Camouflage examples

[StringJunky]

1 hour ago, Genady said:

But I did not ask about any point of view on evolution. I ask a question related to scientific method.

Given a hypothesis, "animals have counter shading because it balances their light reflection and makes them less visible," what test or tests could support or refute this hypothesis?

Not far off I think. Movement is the primary stimulus for detection though. Predators and prey have  high contrast vision to improve acuity. Further reference:

Predator perception and the interrelation between different forms of protective coloration - M Stevens

In the corner of the eye: camouflaging motion in the peripheral visual field - Smart, Cuthill

 

 

[Genady]

There are several alternative hypothetical explanations for the light belly / dark top coloration, for example, thermal regulation and UV protection. I remember reading about a study that tried to test the counter-shading hypothesis "by the book":

Assuming this hypothesis is correct, they made a prediction about how sharp the difference between the belly and the top should be in different environments, and they analyzed available data in this respect. The data seemed to support the hypothesis but was not yet statistically significant. They needed more data.

[StringJunky]

54 minutes ago, Genady said:

There are several alternative hypothetical explanations for the light belly / dark top coloration, for example, thermal regulation and UV protection. I remember reading about a study that tried to test the counter-shading hypothesis "by the book":

Assuming this hypothesis is correct, they made a prediction about how sharp the difference between the belly and the top should be in different environments, and they analyzed available data in this respect. The data seemed to support the hypothesis but was not yet statistically significant. They needed more data.

Could the white underside be to retain heat, as it's more reflective?

Edited June 23, 2023 by StringJunky

[Genady]

6 minutes ago, StringJunky said:

Could the white underside be to retain heat, as it's more reflective?

Sorry, I don't remember the details of how it supposed to work. Perhaps, the white underbelly is just a lack of coloration, while the dark top / melatonin has a function... I'm not sure.

[StringJunky]

9 hours ago, Genady said:

Sorry, I don't remember the details of how it supposed to work. Perhaps, the white underbelly is just a lack of coloration, while the dark top / melatonin has a function... I'm not sure.

Quote

https://indianapublicmedia.org/amomentofscience/soft-white-underbelly.php#:~:text=By having a pale belly,is easier to blend in.

It's because whether you evolved in the savannas of Africa or the woods of North America, the sun was always in the same place: overhead. That means more light comes from above than below. True, light gets reflected back up from the ground, but not as much as comes down from the sky. More light lands on a four-footed animal's back than on its belly, making the back brighter and the belly darker. That's no good for hiding.

By having a pale belly and a dark back, animals balance out the amount of light that reflects off their bodies. The dark back absorbs more, the pale belly reflects more. The contrast between top and bottom is diminished, and it is easier to blend in.

 

[Genady]

2 minutes ago, StringJunky said:

 

Right. But repeating the same story does not make it truer. I don't say, it is not true. I just don't know of a good supporting evidence for it.

[StringJunky]

3 minutes ago, Genady said:

Right. But repeating the same story does not make it truer. I don't say, it is not true. I just don't know of a good supporting evidence for it.

The constant is the sun position, so that feature is reflected all over the globe. 

Edited June 23, 2023 by StringJunky

[Genady]

2 minutes ago, StringJunky said:

The constant is the sun position, so that feature is reflected all over the globe. 

Does this fact support this hypothesis?

[StringJunky]

15 minutes ago, Genady said:

Does this fact support this hypothesis?

Yours?

[Genady]

1 minute ago, StringJunky said:

Yours?

Sorry, I don't understand the question. My what?

[TheVat]

Seems like experimental evidence was minimal until recently.

https://en.wikipedia.org/wiki/Countershading

Despite demonstrations and examples adduced by Cott and others, little experimental evidence for the effectiveness of countershading was gathered in the century since Thayer's discovery. Experiments in 2009 using artificial prey showed that countershaded objects do have survival benefits and in 2012, a study by William Allen and colleagues showed that countershading in 114 species of ruminants closely matched predictions for "self-shadow concealment", the function predicted by Poulton, Thayer and Cott.

If Thayer's Law is valid, then one would expect some predators to favor early morning or near sunset to hunt, when the countershading would be of less use.

Edited June 23, 2023 by TheVat
pckyjridjgdkd

[Genady]

Yes, not much, but recently indeed some supporting studies appeared. This is perhaps the latest, from 2020:

Quote

Surprisingly, no study has examined how countershading alters prey contrast, or investigated how the presence of a dorsoventral luminance gradient affects detection under controlled viewing conditions. It has also been suggested that the direction of the dorsoventral luminance gradient (darkest or lightest on top) may interfere with predators' abilities to resolve prey's three-dimensional shape, yet this intriguing idea has never been tested. We used live fish predators (western rainbowfish, Melanotaenia australis) and computer-generated prey images to compare the detectability of uniformly pigmented (i.e. non-countershaded) prey with that of optimally countershaded prey of varying contrasts against the background. Optimally countershaded prey were difficult for predators to detect, and the probability and speed of detection depended on prey luminance contrast with the background. In comparison, non-countershaded prey were always highly detectable, even though their average luminance closely matched the luminance of the background.

Countershading enhances camouflage by reducing prey contrast - PubMed (nih.gov)

[Genady]

I don't see how the countershading hypothesis applies to the green turtle. I'd rather hypothesize that the top is dark for the camouflage purpose, and the belly is light because of lack of this purpose.

[TheVat]

Yes, more than one type of selective force will drive coloration.  Slow animals with bellies on the ground or near the ground perhaps have less need for countershading.  And more need to look like rocks or other non-mobile surface features.

[StringJunky]

Could the turtles bellies be adapted for when swimming near the surface, to reduce attention from predators lower down in the water?

[Genady]

6 minutes ago, StringJunky said:

Could the turtles bellies be adapted for when swimming near the surface, to reduce attention from predators lower down in the water?

Yes, certainly could. Dark when viewed from above against the dark background and light when viewed from below against the light background. Like the explanation for the sharks which I've mentioned here: https://www.scienceforums.net/topic/128920-camouflage-examples/?do=findComment&comment=1243465.

The same perhaps holds for the manta:

 

[iNow]

48 minutes ago, StringJunky said:

Could the turtles bellies be adapted for when swimming near the surface, to reduce attention from predators lower down in the water?

This is the correct answer 

[Genady]

Neither countershading nor "light against surface" explanations seem applicable to bottom dwelling animals, such as stingrays and countless others with similar dark-top-light-bottom coloration.

[iNow]

4 hours ago, Genady said:

Neither countershading nor "light against surface" explanations seem applicable to bottom dwelling animals, such as stingrays and countless others with similar dark-top-light-bottom coloration.

Are they no longer edible nor subject to standard predator optics when they’re no longer trawling the sand and are instead floating though much higher columns of water? 

The white bottom and dark tops were selected. Do you have an alternative / counter explanation for why this is so if it’s not simply to reduce visibility of prey animals in dark ocean conditions… conditions where down is darker and up is lighter?

Edited June 25, 2023 by iNow

[Genady]

34 minutes ago, iNow said:

Are they no longer edible nor subject to standard predator optics when they’re no longer trawling the sand and are instead floating though much higher columns of water? 

The white bottom and dark tops were selected. Do you have an alternative / counter explanation for why this is so if it’s not simply to reduce visibility of prey animals in dark ocean conditions… conditions where down is darker and up is lighter?

I suspect that they never had or lost pigmentation on the underside because it is not needed.

Also possible, that an ancestor of rays was pelagic with a light underside like in manta rays, for example. The stingrays evolved to be bottom dwellers but retained the light underside of the ancestor.

[StringJunky]

12 hours ago, Genady said:

I suspect that they never had or lost pigmentation on the underside because it is not needed.

Also possible, that an ancestor of rays was pelagic with a light underside like in manta rays, for example. The stingrays evolved to be bottom dwellers but retained the light underside of the ancestor.

Absence of modification may mean it was already adapted... first time lucky, so to speak.

[iNow]

39 minutes ago, StringJunky said:

Absence of modification may mean it was already adapted... first time lucky, so to speak.

Agreed, and it also seems to be a convergent trait across several distinct genetic lineages 

[Saber]

On 6/23/2023 at 4:44 PM, Genady said:

Sorry, I don't remember the details of how it supposed to work. Perhaps

Ohhh   i thought......you said

 

Quote

In fact, many years ago I studied biology, and got Master Degree (M.Sc.) in biology. One of my favorite courses was Animal Behavior, which I passed with A+. I remember well

When  writing to others :   Sorry   / Suppose / Perhaps......

When answering me  :   In fact / I studied / Got masters / My  favorite course / I passed with A+  /  I remember well

[Genady]

30 minutes ago, Saber said:

Ohhh   i thought......you said

 

When  writing to others :   Sorry   / Suppose / Perhaps......

When answering me  :   In fact / I studied / Got masters / My  favorite course / I passed with A+  /  I remember well

Yes, it is true. I remember some things and I don't remember some details of some other things. As I said, "many years ago"...

Yes, I use different expressions in different posts.

So?

[Moontanman]