On August 17th, 2017 we learned about

Chilesaurus diegosuarezi’s plant-digesting gut and the origins of ornithischian dinosaurs

When we first heard about Chilesaurus diegosuarezi, the unusual dinosaur was being labeled as a rare, herbivorous theropod. The creature’s leaf-shaped teeth just didn’t look up to the task of tearing meat compared to the pointed and sometimes serrated chompers seen in most theropods. The was speculation that this strange hodgepodge creature was a weird hiccup in theropod history, but new analysis suggests that C. diegosuarezi wasn’t a plant-eating theropod, but a bipedal ornithischian. If correct, this dinosaur may represent beginnings of the family tree we now associate with Stegosaurus, Ankylosaurus, and various duck-billed dinosaurs like Edmontosaurus.

C. diegosuarezi’s interest in eating plants isn’t being questioned. If anything, it’s thought to be an important factor in why his body has some more ornithischian traits. The big deliminator between theropods and ornithischians is usually the shape of their hip bones. Theropods, both before and after C. deigosaurezi, have what’s been called a “lizard” hipbone, because the pubis bone faces forward like on modern lizards. In contrast, ornithischians have “bird” hips, where the pubis faces backward. It’s all a bit confusing, because modern birds are actually theropods, even with that ornithischian-looking hip bone. With C. deigosaurezi being classified as an ornithischian too, it means that a rear-facing pubis bone must have evolved at least twice— once when the ornithischians first branched off the theropods, then again when with the development of birds.

What pressures moved the pubis bone

This may seem like a lot of arbitrary changes in anatomy, but there are explanations for why they would help each lineage survive. The plant eating of ornithischians would require bigger, more complex guts to digest than chomped flesh would, and so they’d literally need more space their abdomens. A forward facing pubis probably didn’t leave enough room for their digestive demands, giving an advantage to herbivores with “bird” hips.

While we now have birds that eat plant-based foods like nectar and seeds, digestion probably isn’t the reason a crow or sparrow ended up with a rear-facing pubis. In that case, the evolutionary pressure may have been balance. Modern birds don’t have the thick, muscular tails older theropods had, and so as their tails were reduced to the feather-covered stumps we know today, their center of gravity shifted. To avoid tipping over too much, the pubis bone evolved to face backwards, taking a bit of weight with it.

Obviously, C. deigosaurezi’s hips weren’t putting it on the road to flight, but were making room for a bigger tummy. Combined with a mouth well-suited for eating plants, it suggests that adapting to an herbivorous diet was a driving factor in the split between theropods and ornithischians. This then raises questions about what was happening in these creatures’ environment to make plant-eating so enticing that such transitions would occur. Changes in the continents were likely leading to more moisture on land, making the world a much more attractive salad bar, providing options to creatures that were trying out eating more than meat.

Source: One of the Most Puzzling Dinosaurs Ever Discovered Just Got a Major Rebrand by George Dvorsky, Gizmodo

On August 15th, 2017 we learned about

Even the dimmed sunlight from the solar eclipse can pose a danger to your eyes

Odds are that you’ve never directly viewed a solar eclipse, and you probably shouldn’t start any time soon for the sake of your eyeballs. While the eclipse does have interesting effects on our atmosphere, there’s nothing about the Moon blocking the Sun that magically transforms good sunlight into something dangerous. The sunlight is actually always dangerous, but most of the time it’s bright enough to remind us not to try and gawk at it. Even what seems like a small amount of light can be a health hazard to your eyes, so it’s very important to protect your peepers from the sun when things go dark on August 21st.

Our bodies are bathed in sunlight whenever we’re outside, and it’s obviously not such an immediate problem. Most skin can withstand short exposure to ultraviolet light (UV) without too much wear and tear, and our eyes handle the indirect UV light pretty well (although wearing sunglasses is certainly a good idea.) The reason this all compounds when viewing an eclipse is the that you’re looking right at the sun, and that light can be focused through the lens of your eye. Like a magnifying glass focusing sunlight to start a fire, your lenses focus light on the back of your at the retina. The intensity of directly-focused sunlight can quickly damage your cells by creating reactive molecules called free radicals, which then go on to kill the cell.

Safer ways to stare at the Sun

In most cases of this kind of damage, the damage is somewhat limited. The retina will basically be left with gaps where cells have been killed, and you will have a new set of blind spots in your eye to contend with. Sometimes people recover from this damage, but sometimes they’re left legally blind, as they can only see with the peripheral vision that wasn’t torched by the sun.

This isn’t to say that the only way to enjoy an eclipse is to avoid it. While your sunglasses are in no way up to the task of protecting your eyes when viewing an eclipse, solar-viewing glasses are designed to only allow a safe amount of light, meaning around 0.00032 percent of normal sun exposure. Alternatively, you can view the eclipse in the same way you usually take in sunlight— indirectly. A simple pinhole camera will let you safely watch a projected image of the Sun as it gets blocked out, all without staring right into the sky. If you’re looking for a closer look, don’t use your favorite telescope or binoculars unless you have specific filters for that as well, since that’s basically focusing sunlight at your retina even more effectively than your own eye’s lens can do.

My third grader asked: Isn’t the sunlight blocked enough to be less of a problem?

It takes very little sunlight to harm your eyes, especially when it’s being focused into your eyeball. However, once the Moon completely blocks the Sun during totality, it’s recommended that you take off your protective eyewear, as things will otherwise be too dark to see. With luck, you’ll get a peak at the Sun’s atmosphere around the outer rim of the Moon, and this light won’t be coming directly at you to cause harm. As soon as the Moon starts to move out of the way though, get your glasses back on since any direct sunlight can be a problem.

Source: If the Sun Is 93 Million Miles Away, Why Can't We Look Directly at It? by Rachael Rettner, Live Science

On August 8th, 2017 we learned about

The ups and downs of a deer’s annual investment in disposable antlers

For all of the underlying biology we share with other animals, it’s hard to relate to antlers. They grow on heads, but they’re not hair. They’re not the cellular equivalent of fingernails that we find in rhino horns or porcupine quills. Instead, antlers are weird, bony growths that sprout anew every year, demonstrating just how much of a strain and specialization a body can go through in the name of sexual selection.

Exhausting anatomy

An antler starts growing on a deer’s head in early spring each year. Unlike the inert keratin that makes up your fingernails or hair, antlers are made of living cells, and grow inside a fuzzy layer of skin called “velvet.” As the antlers develop over the summer, it’s composed of active blood vessels, nerves and bone cells, all of which can grow up to three-quarters of an inch per day. Keeping this tissue alive isn’t free though, and deer will often have to strip nutrients from other anatomy to keep their growth on track. On top of everything else, it’s an investment that deer make annually, as unlike the horns of rams or rhinos, antlers are shed every year.

Great …or good enough

Theoretically, it’s all worth it though. Deer courtship places a lot of emphasis on antlers both as display structures and weapons. Male deer will butt heads and lock antlers to demonstrate their fitness. Like other famous bits of animal anatomy, bigger antlers help attract and impress mates while staving off potential challengers.

There’s a limit to all that “fitness” though, and studies have found that sporting the biggest rack is not always the most winning reproductive strategy. The increased metabolic demands and risks associated with bigger antlers seems to have given rise to a more subtle population of deer that get by just fine with more modestly-sized head ornaments. The assumption is that smaller antlers are just big enough to catch a mate’s eye without demanding too much upkeep. The fact that they’re less likely to get caught on a tree branch may also help keep their owner alive to try to mate again another year.

Cellular secrets

This isn’t meant to diminish how impressive these head-bones are though. Regardless of an antler’s size, scientists have been studying their cellular properties that let them grow so quickly while also being so resilient. The fibrous structures that compose the bone grow in a staggered pattern that helps them stand up to stress without being damaged. Antlers have been transplanted to other body parts, and even other animals like a mouse, and they keep growing like they were still on a deer’s noggin. Scientists aren’t looking to affix spikes to people’s heads exactly, but the fact that nerves can grow so quickly in an antler may be a model for human therapeutics some day.

My third grader asked: Do only boy deer grow antlers?

Outside of some unusual anomalies, its fair to say that antlers are a male appendage in just about every species of deer. The notable exception is reindeer, as both male and females grow antlers each year. It’s thought that the antlers help females claim territory that might hold precious bits of food. Coupled with a scarcity of predators on the tundra that the deer would need to hide from, it seems that having antlers ends up being a good thing for each and every reindeer.

Source: Antlers Are Miraculous Face Organs That Could Benefit Human Health by Jason Bittel, Smithsonian

On July 27th, 2017 we learned about

Corythoraptor jacobsi appears to connect the cassowary’s head crest to the Cretaceous

An extinct species of dinosaur discovered in China has a lot people thinking about it’s living relative. The fossil remains of Corythoraptor jacobsi were remarkably well-preserved, allowing paleontologists to describe it as something similar to an ostrich and more importantly, a cassowary. In the Cretaceous period, the animal would have stood around five-and-a-half feet tall, topped off with an impressive half-foot of bony crest on its head.  That crest is so similar to what’s on modern cassowaries that researchers have even raised the possibility that the two dinosaur species may be part of a single lineage.

Possible proto-ratite

So what would an ancient, ostro-cassowary be like? Even if C. jacobsi turns out to be a cousin rather than an ancestor to these modern birds, we can still deduce a lot about its life from the fossils alone. This particular specimen was probably eight-years-old, although it wasn’t fully grown yet. It was part of the oviraptorid family of dinosaurs, a group of dinosaurs that generally sported beaks, strong legs and feathers. Those feathers may have never been used in flight though, as they were much fluffier and fringed than the plumage required to fly. Like modern ratites like ostriches, emus and yes, cassowaries, these creatures’ feathers most likely helped with showing off to peers, camouflage, and insulation against heat and cold.

Interestingly, there’s a chance that the tall, flat crest on C. jacobsi’s head served some of those purposes as well. Like a modern cassowary, the crest, or more specifically, casque, wasn’t a solid lump of bone. It was composed of various layers that would have allowed for empty cavities, blood circulation and more. These features suggest a range of uses, including a way to vent heat like a toucan’s bill, show off to potential mates or rivals, and possibly even emit low-pitched vocalizations. Much of this speculation isn’t due to mysteries specific to C. jacobsi’s casque, but that we’re not actually sure what cassowaries do with their heads either.

Figuring out the casque’s function

Cassowaries aren’t easy to observe in the wild, partially thanks to their small ranges in Australia and New Guinea that are difficult to traverse, much less follow occasionally dangerous, six-foot-tall birds. It’s been suggested that their casques protect them from falling fruit, possibly help them dig through loose soil, and vent heat. Their striking appearance is hard to ignore, even among brightly colored plumage and wattles, which begs the notion that they’re a display feature of some sort. Casques are found on males and females, although they tend to be bigger on females which supports the idea of some kind of sexual selection at work. Male cassowaries help with child-rearing, and so both sexes may have reason to be choosy about the health and stature of their partners. Finally, cassowaries are famous for emitting deep, booming vocalizations, and their crests may help them make or possibly hear those calls across long distances.

Understanding the casque on cassowaries and C. jacobsi may end up advancing a few different ideas about dinosaurs. If the value of a good casque can be pinned down, it may help us better understand crests on more distantly related species as well. While head crests were not uncommon among oviraptorids, they’re also found on other groups of dinosaurs, like “duck-billed” hadrosaurs. Of course, there might be more than one use for a huge lump on one’s head, but the resemblance between C. jacobsi and cassowaries raises hopes of a more direct comparison.

Source: Newfound Dino Looks Like the Creepy Love Child of a Turkey and an Ostrich by Laura Geggel, Live Science

On July 18th, 2017 we learned about

Sea spider circulatory systems depend on the digestive tracts in their legs

As a squishy, somewhat elastic human, I don’t have to spend much time thinking about if there is room in my body to accommodate all my organs. If anything, aging has made me more concerned that my abdomen is too flexible about making room for my stomach, intestines and fat. Like many things in life, personal experience shouldn’t be used as a standard against the rest of the world, and indeed there are animals that have succeeded for around 500 million years with the opposite problem. Sea spider bodies are so small and compact that organs we keep in our torso have had to be distributed into the animals’ legs, although rather than suffering or complaining, this unusual arrangement has been leveraged to create a very efficient body plan.

A sea spider isn’t a spider, or even an arachnid, but it does bear a strong resemblance to spindly spiders like a daddy long legs. In fact, with the proportion of their body mass that is actually leg, they may be more deserving of the “long legs” moniker than the spiders. In many species of sea spider, the legs come together at a body that seems to be just big enough to act as a hub for those limbs— there’s hardly any differentiation between the thorax and abdomen, and heads are often just big enough to carry eyes, mouth parts and some eyes. As such, the legs don’t just literally carry the body, but also carry many biological duties we normally associate with bulky midsections.

Fully-loaded legs

While the sea spider bodies are minimal, their legs handle a lot of different functions quite well. They help with respiration by creating a lot of surface area for oxygen to diffuse into the body from the surrounding sea water. They also carry their sex organs in their legs, releasing eggs and sperm through small pores in their “thighs.” Tiny torsos don’t allow enough space for an effective digestive tract, and so the legs also hold coils of the arthropod’s intestines. Fluids are sucked out of sea anemones and sponges, then pumped through each leg in as the digestive organs squeeze and contract. Our guts do this too to an extent, but as invertebrates, sea spiders have exoskeletons that their guts have to push against from the inside. So rather than flexing and expanding, each gut contraction has to squeeze other fluids up or down to make space in the cavity of the leg.

This might sound awkward at first, but sea spiders have been found to use these contractions for two functions. Aside from moving food through a digestive tract, the other fluid that gets squeezed up and down has recently been found to be hemolymph, or the sea spider’s equivalent of blood. This means that the animal’s undersized heart only needs to serve the head and torso, while the legs’ circulatory needs are taken care of thanks to contracting guts. This not only saves space in the body, but also saves energy, as the heart doesn’t need to work nearly as hard to get blood moving down and back through each long limb.  As weird as it sounds, it’s a successful enough system to helped sea spiders find homes in oceans all around the world.

My seven-year-old nephew asked: So if I stepped near a sea spider, would it try to bite me?

Probably not, and if one did, you probably wouldn’t notice. Many species are tiny, and their piercing mouth parts probably couldn’t get through your skin. The largest species, Colossendeis megalonyx, can grow to three feet across with a proboscis as long as a finger, but they’re still basically benign creatures that wouldn’t behave aggressively about your feet. Also, as this species lives in deep water under the Antarctic ocean, chances are you wouldn’t be walking near it in the first place.

Source: Sea Spiders Pump Blood With Their Guts, Not Their Hearts by Ed Yong, The Atlantic

On June 28th, 2017 we learned about

Mice map their world by scanning space with their whiskers

You’ve probably never tried to navigate through a dark room by bumping your face into things. At least not on purpose. Instead, you most likely extended your arms slightly, so that your fingertips could gently come in contact with objects as you walked along. With each bump or poke, you not only felt contact in a specific finger, but you also started building a conceptual map of the room. This somewhat clunky process may be just good enough to get you to the bathroom in the middle of the night, but it’s hugely important for an animal like a mouse. So much so that they even do it with their face.

Not every part of a mouse’s face is that useful for crawling through dark nooks and crannies though. Their eye’s aren’t great at focusing on objects close to their head, which means that a lot of information is needed from the mouse’s 24 whiskers along its snout. While lots of mammals rely on whiskers to help sense their local environment, researchers have found that the way mouse brains use that information goes beyond what your average cat or dog will do. Instead of just perceiving contact from a specific whisker, that input also triggers special structures in the mouse’s somatosensory cortex called barrel columns, which go on to start building mental maps of the mouse’s environment.

Sensing touch, as well as empty space

Researchers were able to watch this activity in multiple layers of a living mouse’s brain at once. Brain cells were cultured to be fluorescent when active, revealing a few stages of activity when a mouse brushed by a small stimulus on one side of it’s head. One layer of the cortex seemed to only keep track of which whisker felt something, much like you know which finger touches something when you can’t see it. The other layers took the movement of the whiskers as if they were scanning the space around that stimulus— even the empty space was providing some feedback, beyond the moment of contact. Humans scan spaces to build mental maps too, but most of our input comes from visual information. For a mouse crawling in the dark, the whiskers seem to be the more reliable source of data.

The next step is to see how much detail mice can really get from their scanning whiskers. Can they recognize specific objects? How is that information processed so that further actions, like hiding or pouncing, take place? The complete picture won’t just help with understanding how cool mouse faces are, but also to build a model of this kind of brain activity in all mammals. We know that our hands can do some to the work these whiskers take on, so seeing what a mouse brain “sees” may provide insight on human brain activity too.

Source: A mouse’s view of the world, seen through its whiskers by Robert Sanders, Berkeley News

On June 15th, 2017 we learned about

Garganornis ballmanni, an extinct waterfowl with wings suited for fighting, not flying

As cool as it must be to soar through the sky, history has plenty of examples of birds who gave up flight altogether. Even ignoring extremes like a hummingbird’s 70 wing-beats per second, getting a body off the ground requires a lot of specialized muscles and the energy to use them. For all the ways that flying seems like it might be fun or useful, researchers are finding that avoiding predators is the biggest motivation to continue leaving the ground. If a species finds itself where that mobility isn’t necessary, it can free up those resources for other pursuits, like beating rivals around the head with their wings.

Grounded goose

Six to nine million years ago, Garganornis ballmanni lived on islands in the Mediterranean Sea. It resembled a goose, but dwarfed all but the largest modern relatives, standing around five feet tall and weighing 48 pounds. With no predators to worry about, the massive bird probably behaved more like a terror bird than today’s bread-nibbling waterfowl, free to stomp through island forests as it saw fit. The only check on these big birds were other members of G. ballmanni, all of whom were armed with shorter wings outfitted with carpal knobs- hardened knobs of skin often used in bird-on-bird skirmishes.

Aside from the carpal knobs, the overall proportions of G. ballmanni support the idea that these animals ancestors traded flying for fighting. The overall weight of the bird may seem like the key giveaway, but weight alone doesn’t determine if an animal can fly— even a 550-pound Hatzegopteryx thambema was still able to fly. The real clue here was G. ballmanni‘s proportions, as large legs and shorter wings have been found to be the best skeletal clues for determining which birds could fly, and which couldn’t.

Predicting flight with limb proportions

A separate study of waterfowl looked at those proportions very closely to ensure that this model made sense. G. ballmanni isn’t the first waterfowl to have abandoned flight, and so 103 modern species were carefully measured to see which anatomy best predicted being grounded. The wing and leg bones were the stand out features, correctly predicting which species can and can’t fly. From there, the experiment was expanded to check some other extinct species, finding that five out of 16 extinct ducks and geese were likely to be flightless as well.

With these models, and further examples like G. ballmanni‘s weaponized wings, researchers have more tools to figure out what these extinct birds’ lives were like. In the case of G. ballmanni, being flightless on an island helps fills in some gaps about the pressures of their world— being grounded probably meant the big birds were pitted against each other hold territory, all in order to have access to fresh water on their island getaway.

Source: Fossils from ancient extinct giant flightless goose suggests it was a fighter by Bob Yirka, Phys.org

On May 25th, 2017 we learned about

Many possible benefits of bird-like air sacs in super-sized sauropods

Sauropod dinosaurs, the long-necked herbivores that were the largest animals to ever walk on Earth, apparently got that big by padding their size a bit. They certainly grew thick, column-like legs to support bodies that in some species were as large as 77 tons, long necks and tails that stretched over 100 feet end-to-end, but they may have achieved those sizes thanks to a fair amount of hollow spaces inside their bulky bodies. These spaces were likely similar to the air sacs found in modern birds, and they raise a number of possibilities as to how these huge dinosaurs made use of them, since it’s safe to say they weren’t about to go airborne like your average sparrow or parrotlet.

Finding space for additional air

Like the muscle and organs of any of these sauropods, we’ve never seen these air sacs “in the flesh,” because that flesh decomposed over 65 million years ago. We do have many sauropod bones though, and the vertebrae in particular bear strong structural similarities to the hollow bones found in modern birds. In a bird, sauropod or even pterosaur, hollow bones would be a way to keep a bone’s strength while decreasing its weight, something no animal would likely complain about. Since birds are part of the dinosaur lineage, this isn’t shocking, but it wasn’t a given since sauropods would be one of a modern bird’s more distant relatives when compared to a two-legged theropod or even other four-legged herbivores. That said, researchers are seeing that these hollowed out bones not only lightened the load for big bodies, but they also look like they had attachment points for organs called air sacs, which offer an array of uses to a massive dinosaur.

In modern birds, air sacs primarily facilitate very efficient breathing. In something like a chicken, there are sacs in the front and back of the body, attached to the spine, and they allow air to continuously circulate for constant respiration, versus the discreet inhalation and exhalation humans and mammals use. This is great for a bird that needs to be flying a lot and burning a lot of energy in the process, but for massive and presumably less-active herbivore, was this kind of respiration really necessary? These huge dinosaurs likely required a lot of food already, and a very active metabolism would have only made things trickier.

Air sacs as air conditioners

Fortunately for our inflated sauropods, air sacs don’t require a “red-hot” metabolism, and may have actually provided some options for cooling a body as well. On one hand, being lighter meant that a big sauropod would have had to work less to move its body, generating less metabolic heat in the process. Additionally, the constant respiration of birds’ air sacs also allow them to effectively dump heat through their breath, exhaling warmed air like a swamp cooler. The combination may have been a compelling advantage to these big dinosaurs, even if they never needed to worry about sprinting or flapping wings.

The most extreme example of a sac-filled sauropod to date is Katepensaurus goicoecheai, a largish rebbachisaurid from South America. Katepensaurus lived in the Cretaceous period, after the heyday of most sauropod species.The climate at that time was especially warm, and so there is speculation that the unusual number of air sacs found in Katepensurus‘ vertebrae may have been an adaption to help the dinosaur beat the heat while being big. However, other sauropods living around the same time don’t turn up with the same specializations, hinting that the heat may not have been a widespread problem. In which case, maybe this sauropod was just looking to be as light and nimble for a good run? As with many things surrounding dinosaurs, the answer may have to wait until more fossils can be found.

Source: Secret Air Sacs Made This Dinosaur Extra Light by Brian Switek, Laelaps

On May 21st, 2017 we learned about

Directional microphones may not be able to match the aural acuity of this parasitic fly

A very important feature of your ears is the space in between them. That’s because a lot of the information you gather about sounds in the world around you gleaned from comparing how they differ from one ear to the other. The 100 milliseconds it takes for a sound to travel past one ear to reach the other, known as the interaural time difference, is automatically processed by our brains to help us determine the spacial source of a sound. That way, you can find where a creak, beep or cry is coming from, or in the case of Ormia ochracea, a male cricket so you can deposit a lethal larva into it’s body.

Hearing potential hosts

Ormia ochracea is a yellow, nocturnal fly, no bigger than your fingernail. At night, females fly through the dark, navigating by their hearing to find male crickets chirping for mates. The female flies are interested in reproduction too, but they’re after the crickets as hosts for their larvae, which will eat their way out of the cricket a few days after being implanted. In broadcasting for a mate, the unwitting bachelors give away their location to the flies, although if you’ve ever had a cricket in your house you’ll know how hard it can be to really locate a hidden cricket, interaural time differences and all.

The flies can do it though, as they have some of the most sensitive directional hearing in the world. Instead of using ears on their head, they use sound-sensitive structures on their front legs (which is similar to the “ears” of a cricket.) A point of interest to researchers is that these membranes are so close together that sound hardly has time to be separated before it passes from ear to ear, so any kind of interaural time comparisons have to be made on a nanosecond timescale. This is of great interest to  engineers designing directional microphones for small spaces, such as hearing aids, but it has also revealed a considerable weakness in the fly’s hearing.

Linked, but more limited

To help calculate the direction of a sound, the fly’s ears two-part structures, coupled in the middle. That coupling means that comparisons between incoming sounds can be made instantly, as sound hitting one side mechanically triggers activity in the other. The fly’s brain gets a clearer one-two signal to process, letting it pick apart these minuscule differences in stimuli. However, that same solution makes the flies very vulnerable to louder, distracting noises. A loud noise in one ear can essentially knock out the second ear, as both end up vibrating. In lab tests, distracting sounds could pull flies off their path towards a cricket, apparently unavoidably.

Researchers now need to figure out how these O. ochracea handles loud noises in the wild, or if noise pollution poses more of a threat to their reproduction than was previously appreciated. Assuming they can somehow cope with distracting sounds, recreating that feat would enable better microphones, radar and other sound-sensitive technologies that we need to pack into spaces the size of fly legs. Until that can be determined, this supremely-accurate hearing remains on our biomimicry wishlist.

Source: This parasitic fly’s incredible hearing remains a curiosity to those trying to develop better hearing aids by Don Campbell, University of Toronto

On April 4th, 2017 we learned about

Frogs’ and toads’ color vision found to function in near total darkness

It may not be easy being green, but frogs, toads and other amphibians may have a a very easy time seeing green. Biologists have have noticed unusual properties in the light-sensing cells in amphibian eyeballs as far back as 1877, but it’s been unclear exactly what difference that made in the animals’ lives. With an accumulation of data on both anatomy and behavior in the intervening centuries, scientists from Lund University have some new answers about frogs’ and toads’ unusual eyes. Through a series of experiments, it seems that these amphibians are able to not only see, but discriminate between colors in nearly perfect darkness.

Frog, toad and even human eyes depend on two types of light-sensing cells to take in visual information. Cone cells pick up light for specific colors, and rod cells are tuned to values of light and darkness. In low light conditions, such as under moonlight, cone cells can’t really keep up, and our vision defaults to a desaturated, nearly grayscale world as seen by our rod cells. The collective group of anurans (frogs and toads,) as well as a few salamanders and newts, have specialized rod cells though, which seemed to have special sensitivity to green or blue portions of the light spectrum. However, knowing what the anatomy was capable of didn’t prove that these animals actually made use of these cells in that capacity, and so a series of tests was required to see if the frogs were as appreciative of their ability as researchers were.

Blue beauties

The first test hinged on the idea that toads like Bufo gargarizans had previously shown a preference for bluer mates, and were willing to demonstrate this preference in a lab setting. Males were given the option of different potential mates in varying lighting conditions to see if they could remain true to their blue preferences in relative darkness. It would seem like mate selection would be important enough to make the right choice, but as the lighting got worse, the toads apparently couldn’t see the difference too well, accidentally lowering their standards up to a point. When things were too dark, the toads actually refused to select any mate at all.

Green grub

The second test looked at food preferences, with frogs and toads being placed in a simple Y-shaped maze, with each path leading to a different bit of fake food. The “flying insect” they could see was fake so that its coloration could be controlled as either blue or green, although real meal worms were made available if the test subject chose the greener option. Anurans had been previously proven to be trainable in such a test, and so now the promise of meal worms was used as motivation to pick pay attention for green as a cue.

The toads seemed to understand the program rather quickly, and showed some preference for green bait. Even with low-light conditions, members of Bufo bufo could pick “correctly.” The Rana temporaria frogs were much more confusing, not even picking a preference in brighter light. Eventually, researchers realized that the frogs were aiming for the darkest bait, no matter the color. Once that was understood, it was at least clear that the frogs were consistent in this preference in just about any light condition.

Leap to the light

If the first trials weren’t terribly conclusive, the final test finally let the anuran’s low-light abilities shine. Each animal was placed in a black bucket, with a lid on top. That lid had windows that would allow either blue or green light to enter the bucket once a light source was placed above it. As found in previous experiments, the frogs were expected to move towards bluer light, presumably as they would move towards the sky to exit a hole they needed to escape from in the wild.

As light levels changed, the frogs complicated things slightly. In very low light, they moved towards green light, and then in brighter conditions switched to blue. Researchers suspect that the frogs are not only discriminating between colors, but demonstrating how they would be useful in the wild (since bugs and mates apparently don’t matter as much.) At night, most ambient light is more likely to be on the red to green end of the color spectrum, so the frogs were responding appropriately to what they maybe thought was a night sky. Brighter conditions made more sense as a daytime sky, which the frogs responded to as the light increased.

Even if this isn’t the true motivation behind this behavior, researchers did find that the frogs were making these choices with incredibly tiny amounts of light hitting their eyes. They were picking up green and blue at the “absolute threshold of the visual system,” in near total darkness. So earlier hypothesis about amphibian eyes were basically correct, but with the caveat that these animals seem to rely on this ability only in very specific circumstances.

Source: The dual rod system of amphibians supports colour discrimination at the absolute visual threshold by Carola A. M. Yovanovich, Sanna M. Koskela, Noora Nevala, Sergei L. Kondrashev, Almut Kelber, Kristian Donner, Philosophical Transactions of the Royal Society B: Biological Sciences