Why do cave creatures lose skin pigmentation?

Forums: Science, Evolution, Cave Creatures, Adaptation, Skin Pigmentation
Email this Topic • Print this Page

Lots of animals that live in caves are white. And it's not that they just don't have a tan, it's that they have lost the genes for skin pigmentation.

Why did this happen? It's not like genes just fall off the DNA strand because they aren't being used. They have to be SELECTED off, right? But in a lightless environment, how can skin COLOR be selected against when nothing can see it?

Topic Stats
Top Replies
Link to this Topic

Type: Discussion • Score: 12 • Views: 5,962 • Replies: 30
Topic Closed

No top replies

@rosborne979,

I don't see it as being selected off. It just isn't being selected on. There becomes no survival disadvantage to losing pigmentation. So it seems. . . .

1 Reply

Perhaps there is a survival advantage to losing the pigment gene in a lightless environment. We just can't see it!

0 Replies

@rosborne979,

I'm no biologist, but I think pigmentation is a reaction to ultra-violet light.

If one is not exposed, reaction is unnecessary. no?

(the damned moles in my garden have no tan either, nor the slugs...)

1 Reply

@Rockhead,

Won't work. The pigmentation differences between a Finn and a Nigerian don't depend on sunlight.

1 Reply

@roger,

both grow darker when exposed to sun, no?

(I'm just filling space till a real expert comes by...)

0 Replies

@rosborne979,

I had one student do a paper on "Troglomorphy" once and the result was a positive correlation with an entire bank of morphological features that were (AS I RECALL) controlled by a very few gene functions. SO, while you posted about the whiteness of troglodytes ( also a common trogmorph is "clearness"), the entire complement for cave related features include several functional groups. (eg as eyes diminsih, other forms of enviro sensing become modified upward, or legs (all from the PAX) become ridiculously extended and cephalon sensor features increase).
Im no experet at all, Ive just recalled all I can remember (we were looking for foissil representatives of cave dwellers in the stratigraphic record and this studentwent on to do aPhD with another advisor because it became a real paleo problem not a geo one).
ID look up "GEnetic control of Troglomorphy" on Google and get back to us with a report. Im late for a fuckin meeting and you go and ask this damn question, Im gonna be late now.

1 Reply

@farmerman,

farmerman wrote:

Im late for a fuckin meeting and you go and ask this damn question, Im gonna be late now.

I've gotta run to work as well, but I'll check into it later. Thanks.

The PAX idea is one I hadn't thought of before. But it might make sense. Just like the experiments that russian guy did on Foxes decades ago...

0 Replies

@roger,

roger wrote:

I don't see it as being selected off. It just isn't being selected on. There becomes no survival disadvantage to losing pigmentation. So it seems. . . .

I don't think it works that way. Things don't just evolve away because they are unused. If they did, then there would be a whole new (as yet undefined) "force" underlying the theory of evolution. We would have to include it along with Founder Principle and Genetic Drift as one of the forces which impact the process.

2 Replies

@rosborne979,

Part of pigmentation is camouflage. No need for it when nobody can see you - heck, some of the predators in those environments don't even have eyes! Another part of pigmentation is sunblock. No need for that either down there. So maybe they don't "fall off" so much as they get pushed off as unnecessary; the space is taken up with adaptations that are more useful, like a better sense of direction or something.

0 Replies

@rosborne979,

rosborne979 wrote:

I don't think it works that way. Things don't just evolve away because they are unused

If it did, there would be lots of guys with no dicks Laughing

0 Replies

I would think there would be some small advantage to be got in not expending the energy necessary to produce pigment. Not a strong selective pressure, perhaps, but maybe enough of one to favor albinism over pigmentation over tens of thousands of generations in an environment where there is absolutely no advantage to be gained by maintaining pigmentation.

2 Replies

@patiodog,

I know in caves under the Alps speleologists found frogs indistinguishable from other frogs living outside, but without eyes. Not atrophied eyes, not blind frogs - just completely covered with skin where the eyes would have been.

If I can find a reference on DNA or MRIs of brain sections of these cave dwellers I'll post it; have a vague recollection that the parts of the brain corresponding to vision were also gone.

1 Reply

@patiodog,

patiodog wrote:

I would think there would be some small advantage to be got in not expending the energy necessary to produce pigment. Not a strong selective pressure, perhaps, but maybe enough of one to favor albinism over pigmentation over tens of thousands of generations in an environment where there is absolutely no advantage to be gained by maintaining pigmentation.

This was my original thought as well, that there might be some level of "energy cost" to every structure in the genome, no matter how inconsequential.

But if this is the case, then it's an important "force" in evolution. I would think such a thing would have far reaching effects on the overall process.

The other possibility is that genes become damaged over time simply through errors in reproduction and unless there is a selective pressure to repair them, the structures they represent simply fade away. But again, this would seem to be a significant force in the evolutionary process. One which I haven't seem mentioned before.

0 Replies

@rosborne979,

rosborne979 wrote:

roger wrote:
I don't see it as being selected off. It just isn't being selected on. There becomes no survival disadvantage to losing pigmentation. So it seems. . . .

I don't think it works that way. Things don't just evolve away because they are unused.

Yes, they do, even if they aren't being selected against. It's enough that they aren't being selected for. That's why our toes, once used to grip tree branches, are going away, slowly over time. Characteristics which no longer provide a selection advantage fade away slowly over the generations, as countless mutations take place.

1 Reply

@High Seas,

High Seas wrote:

I know in caves under the Alps speleologists found frogs indistinguishable from other frogs living outside, but without eyes. Not atrophied eyes, not blind frogs - just completely covered with skin where the eyes would have been.

If I can find a reference on DNA or MRIs of brain sections of these cave dwellers I'll post it; have a vague recollection that the parts of the brain corresponding to vision were also gone.

The reason I didn't want to use the loss of eyes (or the loss of wings on flightless birds) as the example in this discussion is because there can be a selective pressure to remove those organs, whereas skin color in a lightless environment would seem to be free from selective pressure (at least at the morphological level).

For example, eyes might devolve because they are prone to getting damaged and infected in a lightless environment. This could lead to a strong selection for smaller (and eventually no) eyes. The same for wings on flightless birds. Wings can get damaged, and they certainly take up extra muscle and add extra weight to the bird. All of that is strongly selectable.

0 Replies

Here is the thread on Silver Foxes if anyone wants to get some background on those russian experiments which linked domesticity of canines to skin/hair color through genes associated (coincidentally) with the adrenal gland.

0 Replies

@Brandon9000,

Brandon9000 wrote:

Yes, they do, even if they aren't being selected against. It's enough that they aren't being selected for.

I think you're making an assumption. Can you provide a reference to that.

Brandon9000 wrote:

That's why our toes, once used to grip tree branches, are going away, slowly over time.

How do you know that toes aren't acquiring their present configuration due to the selective forces which improved our feet for walking?

Brandon9000 wrote:

Characteristics which no longer provide a selection advantage fade away slowly over the generations, as countless mutations take place.

Again, I think you're making an assumption. Can you provide a reference to that.
Thanks.

1 Reply

@rosborne979,

Well, of course they're assumptions. Do we have anything else that comply with known observations?

1 Reply

@roger,

roger wrote:

Well, of course they're assumptions. Do we have anything else that comply with known observations?

Perhaps I should have said, "conjecture" instead of "assumption".

In any case, I don't think there's any defined theory to back up Brandon's statements.

0 Replies

Why do cave creatures lose skin pigmentation?

Related Topics

Quick Links

My Account

able2know