural History Museum added: "Most of our theories on how the head of arthropods evolved were based on these early-branching species having fewer segments than living species. Discovering two previously undetected pairs of legs in Kylinxia suggests that living arthropods inherited a six-segmented head from an ancestor at least 518 million years ago."

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This fish doesn't just see with its eyes -- it also sees with its skin

A few years ago while on a fishing trip in the Florida Keys, biologist Lori Schweikert came face to face with an unusual quick-change act. She reeled in a pointy-snouted reef fish called a hogfish and threw it onboard. But later when she went to put it in a cooler she noticed something odd: its skin had taken on the same color and pattern as the deck of the boat.

A common fish in the western Atlantic Ocean from North Carolina to Brazil, the hogfish is known for its color-changing skin. The species can morph from white to mottled to reddish-brown in a matter of milliseconds to blend in with corals, sand or rocks.

Still, Schweikert was surprised because this hogfish had continued its camouflage even though it was no longer alive. Which got her wondering: can hogfish detect light using only their skin, independently of their eyes and brain?

"That opened up this whole field for me," Schweikert said.

In the years that followed, Schweikert started researching the physiology of "skin vision" as a postdoctoral fellow at Duke University and Florida International University.

In 2018, Schweikert and Duke biologist Sönke Johnsen published a study showing that hogfish carry a gene for a light-sensitive protein called opsin that is activated in their skin, and that this gene is different from the opsin genes found in their eyes.

Other color-changing animals from octopuses to geckos have been found to make light-sensing opsins in their skin, too. But exactly how they use them to help change color is unclear.

"When we found it in hogfish, I looked at Sönke and said: Why have a light detector in the skin?" said Schweikert, now an assistant professor at the University of North Carolina Wilmington.

One hypothesis is that light-sensing skin helps animals take in their surroundings. But new findings suggest another possibility -- "that they could be using it to view themselves," Schweikert said.

In a study appearing Aug. 22 in the journal Nature Communications, Schweikert, Johnsen and colleagues teamed up to take a closer look at hogfish skin.

The researchers took pieces of skin from different parts of the fish's body and took pictures of them under a microscope.

Up close, a hogfish's skin looks like a pointillist painting. Each dot of color is a specialized cell called a chromatophore containing granules of pigment that can be red, yellow or black.

It's the movement of these pigment granules that changes the skin color. When the granules spread out across the cell, the color appears darker. When they cluster together into a tiny spot that's hard to see, the cell becomes more transparent.

Next, the researchers used a technique called immunolabeling to locate the opsin proteins within the skin. They found that in the hogfish, opsins aren't produced in the color-changing chromatophore cells. Instead, the opsins reside in other cells directly beneath them.

Images taken with a transmission electron microscope revealed a previously unknown cell type, just below the chromatophores, packed with opsin protein.

This means that light striking the skin must pass through the pigment-filled chromatophores first before it reaches the light-sensitive layer, Schweikert said.

The researchers estimate that the opsin molecules in hogfish skin are most sensitive to blue light. This happens to be the wavelength of light that the pigment granules in the fish's chromatophores absorb best.

The findings suggest that fish's light-sensitive opsins act somewhat like internal Polaroid film, capturing changes in the light that is able to filter through the pigment-filled cells above as the pigment granules bunch up or fan out.

"The animals can literally take a photo of their own skin from the inside," Johnsen said. "In a way they can tell the animal what it's skin looks like, since it can't really bend over to look."

"Just to be clear, we're not arguing that hogfish skin functions like an eye," Schweikert added. Eyes do more than merely detect light -- they form images. "We don't have any evidence to suggest that's what's happening in their skin," Schweikert said.

Rather, it's a sensory feedback mechanism that lets the hogfish monitor its own skin as it changes color, and fine-tune it to fit what it sees with its eyes.

"They appear to be watching their own color change," Schweikert said.

The researchers say the work is important because it could pave the way to new sensory feedback techniques for devices such as robotic limbs and self-driving cars that must fine-tune their performance without relying solely on eyesight or camera feeds.

"Sensory feedback is one of the tricks that technology is still trying to figure out," Johnsen said. "This study is a nice dissection of a new sensory feedback system."

"If you didn't have a mirror, and you couldn't bend your neck, how would you know if you're dressed appropriately?" Schweikert said. "For us it may not matter," she added. But for creatures that use their color-changing abilities to hide from predators, warn rivals or woo mates, "it could be life or death."

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Illusions are in the eye, not the mind

Numerous visual illusions are caused by limits in the way our eyes and visual neurones work -- rather than more complex psychological processes, new research shows.

Researchers examined illusions in which an object's surroundings affect the way we see its colour or pattern.

Scientists and philosophers have long debated whether these illusions are caused by neural processing in the eye and low-level visual centres in the brain, or involve higher-level mental processes such as context and prior knowledge.

In the new study Dr Jolyon Troscianko, from the University of Exeter, co-developed a model that suggests simple limits to neural responses -- not deeper psychological processes -- explain these illusions.

"Our eyes send messages to the brain by making neurones fire faster or slower," said Dr Troscianko, from the Centre for Ecology and Conservation on Exeter's Penryn Campus in Cornwall.

"However, there's a limit to how quickly they can fire, and previous research hasn't considered how the limit might affect the ways we see colour."

The model combines this "limited bandwidth" with information on how humans perceive patterns at different scales, together with an assumption that our vision performs best when we are looking at natural scenes.

The model was developed by researchers from the Universities of Exeter and Sussex to predict how animals see colour, but it was also found to correctly predict many visual illusions seen by humans.

"This throws into the air a lot of long-held assumptions about how visual illusions work," Dr Troscianko said.

He said the findings also shed light on the popularity of high-definition televisions.

"Modern high dynamic range televisions create bright white regions that are over 10,000 times brighter than their darkest black, approaching the contrast levels of natural scenes," Dr Troscianko added.

"How our eyes and brains can handle this contrast is a puzzle because tests show that the highest contrasts we humans can see at a single spatial scale is around 200:1.

"Even more confusingly, the neurones connecting our eyes to our brains can only handle contrasts of about 10:1.

"Our model shows how neurones with such limited contrast bandwidth can combine their signals to allow us to see these enormous contrasts, but the information is 'compressed' -- resulting in visual illusions.

"The model shows how our neurones are precisely evolved to use of every bit of capacity.

"For example, some neurones are sensitive to very tiny differences in grey levels at medium-sized scales, but are easily overwhelmed by high contrasts.

"Meanwhile, neurones coding for contrasts at larger or smaller scales are much less sensitive, but can work over a much wider range of contrasts, giving deep black-and-white differences.

"Ultimately this shows how a system with a severely limited neural bandwidth and sensitivity can perceive contrasts larger than 10,000:1."

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Human eyes really do play 'tricks' on the mind, say experts

A new study has shown that the human visual system can 'trick' the brain into making inaccurate assumptions about the size of objects in the world around them.

The research findings could have implications for many aspects of everyday life, such as driving, how eye witness accounts are treated in the criminal justice system, and security issues, such as drone sightings.

The research team from the University of York and Aston University presented participants with photographs of full-scale railway scenes, which had the upper and lower parts of the image blurred, as well photographs of small-scale models of railways that were not blurred.

Participants were asked to compare each image and decide which was the 'real' full-scale railway scene. The results were that participants perceived that the blurred real trains were smaller than the models.

Dr Daniel Baker, from the University of York's Department of Psychology, said: "In order for us to determine the real size of objects that we see around us, our visual system needs to estimate the distance to the object.

"To arrive at an understanding of absolute size it can take into account the parts of the image that are blurred out -- a bit like the out-of-focus areas that a camera produces -- which involves a bit of complicated mathematics to give the brain the knowledge of spatial scale.

"This new study, however, shows that we can be fooled in our estimates of object size. Photographers take advantage of this using a technique called 'tilt-shift miniaturisation', that can make life-size objects appear to be scale models."

The findings demonstrate that the human visual system is highly flexible -- sometimes capable of accurate perception of size by exploiting what is known as 'defocus blur', but at other times subject to other influences and failing to make sense of real-world object size.

Professor Tim Meese, from Aston University, said: "Our results indicate that human vision can exploit defocus blur to infer perceptual scale but that it does this crudely.

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Scientists achieve promising results towards restoring vision in blindness caused by cellular degeneration in the eye

A preclinical study using stem cells to produce progenitor photoreceptor cells -- light-detecting cells found in the eye -- and then transplanting these into experimental models of damaged retinas has resulted in significant vision recovery. This finding, by scientists at Duke-NUS Medical School, the Singapore Eye Research Institute and the Karolinska Institute in Sweden, marks a first step towards potentially restoring vision in eye diseases characterised by photoreceptor loss.

"Our laboratory has developed a novel method that enables the production of photoreceptor progenitor cells resembling those in human embryos," said Assistant Professor Tay Hwee Goon, first author of the study from Duke-NUS' Centre for Vision Research. "Transplantation of these cells into experimental models has yielded partial restoration of the retinal function."

The degeneration of photoreceptors in the eye is a significant cause of declining vision that can eventually lead to blindness and for which there is currently no effective treatment. Photoreceptor degeneration occurs in a variety of inherited retinal diseases, such as retinitis pigmentosa -- a rare eye disease that breaks down cells in the retina over time and eventually causes vision loss -- and age-related macular degeneration, a leading cause of vision impairment worldwide.

Asst Prof Tay and her team developed a procedure to grow human embryonic stem cells in the presence of purified laminin proteins that are involved in normal development of human retinas. In the presence of the laminins, stem cells could be directed to differentiate into photoreceptor progenitor cells responsible for converting light into signals that are sent to the brain.

When these cells were transplanted into damaged retinas, the preclinical models showed significant recovery of vision. A diagnostic test called electroretinogram also identified significant recovery in the retinas via electrical activity in the retina in response to a light stimulus. The transplanted cells established connections with surrounding retinal cells and nerves in the inner retina. They also survived and functioned for many weeks after transplantation.

Moving forward, the team hopes to refine their method to make it simpler and achieve more consistent results than earlier attempts to explore stem cell therapy for photoreceptor cell replacement.

"It is exciting to find these results, which suggest a promising route towards using stem cells to treat those forms of visual deterioration and blindness caused by the loss of photoreceptors," said Dr Helder Andre, Head of Molecular and Cellular Research from Karolinska Institute's Department of Clinical Neuroscience and a senior author of the study.

Associate Professor Enrico Petretto, Director of the Centre for Computational Biology at Duke-NUS and the study's bioinformatics analysis lead, added: "Our method may also be useful for understanding the molecular and cellular pathways that drive the progression of macular degeneration, perhaps leading to the development of other therapeutic approaches."

The next challenge for the researchers is to explore the efficacy of their method in models of photoreceptor degeneration that more closely match the human condition.

"If we get promising results in our future studies, we hope to move to clinical trials in patients," said Professor Karl Tryggvason, from Duke-NUS' Cardiovascular and Metabolic Disorders Programme, and the corresponding author of the study. "That would be an important step towards for being able to reverse damage of the retina and restore vision."

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Psychology: What gazes reveal about us

A new study by the TU Dresden shows that eye movements during the processing of tasks provide information about what the respective person is currently occupied with and what goals are being pursued within the task. These findings could play a role in the organization of screen work in the future.

We constantly move our eyes to obtain important information from the environment. Measuring eye movements allows to understand how information is processed. Previous work has shown that new visual information leads to a certain pattern of eye movements In particular, two types of visual processing are distinguished. In the so-called ambient mode, the eyes move rapidly over large distances to initially gain rough impressions of potentially interesting targets. It is therefore used for general spatial orientation. Once this process is complete, specific information is viewed for longer periods of time and processed more deeply, depending on the target and the level of interest. This is the so-called focus mode. So far, these changes in gaze patterns have mainly been found in the context of changes in the environment, that is external stimuli.

In a recent study by the Chair of Engineering Psychology at Technische Universität Dresden, Sebastian Pannasch and his team have now investigated the extent to which such patterns also occur as a result of internal stimuli. For this purpose, the test subjects were asked to solve a task on a computer screen in which they had to assemble a Rubik's cube according to a model so that all sides corresponded exactly to the model specifications. The external stimulus, i.e., the setting on the screen and the task, remained the same. Evaluation of the measured eye movements showed that the environmental mode for reorientation always occurred when information was taken in during different subtasks of the puzzle, e.g., when a puzzle piece was selected or checked to see if it matched the specification.

For Sebastian Pannasch, professor of engineering psychology and applied cognitive research at Technische Universität Dresden, the new findings are promising: "Our results show that the eyes are not only a proverbial mirror of the soul, but actually and measurably provide information about what we are currently engaged in and what goals we are pursuing within a task. Eye movements could be an indicator of the state of attention during task processing. In further studies, we will therefore investigate whether these new findings can be used to organize screen work."

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New study shows repeated stress accelerates aging of the eye

New research from the University of California, Irvine, suggests aging is an important component of retinal ganglion cell death in glaucoma, and that novel pathways can be targeted when designing new treatments for glaucoma patients.

The study, titled, "Stress induced aging in mouse eye," was published today in Aging Cell. Along with her colleagues, Dorota Skowronska Krawczyk, PhD, assistant professor in the Departments of Physiology & Biophysics and Ophthalmology and the faculty of the Center for Translational Vision Research at the UCI School of Medicine, describes the transcriptional and epigenetic changes happening in aging retina. The team shows how stress, such as intraocular pressure (IOP) elevation in the eye, causes retinal tissue to undergo epigenetic and transcriptional changes similar to natural aging. And, how in young retinal tissue, repetitive stress induces features of accelerated aging including the accelerated epigenetic age.

Aging is a universal process that affects all cells in an organism. In the eye, it is a major risk factor for a group of neuropathies called glaucoma. Because of the increase in aging populations worldwide, current estimates show that the number of people with glaucoma (aged 40-80) will increase to over 110 million in 2040.

"Our work emphasizes the importance of early diagnosis and prevention as well as age-specific management of age-related diseases, including glaucoma," said Skowronska-Krawczyk. "The epigenetic changes we observed suggest that changes on the chromatin level are acquired in an accumulative way, following several instances of stress. This provides us with a window of opportunity for the prevention of vision loss, if and when the disease is recognized early."

In humans, IOP has a circadian rhythm. In healthy individuals, it oscillates typically in the 12-21 mmHg range and tends to be highest in approximately two thirds of individuals during the nocturnal period. Due to IOP fluctuations, a single IOP measurement is often insufficient to characterize the real pathology and risk of disease progression in glaucoma patients. Long-term IOP fluctuation has been reported to be a strong predictor for glaucoma progression. This new study suggests that the cumulative impact of the fluctuations of IOP is directly responsible for the aging of the tissue.

"Our work shows that even moderate hydrostatic IOP elevation results in retinal ganglion cell loss and corresponding visual defects when performed on aged animals," said Skowronska-Krawczyk. "We are continuing to work to understand the mechanism of accumulative changes in aging in order to find potential targets for therapeutics. We are also testing different approaches to prevent the accelerated aging process resulting from stress."

Researchers now have a new tool to estimate the impact of stress and treatment on the aging status of retinal tissue, which has made these new discoveries possible. In collaboration with the Clock Foundation and Steve Horvath, PhD, from Altos Labs, who pioneered the development of epigenetic clocks that can measure age based on methylation changes in the DNA of tissues, it was possible for researchers to show that repetitive, mild IOP elevation can accelerate epigenetic age of the tissues.

"In addition to measuring vision decline and some structural changes due to stress and potential treatment, we can now measure the epigenetic age of retinal tissue and use it to find the optimal strategy to prevent vision loss in aging," said Skowronska-Krawczyk.

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Eye-opening discovery about adult brain's ability to recover vision

A discovery about how some visually impaired adults could start to see offers a new vision of the brain's possibilities. The finding that the adult brain has the potential to partially recover from inherited blindness comes from a collaboration between researchers in the University of California, Irvine School of Biological Sciences and the School of Medicine. Their paper appears in Current Biology.

The team was examining treatment for Leber congenital amaurosis, known as LCA. The term refers to a group of inherited retinal diseases distinguished by severe visual impairment at birth. The condition, which stems from mutations in any of over two dozen genes, causes degeneration or dysfunction in the retina's photoreceptors.

Administering chemical compounds that target the retina, called synthetic retinoids, can restore a notable amount of vision in children with LCA. The UCI team wanted to find out if the treatment could make a difference for adults who have the condition.

"Frankly, we were blown away by how much the treatment rescued brain circuits involved in vision," said Sunil Gandhi, professor of neurobiology and behavior and the corresponding author. Gandhi is a fellow of UCI's Center for the Neurobiology of Learning and Memory and a member of the Center for Translational Vision Research. "Seeing involves more than intact and functioning retinae. It starts in the eye, which sends signals throughout the brain. It's in the central circuits of the brain where visual perception actually arises." Until now, scientists believed that the brain must receive those signals in childhood so that central circuits could wire themselves correctly.

Working with rodent models of LCA, the collaborators were surprised by what they found. "The central visual pathway signaling was significantly restored in adults, especially the circuits that deal with information coming from both eyes," Gandhi said. "Immediately after the treatment, the signals coming from the opposite-side eye, which is the dominant pathway in the mouse, activated two times more neurons in the brain. What was even more mind-blowing was that the signals coming from the same-side eye pathway activated five-fold more neurons in the brain after the treatment and this impressive effect was long-lasting. The restoration of visual function at the level of the brain was much greater than expected from the improvements we saw at the level of the retinae. The fact that this treatment works so well in the central visual pathway in adulthood supports a new concept, which is that there is latent potential for vision that is just waiting to be triggered."

The finding opens exciting research possibilities. "Whenever you have a discovery that breaks with your expectations about the possibility for the brain to adapt and rewire, it teaches you a broader concept," Gandhi said. "This new paradigm could aid in the development of retinoid therapies to more completely rescue the central visual pathway of adults with this condition."

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All the better to better eat you with -- dinosaurs evolved different eye socket shapes to allow stronger bites

Large dinosaur predators, such as Tyrannosaurus rex, evolved different shapes of eye sockets to better deal with high bite forces, new research has shown.

While in many animals -- and most dinosaurs -- the eye socket is just a circular hole in the skull housing the eyeball, this is very different in large carnivores.

In a new study, published today in Communications Biology, researchers at the University of Birmingham reveal how the unusual elliptical, or oval eye sockets found in the skulls of these predators, could have evolved to help the skull absorb impact as they pounced on prey.

Dr Stephan Lautenschlager, Senior Lecturer for Palaeobiology at the University of Birmingham and author of the new study, analysed the shape of the eye sockets of ca. 500 different dinosaurs and related species.

"The results show that only some dinosaurs had eye sockets that were elliptical or keyhole-shaped," said Dr Stephan Lautenschlager. "However, all of those were large, carnivorous dinosaurs with skull lengths of 1 m or more."

Using computer simulations and stress analysis, Dr Lautenschlager tested what purpose these unusual eye socket shapes could have.

The results demonstrated that a skull with a circular eye socket was more prone to high stresses during biting. However, if these were replaced with other eye socket shapes stresses were considerably reduced allowing top predators, including Tyrannosaurus rex, to evolve high bite forces without compromising skull stability.

The study also showed that most plant-eating species and juvenile individuals retained a circular eye socket. Only large carnivores adopted other morphologies, such as elliptical, keyhole-shaped or figure-of-eight-shaped eye sockets.

Dr Lautenschlager added: "In these species, just the upper part of the eye socket was actually occupied by the eyeball. This also led to a relative reduction of eye size compared with skull size."

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Researchers take step toward developing 'electric eye'

Georgia State University researchers have successfully designed a new type of artificial vision device that incorporates a novel vertical stacking architecture and allows for greater depth of color recognition and scalability on a micro-level. The new research is published in the top journal ACS Nano.

"This work is the first step toward our final destination-to develop a micro-scale camera for microrobots," says assistant professor of Physics Sidong Lei, who led the research. "We illustrate the fundamental principle and feasibility to construct this new type of image sensor with emphasis on miniaturization."

Lei's team was able to lay the groundwork for the biomimetic artificial vision device, which uses synthetic methods to mimic biochemical processes, using nanotechnology.

"It is well-known that more than 80 percent of the information is captured by vision in research, industry, medication, and our daily life," he says. "The ultimate purpose of our research is to develop a micro-scale camera for microrobots that can enter narrow spaces that are intangible by current means, and open up new horizons in medical diagnosis, environmental study, manufacturing, archaeology, and more."

This biomimetic "electric eye" advances color recognition, the most critical vision function, which is missed in the current research due to the difficulty of downscaling the prevailing color sensing devices. Conventional color sensors typically adopt a lateral color sensing channel layout and consume a large amount of physical space and offer less accurate color detection.

Researchers developed the unique stacking technique which offers a novel approach to the hardware design. He says the van der Waals semiconductor-empowered vertical color sensing structure offers precise color recognition capability which can simplify the design of the optical lens system for the downscaling of the artificial vision systems.

Ningxin Li, a graduate student in Dr. Lei's Functional Materials Studio who was part of the research team, says recent advancements in technology make the new design possible.

"The new functionality achieved in our image sensor architecture all depends on the rapid progress of van der Waals semiconductors during recent years," says Li. "Compared with conventional semiconductors, such as silicon, we can precisely control the van der Waals material band structure, thickness, and other critical parameters to sense the red, green, and blue colors."

The van der Waals semiconductors empowered vertical color sensor (vdW-Ss) represent a newly-emerged class of materials, in which individual atomic layers are bonded by weak van der Waals forces. They constitute one of the most prominent platforms for discovering new physics and designing next-generation devices.

"The ultra-thinness, mechanical flexibility, and chemical stability of these new semiconductor materials allow us to stack them in arbitrary orders. So, we are actually introducing a three-dimensional integration strategy in contrast to the current planar micro-electronics layout. The higher integration density is the main reason why our device architecture can accelerate the downscaling of cameras," Li says.

The technology currently is patent pending with Georgia State's Office of Technology Transfer & Commercialization (OTTC). OTTC anticipates this new design will be of high interest to certain industry partners. "This technology has the potential to overcome some of the key drawbacks seen with current sensors, says OTTC's Director, Cliff Michaels. "As nanotechnology advances and devices become more compact, these smaller, highly sensitive color sensors will be incredibly useful."

Researchers believe the discovery could even spawn advancements to help the vision-impaired one day.

"This technology is crucial for the development of biomimetic electronic eyes and also other neuromorphic prosthetic devices," says Li. "High-quality color sensing and image recognition function may bring new possibilities of colorful item perception for the visually impaired in the future."

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What lies behind a baby’s eyes

We give meaning to our world through the categorisation of objects. When and how does this process begin? By studying the gaze of one hundred infants, scientists at the Institut des Sciences Cognitives Marc Jeannerod (CNRS/Université Claude Bernard Lyon 1) have demonstrated that, by the age of fourth months, babies can assign objects that they have never seen to the animate or inanimate category. These findings, published in PNAS on 15 February 2022, reveal measurable changes in neural organisation, which reflect the transition from simply viewing the world to understanding it.

The way babies look at the world is a great mystery. What do they really see? What information do they get from seeing? One might think they look at things that stand out the most -- by virtue of size or colour, for example. But when do babies begin to see and interpret the world like adults?

To answer this question, researchers from the Institut des Sciences Cognitives Marc Jeannerod (CNRS / Université Claude Bernard Lyon 1) studied one hundred babies aged between 4 and 19 months. The scientists recorded the babies' eye movements and the durations of their gaze as they looked at pairs of pictures representing animate or inanimate things from eight different categories (e.g., human faces and natural or artificial objects). The data obtained from eye tracking on babies were matched with measures of brain activity obtained from a group of adults using fMRI, in order to determine the correspondence between the categorical object organisation emerging from the babies' eyes and that mapped on the adults' visual cortex.

The methodology used in the study has revealed the transition from the visual exploration guided by the salience of objects, in the youngest babies, to an object representation towards the mature categorical organisation of the adult brain, in the older babies. Already at four months, babies can distinguish between animate and inanimate objects. For instance, they can tell that a man and a crocodile, being animals, are more similar to each other than they are to a tree, which is an inanimate object. This ability appears astonishing as, at that age, babies are unlikely to know what a tree or crocodile is.

Between 10 and 19 months of age, more refined categories emerge and the infants' organisation of objects into categories increasingly approaches that in the adult brain. Children in this age range immediately recognise a soft, furry object with a face as a nonhuman animal.

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Using the eye as a window into heart disease

Scientists have developed an artificial intelligence (AI) system that can analyse eye scans taken during a routine visit to an optician or eye clinic and identify patients at a high risk of a heart attack.

Doctors have recognised that changes to the tiny blood vessels in the retina are indicators of broader vascular disease, including problems with the heart.

In the research, led by the University of Leeds, deep learning techniques were used to train the AI system to automatically read retinal scans and identify those people who, over the following year, were likely to have a heart attack.

Deep learning is a complex series of algorithms that enable computers to identify patterns in data and to make predictions.

Writing in the journal Nature Machine Intelligence, the researchers report that the AI system had an accuracy of between 70% and 80% and could be used as a second referral mechanism for in-depth cardiovascular investigation.

The use of deep learning in the analysis of retinal scans could revolutionise the way patients are regularly screened for signs of heart disease.

Professor Alex Frangi, who holds the Diamond Jubilee Chair in Computational Medicine at the University of Leeds and is a Turing Fellow at the Alan Turing Institute, supervised the research. He said: "Cardiovascular diseases, including heart attacks, are the leading cause of early death worldwide and the second-largest killer in the UK. This causes chronic ill-health and misery worldwide.

"This technique opens-up the possibility of revolutionising the screening of cardiac disease. Retinal scans are comparatively cheap and routinely used in many optician practices. As a result of automated screening, patients who are at high risk of becoming ill could be referred to specialist cardiac services.

"The scans could also be used to track the early signs of heart disease."

The study involved a worldwide collaboration of scientists, engineers and clinicians from the University of Leeds; Leeds Teaching Hospitals' NHS Trust; the University of York; the Cixi Institute of Biomedical Imaging in Ningbo, part of the Chinese Academy of Sciences; the University of Cote d'Azur, France; the National Centre for Biotechnology Information and the National Eye Institute, both part of the National Institutes for Health in the US; and KU Leuven in Belgium.

The UK Biobank provided data for the study.

Chris Gale, Professor of Cardiovascular Medicine at the University of Leeds and a Consultant Cardiologist at Leeds Teaching Hospitals NHS Trust, was one of the authors of the research paper.

He said: "The AI system has the potential to identify individuals attending routine eye screening who are at higher future risk of cardiovascular disease, whereby preventative treatments could be started earlier to prevent premature cardiovascular disease."

Deep learning

During the deep learning process, the AI system analysed the retinal scans and cardiac scans from more than 5,000 people. The AI system identified associations between pathology in the retina and changes in the patient's heart.

Once the image patterns were learned, the AI system could estimate the size and pumping efficiency of the left ventricle, one of the heart's four chambers, from retinal scans alone. An enlarged ventricle is linked with an increased risk of heart disease.

With information on the estimated size of the left ventricle and its pumping efficiency combined with basic demographic data about the patient, their age and sex, the AI system could make a prediction about their risk of a heart attack over the subsequent 12 months.

Currently, details about the size and pumping efficiency of a patient's left ventricle can only be determined if they have diagnostic tests such as echocardiography or magnetic resonance imaging of the heart. Those diagnostic tests can be expensive and are often only available in a hospital setting, making them inaccessible for people in countries with less well-resourced healthcare systems -- or unnecessarily increasing healthcare costs and waiting times in developed countries.

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Primordial ‘hyper-eye’ discovered

An international research team has found an eye system in trilobites of the suborder Phacopina from the Devonian (390 million years B.P.) that is unique in the animal kingdom: each of the about 200 lenses of a hyper-facet eye spans a group of six normal compound-eye-facets, forming a compound eye itself. In addition to the hyper-facetted eyes, the researchers, led by zoologist Dr. Brigitte Schoenemann at the University of Cologne's Institute for Didactics of Biology, identified a structure that they believe to be a local neural network which directly processed the information from this special eye, and an optic nerve that carried information from the eye to the brain. The article, 'A 390 million-year-old hyper-compound eye in Devonian phacopid trilobites,' has been published in Scientific Reports.

Trilobites are arthropods that once inhabited the world's oceans and became extinct about 251 million years ago. The discovery was made when Schoenemann and her colleagues examined X-ray images taken by radiologist and amateur paleontologist Wilhelm Stürmer in the 1970s. Stürmer had already believed the filaments under the trilobite eyes to be nerves, or a light guiding system. Schoenemann also found markings by Stürmer on the images designating the six subfacets. However, scientists at the time did not believe his interpretations. Now, however, the re-examination of the images and verification with modern computed tomography succeeded in confirming his conjectures.

Most trilobites had compound eyes similar to those that are still found in insects today: a large number of hexagonal facets form the eye. There are usually eight photoreceptors under each facet. Comparable to the image of a computer screen, which is built up from individual pixels, an image is built up from the individual facets. In dragonflies, there are up to ten thousand individual facets. In order to produce a coherent image, the facets must be very close together and connected by neurons. However, in the trilobite suborder Phacopinae, the externally visible lenses of the compound eyes are much larger, up to 1 mm in diameter and more. In addition, they are set farther apart. Until now, scientists had not been able to explain this because space is wasted where light could be captured. Since a small cup sits under the lens, they assumed that at the bottom of the capsule was a small retina comparable to that of humans.

Dr Schoenemann's analysis of Wilhelm Stürmer's 40-year-old X-ray archive now suggests a different interpretation: a hyper-compound eye. Each phacopid had two eyes, one on the left and one on the right. 'Each of these eyes consisted of about 200 lenses up to 1 mm in size,' said Schoenemann. 'Under each of these lenses, in turn, at least 6 facets are set up, each of which together again makes up a small compound eye. So we have about 200 compound eyes (one under each lens) in one eye.' These sub-facets are arranged in either one ring or two rings. 'Underneath sat a foam-like nest that was probably a small neural network to process the signals,' the zoologist added. The filaments Stürmer found in fact did turn out to be nerves leading from the eyes to the trilobite's brain. Further examination with modern computer tomography confirmed these structures.

Wilhelm Stürmer was the head of the X-ray department at Siemens and an avid paleontologist. With a VW bus equipped as an X-ray station, he drove from quarry to quarry to X-ray fossils. Among other things, he discovered structures called filaments under the animals' eyes, which he thought were fossils of soft tissues, especially optic nerves. 'At that time, the consensus was that only bones and teeth, the hard parts of living things, could be seen in the fossils, but not the soft parts, such as intestines or nerves,' Schoenemann explained. Stürmer's heir gave the zoologist his archive. But the hobby-paleontologist had not only correctly identified the optic nerve, she notes: 'On an X-ray negative, there was an arrow in red pen pointing to the structure of the six lower facets under a main lens. This probably indicated that Stürmer had already recognized the hyper-compound eye.' At the time, however, scientists assumed that nerves did not fossilize, nor that light guides existed in natural optical system. Optical fibres were not discovered until the 1980s in the compound eyes of a deep-sea crab.

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Birds’ eye size reflects habitat and diet, may predict sensitivity to environmental change

A new study shows the eye size of birds can reveal broad patterns of their biology and behavior, including where they live, what they eat and how they hunt, providing a potential roadmap for future conservation efforts.

Birds have some of the largest eyes relative to their bodies of all vertebrate land animals, second only to frogs. With a limited range of taste and smell, birds primarily rely on vision to navigate, find food and avoid predators. Yet surprisingly little is known about how eye size in birds influences their behavior compared with other traits, such as beak shape and body size, which scientists have meticulously studied since Charles Darwin's classic work on finches.

"I was really shocked to find out while doing literature searches that there was no definitive publication on how eye size in birds relates to their environment," said Ian Ausprey, a recent doctoral graduate of the Florida Museum of Natural History's Ordway Lab of Ecosystem Conservation.

Previous studies on bird eyes have been limited in scope, typically including only a few dozen species or birds in specific regions. This gap in scientific knowledge was all the more glaring given that a graduate student measured the eyes of more than 4,000 species of birds in museum collections in the late 1970s, creating the largest dataset of its kind.

Ausprey relied on this resource to analyze eye size for 2,777 species -- about one-third of the world's bird diversity -- revealing that this single trait more powerfully predicts where birds live and how they behave than better-studied characteristics such as size, anatomy and movement.

Large eyes increase sensitivity to deforestation

Ausprey had the idea for the study while conducting fieldwork with colleagues in the Andean forests of Peru. Over the course of five years, the researchers measured the eyes of Peruvian birds and attached small light sensors to more than a dozen species of tanagers, finches, wrens and woodpeckers to determine how these birds were coping with increased amounts of forest fragmentation due to agriculture.

Their results were troubling: Birds with large eyes avoided agricultural fields, keeping to diminishing forest habitats. But the researchers could also use eye size to predict where these birds mated and laid eggs and what they were eating, valuable information for future conservation efforts.

Ausprey wanted to know whether this pattern held true for all birds, not just those in Peru. But with over 10,000 species spread out across all seven continents, answering a question as broad as how eye size influences bird behavior would have taken years.

Fortunately, the data Ausprey needed had already been collected in the form of a dissertation, a nearly 2,000-page tome completed by Stanley Ritland during his time as a doctoral student at the University of Chicago.

"He spent his time traveling around museums, extracting eyes out of specimens preserved in alcohol and then measuring them," Ausprey said. "He did it for several thousand species of birds, as well as mammals and reptiles."

Ritland left academia upon graduating, however, and never published his data in a scientific journal. Researchers have used small portions of the massive dataset, initially relegated to the stacks of the University of Chicago library, to answer small-scale questions, but comprehensive analyses have so far been lacking.

Although the data was available, the time-consuming task of digitizing it still remained. Ausprey hired two undergraduate students, Savannah Montgomery and Kristie Perez, who spent five months transcribing Ritland's measurements into spreadsheets so they could be analyzed and shared more broadly with the scientific community.

Because eye size tends to increase with body size, Ausprey standardized all the measurements for each species by mass and intentionally omitted birds that operate at optical extremes, such as far-sighted raptors and nocturnal owls. Scientists already know these species have unusually large eyes.

Instead, he focused on land-dwelling birds that hunt for food close to the ground and are most active during daylight hours.

Light and shadow define bird vision

Stark patterns began to take shape as eye size was compared with a host of behavioral traits.

Birds with larger eyes live closer to the equator, where the planet's belt of rainforests create dark understory habitats. Regardless of latitude, birds that hunt or forage closest to the forest floor have large eyes to take in as much light as possible, while those that spend more time in the sky had correspondingly smaller eyes to reduce glare.

"Bright lights can cause something called disability glare," Ausprey said. "When you shine a light on birds, they change the way they forage. They also respond differently to vocalizations of experimental predators."

Scientists worry that such behavioral changes may negatively affect avian understory specialists, many of which have already been displaced because of deforestation.

"Understory tropical birds may be especially sensitive to fragmentation because they are adapted to dark forested environments and are unable to cope with rapid changes in brightness associated with forest edges and human-modified habitats," Ausprey said.

Eye size is also strongly correlated with diet. Larger eyes not only absorb more light, but they can also confer increased focal length and resolution, the equivalent of upgrading your camera with a longer lens.

Birds that eat insects have larger eyes, which are better suited for spotting prey at long distances, regardless of whether they lived in the forest understory or open habitats. Birds with the smallest eyes relative to body size were often nectar feeders, hinting that they may rely on color more than shape when looking for food.

Ausprey also analyzed how eyes have changed throughout the birds' evolution, finding that once eyes became larger in a particular group, they stayed that way. This meant that closely related groups, such as the hummingbird and swift families, could have eyes of vastly different sizes.

Within a family, however, size didn't change much among species. Fly catchers, for example, spend a lot of time sallying out and catching prey, which requires long-distance, binocular vision, Ausprey said.

"And it turns out, flycatchers tend to have larger eyes, as you'd expect. All the finches and tanagers and such that eat fruits and seeds tend to have very small eyes."

Collections provide tools for understanding the natural world

To Ausprey, the data collected by Ritland decades ago offer an unparalleled glimpse into bird diversity and behavior, which may help conserve species for the future.

"Nearly half a century of time has passed, and yet the same datasets are relevant," Ausprey said.

Ritland relied entirely on alcohol-preserved museum collections, meaning the same specimens he measured are still accessible to scientists stitching together patterns in the natural world.

Some of the birds he encountered during his museum visits were already of considerable antiquity by the time he began taking his measurements, including two birds collected during Captain Cook's first voyage around the world.

"Museum collections are invaluable, indispensable and essentially irreplaceable," Ritland said in an email.

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Eyes wide shut: How newborn mammals dream the world they're entering

As a newborn mammal opens its eyes for the first time, it can already make visual sense of the world around it. But how does this happen before they have experienced sight?

A new Yale study suggests that, in a sense, mammals dream about the world they are about to experience before they are even born.

Writing in the July 23 issue of Science, a team led by Michael Crair, the William Ziegler III Professor of Neuroscience and professor of ophthalmology and visual science, describes waves of activity that emanate from the neonatal retina in mice before their eyes ever open.

This activity disappears soon after birth and is replaced by a more mature network of neural transmissions of visual stimuli to the brain, where information is further encoded and stored.

"At eye opening, mammals are capable of pretty sophisticated behavior," said Crair, senior author of the study, who is also vice provost for research at Yale." But how do the circuits form that allow us to perceive motion and navigate the world? It turns out we are born capable of many of these behaviors, at least in rudimentary form."

In the study, Crair's team, led by Yale graduate students Xinxin Ge and Kathy Zhang, explored the origins of these waves of activity. Imaging the brains of mice soon after birth but before their eyes opened, the Yale team found that these retinal waves flow in a pattern that mimics the activity that would occur if the animal were moving forward through the environment.

"This early dream-like activity makes evolutionary sense because it allows a mouse to anticipate what it will experience after opening its eyes, and be prepared to respond immediately to environmental threats," Crair noted.

Going further, the Yale team also investigated the cells and circuits responsible for propagating the retinal waves that mimic forward motion in neonatal mice. They found that blocking the function of starburst amacrine cells, which are cells in the retina that release neurotransmitters, prevents the waves from flowing in the direction that mimics forward motion. This in turn impairs the development of the mouse's ability to respond to visual motion after birth.

Intriguingly, within the adult retina of the mouse these same cells play a crucial role in a more sophisticated motion detection circuit that allows them to respond to environmental cues.

Mice, of course, differ from humans in their ability to quickly navigate their environment soon after birth. However, human babies are also able to immediately detect objects and identify motion, such as a finger moving across their field of vision, suggesting that their visual system was also primed before birth.

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New study explains why you should look at your food before casting judgment

 The order in which your senses interact with food has a tremendous impact on how much you like it. That's the premise of a new study led by the University of South Florida (USF). The findings published in the Journal of Consumer Psychology show that food tastes better if you see it before smelling it.

Researchers came to this conclusion following four experiments involving cookies, fruit snacks and lemonade. In the first study, nearly 200 participants interacted with the food, each item wrapped in an opaque versus a transparent package. The team administered each item in different orders: visual before scent, scent before visual, only visual and only scent. Despite being the same product, participants rated the strawberry-flavored fruit snacks packaged in an envelope as tasting better when they could see the item before smelling it compared to their counterparts who smelled the item before seeing it. Researchers experienced the same results when they tested taste perception of the cookies.

"This is because being able to see a food item before smelling it helps in processing the scent cue with greater ease, which in turn enhances the food taste perception," said Dipayan Biswas, Frank Harvey Endowed Professor of Marketing at USF. "Basically, scents play a very critical role in influencing taste perceptions; however, interestingly, people can process a scent better in their brains when the scent is preceded by a corresponding visual cue, such as color."

The research team, which includes collaborators from Columbia University and the University of Rhode Island, experienced the same results when it focused on beverages. Researchers poured the same, yellow-colored lemonade into lidded clear plastic cups and lidded solid-colored plastic cups that were splashed with artificial lemon-scented oil. Similarly, participants preferred the drink that they could see before smelling and they drank more of it. Researchers tested consumption by purposely leaving the drinks in front of participants as they undertook an unrelated task. Additionally, the researchers provided the same drinks with the addition of odorless purple food coloring, a color typically not associated with lemon flavor. In this case, it had a negative effect on taste perception, as the color contradicted expectations.

"We tested this to get a better understanding of how the human sensory processing system evaluates a sequence of visual and scent-related cues," Biswas said.

These findings are highly beneficial to supermarkets and Biswas suggests they consider installing more glass cases to help facilitate a customer's ability to see a food item at a distance before smelling it. He suggests strategic displays with photos or samples be visible prior to entering a business, helping strengthen taste perceptions of food items, which can increase sales and overall impression of the business. Biswas emphasizes that the theory also applies to pantry food items, such as potato chips, which may attract more interest if they were sold in transparent packaging.

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Gene therapy shows promise in treating rare eye disease in mice

 A gene therapy protects eye cells in mice with a rare disorder that causes vision loss, especially when used in combination with other gene therapies, shows a study published today in eLife.

The findings suggest that this therapy, whether used alone or in combination with other gene therapies that boost eye health, may offer a new approach to preserving vision in people with retinitis pigmentosa or other conditions that cause vision loss.

Retinitis pigmentosa is a slowly progressive disease, which begins with the loss of night vision due to genetic lesions that affect rod photoreceptors -- cells in the eyes that sense light when it is low. These photoreceptors die because of their intrinsic genetic defects. This then impacts cone photoreceptors, the eye cells that detect light during the day, which leads to the eventual loss of daylight vision. One theory about why cones die concerns the loss of nutrient supply, especially glucose.

Scientists have developed a few targeted gene therapies to help individuals with certain mutations that affect the photoreceptors, but no treatments are currently available that would be effective for a broad set of families with the disease. "A gene therapy that would preserve photoreceptors in people with retinitis pigmentosa regardless of their specific genetic mutation would help many more patients," says lead author Yunlu Xue, Postdoctoral Fellow at senior author Constance Cepko's lab, Harvard Medical School, Boston, US.

To find a widely effective gene therapy for the disease, Xue and colleagues screened 20 potential therapies in mouse models with the same genetic deficits as humans with retinitis pigmentosa. The team chose the therapies based on the effects they have on sugar metabolism.

Their experiments showed that using a virus carrier to deliver a gene called Txnip was the most effective approach in treating the condition across three different mouse models. A version of Txnip called C247S worked especially well, as it helped the cone photoreceptors switch to using alternative energy sources and improved mitochondria health in the cells.

The team then showed that giving the mice gene therapies that reduced oxidative stress and inflammation, along with Txnip gene therapy, provided additional protection for the cells. Further studies are now needed to confirm whether this approach would help preserve vision in people with retinitis pigmentosa.

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Sign-language exposure impacts infants as young as 5 months old

 While it isn't surprising that infants and children love to look at people's movements and faces, recent research from Rochester Institute of Technology's National Technical Institute for the Deaf studies exactly where they look when they see someone using sign language. The research uses eye-tracking technology that offers a non-invasive and powerful tool to study cognition and language learning in pre-verbal infants.

NTID researcher and Assistant Professor Rain Bosworth and alumnus Adam Stone studied early-language knowledge in young infants and children by recording their gaze patterns as they watched a signer. The goal was to learn, just from gaze patterns alone, whether the child was from a family that used spoken language or signed language at home.

They tested two groups of hearing infants and children that differ in their home language. One "control" group had hearing parents who spoke English and never used sign language or baby signs. The other group had deaf parents who only used American Sign Language at home. Both sets of children had normal hearing in this study. The control group saw sign language for the first time in the lab, while the native signing group was familiar with sign language.

The study, published in Developmental Science, showed that the non-signing infants and children looked at areas on the signer called "signing space," in front of the torso. The hands predominantly fall in this area about 80 percent of the time when signing. However, the signing infants and children looked primarily at the face, barely looking at the hands.

According to the findings, the expert sign-watching behavior is already present by about 5 months of age.

"This is the earliest evidence, that we know of, for effects of sign-language exposure," said Bosworth. "At first, it does seem counter-intuitive that the non-signers are looking at the hands and signers are not. We think signers keep their gaze on the face because they are relying on highly developed and efficient peripheral vision. Infants who are not familiar with sign language look at the hands in signing space perhaps because that is what is perceptually salient to them."

Another possible reason why signing babies keep their gaze on the face could be because they already understand that the face is very important for social interactions, added Bosworth.

"We think the reason perceptual gaze control matures so rapidly is because it supports later language learning, which is more gradual," Bosworth said. "In other words, you have to be able to know where to look before you learn the language signal."

Bosworth says more research is needed to understand the gaze behaviors of deaf babies who are or are not exposed to sign language.

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50 new genes for eye color

 The genetics of human eye colour is much more complex than previously thought, according to a new study published today.

An international team of researchers led by King's College London and Erasmus University Medical Center Rotterdam have identified 50 new genes for eye colour in the largest genetic study of its kind to date. The study, published today in Science Advances, involved the genetic analysis of almost 195,000 people across Europe and Asia.

These findings will help to improve the understanding of eye diseases such as pigmentary glaucoma and ocular albinism, where eye pigment levels play a role.

In addition, the team found that eye colour in Asians with different shades of brown is genetically similar to eye colour in Europeans ranging from dark brown to light blue.

This study builds on previous research in which scientists had identified a dozen genes linked to eye colour, believing there to be many more. Previously, scientists thought that variation in eye colour was controlled by one or two genes only, with brown eyes dominant over blue eyes.

Co-senior author Dr Pirro Hysi, King's College London, said: "The findings are exciting because they bring us to a step closer to understanding the genes that cause one of the most striking features of the human faces, which has mystified generations throughout our history. This will improve our understanding of many diseases that we know are associated with specific pigmentation levels."

Co-senior author Dr Manfred Kayser, Erasmus University Medical Center Rotterdam, said:

"This study delivers the genetic knowledge needed to improve eye colour prediction from DNA as already applied in anthropological and forensic studies, but with limited accuracy for the non-brown and non-blue eye colours."

From Science Daily

Eyes reveal life history of fish

 If you look deep into the eyes of a fish, it will tell you its life story.

Scientists from the University of California, Davis, demonstrate that they can use stable isotopic analysis of the eye lenses of freshwater fish -- including threatened and endangered salmon -- to reveal a fish's life history and what it ate along the way.

They conducted their study, published today in the journal Methods in Ecology and Evolution, through field-based experiments in California's Central Valley. The study carries implications for managing floodplains, fish and natural resources; prioritizing habitat restoration efforts; and understanding how landscape disturbances impact fish.

The technique had previously been used in marine environments, but this is its first use for freshwater fish, many of which are threatened or endangered in California. Lead author Miranda Bell Tilcock, an assistant specialist with the UC Davis Center for Watershed Sciences, helped pioneer the technique for freshwater fish.

"Even the nerdiest fish biologists say, 'You can do what with fish eyes?'" said co-author and team co-lead Rachel Johnson, a research fisheries biologist with NOAA Fisheries' Southwest Fisheries Science Center and associate with the UC Davis Center for Watershed Sciences. "This is an exciting new tool we can use to measure the value of different habitats and focus conservation work."

THE EYES HAVE IT

Much like tree rings, fish eyeballs are archival. The lenses grow in layers throughout a fish's life, recording as chemical signatures the habitats used while each layer was forming and locking in the dietary value of what the fish ate in each habitat.

"It's like a little diet journal the fish keeps for us, which is really nice," Tilcock said.

To uncover that history, researchers perform what Tilcock said is "like peeling the world's tiniest onion." With fine-tipped forceps, they remove layer after layer, revealing a veritable Russian nesting doll of eye lenses. At the end is a tiny ball, like what you'd find in a silica packet, that can shatter like glass. This is the core, where the fish's eyes first began to develop.

Relative to other archival tissue, fish eyeballs are especially rich in protein. The isotopic values in the food webs bind to protein in the eye, leaving tell-tale geochemical fingerprints that isotopic analysis can uncover.

HABITAT IN THE EYES OF THE BEHOLDER

The first field-based experiments using the technique for freshwater fish took place on the Yolo Bypass of California's Central Valley. Here, fall-run, juvenile chinook salmon grew in three distinct food webs: river, floodplain and hatchery.

Scientists then conducted stable isotope analyses on the eye lenses of an adult salmon to reveal its diet history from birth to death. Stable isotopes are forms of atoms that don't decay into other elements and are incorporated into a fish's tissue through its diet. They can be used to trace origins, food webs and migratory patterns of species.

Taking the premise of "you are what you eat," the study's authors looked at the chemical crumbs of carbon, nitrogen and sulfur values in the eye lenses to determine which food webs and habitats the fish used at various life stages.

They found that fish on the floodplain grew quickly and appeared to grow additional laminae, or layers of lenses, during the 39-day study compared to fish reared in the river or hatchery. Also, the Yolo Bypass is home to rice fields, which decompose to add unique sulfur and carbon values -- a strong clue for researchers tracing which habitats fish use.

"This tool is not just unique to salmon in the Central Valley," Tilcock said. "There are many migratory species all over the world that need freshwater habitat. If you can isolate their habitat and value for diet, you can quantify it for long-term success."

For example, co-author and team co-leader Carson Jeffres, field and lab director at UC Davis' Center for Watershed Science, used the technique recently on fish in Brazil to look at changes in the food web there following a dam's construction.

EYES AND EARS WORK TOGETHER

Tilcock, Johnson and Jeffres are part of an "Eyes and Ears" project at UC Davis funded by the California Department of Fish and Wildlife. The project studies fish life history through eye lenses and otoliths, which are found within a fish's ears.

"You use the otolith to trace the river or hatchery where a fish was born based on the unique geology and water chemistry of the tributaries in the San Francisco Bay watershed," Johnson said. "Then you have the eye lens, which tells you where it's eating to help identify floodplain habitats."

"They really work together to present a fuller picture of how salmon move and what they eat as they use different mosaics of habitats across the landscape over their lifetime" said Jeffres. "Now we have the tool we have been looking for to link juvenile floodplain benefits across the salmon life cycle to adulthood. It's the holy grail of measuring restoration success."

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