Wednesday, November 22, 2017

Eye Didn’t See That

By Evan Hovey

A grandmother and her grandson watching the television.
The elder is straining to see while the young man is not having any troubles.
Photo by Evan Hovey.

It’s Thanksgiving and the family just finished stuffing their faces full of turkey and cranberry fluff. Everyone meanders into the living room to sit down, let the tryptophan sink in, and watch some football. As you sit there, you start to observe the older family members around you take out their glasses or bifocals and squint towards the television in attempts to see what is going on. You begin to ponder the thought, “am I going to start to lose my eye sight as well?” Well, as it turns out, as you age, the number of cells that respond to light and color (called photoreceptors) begins to decrease.

Songhomitra Panda-Jonas, Jost Jonas, and Martha Jakobczyk-Zmija at the University of Erlangen-Nurnberg, Germany, looked into the number of photoreceptors in the retina of the eye to determine whether there was a loss as you age. The retina is the thin layer of tissue that lines the back of the eye. It is the location where your eye transfers what you see to the brain. There are two different kinds of photoreceptors in your eyes: rods and cones. Rods are those that detect light at low levels, which is what helps us see at night. Cones, on the contrary, are those that take in high light levels and help decode color. The authors believed that there would be a decrease in both kinds of photoreceptors as the eye got older (the older the person, the fewer photoreceptors). They came up with this hypothesis in part because of prior knowledge of a loss of tissue associated with vision in other parts of the eye as you age.

The researchers approached this study by obtaining fifty-five eyes from human donors that died at ages ranging from 18-85. The eyes were removed from the bodies less than eleven hours after death. Then the eyes were cut open and tissue samples from the retina were obtained. To determine the amount of photoreceptors in the tissue samples, the researchers used an ultrasound to view the retina and counted the photoreceptors on a photograph taken with the ultrasound. The two different kinds of cells were distinguished by their sizes (the larger cells were the cones and the smaller cells were the rods).

The results they found were as expected: the older you get, the fewer photoreceptors you have and the worse your eyesight is. The decline of the number of photoreceptors was at a constant rate throughout all ages of life. However, the number of rods declined faster than the number of cones. The loss of these photoreceptors causes you to view things with more difficulty. As your rods die, you begin to develop night blindness (the inability to see well in poor lighting or darkness). When your cones die, you begin to lose more of your visual perception, which includes straining when looking at something from a distance, as well as affecting how you see fine detail such as reading a book or looking at a television. The combined loss of your rods and cones is part of what causes older individuals to have more vision problems.

As you progress through life, your photoreceptors decline, causing your vision to get worse. As you sit down after Thanksgiving to enjoy some good old-fashioned fall football and the elderly people strain to see the television, you now know that the oldest person in your family is most likely having the hardest time seeing that big touchdown.


If you would like to read the actual paper, the source is located below:

Panda-Jonas, S., Jonas J., Jakobczyk-Zmija, M. (1995). Retinal photoreceptor density decreases with age: Ophthalmology, 102 (12), 1853-1859

Tuesday, November 14, 2017

Let’s Talk Turkey: 8 Surprising Facts About Turkeys

A reposting of an article from November 24, 2014.

A wild male turkey struts his stuff.
Photo by Lupin at Wikimedia Commons.
1. Turkeys are all-American. The modern domesticated turkey is descended from the wild turkey of North America, which is essentially a pheasant.

2. Domestic turkeys can’t fly or have sex. Domestic turkeys have been bred to have enormous breast muscles for our dinner tables. Their breast muscles have become so large that these top-heavy birds have lost the ability to fly and even to have sex! Domestic turkey eggs now have to be fertilized by artificial insemination. Wild turkeys with their functionally-sized breast muscles, however, can fly up to 55 mph for short distances and have sex just fine.

3. Male turkeys (called toms) are courtship-machines. Wild turkey males are substantially larger than females, and their 5,000 to 6,000 feathers have red, purple, green, copper, bronze, and gold iridescence. Like peacocks, male turkeys puff up their bodies and spread their elaborate feathers to attract mates and intimidate rivals. In comparison, female wild turkey feathers are duller shades of brown and grey to better hide from predators. And as if their flashy feathers weren’t enough, toms also have fleshy body appendages called snoods (the fleshy snotsicle that hangs over their beak) and wattles (the thing that looks like a scrotum under their chin). When the male is excited, the snood and wattle fill with blood and turn bright red. Sexy!

4. Turkeys are intelligent animals. They even have the ability to learn the precise details of a 1,000-acre area. And no, turkeys will not drown if they look up into the sky during a rainstorm.

5. Turkeys are social animals. They create lasting social bonds with each other and are very affectionate. Turkeys can produce over 20 different vocalizations, including the distinctive gobble (produced only by males), which can be heard up to a mile away! Individual turkeys have unique voices that they use to recognize each other.

6. Female turkeys (called hens) are good moms. Wild turkey babies (called poults) are precocial, which means that they hatch out of their eggs already covered in fluffy down and able to walk, run and feed themselves. They stick close to their mother for protection from predators, but unlike many other species of bird mothers, she doesn't have to feed them. Although wild turkeys roost in the trees at night to avoid predators, poults are unable to fly for their first few weeks of life. The mother stays with them at ground level to keep them safe and warm until they are strong enough to all roost in the trees with her.

A wild turkey mom and her poults. Photo by Kevin Cole at Wikimedia Commons.

7. Ben Franklin wanted the turkey to be America’s national bird. Benjamin Franklin famously argued that the wild turkey, not the bald eagle, should be America's national bird. In a letter to his daughter, he wrote, "For my own part, I wish the bald eagle had not been chosen as the representative of our country; he is a bird of bad moral character; he does not get his living honestly...like those among men who live by sharping and robbing...he is generally poor, and often very lousy. Besides, he is a rank coward; the little king-bird, not bigger than a sparrow, attacks him boldly and drives him out of the district...For in truth, the turkey is in comparison a much more respectable bird, and withal a true original native of America. Eagles have been found in all countries, but the turkey was peculiar to ours...".

8. Turkeys were once endangered. Although millions of wild turkeys used to live across the Americas, they were almost completely wiped out due to a combination of over-hunting and habitat destruction. Thanks to strong conservation efforts that included better hunting management, habitat protection, captive breeding, and reintroduction into the wild, wild turkey populations are now healthy and found in all of the lower 48 states.

Tuesday, November 7, 2017

Science Beat: Round 8

It is midterm time again. If you learn science better with a beat, check these out:


Chemistry:




Cellular Biology:




Anatomy and Physiology:




Vote for your favorite in the comments section below and check out other science songs worth learning at Science Beat, Science Beat: Round 2, Science Beat: Round 3, Science Beat: Round 4, Science Beat: Round 5, Science Beat: Round 6, Science Beat: Round 7, and Science Song Playlist. Check out some song battles about the life of scientists at The Science Life, Scientist Swagger and Battle of The Grad Programs! And if you feel so inspired, make a video of your own, upload it on YouTube and send me a link to include in a future battle!

Wednesday, November 1, 2017

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

Tuesday, October 24, 2017

The Smell of Fear

A reposting of an article from October 24, 2012.

Several animals, many of them insects, crustaceans and fish, can smell when their fellow peers are scared. A kind of superpower for superwimps, this is an especially useful ability for prey species. An animal that can smell that its neighbor is scared is more likely to be able to avoid predators it hasn’t detected yet.

Who can smell when you're scared? Photo provided by Freedigitalphotos.net.
“What does fear smell like?” you ask. Pee, of course.

I mean, that has to be the answer, right? It only makes sense that the smell of someone who has had the piss scared out of them is, well… piss. But do animals use that as a cue that a predator may be lurking?

Canadian researchers Grant Brown, Christopher Jackson, Patrick Malka, Élisa Jaques, and Marc-Andre Couturier at Concordia University set out to test whether prey fish species use urea, a component of fish pee, as a warning signal.


A convict cichlid in wide-eyed
terror... Okay, fine. They're
always wide-eyed. Photo by
Dean Pemberton at Wikimedia.
First, the researchers tested the responses of convict cichlids and rainbow trout, two freshwater prey fish species, to water from tanks of fish that had been spooked by a fake predator model and to water from tanks of fish that were calm and relaxed. They found that when these fish were exposed to water from spooked fish, they behaved as if they were spooked too (they stopped feeding and moving). But when they were exposed to water from relaxed fish, they fed and moved around normally. Something in the water that the spooked fish were in was making the new fish act scared!

To find out if the fish may be responding to urea, they put one of three different concentrations of urea or just plain water into the tanks of cichlids and trout. The cichlids responded to all three doses of urea, but not the plain water, with a fear response (they stopped feeding and moving again). The trout acted fearfully when the two highest doses of urea, but not the lowest urea dose or plain water, were put in their tank. Urea seems to send a smelly signal to these prey fish to “Sit tight – Something scary this way comes”. And the more urea in the water, the scarier!

But wait a minute: Does this mean that every time a fish takes a wiz, all his buddies run and hide? That would be ridiculous. Not only do freshwater fish pee a LOT, many are also regularly releasing urea through their gills (I know, gross, right? But not nearly as gross as the fact that many cigarette companies add urea to cigarettes to add flavor).

The researchers figured that background levels of urea in the water are inevitable and should reduce fishes fear responses to urea. They put cichlids and trout in tanks with water that either had a low level of urea, a high level of urea, or no urea at all. Then they waited 30 minutes, which was enough time for the fish to calm down, move around and eat normally. Then they added an additional pulse of water, a medium dose of urea, or a high dose of urea. Generally, the more urea the fish were exposed to for the 30 minute period, the less responsive they were to the pulse of urea. Just like the scientists predicted.

A rainbow trout smells its surroundings.
Photo at Wikimedia taken by Ken Hammond at the USDA.

But we still don’t know exactly what this means. Maybe the initial dose of urea makes the fish hide at first, but later realize that there was no predator and decide to eat. Then the second pulse of urea may be seen by the fish as “crying wolf”. Alternatively, maybe the presence of urea already in the water masks the fishes’ ability to detect the second urea pulse. Or maybe both explanations are true.

Urea, which is only a small component of freshwater fish urine, is not the whole story. Urea and possibly stress hormones make up what scientists refer to as disturbance cues. Steroid hormones that are involved in stress and sexual behaviors play a role in sending smelly signals in a number of species, so it makes sense that stress hormones may be part of this fearful fish smell. But fish also rely on damage-released alarm cues and the odor of their predators to know that a predator may be near. Scientists are just starting to get a whiff of what makes up the smell of fear.

Want to know more? Check these out:

1. Brown, G.E., Jackson, C.D., Malka, P.H., Jacques, É., & Couturier, M-A. (2012). Disturbance cues in freshwater prey fishes: Does urea function as an ‘early warning cue’ in juvenile convict cichlids and rainbow trout? Current Zoology, 58 (2), 250-259

2. Chivers, D.P., Brown, G.E. & Ferrari, M.C.O. (2012). Evolution of fish alarm substances. In: Chemical Ecology in Aquatic Systems. C. Brömark and L.-A. Hansson (eds). pp 127-139. Oxford University Press, Oxford.

3. Brown, G.E., Ferrari, M.C.O. & Chivers, D.P. (2011). Learning about danger: chemical alarm cues and threat-sensitive assessment of predation risk by fishes. In: Fish Cognition and Behaviour, 2nd ed. C. Brown, K.N. Laland and J. Krause (eds). pp. 59-80, Blackwell, London. 3.