Nature's Halloween Costumes

A repost of an original article from October 23, 2013.

Image by Steve at Wikimedia Commons.

It seems like everyone is racking their brains to come up with a great Halloween costume. But we’re not the only ones to disguise ourselves as something we’re not. Many animals put on costumes just like we do. Take this gharial crocodile for example (do you see him?), covering himself in parts of his environment to hide.

Other animals, like this tawny frogmouth below, develop physical appearances that help them blend in with their surroundings. When threatened, these birds shut their eyes, erect their feathers and point their beak in such a way to match the color and texture of the tree bark.


Image by C Coverdale at Wikimedia Commons.

Rather than hide, some animals have a physical appearance to disguise themselves as other species that are often fierce, toxic or venomous. This type of mimicry is called Batesian mimicry, named after Henry Walter Bates, the English naturalist who studied butterflies in the Amazon and gave the first scientific description of animal mimicry. This plate from Bates’ 1862 paper, Contributions to an Insect Fauna of the Amazon Valley: Heliconiidae, illustrates Batesian mimicry between various toxic butterfly species (in the second and bottom rows) and their harmless mimics (in the top and third rows).


This plate from Bates’ 1862 paper, Contributions to an Insect Fauna of
the Amazon Valley: Heliconiidae is available on Wikipedia Commons.

The bluestriped fangblenny takes its costume another step further, by changing its shape, colors, and behavior to match the company. This fish changes its colors to match other innocuous fish species that are around so it can sneak up and bite unsuspecting larger fish that would otherwise bite them back! Learn more about them here.

The fish on the far left is a juvenile cleaner wrasse in the act of cleaning another fish. The two fish in
the middle and on the right are both bluestriped fangblennies, one in its cleaner wrasse-mimicking
coloration (middle) and the other not (right). Figure from the Cheney, 2013 article in Behavioral Ecology.

But the Master of Disguise title has got to go to the mimic octopus. This animal can change its color, shape and behavior to look and behave like a wide range of creatures, including an innocuous flounder, a poisonous lionfish, or even a dangerous sea snake! Check it out in action:

Body Clocks: What They Are and How They Work

Lately, with the new year, the #TimesUp movement, awaiting Disney’s movie A Wrinkle in Time based on one of my favorite childhood book series, and just watching my children grow faster than I thought possible, I have been thinking a lot about time. The continuous march forward, the constant rotation of the planet, and the revolution of the Earth around a distant star in its determined path all have far-reaching effects on our physiology and behavior. Our biological clocks affect everything from our sleep-wake cycles to our fertility to our mental and physical health. And it’s not just us that have them: Every living thing on Earth, including bacteria, protists, fungi, plants and animals, has them. But what do they do and how do they work?

A sleepy ferret minds his biological rhythms. Photo by Kimberly Tamkun at Wikimedia Commons.

Generally speaking, a biological clock is an organism’s inborn way of regulating its functions with respect to time. Many of these biological clocks follow circadian rhythms (changes that follow a 24-hour cycle). Vast portions of our planet have been exposed to dramatic but mostly predictable environmental changes on a 24-hour cycle since long before life existed, so it makes sense that us lifeforms have developed a means to make the best of those changes: sleeping when food is less available, having higher metabolisms when we are active, being more alert during times we are most likely to be interacting with the world.

Diagram of a human circadian rhythm by YassineMrabet at Wikimedia Commons.

Melatonin is a hormone widely known to synchronize circadian rhythms in vertebrates (animals with backbones) to the light-dark cycle of the day and night (or to an indoor room with a light timer). Melatonin is produced in response to darkness, and the longer the night, the more melatonin is produced. Rising and falling melatonin levels help determine sleep-wake cycles in animals. In animals that breed seasonally, the changing peaks of melatonin levels that correspond with dark nights getting longer or shorter stimulate the reproductive system to help synchronize breeding physiology and behavior with the seasons. Although we have known about melatonin and its effects for nearly a hundred years, we are now learning that it seems that all organisms, including bacteria, protists, fungi, plants and animals, make it. Whether it has the same effect in all organisms is yet to be determined.

In vertebrates, melatonin is produced by the pineal gland, a small structure in the center of the brain. In birds, reptiles, amphibians and fish, the pineal gland has light-sensitive cells that receive light as it passes directly through the skull and the brain! In mammals, the pineal gland receives a light signal through a more complicated pathway: Light is detected by light sensitive cells in the retinas of the eyes. They send this signal to the suprachiasmatic nucleus (SCN) in the brain, which relays it to other brain areas and then to the pineal gland. The SCN in mammals is commonly called “the master clock” due to its important role in synchronizing body rhythms with light cues.

Diagram of the human brain and the SCN by the
National Institute of General Medical Sciences at Wikimedia Commons.

Body rhythms are determined at the cellular level through the interaction of a small number of genes called clock genes. Clock genes have been found in every animal, plant and fungus studied so far. Originally, it was thought that in mammals, clock genes would only be found in the SCN. However, it now looks like clock genes are active in all cells and the SCN functions more like an orchestra conductor synchronizing the rhythms of the organs throughout the body.

Many clock genes have been discovered, and they all seem to work based on similar processes. Just last year, scientists Jeffrey Hall, Michael Rosbash, and Michael Young, were awarded the 2017 Nobel Prize in medicine for their research on clock genes in fruitflies. They found that biological clocks are self-regulated within the cell: Morning sunlight turns on a gene called the PERIOD gene, which starts to produce a protein called the Period protein. As long as there is light, Period protein accumulates to higher and higher levels. Another protein, named Timeless, shuttles Period proteins into the nucleus, where the DNA lives. The Period proteins shut down the activity of the PERIOD gene, while a third protein, called Doubletime, regulates the destruction of the excess Period proteins. The result of this process is that by nightfall, Period proteins have disappeared and sunlight is needed to start the cycle anew. This work by Hall, Rosbash and Young inspired a whole new field of molecular biology of circadian rhythms.

We have a lot more to learn about biological clocks and circadian rhythms, but what we do know is that their effects are wide-ranging. Whacky circadian rhythms have been implicated in sleep disorders, depression, bipolar disorder, cancer, obesity, and diabetes. And what else will we learn about them? Only time will tell.

What Do Animals Think of Their Dead?

A reposting of an article from September 12, 2012.

You’re running around, going about your day, and suddenly you see a dead guy lying in the sidewalk. What do you feel? Sad? Scared? Do you look around to see if you might be in danger too? Would you feel any differently if the dead body on the sidewalk were that of a squirrel, and not a human? Do animals share these same emotional and thought processes when they come across their own dead?

Teresa Iglesias, Richard McElreath and Gail Patricelli at the University of California at Davis pondered this philosophical question themselves. Then they set off to scientifically test it. 

A western scrub-jay collecting peanuts from a windowsill.
Photo by Ingrid Taylar at Wikimedia.

Teresa, Richard and Gail had noticed that when a live western scrub-jay encounters a dead western scrub-jay, it hops from perch to perch while calling loudly, a response the researchers called a “cacophonous reaction”. This boisterous response usually attracts other scrub-jays, which either join in with their own cacophonous reaction or just sit quietly observing. Is this truly a response to seeing their own dead?

The researchers put bird feeders baited with peanuts in backyards all over Davis, California (with the permission of the backyard-owners, of course). Once they find a feeder, western scrub-jays take the peanuts one at a time and fly off to cache them away before returning for another peanut. While the scrub-jays were away caching a peanut, the researchers put a collection of painted wood pieces on the ground, arranged to vaguely look like a dead scrub-jay. Then they snuck away to watch if the scrub-jays responded when they returned. Several days later, they came back to the same feeders, waited until the scrub-jay was away caching a peanut, and then placed an actual scrub-jay carcass and feathers (usually found somewhere in the area). Then they snuck away again to watch if the scrub-jays responded any differently when they returned.

Watch the behavior of western scrub-jays before and after

the placement of a dead scrub-jay. The “after” response starts

about one minute into the video. Video by Teresa Iglesias.

And in a nutshell, they did. When the scrub-jays returned to find a dead scrub-jay, they called like crazy and hopped around in a full-blown cacophonous reaction. In most cases, this reaction attracted other scrub-jays who joined in the lively response. Additionally, when the dead scrub-jay was present, they took 90% fewer peanuts. None of this ever happened in response to a pile of painted wood. When a scrub-jay returned to find painted wood, it went about its day, calling at normal rates and collecting peanuts as usual. One jay was so unconcerned by the painted wood, it even cached peanuts under it!

A western scrub-jay thinks the painted wood makes

a good peanut-hideaway. Video by Teresa Iglesias.

This convinced the researchers that the scrub-jays were not simply responding to something new near the feeder, but were instead responding to dead bodies. But does it matter whether the body is a conspecific (the same species) or a heterospecific (different species)? And what do these group responses mean? Are they gathering in mourning? Or is their response a way of hollering, “Look out! Something out there is killing us!”?

To find out, the researchers did the same thing they had done before, but this time, they placed either a scrub-jay carcass or a mounted great horned owl (a scrub-jay predator). Interestingly, the scrub-jays responded with the same cacophonous reactions and avoided the peanuts in both cases. However, the scrub-jays called for longer and defensively swooped at the mounted owl, something they didn’t do to the scrub-jay carcass. To check if this heightened response to the owl mount was due to its lifelike position, they repeated the study, comparing scrub-jay responses to a scrub-jay carcass or a mounted scrub-jay. Although the dead-looking carcass always elicited cacophonous aggregations, mounted scrub-jays only elicited cacophonous aggregations a third of the time. But when jays did respond to the scrub-jay mounts, they often swooped at it as if it were a competitor, something they never did to a scrub-jay carcass.
What does this all mean? Western scrub-jays respond to conspecific (scrub-jay) carcasses not just because their appearance is surprising, but because they may represent some kind of risk. They seem to recognize that the carcass is not a living threat, because they don’t swoop at it like they do to both owl and scrub-jay mounts. But they do produce an alarm response, much as they do when a predator is present. So their responses to dead scrub-jays are not so much “funerals” in the way that people mourn and reflect on their dead, but rather a way to announce a risk of getting hurt or killed.

Are western scrub-jays uniquely aware of the risk a dead conspecific may represent? Maybe not. Although this was the first comprehensive study of this phenomenon, similar behavioral responses to dead conspecifics have been observed in ravens, crows and magpies, all members of the corvid family of birds, like scrub-jays. But rats and even bees have also been observed to avoid dead conspecifics. Many animals may be more cognizant of death than we give them credit for.

Want to know more? Check this out:

Iglesias, T.L., McElreath, R., & Patricelli, G.L. (2012). Western scrub-jay funerals: cacophonous aggregations in response to dead conspecifics Animal Behaviour DOI: 10.1016/j.anbehav.2012.08.007

What Animals Contagiously Yawn?

Does this sight make you want to yawn?

A yawning Japanese macaque by Daisuke Tashiro at Wikimedia Commons.

Do you think it would make other animals want to yawn? Many animals yawn spontaneously, but yawning in response to sensing or thinking about someone else doing it may be a completely different thing. Contagious yawning requires a sense of social connection and emotional empathy that not all species share. So far, scientists have found experimental evidence of contagious yawning in humans, chimpanzees, domestic dogs (who interestingly yawn when people yawn, but not when other dogs do), and an abnormally yawny genetic line of rats. However, there have also been reports of bonobos, baboons, wolves, and budgerigars (small social parrots, also called budgies or parakeets) yawning contagiously in the wild, so this phenomenon may be more widespread than previously thought.

Andrew Gallup, Lexington Swartwood, Janine Militello and Serena Sackett from the State University of New York at Oneonta set out to experimentally test if budgerigars do in fact yawn contagiously. In one experiment, the researchers placed pairs of birds in separate adjacent cages with perches facing one another. They video recorded the birds both with an opaque barrier between them and without the opaque barrier. The researchers found that when the birds could see one another they were three times more likely to yawn within 5 minutes of the other bird yawning, although there was no difference in the overall number of spontaneous yawns.

Images of a yawning budgie from Gallup et al., 2015.

Next, the researchers decided to test if budgerigars contagiously yawn in response to videos of another budgerigar yawning. They played 10-minute videos of either yawning or non-yawning budgerigars on a laptop facing the birdcage. And who would have guessed that the budgies yawned twice as much in response to the yawning video than to the non-yawning video, showing that even our pet birds can get something out of watching TV!

Budgerigars are now the first non-mammalian species to display contagious yawning. Contagious yawning is not just interesting in itself, but it may also indicate a sense of empathy. Although we often limit our thinking of empathy to our own species, it makes sense to find empathetic behavior among social species like budgerigars. Now if we could just find more of it amongst our own species…

Want to know more? Check this out:

Gallup, A., Swartwood, L., Militello, J., & Sackett, S. (2015). Experimental evidence of contagious yawning in budgerigars (Melopsittacus undulatus) Animal Cognition, 18 (5), 1051-1058 DOI: 10.1007/s10071-015-0873-1

How We Know the Colors of Prehistoric Animals

Image from Vinther's 2015 paper in Bioessays.

Through their studies of bones, fossils, and geology, paleontologists have uncovered the prehistoric worlds of Earth's past. We watch movies and TV shows of computer generated versions of long-extinct dinosaurs, fish, birds, and even mammals and it seems obvious how we know about the sizes and shapes of these animals...but how do we know what their colors were like? A new scientific field is emerging, called paleocolor (or palaeo colour, if you're British), in which scientists use fossils, chemistry, cellular biology and comparative biology to reconstruct the color patterns and related behaviors of animals long since passed.

Today at Accumulating Glitches, I discuss the major findings of paleocolor and how we know what colors the dinosaurs and other long-extinct animals actually were. Check out the full article here.

Further reading:
Vinther, J. A guide to the field of palaeo colour, Bioessays, 37, 643-656 (2015). DOI: 10.1002/bies.201500018.

Vole Pee: An Epiphany (A Guest Post)

By Nate Kueffer

You’re driving down the road, looking out the window, and you see a large raptor hovering above a field. Have you ever wondered what exactly the raptor could see that you couldn’t? Well, it is thought that raptors may be able to sense ultraviolet light and use it to track voles through urine and feces trails.

A hovering kestrel, possibly tracking a vole. Photo by Mark Likner at Flickr.

Ultraviolet light is a non-detectable form of radiation by the human eye and is similar to X-rays and gamma rays. However, with the help of a black light human eyes can see different materials that we couldn’t see in visible light. The objects that humans can typically see under a black light are fluorescent. This means that the object has the ability to soak up ultraviolet light and then emit the light it took in and produce a light frequency that humans are able to detect.

Jussi Viitala from the University of Jyvaskyla in Finland, and Erkki Korpimäki, Päivi Palokangas (now Lundvall) and Minna Koivula from the University of Turku in Finland set out to find more conclusive evidence on raptors using ultraviolet light to hunt. The four researchers tested the hypothesis that in order to find prey patches, Eurasian kestrels, a species of raptor, look for vole scent marks visible in ultraviolet light. The voles’ scent marks are their urine and feces droppings, which show up under ultraviolet light. The researchers set up experiments in the field and in a laboratory setting.

Kestrel with a captured vole after a successful hunt. Photo by Eugene Beckes at Flickr.

In the laboratory setting, wild captured kestrels were released into a large area made up of four different arenas. All arenas were different, but did not allow any external visual cues. One arena had vole trails in ultraviolet light, another was clean with ultraviolet light, a third arena had visible light and vole trails, and the final arena was clean with visible light. The kestrels were then measured by their time spent over each arena. The kestrels in the laboratory seemed to prefer the arena with ultraviolet light and vole trails. The clean, ultraviolet-lit arena had the least amount of scans and time spent over that arena compared to the other three arenas. The kestrels had no preference over either arena with visible light.

The field setting had 3 experimental groups for 45 kestrel nest boxes: the first had artificial vole trails with urine and feces, the second had artificial vole trails, but no urine or feces, and the last was the control with no vole trails, urine, or feces. The 45 boxes were observed over 24 mornings when the researchers recorded the number of kestrels near each nest and their behavior (hunting, paired, or resting). For the field experiment, 27 of the 45 nest boxes attracted kestrels near them. The most commonly used nest boxes were near artificial trails with urine and feces. The kestrels avoided the other two nest box areas: the one with trails, but no urine, and one with no trails and no urine. This showed that the trails weren’t used as hunting cues. Paired or hunting kestrels preferred to spend time hunting near trails with urine or feces, and resting kestrels were seen evenly in all three areas. Also, four rough-legged hawks were seen hunting near the trails with urine and feces.

Both experiments showed kestrels using trails with markings from voles suggesting that the vole markings may be used to select hunting and nest sites. The researchers propose that the kestrels, in fact, use vole scent markings as visual cues. Kestrels and other predatory birds may use the ultraviolet light from vole markings to scan over large areas new to them before deciding to hunt or nest in the area. The next raptor you see out of your car window could be tracking its prey’s markings using ultraviolet light.


References
Olson, V. (n.d.). Raptor Vision. Retrieved December 10, 2014, from http://www.moremesa.org/wordpress/raptor-vision/

Q & A: Why does a black light make objects glow? (2007, October 22). Retrieved January 21, 2015, from https://van.physics.illinois.edu/qa/listing.php?id=1913

Viitala, J., Korplmäki, E., Palokangas, P., & Koivula, M. (1995). Attraction of kestrels to vole scent marks visible in ultraviolet light Nature, 373 (6513), 425-427 DOI: 10.1038/373425a0

Choosing Mates Wisely Is All The More Important When They Try To Eat You

A praying mantid pair.
Photo by Oliver Koemmerling
at Wikimedia Commons.

Choosing our mates is among the most important decisions of our lives. We agonize over finding "the one", and for good reason. If we are going to spend the rest of our lives with one person and depend on that person to help create and raise our children, the stakes of choosing that person well are high. But at least we don't have to worry that if we choose wrong our partner will bite our head off... not literally, anyway.

Today at Accumulating Glitches, I talk about sexual cannibalism in praying mantids and how it has led to males now choosing less aggressive mates. Check out the article here.

Crocodilians Hunt With Tools!

A crocodile lures in birds with sticks that would make a nice nest.
Photo by Dinets published in Ethology, Ecology & Evoluton 2013.

What would happen to mankind if crocodiles and alligators were to develop enough intelligence that they could hunt with tools? Would we see the rise of new dominant species as in Rise of the Planet of the Apes?

Well, shudder in your boots, people, because we are already there!

This week at Accumulating Glitches I talk about the discovery of how at least two species of crocodilians use tools to lure in prey. Check it out here.

And to learn more, check this out:

Dinets, V., Brueggen, J.C.. and Brueggen, J.D. Crocodilians use tools for hunting, Ethology Ecology & Evolution, (2013). DOI: 10.1080/03949370.2013.858276.

Metabolism and Body Size Influence the Perception of Movement and Time

Zoetropes like this one have been used
for almost 2000 years. If you look in the
slits from the side, the image appears to
be animated. Image by Andrew Dunn
at Wikimedia Commons.

When we watch TV or a movie, we are essentially watching a series of still images presented in rapid succession… so rapid, in fact, that we perceive them to be a single moving image. The ability of movie-makers to convince us that still images are fluid in time is based on our physiology. Specifically, moving-pictures, as they were once called, rely on our critical flicker fusion frequency (CFF), the lowest speed at which we perceive a flashing light source to be a constant light. But we don't have our CFF so we can enjoy movies and TV; it came about from our need to identify and track moving objects.

The ability to identify and track moving objects is critically important for finding and catching prey, avoiding predators, and finding mates. It is these visual abilities that rely on an animal’s CFF. An animal with a low CFF will miss many visual details, like watching your TV with a fast-forward function that jumps ahead 15 seconds at a time. An animal with a high CFF will see all the details that happen in between with a fine-time-scale resolution. But if having a high CFF conveys such an advantage, why don’t all animals have a high CFF?

This week at Accumulating Glitches I talk about how an animal's size and metabolism can influence how it sees the world. Check it out here.

And to learn more, check this out:

Healy, K., McNally, L., Ruxton, G.D., Cooper, N., & Jackson, A.L. (2013). Metabolic rate and body size are linked with perception of temporal information Animal Behaviour, 86, 685-696 DOI: 10.1016/j.anbehav.2013.06.018

The Mimic Octopus: Master of Disguise

The disguises of the mimic octopus: (a) shows a mimic
octopus looking out of its burrow; (b) is a foraging mimic
octopus with coloration to blend with the sand; (c) shows
a mimic octopus as a sole fish and (d) is an actual
sole fish; (e) shows a mimic octopus as a lion-fish and
(f) is an actual lion-fish; and (g) shows a mimic octopus
as a banded sea-snake and (h) is an actual banded
sea-snake. Images from the Norman, 2001 article
 in Proc. R. Soc. Lond. B.

Different animal species have evolved a number of ways to hide in their environments. One of the most popular tactics is by camouflage, often by matching the background or by having patterns that break up the animal's outline (think: zebras and leopards). Others have evolved to resemble other species that are generally toxic or venomous, in a technique called mimicry. But a few amazing species have been recently discovered to have the ability to alter their mimicry to actively imitate a range of species, depending on their circumstances. The most remarkable of these is the mimic octopus, which shifts its shape and behavior to mimic a number of different species as fluidly as a real-life Mystique from the X-Men.

This week at Accumulating Glitches I talk about the remarkable acts of mimicry by one of our planet's most fascinating species, the mimic octopus. Check it out here.

And to learn more, check these out:

1. Norman, M.D., Finn, J., & Tregenza, T. (2001). Dynamic mimicry in an Indo-Malayan octopus Proc. R. Soc. Lond. B,, 268, 1755-1758 DOI: 10.1098/rspb.2001.1708

2. Hanlon, R.T., Conroy, L., & Forsythe, J.W. (2008). Mimicry and foraging behaviour of two tropical sand-flat octopus species off North Sulawesi, Indonesia Biological Journal of the Linnean Society, 93, 23-38 DOI: 10.1111/j.1095-8312.2007.00948.x

Nature’s Halloween Costumes

Image by Steve at Wikimedia Commons.

It seems like everyone is racking their brains to come up with a great Halloween costume. But we’re not the only ones to disguise ourselves as something we’re not. Many animals put on costumes just like we do. Take this gharial crocodile for example (do you see him?), covering himself in parts of his environment to hide.

Other animals, like this tawny frogmouth below, develop physical appearances that help them blend in with their surroundings. When threatened, these birds shut their eyes, erect their feathers and point their beak in such a way to match the color and texture of the tree bark.


Image by C Coverdale at Wikimedia Commons.

Rather than hide, some animals have a physical appearance to disguise themselves as other species that are often fierce, toxic or venomous. This type of mimicry is called Batesian mimicry, named after Henry Walter Bates, the English naturalist who studied butterflies in the Amazon and gave the first scientific description of animal mimicry. This plate from Bates’ 1862 paper, Contributions to an Insect Fauna of the Amazon Valley: Heliconiidae, illustrates Batesian mimicry between various toxic butterfly species (in the second and bottom rows) and their harmless mimics (in the top and third rows).


This plate from Bates’ 1862 paper, Contributions to an Insect Fauna of
the Amazon Valley: Heliconiidae is available on Wikipedia Commons.

The bluestriped fangblenny takes its costume another step further, by changing its shape, colors, and behavior to match the company. This fish changes its colors to match other innocuous fish species that are around so it can sneak up and bite unsuspecting larger fish that would otherwise bite them back! Learn more about them here.

The fish on the far left is a juvenile cleaner wrasse in the act of cleaning another fish. The two fish in
the middle and on the right are both bluestriped fangblennies, one in its cleaner wrasse-mimicking
coloration (middle) and the other not (right). Figure from the Cheney, 2013 article in Behavioral Ecology.

But the Master of Disguise title has got to go to the mimic octopus. This animal can change its color, shape and behavior to look and behave like a wide range of creatures, including an innocuous flounder, a poisonous lionfish, or even a dangerous sea snake! Check it out in action:

Did that Rock Just Ink on Me? (A Guest Post)

By Sam Brunner and Ian Straus

Image from NOAA.

Cephalopods, like octopuses, squid, and cuttlefish, are well known for their ability to alter the color and patterns on their bodies for better camouflage, mimicry, and even communication. By developing a unique set of camouflage tools, cephalopods excel at not being seen or being seen but not detected as a cephalopod. There are videos all over the internet showcasing how squid can terrify divers with their flashing red displays, or how some octopuses avoid their predators by mimicking the local venomous snakes. This video provides the perfect example of an octopus using its incredible camouflage to become invisible while convincing you it is merely a clump of algae.

You see, where many animals have lowly organelles in their skin cells responsible for pigments, cephalopods are unique in having a whole organ dedicated to this task. They’re called chromatophores. Each chromatophore is made up of colored pigment granules held in the ever so eloquently named cytoelastic sacculus, which is surrounded by 15 to 25 radially arranged muscle cells (like spokes on a wheel). Each muscle cell is also associated with a neural axon and its supportive glial cells, which puts it under the control of the nervous system.

Image created by Ian Straus.

So, when an octopus wants to change color, a signal travels from the brain and down the neural axon to the chromatophore, telling the muscles to contract. The muscle contraction pulls on the pigment-filled sac, stretching it to change its translucence and thereby changing the amount of color showing through. The chromatophores can produce yellow, orange, red, brown, and occasionally black pigments. The intensity of the color depends on how many muscle fibers are contracted, and therefore how much the sac expands and the pigment is spread out. Once a chromatophore develops, it will stay put for the rest of the animal’s life. As the animal grows, new, smaller chromatophores develop in the spaces between the old ones. These new organs are only able to produce yellow pigment at first, but darken as they get older.

Dieter Froesch of the Zoological Station of Naples conducted an experiment using the common octopus (Octopus vulgaris) to determine which of their nerves control the chromatophore organs in each part of the body. Each octopus examined was anaesthetized, had a nerve cut and was then checked a few days later for the results.

Froesch found that of the thirty nerves leaving the brain of O. vulgaris, ten have control over chromatophores, with each nerve controlling a different region of the body. These regions have well defined borders with no overlap. The head region alone is controlled by five different nerves, especially around the eyes. This suggests that fine control over color patterns around the eye may play an important role in effective camouflage. Furthermore, the coloration and chromatophores in one area of the body, the funnel, didn’t appear to be controlled by any of the nerves cut in this experiment.



This image shows the different chromatophore regions that each nerve controls. The funnel, which does not have nerve-controlled chromatophores, is the tube near the eye. Image is from Froesch’s Marine Biology paper (1973).

In most cephalopods, vision is the most important sense. Information about their surroundings is processed in vision regions of the brain, which then send along information to chromatophore regions of the brain. The chromatophore brain regions, which contain motor neurons, send signals to the chromatophores throughout the body telling them to contract. So, if an octopus sees a bright orange coral structure, the chromatophores will contract in a way that results in bright orange skin being displayed.

The vision-chromatophore pathway may be the most important part of cephalopod camouflage, but it isn’t the only set of structures that play a role. Leucophores allow for white pigment and reflective iridophores are responsible for blues and greens. Cuttlefish and many octopuses also have muscles throughout the skin arranged into papillae, which can form bumps or spikes that transform the texture of the animal into that of seaweed or an inconspicuous rock. In Octopus vulgaris, all these components are arranged into 1 mm wide units distributed across the skin, with the leucophores and iridophores in the central region, papillae at the exact center, and chromatophores distributed throughout. This complex physiological system grants cephalopods the greatest array of possible camouflages and firmly positions them as the coolest of the invertebrates.

Want to know more?  Check these out:

1. Froesch, D. (1973). Projection of chromatophore nerves on the body surface of Octopus vulgaris Marine Biology, 19 (2), 153-155 DOI: 10.1007/BF00353586

2. Messenger JB (2001). Cephalopod chromatophores: neurobiology and natural history. Biological reviews of the Cambridge Philosophical Society, 76 (4), 473-528 PMID: 11762491

The Real Catfish of Lake Tanganyika

Photo of Manti Te'o by Shotgun Spratling
and Neon Tommy at Wikimedia

Poor Manti Te’o may just be the most gullible schlub on the planet. For those of you that haven’t heard the story, the Notre Dame linebacker and runner-up for the 2012 Heisman Trophy led his team to the BCS National Championship Game, despite (or perhaps inspired by) the tremendous personal losses he has suffered this season. Last September, Te’o learned first of the death of his grandmother, and then within hours learned of the death of his girlfriend, Lennay Kekua. But after months of grieving and playing his heart out, Te’o began to receive phone calls from his “dead” girlfriend, telling him she missed him. Totally freaky, right? Notre Dame hired investigators to look into the undead girlfriend and they discovered that not only is Kekua not dead, she was never alive. The girl never existed. And what of Te’o’s relationship with her? According to Te’o, he never actually met her in person: Their entire long-term relationship took place online and over the phone, so he never realized that her entire persona was a fraud. He was completely and totally catfished.

He was what?

The top definition of catfish at Urban Dictionary reads:

“A catfish is someone who pretends to be someone they're not using Facebook or other social media to create false identities, particularly to pursue deceptive online romances.

Did you hear how Dave got totally catfished last month?! The fox he thought he was talking to turned out to be a pervy guy from San Diego!”

The term apparently originates with the 2010 documentary, Catfish, about a young man who falls in love with a woman on Facebook… who turns out to be someone else. Ew. But why the term catfish? A story in the movie explains that when cod are shipped from North America to Asia, their inactivity can result in mushy meat. Fishermen discovered that putting catfish in the cod tanks will keep the cod active and preserve meat quality. Like catfish for cod, the guy philosophizes, people that have deceptive identities keep idle people active. (The producers of the documentary now produce an MTV series by the same name about this online phenomenon).

But it’s not like real catfish can imitate others… Or do they?

Three poisionous Lake
Tanganyikan catfish. Figure from
Jeremy's 2010 Evolution paper.

A 2010 paper by Jeremy Wright at the University of Michigan at Ann Arbor documents the first known case of mimicry in catfish. There are several types of mimicry in the animal world. In this case, Jeremy was investigating functional Müllerian mimicry, a phenomenon in which two or more poisonous species mimic each other's predator-deterring warning signals (as opposed to Batesian mimicry, where a non-poisonous animal looks like a poisonous one). It may seem excessive to have both poison and warning coloration, but poison only helps after you’ve been bit. If your predators are smart enough to learn from experience, you can benefit from having more poisonous buddies around that look just like you so that if a predator bites just one of you it will then learn to avoid all of you. Sometimes it pays to look just like everyone else.

But just because you look like everyone else doesn’t mean that it is because you’re imitating others. I mean, maybe that’s just the way you look. So how do you know if a bunch of animals that look like one another are using functional Müllerian mimicry?

Jeremy studied a number of similarly-colored, poisonous and closely-related catfish species in the African Great Lake, Lake Tanganyika. All of these Tanganyikan catfish species (from the Synodontis genus) have dark spots on a yellowish background and dark fins with white borders. Could this be because of functional Müllerian mimicry?

Jeremy put a bunch of largemouth bass each into their own tank. Largemouth bass are predators that use their vision to find and eat most any fish that will fit in their mouths. But these bass were from Michigan, so they’d never had any experience with a poisionous, spotted Synodontis catfish. A clear barrier divided each tank in half and the bass was placed on one side of the divider, and a bite-sized fish was put on the other. The bite-sized fish was either a spotted and poisonous Synodontis multipunctata catfish, a spotted and poisonous Synodontis petricola catfish, or a not-spotted and not-poisonous minnow. He then counted how many times the bass struck the plastic divider in 5 minutes as a measure of how much that bass wanted to eat the bite-sized fish. After the 5 minutes were up, Jeremy removed the divider and watched to see if the bass ate the bite-sized fish. For each bass, he did this every day for 5 days, giving each bass the same species of bite-sized fish every day, so it could learn from its past experiences.

A naïve largemouth bass excited to eat a bitesized, but poisonous Synodontis petricola catfish.

A naïve largemouth bass gets to try to eat a bitesized, but poisonous Synodontis petricola catfish… and it doesn’t go so well for him.

A no-longer naïve largemouth bass gives his best death stare to a bitesized, but poisonous Synodontis petricola catfish. Videos provided by Jeremy Wright.

On the first day with the bite-sized fish, all the bass struck at the divider equally regardless of whether it was a spotted poisonous catfish or a minnow. But after their first bite, the bass given spotted poisonous catfish quickly lost their interest in them even though the bass given minnows continued to vigorously strike at them every day. When Jeremy later gave them a different species of bite-sized fish, those previously given a spotted poisonous catfish avoided both species of spotted poisonous catfish, but readily ate the minnows. So the bass had learned. Spotted catfish: bad! Minnows: yum! And the spotted catfish look was transferable between the two species… the hallmark of functional Müllerian mimicry. Further analysis of the venom revealed that these catfish species were all equally poisonous: Painful, but not deadly.

Online catfish like Lennay Kekua are usually like these real-life spotted poisonous catfish: painful, but not (usually) deadly. And they typically have facebook pages and twitter accounts full of sexy photos and superficial chatter. If we’re smart, we can learn to avoid them. Do you know if all your “friends” on social media sites are who they say they are?

Want to know more? Check this out:

Wright, J. (2011). CONSERVATIVE COEVOLUTION OF MÜLLERIAN MIMICRY IN A GROUP OF RIFT LAKE CATFISH Evolution, 65 (2), 395-407 DOI: 10.1111/j.1558-5646.2010.01149.x

What Do Animals Think of Their Dead?

You’re running around, going about your day, and suddenly you see a dead guy lying in the sidewalk. What do you feel? Sad? Scared? Do you look around to see if you might be in danger too? Would you feel any differently if the dead body on the sidewalk were that of a squirrel, and not a human? Do animals share these same emotional and thought processes when they come across their own dead?

Teresa Iglesias, Richard McElreath and Gail Patricelli at the University of California at Davis pondered this philosophical question themselves. Then they set off to scientifically test it. 

A western scrub-jay collecting peanuts from a windowsill.
Photo by Ingrid Taylar at Wikimedia.

Teresa, Richard and Gail had noticed that when a live western scrub-jay encounters a dead western scrub-jay, it hops from perch to perch while calling loudly, a response the researchers called a “cacophonous reaction”. This boisterous response usually attracts other scrub-jays, which either join in with their own cacophonous reaction or just sit quietly observing. Is this truly a response to seeing their own dead?

The researchers put bird feeders baited with peanuts in backyards all over Davis, California (with the permission of the backyard-owners, of course). Once they find a feeder, western scrub-jays take the peanuts one at a time and fly off to cache them away before returning for another peanut. While the scrub-jays were away caching a peanut, the researchers put a collection of painted wood pieces on the ground, arranged to vaguely look like a dead scrub-jay. Then they snuck away to watch if the scrub-jays responded when they returned. Several days later, they came back to the same feeders, waited until the scrub-jay was away caching a peanut, and then placed an actual scrub-jay carcass and feathers (usually found somewhere in the area). Then they snuck away again to watch if the scrub-jays responded any differently when they returned.

Watch the behavior of western scrub-jays before and after
the placement of a dead scrub-jay. The “after” response starts
about one minute into the video. Video by Teresa Iglesias.

And in a nutshell, they did. When the scrub-jays returned to find a dead scrub-jay, they called like crazy and hopped around in a full-blown cacophonous reaction. In most cases, this reaction attracted other scrub-jays who joined in the lively response. Additionally, when the dead scrub-jay was present, they took 90% fewer peanuts. None of this ever happened in response to a pile of painted wood. When a scrub-jay returned to find painted wood, it went about its day, calling at normal rates and collecting peanuts as usual. One jay was so unconcerned by the painted wood, it even cached peanuts under it!

A western scrub-jay thinks the painted wood makes
a good peanut-hideaway. Video by Teresa Iglesias.

This convinced the researchers that the scrub-jays were not simply responding to something new near the feeder, but were instead responding to dead bodies. But does it matter whether the body is a conspecific (the same species) or a heterospecific (different species)? And what do these group responses mean? Are they gathering in mourning? Or is their response a way of hollering, “Look out! Something out there is killing us!”?

To find out, the researchers did the same thing they had done before, but this time, they placed either a scrub-jay carcass or a mounted great horned owl (a scrub-jay predator). Interestingly, the scrub-jays responded with the same cacophonous reactions and avoided the peanuts in both cases. However, the scrub-jays called for longer and defensively swooped at the mounted owl, something they didn’t do to the scrub-jay carcass. To check if this heightened response to the owl mount was due to its lifelike position, they repeated the study, comparing scrub-jay responses to a scrub-jay carcass or a mounted scrub-jay. Although the dead-looking carcass always elicited cacophonous aggregations, mounted scrub-jays only elicited cacophonous aggregations a third of the time. But when jays did respond to the scrub-jay mounts, they often swooped at it as if it were a competitor, something they never did to a scrub-jay carcass.

What does this all mean? Western scrub-jays respond to conspecific (scrub-jay) carcasses not just because their appearance is surprising, but because they may represent some kind of risk. They seem to recognize that the carcass is not a living threat, because they don’t swoop at it like they do to both owl and scrub-jay mounts. But they do produce an alarm response, much as they do when a predator is present. So their responses to dead scrub-jays are not so much “funerals” in the way that people mourn and reflect on their dead, but rather a way to announce a risk of getting hurt or killed.

Are western scrub-jays uniquely aware of the risk a dead conspecific may represent? Maybe not. Although this was the first comprehensive study of this phenomenon, similar behavioral responses to dead conspecifics have been observed in ravens, crows and magpies, all members of the corvid family of birds, like scrub-jays. But rats and even bees have also been observed to avoid dead conspecifics. Many animals may be more cognizant of death than we give them credit for.

Want to know more? Check this out:

Iglesias, T.L., McElreath, R., & Patricelli, G.L. (2012). Western scrub-jay funerals: cacophonous aggregations in response to dead conspecifics Animal Behaviour DOI: 10.1016/j.anbehav.2012.08.007

Friends with Benefits

"It is not so much our friends' help that helps us
as the confident knowledge that they will help us."
-Epicurus, Greek philosopher (341 - 270 BC)

“Silences make the real conversations between friends.
Not the saying but the never needing to say is what counts.”
-Margaret Lee Runbeck, American author (1905 - 1956)

photo by Jérôme Micheletta, Macaca Nigra Project

Where would we be without our friends? Friends lend a hand in bad times and cheer us on in good times. They make us laugh, share their food, and tell us where to find interesting things… like fruit or coconuts!

Okay, so maybe finding fruit and coconuts isn’t that high on your priority list, but it seems to be pretty high on the list for crested macaques. And lucky for them, they have friends to rely on too.

Jérôme Micheletta and Bridget Waller at the University of Portsmouth in the United Kingdom set out to determine whether social factors influence the ability of crested macaques to follow the eye gaze of a group-mate and potentially gain important information. To do this, they hung out at the Marwell Wildlife Zoological Park in Winchester, U.K. every day to watch and video record the crested macaques. An experimenter would wait for two crested macaques to be within 1 meter of each other with one individual facing the experimenter (they called this animal “the informant”… not to be confused with Matt Damon) and the other individual facing the informant and facing away from the experimenter (they called this animal “the subject”). You can imagine, this process involved a lot of waiting around. Once the animals were in place, the experimenter held up a yummy treat (an orange, a banana, or a coconut). The informant would see the treat and then the subject would either look at the treat or not. In these cases, the subjects looked at the treats 64% of the time.

This figure from Micheletta and Waller's Animal Behaviour
paper shows their experimental procedures.

But how do we know that the subjects followed the informants’ gaze and didn’t respond to something the experimenter or some distant cage-mate did? Micheletta and Waller also recorded the responses of the same animals in a control situation: the experimenter would wait for a subject to be away from its cage-mates, but with its back turned to the experimenter. Then the experimenter would hold up the yummy treat. In these control trials, the subjects looked at the treats only 7% of the time.

So it looks like crested macaques use their peers’ eye gaze as information on where to look. They also were faster to look if their cage-mate moved his/her head in combination with an eye movement, rather than just the eyes. But, does the social context matter? For each pair of macaques, Micheletta and Waller calculated the relative dominance status and friendship strength. They used months of observations of aggressive encounters in which they knew the winners and losers of each encounter to rank the overall dominance hierarchy of each animal in the group. A typical aggressive encounter either involved one monkey chasing another (which would either run away or crouch) or a monkey approaching another and taking away his/her food or grooming-buddy or mate (How rude!). They also determined friendship strength by calculating the average number of times they sat in contact with or groomed a specific individual versus other animals in the group.

If the informant was a friend, the subject was quicker to look at the food than if the informant was not a friend, although friendship did not influence the overall success rate. And the relative dominance status didn’t seem to have any effect.

Why might macaques follow their friends’ gazes faster than nonfriends’ gazes? Maybe they are generally more visually attentive to their friends than their nonfriends, as is true in chimpanzees, siamangs, chacma baboons and ring-tailed lemurs.  Or maybe a friend’s information is more relevant than a nonfriend’s information. Friends often share motivations and needs and often compete less and share more with each other than with nonfriends (although there are many exceptions to this, as you may have experienced). All of these possibilities leave open new avenues for future research. But one thing is clear: It sure is good to have friends.

Want to know more? Check this out:

Micheletta, J., & Waller, B. (2012). Friendship affects gaze following in a tolerant species of macaque, Macaca nigra Animal Behaviour, 83 (2), 459-467 DOI: 10.1016/j.anbehav.2011.11.018

Do you have a thought on friends that you would like to share? Comment below.