Tastes like Chicken?

Jlhopgood, CC BY-ND 2.0 (adjusted).

Birds evolved from dinosaurs 165 million to 150 million years ago. Of all the birds in the world, the one that shares the most DNA with the ancestor of all birds is…the chicken! This means that the closest living relative of the dinosaurs is the chicken.

But that doesn’t mean Tyrannosaurus rexes tasted like chicken, which is unfortunate since the Kentucky-fried drumstick would have been larger than you are. Taste is determined by other factors, such as what the animal ate and how much fat is in the meat. Those using their muscles slowly for extended periods (like cows and most larger animals) have red meat, while those who used them twitchily for short periods (like cheetahs, chickens and most smaller animals) would have white meat. Contrary to popular opinion, pigs and humans have red meat. But more to the point, predators, and scavengers tend to taste gamey. T. Rex was both, so would have had very strong-tasting red meat. But some smaller vegetarian dinos may have tasted like chicken.

The chicken or the egg?

Also, if anyone asks you which came first, the chicken or the egg, say “the egg”. Eggs have been around for about 600 million years, while chickens have only existed for about 10,000 years. All female vertebrates have eggs. The earliest external eggs with shells evolved in diapsids, an ancestor of reptiles, roughly 350 million years ago. Our synapsid ancestor split off not long before this from the shared ancestor of mammals, reptiles, and birds. All of the subsequent dinosaurs laid eggs, so the egg came before them as well.

Fossilized dinosaur eggs. Gary Todd.

 

Hard-shell eggs are important because it allows reptiles and birds to live completely on land, while the older amphibians are still tied to water for laying their eggs. It’s the same for the few fish that are able to live out of the water, like mudskippers.

Looking at the question from the point of view of an individual chicken, then again that chicken’s egg came first. If you look at it metaphorically, this conundrum is intended to point out the futility of trying to determine the cause of self-perpetuating cycles. It can be puzzling at first, but ultimately fails because the cause can be determined.

If you change the question to, “which came first, the chicken or the chicken egg?” then it becomes a bit tricky because you can’t have a chicken egg unless you have a chicken. The problem then becomes was there a first chicken? Animals are constantly evolving, going through intermediate stages before they gain the set of features that taxonomists use to determine whether an animal is a new species.

It’s all a bit messy because taxonomy tries to force animals into artificial categories. Before the chicken, there was a bird classified as something else, and as it evolved into a chicken there would have proto-chickens, or those who were partially ancestor and partially chicken. There isn’t a clean break between the two. You don’t have a situation where the parent is not a chicken, but the offspring are.

But for the sake of argument, let’s just say there was one particular feature that suddenly evolved that made one individual a chicken. Then its egg would have come from a non-chicken, but it’s the egg that the chicken embryo developed in, so which would it be? Either the non-chicken laid a chicken egg or the chicken developed in a non-chicken egg. The answer depends on the features of that particular egg, so we’ll never know. It would have had to have been caused by a single DNA mutation, but evolution usually works gradually over the course of many mutations, so there probably a first chicken.

To explain this in another way, there are salamanders in California that live around most of a lake. They live on the north and south sides and are one continuous community that connects along one side of the lake. Those in the north look different from those in the south and the two won’t breed with each other, but the community breeds all the way along the lake.[1]

Are they two species or one? Or are they in the process of becoming two species? Because of the connection along the side, they’re still considered to be one species, but if that connection is broken, the middle salamanders will become one or the other and there will be two. It’s isolation that usually causes a species to gradually separate into two, but the key is “gradually”. It doesn’t usually happen overnight.

Taxonomy is a very useful tool, but it has its flaws and you can’t fit nature into pigeonholes. The flaws become much more apparent when you look back in time, since lineages of animals blend into one another, which is why looking for “missing links” doesn’t make sense. All animals are links on the way to becoming something else—unless they go extinct. What that something else is will depend on how taxonomists decide to pigeonhole animals in the future.

Getting back to chickens and dinosaurs: While chickens are the dinosaurs’ closest living relatives, the few available fossils suggest the earliest birds looked more like a loon, but honked like geese.[2]

And one last thing, there are now 22 billion chickens on the planet, so they outnumber us three to one. On the other hand, people are working hard to eat as many of them as we can.

 

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If you'd like to comment, please email me at John@AWondrousWorld.com.

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[1] Robert A. Wallace, Jack L. King, and Gerald P. Sanders, Biology: The Science of Life, Glenview, IL: Scott, Foresman & Co., 1981, pp. 388-90.

[2] Jeff Hecht, “Goose-like birds survived the dino wipeout”, New Scientist, no. 3149, October 28, 2017, p. 9, and a longer version as “Geese-like birds seem to have survived the dinosaur extinction”, https://www.newscientist.com/article/2151059-geese-like-birds-seem-to-have-survived-the-dinosaur-extinction/, citing Federico L. Agnolín, Federico Brissón Egli, Sankar Chatterjee, Jordi Alexis Garcia Marsà, and Fernando E. Novas, “Vegaviidae, a new clade of southern diving birds that survived the K/T boundary”, The Science of Nature, vol. 104, p. 87, October 7, 2017, https://dx.doi.org/10.1007/s00114-017-1508-y.

 

How Far Can a Dung Beetle See?

A dung beetle atop a ball of dung it made. Bernard Dupont, CC BY-SA 2.0.

How far can a dung beetle see? You’d probably think they can see a few feet or a few dozen feet (or a few dozen meters) at the most, but this is a bit of a trick question.

The Ancient Egyptians considered scarabs—one species of dung beetle, Scarabaeus sacer—to be sacred. Dung beetles are also famous for rolling manure into a ball larger than themselves and pushing it across the landscape with their hind legs to bury in a hole where they lay their eggs, since dung is what they eat. Periodically during this excursion they stop to crawl on top of the ball and do a little dance.

What they are actually doing is using clues to navigate. These signs include their surroundings, the sun, polarized light from the moon, the orientation of the Milky Way, and some star clusters. Much like us, the relatively small dung beetle can see some of the galaxy we live in.

The farthest stars we can see with the naked eye are about 16 thousand light years away, but we can also see the collective light of the Andromeda Galaxy, which appears as a faint cloud and is 2.5 million light years from us—that’s 13 million trillion miles (21 million trillion km). Theoretically we could see a supernova that’s 13 billion light years away, if it’s bright enough. How far into the Milky Way we can see is difficult to say, but a dung beetle can at least see enough of it to orient itself—perhaps a couple of thousand light years. The beetles see stars as fuzzy blobs, but the light is brighter to them since they’re more sensitive to dim light than we are. Nearly every animal can see the sun, which is only eight light-minutes away—about 93 million miles (150 million km).

You can see that it’s not really the distance that matters, it’s how bright the light source is, but since our rods can detect a single photon, if that photon comes from across the universe, that’s technically how far we can see.

Besides dung beetles, some birds also use the stars and constellations to navigate.

At the other end of the spectrum, about the smallest things we can see are the largest bacteria. Pea aphids can use their eyesight to avoid a type of bacteria that is deadly to them. They have no defense against this bacteria and will die if infected. The bacteria lights up in ultraviolet and the aphids can see this, so they avoid it like the plague.[1]

Our relatively complex eyes evolved slowly over hundreds of millions of years. Many early types of eyes still exist in some animals and they range from patches of photoreceptors to cup-shaped dents to pin-hole camera-like eyes to eyes with lenses and retinas. The more primitive forms of sight can only detect the presence and absence of light. As sight became more advanced the animal could tell the direction of the light, then came the ability to make out shadows, and resolution gradually improved. Some creatures gained the ability to see color, ultraviolet, infrared, polarized light, and—in the case of the mantis shrimp—circular polarized light.

Our way of seeing color using receptors in our eyes may not be the only way. Some non-mammalian vertebrates, like fish, detect brightness and colors using receptors in their pineal glands in their brains, although it’s not yet known if or how this affects vision.

While we tend to look at this as a progression from the primitive to the advanced, that’s not the case. That implies eyes evolved towards a goal, which doesn’t happen. Evolution only makes random changes—it tinkers, if you will—and the changes that work better are usually the ones that survive. Mutations modify what is already there and natural selection causes bad mutations to vanish, while the good ones spread through a population. Each creature’s eyes adapt to its own needs and environment. If an advantageous mutation appears in one lineage, it won’t appear in another unless it develops independently or, in very rare cases, crosses over through horizontal gene transfer.

While more advanced eyes progressed through various stages, that doesn’t mean only advanced animals have them. There is a protozoa that appears to contain an eye with a lens and a retina. Nature is unpredictable. The eyeless roundworm C. elegans has photoreceptors that are 50 times better at catching light than ours are. At some point geckos or their ancestors lost their rods, so their cones evolved larger and are now 350 times more sensitive to light than ours.

Our eyes work pretty good in a generalized way. Birds seem to be able to detect colors better than us. Eagles and other birds of prey can see much sharper at farther distances than we can. If we had raptor vision we would be able to stand on top of a ten-story tall building and see an ant walking on the ground. And you could read this book from the other end of a football field. They have sharper vision because their foveae are deeper than ours, acting as a telephoto lens. They actually have two foveae that are denser with receptors with thinner capillaries in front blocking less of the view, as their retinas are backwards like ours. It’s thought that the central foveae is for seeing prey in the distance, while the other is for focusing close up.

But there’s a trade off. Eagles have sharper vision because their photoreceptors are smaller and densely packed, but this has reduced their sensitivity, so they can’t see much at night.

At the other end of the spectrum, many animals, such as lions, hyenas, cats, and dogs, have sacrificed distance acuity and some of their color vision to be able to see well at night, though they’re probably sensitive to movement in the distance. And some prioritize close-up vision. If you had the eyes of a rhesus monkey, you could read this if it was less than an inch in front of your face. According to Phillip Pickett, a veterinary ophthalmologist at Virginia Tech, on a scale of one to ten, with rats at one and raptors at ten, our vision would be about a seven.[2]

Many top golfers, including Tiger Woods, Vijay Singh, Fred Funk, and Zach Johnson, improved their vision to 20/15 or better by getting laser eye surgery. Baseball legend Pete Rose once described how when batting he could tell each type of pitch by how the ball looked. For example, he said a slider looked like white circle with a red dot in the middle, because of the way the red stitches on the ball were spinning. Remember, these were balls that were approaching him at nearly a hundred miles per hour.

As far as I can remember, I was nearsighted from a very young age. I remember, when in high school I first got glasses, being totally amazed that I could see individual leaves on trees. After getting tired of dealing with glasses and contacts, I got laser surgery—once in one eye and three times in the other because of some complications. I lost some close vision, but we lose that as we age anyway. It was amazing to suddenly be able to see so clearly. It’s been twenty-five years and I can still see clearly farther than anyone I know, though I now have more trouble close up. I occasionally point out ships or whales leaping on the horizon that my friends can’t see. But I’ll never see as well as an eagle, even though my eyes are larger than theirs.

Much of what is good about our vision comes from our foveae. Even though they make up a tiny portion of our field of view, they provide our brains with more than half of the visual information. Primates have foveae, as do some fish, reptiles, and birds—such as chickens—but most other animals don’t have them. Our foveae give us sharp color vision, but it’s slow, which is why we can’t see the flicker of TV, computer, and cell phone screens, while other animals can.

Eyes have been evolving for around 700 million years. Theoretically, the most advanced eyes could have evolved within half-a-million years, but because of the meandering routes taken, it actually takes much longer. Since eyes are very useful for survival, it’s not surprising that they’ve evolved many times. In fact the various types of eyes have evolved independently between forty and sixty times in a wide variety of animals, using nine different optical principles, including pinhole eyes, several kinds of compound eyes, two types of camera-lens eyes, and curved-reflector eyes.[3] Green algae have eyespots good enough to make out a vague image of their environment. Some mollusks have eyespots with spherical lenses. Scallops and limpets have reflecting mirrors behind their retinas—much like cats and owls. The marine copepod Pontella has an arrangement of three lenses, while another copepod, Copilia, has two lenses arranged like a telescope. Our eyes also have two lenses, but one is fixed and the other adjustable. Chameleons have eyes like telephoto lenses.

When you think about it, vision is a pretty amazing sense—to be able to discern things off in the distance. Our other senses have ranges that are quite a bit closer to home.

Weird Senses

Fruit flies have a structure between their eyes that both hears and smells…and it swivels. So, would you say they smell by rotating their ears, or do they hear through their nose? Or both?

The star-nose mole’s nostrils are surrounded by 22 short tentacles that sense electric fields arising from sweat or mucus on the skin of their prey—usually worms—buried in earth or mud. Its tentacles are about five times as sensitive as our fingers. This electric sense is usually found in fish, although the fish don’t have tentacles.

Giant squid and colossal squid have eyes the size of basketballs, but their bodies are about the same size a large swordfish—about the size and weight of five men—yet a swordfish’s eye is only about the size of a softball. One hypothesis for this is that the squids’ large eyes enable them to detect the faint glow of bacteria in the distance being disturbed by a sperm whale that is coming to eat the squid for dinner, the whale having picked up the squid on its sonar. Being able to see that faint glow warns the squid it’s time for evasive action, which is difficult since it has no where to hide and the whale swims faster, though it’s not as maneuverable.

Crabs smell with their feet, which may be a good thing since they pee through their heads near the base of their antennae. That’s after they run it through their gills to extract extra salt.

And Japanese swallowtail butterflies (Papilio xuthus) have eye-spots on their genitals enabling them to see what they’re doing, and both males and females have a very difficult time reproducing without them.

 

Go to my index of posts to see more. 

If you'd like to comment, please email me at John@AWondrousWorld.com.

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[1] Cornell University press release, “Aphids use sight to avoid deadly bacteria, could lead to pest control,” ScienceDaily, September 27, 2018, https://www.sciencedaily.com/releases/2018/09/180927135145.htm, citing Tory A. Hendry, Russell A. Ligon, Kevin R. Besler, Rachel L. Fay, and Melanie R. Smee, “Visual Detection and Avoidance of Pathogenic Bacteria by Aphids”, Current Biology, 2018, https://doi.org/10.1016/j.cub.2018.07.073.

[2] G.C., “Who’s Got Good Eyes?”, Discover Magazine, August 2001, p. 53, and as James Smolka and Gregory Cerio, “Artificial Sight”, July 31, 2001, https://www.discovermagazine.com/mind/artificial-sight.

[3] Richard Dawkins, “Where d’you get those peepers?”, New Statesman & Society, June 16, 1995, vol. 8, pp. 29.

An exceptional explanation of the many different types of eyes and how they evolved can be found in Richard Dawkins’ book Climbing Mount Improbable.

 

They Have No Eyes But Sight

 

A brittle star on an octocoral skeleton. They climb to get higher in the current. NOAA.

Most creatures have some way of perceiving and responding to light. Many can do it without having any eyes.

Brittle stars have photoreceptors scattered across their bodies. Some can only tell whether they’re in light or darkness, but others can detect different contrasts of light, enabling them to seek shelter under a dark shape in the distance. Sea urchins can also see without having any eyes. They have clusters of photoreceptors in their tentacle-like tube feet and use their own shadows to discern the direction of light.[1]

Similarly, the hydra can see without eyes. This freshwater predator is basically a tube-shaped stalk with tentacles on one end. They can grow up to two inches in length (5 cm), but can stretch themselves to eight inches (20 cm). They use their minimal sight to detect and shoot their prey with harpoon-like stingers.

Scorpions have eyes, but they can also detect ultraviolet light with the waxy cuticle covering their bodies, making their exoskeleton a sort of eye. Creatures that can see with their skin include octopuses, a chameleon, a gecko, a wall lizard, a sea snake, a fish, a pond snail, a caterpillar, new-born pigeons and rats, and fruit flies. Even earthworms can detect light with photoreceptors in their skin. We do too, although we’re not aware of it. These receptors launch immediate repairs when our skin becomes sunburned.[2]

I See You

Many animals that we wouldn’t expect to be able to see, actually do have eyes. Chitons, the tide pool mollusk that looks like a flattened slug protected by a series of eight armored plates, have hundreds of tiny eyes built into their shells that have retinas and aragonite crystals as lenses. This relative of limpets and abalones can actually see the shadow of an eight-inch fish (20 cm) that’s six and a half feet away (2 m). And these are animals that mainly consist of a snail-like foot that can grip rock faces. Their brains are just a simple ganglion—a group of neuron cell bodies—but on seeing an approaching fish, the chiton clamps down on the rock. Even though these eyes seem primitive, they evolved in just the last 10 million years, so they’re pretty new, evolutionarily speaking. Other chitons that don’t have lenses or retinas are still able to detect small changes in brightness.[3]

Some species of starfish have between five and 50 eyes that are on the tips of their arms. They only see in black and white, but, judging from the position of their eyes, it’s likely they can see all around them for a distance, detecting things up to a dozen feet (nearly 4 m) away, including the surface of the water and whatever is right in front of them. They most likely use their sight to stay on or near the reef.

A scallop with blue eyes and a close-up from another scallop. Top: Rachael Norris and Marina Freudzon. Bottom: Matthew Krummins, CC BY 2.0.

Scallops also have dozens of eyes—some have 200 of them—that protrude from their mantel between their shells. They move around a lot, so their eyes are quite useful. Oysters and mussels don’t have them, but then they’re mostly immobile. Scallop eyes are on the end of tentacles and protrude from under their mantle in a line along the edge of each of their shells. Some have red eyes, but many have blue eyes. Their eyes also have pupils that expand and contract simultaneously. Light passing into one of their eyes reflects off of a curved mirror and onto two retinas that detect different things, but it’s thought they’re mostly looking for movement. When they see large enough particles drifting by, they open their shells to investigate, probably by using their sense of smell.

Scallops can detect large objects, but their visual system is so slow that it’s probably not much use in detecting predators. Although the eyes of one species—the venomous crown-of-thorns starfish (Acanthaster planci)—are good enough to see predators. They also use their sight to hunt for prey, and they’re fast enough to chase it. It’s possible that all sea stars with eyes can detect the bioluminescence of other nearby starfish and they might even be able to communicate with each other using flashes of light.[4]

Even box jellies, which are nearly transparent, have 24 eyes distributed among four eye stalks. With eight of their eyes, which are similar to ours, they can probably see silhouettes at least 26 feet (8 m) above the water. This helps them hunt prey and the navigate mangrove swamps they sometimes live in.[5]

Scientists have found thousands of creatures that produce their own light. They include fireflies and mushrooms, but most of them live deep in the ocean, such as some sharks, fish, jellies, crustaceans, and octopuses. It’s thought that 80 to 90 percent of sea organisms luminesce. These creatures use light to communicate, attract mates, attract prey, camouflage themselves, ward off predators, and to attract bigger predators that eat their predators, among other things. The lights range from blue to green, but in barbeled dragonfish it can be red. Bioluminescence has evolved independently at least 50 times. Genetic engineers have transferred the ability to glow in the dark to other creatures, such as plants, marmosets, rabbits, cats, and dogs.

Oysters don’t have ears, but they hear sounds through a different organ called a statocyst. We don’t know how things sound to them, but it probably wouldn’t be like how our brains interpret sounds. Still, they can hear breaking waves, water currents, the approach of predators, thunderstorms, and they’re particularly sensitive to man-made noise pollution. They use the sounds to decide when to clam up, feed, and spawn. Also, oyster larva navigate towards the sound of snapping shrimp, which helps lead them to reefs. Scientists found that mussels and hermit crabs can also hear[6], and there are likely many other sea creatures that can. We don’t yet know how noise pollution affects them[7], but it can destroy the statocysts in octopuses, squid, and cuttlefish, making them permanently deaf and unable to move or hunt—effectively killing them.[8]

Also, since many people like to eat them alive, we can imagine what that experience might be like for them. Just as we can’t know what it’s like to be a bat. We may never truly know, but we can get a better idea the more we learn about them.

 

Go to my index of posts to see more. 

If you'd like to comment, please email me at John@AWondrousWorld.com.

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[1] Ed Yong, “Sea urchins use their entire body as an eye”, National Geographic, May 2, 2011, https://www.nationalgeographic.com/science/article/sea-urchins-use-their-entire-body-as-an-eye, citing Esther M. Ullrich-Lüter, Sam Dupont, Enrique Arboleda, and Maria Ina Arnone, “Unique system of photoreceptors in sea urchin tube feet”, PNAS, 2011, https://www.pnas.org/doi/full/10.1073/pnas.1018495108, https://doi.org/10.1073/pnas.1018495108.

And University of Gothenburg press release, “Sea urchins see with their whole body”, ScienceDaily, September 12, 2011, http://www.sciencedaily.com/releases/2011/06/110630111538.htm, citing Esther M. Ullrich-Lüter, Sam Dupont, Enrique Arboleda, and Maria Ina Arnone, “Unique system of photoreceptors in sea urchin tube feet”, PNAS, 2011, https://doi.org/10.1073/pnas.1018495108.

[2] Wendy Zukerman, “Skin ‘sees’ light to prevent UV harm”, New Scientist, no. 2838, November 12, 2011, p. 20, and as “Skin ‘sees’ the light to protect against sunshine”, https://www.newscientist.com/article/dn21127-skin-sees-the-light-to-protect-against-sunshine/, citing Nadine L. Wicks, Jason W. Chan, Julia A. Najera, Jonathan M. Ciriello, and Elena Oancea, “UVA Phototransduction Drives Early Melanin Synthesis in Human Melanocytes”, Current Biology, vol. 21, no. 22, November 22, 2011, pp. 1906-1911, https://doi.org/10.1016/j.cub.2011.09.047.

[3] Ed Yong, “Chitons see with eyes made of rock”, National Geographic, April 14, 2011, https://www.nationalgeographic.com/science/article/chitons-see-with-eyes-made-of-rock, citing Daniel I. Speiser, Douglas J. Eernisse, and Sönke Johnsen, “A Chiton Uses Aragonite Lenses to Form Images”, Current Biology, vol. 21, no. 8, April 26, 2011, pp. 665-670, https://www.cell.com/current-biology/fulltext/S0960-9822(11)00305-8, https://doi.org/10.1016/j.cub.2011.03.033.

And Anna Nowogrodzki, “Mollusc sees the world through hundreds of eyes made out of rock”, New Scientist, November 19, 2015, https://www.newscientist.com/article/dn28520-mollusc-sees-the-world-through-hundreds-of-eyes-made-out-of-rock/, citing Ling Li, Matthew J. Connors, Mathias Kolle, Grant T. England, Daniel I. Speiser, Xianghui Xiao, Joanna Aizenberg, and Christine Ortiz, “Multifunctionality of chiton biomineralized armor with an integrated visual system”, Science, vol. 350, no. 6263, November 20, 2015, pp. 952-956, https://doi.org/10.1126/science.aad1246.

[4] Laura Geggel, “Starfish Can See You … with Their Arm-Eyes”, Live Science, February 7, 2018, https://www.livescience.com/61682-starfish-eyes.html.

And Christie Wilcox, “Sea Stars See!”, Discover Magazine, January 7, 2014, https://www.discovermagazine.com/planet-earth/sea-stars-see.

And Ed Yong, “Starfish Spot The Way Home With Eyes On Their Arms”, National Geographic, January 8, 2014, https://www.nationalgeographic.com/science/article/starfish-spot-the-way-home-with-eyes-on-their-arms.

All three citing A. Garm and D-E. Nilsson, “Visual navigation in starfish: first evidence for the use of vision and eyes in starfish”, Proc Roy Soc B, 281, 2013, http://dx.doi.org/10.1098/rspb.2013.3011.

[5] Cell Press press release, “Through unique eyes, box jellyfish look out to the world above the water”, ScienceDaily, April 30, 2011, http://www.sciencedaily.com/releases/2011/04/110428123938.htm, citing Anders Garm, Magnus Oskarsson, and Dan-Eric Nilsson, “Box Jellyfish Use Terrestrial Visual Cues for Navigation”, Current Biology, April 28, 2011, https://doi.org/10.1016/j.cub.2011.03.054.

And Ed Yong, “Single-Celled Creature Has Eye Made of Domesticated Microbes”, National Geographic, July 2, 2015, https://www.nationalgeographic.com/science/article/single-celled-creature-has-eye-made-of-domesticated-microbes, citing Gregory S. Gavelis, Shiho Hayakawa, Richard A. White III, Takashi Gojobori, Curtis A. Suttle, Patrick J. Keeling, and Brian S. Leander, "Eye-like ocelloids are built from different endosymbiotically acquired components", Nature, 2015, http://dx.doi.org/10.1038/nature14593.

[6] Louise Roberts, Harry R. Harding, Irene Voellmy, Rick Bruintjes, Steven D. Simpson, Andrew N. Radford, Thomas Breithaupt, and Michael Elliott, “Exposure of benthic invertebrates to sediment vibration”, Proceedings of Meetings on Acoustics, vol. 27, no. 1, 010029, January 5, 2017, https://doi.org/10.1121/2.0000324.

[7] Andy Coghlan, “Oysters can ‘hear’ without ears”, New Scientist, no. 3149, October 28, 2017, p. 18, and the longer version “Oysters can ‘hear’ the ocean even though they don’t have ears, https://www.newscientist.com/article/2151281-oysters-can-hear-the-ocean-even-though-they-dont-have-ears/, citing Mohcine Charifi, Mohamedou Sow, Pierre Ciret, Soumaya Benomar, Jean-Charles Massabuau, “The sense of hearing in the Pacific oyster, Magallana gigas”, PLoS ONE, October 25, 2017, https://doi.org/10.1371/journal.pone.0185353.

[8] Andy Coghlan, “Shipping noise pulps organs of squid and octopuses”, New Scientist, no. 3328, April 3, 2011, https://www.newscientist.com/article/dn20364-shipping-noise-pulps-organs-of-squid-and-octopuses/, citing Frontiers in Ecology and the Environment, https://doi.org/10.1890/100124.

Sense and Sensibilities

Top left: Thirty percent of people have harmless Staphylococcus aureus (staph) on their skin and in their nose, but occasionally it causes infections, such as gastroenteritis (sometimes called stomach flu) and can be a cause of food poisoning. USDA. Top right: Helicobacter bilis. Some strains are common in people and on occasion they can cause peptic ulcers, chronic gastritis, and stomach cancer. CDC. Bottom left: Bacteria. Brandon Antonio Segura Torres and Priscilla Vieto Bonilla, CC BY-SA 4.0. Bottom right: Escherichia coli (E. coli) is a common bacteria often found in our lower intestines. Some strains are harmful, causing such ailments as gastroenteritis, urinary tract infections, and inflammatory bowel disease. USDA. Three of these photographs are colorized

Every living organism has to be able to sense their environment in order to survive. This includes the ability to process the information it receives, so it can respond, and to store and retrieve information for it can use in a similar situation in the future. That sounds like a lot, but even bacteria—the simplest known living creature—can do it. (I’m setting aside viruses for now, since we’re not sure they’re actually alive, although viruses can taste.) All life needs to sense its surroundings in some way.

Touch is one of the oldest senses. Even single cell organisms will recoil when you poke them. They feel their way around their environment, determining whether to move towards or away from whatever they encounter. By using this sense they can even all move in the same direction as a group. They can tell when they come in contact with a surface and can release glue to adhere to it.

Interestingly, touch in other animals works pretty much the same way as it does in us, and fish sense with their pectoral fins like we do our hands[1], but some animals do have unusual capabilities.

When a duck dabbles in water, it is actually feeling around for food. The tip of its bill, and that of similar wading birds, is packed with sensors and is thought to be just as sensitive as our fingertips. When probing in mud and sand, they create a pressure wave, and by feeling distortions in the wave they can detect hidden food without actually touching it.[2] Mallards have a few taste buds in clusters on their jaws, but none on their tongues. Other ducks may be the same.

The narwhal’s long tusk is packed with sensors. This unusual toothed whale has two large teeth, but the left one grows out to an enormous size, apparently becoming a sense organ. The other remains in its mouth and only becomes about a foot long. Narwhals grow up to fifteen feet and their spiral-shaped tusk can grow to nine. It’s mostly males that have them, but some females do too, and in some males both of the teeth become tusks. Scientists think these tusks can detect changes in pressure, temperature, and the saltiness of the water, indicating when the water is about to freeze. They also float with the tusk pointing up in the air like an antenna, probably sensing air pressure and temperature to predict the weather.[3]

Snakes and some lizards have raised scales on their heads that they use for feeling things. Sea snakes also use them to sense ripples in the water and track down prey. Likewise, crocodiles, alligators, and caimans are armored with scales, yet they can feel light touches through small bumps on their scales that are sensitive to touch, temperature, and chemicals. In fact, their tough scales are ten times more sensitive to touch than our fingers. Alligators have them on their heads, while crocodiles have them all over their bodies. So if you softly pet a crocodile, he or she will feel it. And they’re most sensitive around their teeth, which may be especially important since they carry their babies around in their jaws.[4]

Crocodiles are very sensitive to touch in spite of their armor plates, so they might like it if you pet them, although I wouldn’t recommend it. © John Richard Stephens, 2010

 

“How doth the little crocodile

Improve its shining tail,

And pour the waters of the Nile

On every golden scale!

“How cheerfully it seems to grin!

How neatly spreads its claws!

And welcomes little fishes in

With gently-smiling jaws!”

—Lewis Carroll, Alice’s Adventures Under Ground

 

Getting back to bacteria, they can sense tiny changes in chemical gradients, which enable them to move towards food and they can tell whether they’re getting closer. They also use this sense to avoid competitors and flee from toxins. Many types of bacteria seek out the walls of your intestines as the ideal place to live—both pathogenic and helpful bacteria. Once they’ve arrived, they sense it and alter their gene expression for the new environment. Bacteria have four or five types of receptors in their membrane wall that send signals to their flagellum—a spinning whip-like hair that serves as their propeller.[5] And they can smell gases.[6]

It turns out that much of the distinctive smell of a forest after it rains comes from bacteria that are communicating with each other. Bacteria give off a number of scents that influence and coordinate their behavior, some of which we can smell. Their single-celled predators can smell it too, but for them it signals the location of food, and not just that, it tells them the type of bacteria, so they can head for the kind they like best. Normally the scents travel about four inches (10 cm), but when there’s lots of bacteria communicating at once, they can fill a forest with that wonderful damp forest smell.

Terpenes are the most common component of bacterial scents, but bacteria aren’t the only ones that produce it. Plant terpenes are what gives lavender, tangerines, and pine trees their fragrances. Plants use them to warn their neighbors that predators are in the area. Animals also use them and they’re often included in perfumes. Terpenes and other chemical communicators are called pheromones.

So, when the soil bacteria Serratia picks up the scent from a deadly fungi Fusarium, they give off their own scent, warning their relatives it’s time to hightail it out of Dodge. And that’s just one example of interspecies communication among some of the most basic creatures you can find.[7]

Bacteria can also use scents to scare away predators, such as the round worm Caenorhabditis elegans. When bacteria become poisonous, they release a scent—geosmin—to warn their predators to stay away, similar to how the bright colors of the poison dart frogs warn predators to steer clear of them. This scent is what we smell when working in the garden with damp soil or right after it rains. If bacteria produce it in water, it can cause the water to taste like dirt.[8]

While most bacteria use taste, smell, and touch to sense their environment, so far they don’t appear to be able to hear or sense vibrations. Still, simple single-celled bacteria have four of the five primary senses. They do respond to light, meaning they have a very basic form of sight.

Cyanobacteria—also known as blue-green algae, although it’s not really an algae—have been around for 2.5 billion years making them one of the oldest creatures on the planet and they were the first organisms to produce oxygen. They can be found just about everywhere all over the Earth. They’re the green slime growing in your aquarium, when you forget to clean it. These are one type of single-celled microorganism that can detect light and respond to it. Using the same principle as our eyes, light hits one side of the cell and is focused onto the other side where they sense it. They then move away from that side in order to head towards the light, or they towards that side to move away from the light.[9]

A single-celled warnowiid. The dark spot at the base of its eye is its retina. Mona Hoppenrath, Tsvetan R. Bachvaroff, Sara M. Handy, Charles F. Delwiche, and Brian S. Leander, CC BY 2.0 (modified).

Several might even have a primitive eye built into them, which is pretty astonishing for single-celled organisms. One is a warnowiid, a rare free-swimming predatory plankton—it’s also a protozoa, a protist, and a dinoflagellate—that’s smaller than this period “.”, yet it contains a clear sphere with parts that look like a retina, lens, cornea, and an iris—all arranged like an eye. We’re not sure yet what this possible eye does because these creatures are difficult to find, hard to keep alive, and so far, impossible to raise, so researchers haven’t been able to run many tests on them. Pretty much all it could sense would be light and dark, or perhaps the presence of circular polarized light reflected from their prey. This would enable warnowiids to swim towards their victims where they could attack it with their harpoon-like stingers.[10]

Our own cells have senses too. We were once a single cell, when two of our parents’ cells fused. Now our cells are much more specialized, compared to single-celled organisms. Our cells travel to where they’re supposed to be, seeking out other cells in their specialty, and then line up in rows, even when there’s a plate of glass between them, possibly by sensing infrared light.[11]

Some cells are so sensitive that they can locate a molecule within a nanometer, which is about a third the diameter of a carbon atom. Some seem to be able to determine distances.[12] They have finger-like projections they can extend, retract, and bend, that they use to feel their environment. When they sense food, they curve around it so they can engulf it.[13]

Many of your cells are constantly awash in chemical information, yet are able to determine which signals to act on, in addition to how and when to act.[14] They use chemicals to communicate and to know where to congregate. Others that are part of your immune system swim to threats and destroy them. A study by scientists at the Marine Biological Laboratory in Massachusetts suggests that cells can sense their shape, even when it’s constantly changing.[15] They can also sense the curvature and the density of the cells near them.[16]

And they do all of this without any nervous system or a brain.

Sneezing Sponges

A yellow tube sponge, a gray rope sponge, a red encrusting sponge, and a purple vase sponge together in the Caribbean Sea. Twilight Zone Expedition Team 2007, NOAA-OE, CC BY 2.0.

Sponges sneeze. This is pretty amazing since they're among the simplest animals in the world and don’t have muscles or even a nervous system. They are filter feeders, which is a pretty passive way to survive, relying on water currents to bring them food, but sometimes they sneeze to cast out sediment, waste, and mucus (snot). Biologists can also use certain chemicals to get them to sneeze. It’s not quick, though. A sneeze can take up to forty-five minutes.

The question is, how does a simple sponge know when it needs to sneeze? It must sense it somehow, so what kind of senses does a sponge have? We’re not sure. What we do know is that they sense with cilia—tiny hair-like structures—which have been repurposed in us and other animals for use in hearing and smell.

And I’ll bet you didn’t know that roundworms (Caenorhabditis elegans—the laboratory favorite commonly shortened to C. elegans) can spit. Normally they float around in water hoovering up whatever bacteria they find, but when they taste something they don’t like, they immediately spit it out and run away…that is, as fast as they can crawl.

 

Go to my index of posts to see more. 

If you'd like to comment, please email me at John@AWondrousWorld.com.

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[1] University of Chicago Medical Center, “Fish fins can sense touch: New study finds pectoral fins feel touch through a surprisingly similar biological mechanism to mammals”, ScienceDaily, February 10, 2016, http://www.sciencedaily.com/releases/2016/02/160210165859.htm, citing Adam R. Hardy, Bailey M. Steinworth, and Melina E. Hale, “Touch sensation by pectoral fins of the catfish Pimelodus pictus”, Proceedings of the Royal Society B: Biological Sciences, 2016, 283 (1824): 20152652, https://doi.org/10.1098/rspb.2015.2652.

[2] Tim Birkhead, “Instant Expert 34: Bird Senses”, New Scientist, no. 2928, August 3, 2013, pp. i-viii, and as “Bird senses: Touch and hearing”, July 31, 2013, https://www.newscientist.com/article/mg21929282-700-bird-senses-touch-and-hearing/, citing Proceedings of the Royal Society B, vol. 265, p 1377.

[3] John M. Henshaw, A Tour of the Senses, Baltimore: The Johns Hopkins University Press, 2012.

[4] BioMed Central, “Croc supersense: Multi-sensory organs in crocodylian skin sensitive to touch, heat, cold, environment”, ScienceDaily, July 2, 2013, http://www.sciencedaily.com/releases/2013/07/130702101506.htm, citing Nicolas Di-Poï, Michel C Milinkovitch, “Crocodylians evolved scattered multi-sensory micro-organs”, EvoDevo, 2013; 4 (1): 19 https://doi.org/10.1186/2041-9139-4-19.

And Ed Yong, “Crocodile Faces Are More Sensitive Than Human Fingertips”, National Geographic, November 8, 2012, https://www.nationalgeographic.com/science/article/crocodile-faces-are-more-sensitive-than-human-fingertips, citing Duncan B. Leitch and Kenneth C. Catania, “Structure, innervation and response properties of integumentary sensory organs in crocodilians”, Journal of Experimental Biology, 2012, http://dx.doi.org/10.1242/jeb.076836.

[5] Institute of Industrial Science, The University of Tokyo, “E. Coli calculus: Bacteria find the derivative optimally”, ScienceDaily, March 24, 2021, https://www.sciencedaily.com/releases/2021/03/210324094729.htm.

And Hebrew University of Jerusalem. “ ‘Smart’ bacteria remodel their genes to infect our intestines”, ScienceDaily, February 22, 2017. https://www.sciencedaily.com/releases/2017/02/170222082914.htm, citing Naama Katsowich, Netanel Elbaz, Ritesh Ranjan Pal, Erez Mills, Simi Kobi, Tamar Kahan, and Ilan Rosenshine, “Host cell attachment elicits posttranscriptional regulation in infecting enteropathogenic bacteria”, Science, 2017; 355 (6326): 735, https://doi.org/10.1126/science.aah4886.

And David H Freedman, “In the Realm of the Chemical”, Discover Magazine, June 1993, pp. 68-76.

[6] Newcastle University, “Bacteria can have a ‘sense of smell’ ”, ScienceDaily, August 17, 2010, http://www.sciencedaily.com/releases/2010/08/100816095719.htm, citing Reindert Nijland and Grant Burgess, “Bacterial Olfaction”, Biotechnology Journal, 2010, https://doi.org/10.1002/biot.201000174.

[7] Netherlands Institute of Ecology (NIOO-KNAW), “How miniature predators get their favorite soil bacteria: Sniffing out your dinner in the dark”, ScienceDaily, December 8, 2016, https://www.sciencedaily.com/releases/2016/12/161208125841.htm, citing Kristin Schulz-Bohm, Stefan Geisen, E R Jasper Wubs, Chunxu Song, Wietse de Boer, and Paolina Garbeva, “The prey’s scent: Volatile organic compound mediated interactions between soil bacteria and their protist predators”, The ISME Journal, 2016, https://doi.org/10.1038/ismej.2016.144.

And Netherlands Institute of Ecology (NIOO-KNAW), “World’s most spoken language is ‘Terpene’: Micro-organisms communicate with each other, and the rest of the world, through smells”, ScienceDaily, April 13, 2017, https://www.sciencedaily.com/releases/2017/04/170413190718.htm, citing Ruth Schmidt, Victor de Jager, Daniela Zühlke, Christian Wolff, Jörg Bernhardt, Katarina Cankar, Jules Beekwilder, Wilfred van Ijcken, Frank Sleutels, Wietse de Boer, Katharina Riedel, and Paolina Garbeva, “Fungal volatile compounds induce production of the secondary metabolite Sodorifen in Serratia plymuthica PRI-2C”, Scientific Reports, vol. 7, no. 1, 2017, https://doi.org/10.1038/s41598-017-00893-3.

[8] Concordia University, “The pleasant smell of wet soil indicates danger to bacteria-eating worms, researchers find: The chemical compound geosmin’s powerful taste warns predators to keep away from certain microbes”, ScienceDaily, April 5, 2022, https://www.sciencedaily.com/releases/2022/04/220405143530.htm, citing Liana Zaroubi, Imge Ozugergin, Karina Mastronardi, Anic Imfeld, Chris Law, Yves Gélinas, Alisa Piekny, and Brandon L. Findlay, “The Ubiquitous Soil Terpene Geosmin Acts as a Warning Chemical”, Applied and Environmental Microbiology, 2022, https://doi.org/10.1128/aem.00093-22.

[9] Albert-Ludwigs-Universität Freiburg, “Slime can see: Tiny cyanobacteria use principle of the lens in the human eye to perceive light direction”, ScienceDaily, February 9, 2016, https://www.sciencedaily.com/releases/2016/02/160209090620.htm, citing Nils Schuergers, Tchern Lenn, Ronald Kampmann, Markus V Meissner, Tiago Esteves, Maja Temerinac-Ott, Jan G Korvink, Alan R Lowe, Conrad W Mullineaux, and Annegret Wilde, “Cyanobacteria use micro-optics to sense light direction”, eLife, 5, 2016, https://doi.org/10.7554/eLife.12620.

[10] Ed Yong, “Single-Celled Creature Has Eye Made of Domesticated Microbes”, National Geographic, July 2, 2015, https://www.nationalgeographic.com/science/article/single-celled-creature-has-eye-made-of-domesticated-microbes, citing Gregory S. Gavelis, Shiho Hayakawa, Richard A. White III, Takashi Gojobori, Curtis A. Suttle, Patrick J. Keeling, and Brian S. Leander, “Eye-like ocelloids are built from different endosymbiotically acquired components”, Nature, vol. 523, pp. 204-207, 2015, http://dx.doi.org/10.1038/nature14593.

[11] Guenter Albrecht-Buehler, “Rudimentary form of cellular ‘vision’ ”, PNAS, vol. 89, no. 17, September 1992, pp. 8288-8292, https://www.pnas.org/content/pnas/89/17/8288.full.pdf, https://doi.org/10.1073/pnas.89.17.8288.

[12] Universidad de Barcelona, “Cells sense their environment to explore it”, ScienceDaily, December 13, 2017, https://www.sciencedaily.com/releases/2017/12/171213125821.htm, citing Roger Oria, Tina Wiegand, Jorge Escribano, Alberto Elosegui-Artola, Juan Jose Uriarte, Cristian Moreno-Pulido, Ilia Platzman, Pietro Delcanale, Lorenzo Albertazzi, Daniel Navajas, Xavier Trepat, José Manuel García-Aznar, Elisabetta Ada Cavalcanti-Adam, and Pere Roca-Cusachs, “Force loading explains spatial sensing of ligands by cells”, Nature, 2017, https://doi.org/10.1038/nature24662.

[13] Ohio State University, “High-resolution lab experiments show how cells ‘eat’: Study solves a 40-year-old problem in cell biology”, ScienceDaily, December 30, 2021, https://www.sciencedaily.com/releases/2021/12/211230130936.htm, citing Nathan M. Willy, Joshua P. Ferguson, Ata Akatay, Scott Huber, Umidahan Djakbarova, Salih Silahli, Cemal Cakez, Farah Hasan, Henry C. Chang, Alex Travesset, Siyu Li, Roya Zandi, Dong Li, Eric Betzig, Emanuele Cocucci, and Comert Kural, “De novo endocytic clathrin coats develop curvature at early stages of their formation”, Developmental Cell, 56 (22): 3146 2021, https://doi.org/10.1016/j.devcel.2021.10.019.

[14] University of California – Irvine, “Researchers eavesdrop on cellular conversations: New computational tool decodes biological language of signaling molecules”, ScienceDaily, February 18, 2021, https://www.sciencedaily.com/releases/2021/02/210218160357.htm.

[15] Diana Kenney, “A Cell Senses Its Curves: New Research from the Whitman Center”, April 28, 2016, https://www.mbl.edu/blog/a-cell-senses-its-curves-new-research-from-the-whitman-center/, citing Andrew A. Bridges, Maximilian S. Jentzsch, Patrick W. Oakes, Patricia Occhipinti, and Amy S. Gladfelter, “Micron-scale plasma membrane curvature is recognized by the septin cytoskeleton”, The Journal of Cell Biology, 213 (1): 23, 2016, https://doi.org/10.1083/jcb.201512029.

[16] Institute of Science and Technology Austria, “How cells feel curvature: Scientists find mechanism that allows cells to sense the curvature of tissue around them”, ScienceDaily, November 18, 2021, https://www.sciencedaily.com/releases/2021/11/211118203618.htm, citing Marine Luciano, Shi-Lei Xue, Winnok H. De Vos, Lorena Redondo-Morata, Mathieu Surin, Frank Lafont, Edouard Hannezo, and Sylvain Gabriele, “Cell monolayers sense curvature by exploiting active mechanics and nuclear mechanoadaptation”, Nature Physics, 2021, https://doi.org/10.1038/s41567-021-01374-1.