Evolution of color variation: Discussion

[drcrossfire]

What do you think could cause the selective pressure to create such variation in locales?

IE maybe the island species of Faly/Be benefit from being of similar color to the water. Predators may have more difficulty seeing a blue chameleon against a blue backdrop of water?

 

[Simon1986]

In theory surely it comes down to darwins "survival of the fittest" theory. Evolution favours the fittest and I'm thinking that some natural predator, environmental change would cause chameleons to evolve to survive e.g colour size etc

 

[Olimpia]

I've never read anything about it, but if I were to bet some money it would be that they owe their colors to female sexual selection, as in pretty much every other species where the males are flashy and the females are drab. They have two pressures on their coloration: camouflage against predators and female sexual preference, so they always have to balance those two pressures. In species where predators are few, males are free to indulge females more and thus have flashier colors (not just because the ladies like them but because you want to stand out from your background, to get their attention faster.)

Panthers have the added benefit of being able to alter their coloration, so unlike the poor guppy fish in studies by Dr. John Endler (1980, 1983, 1986) (he put fish into 10 ponds, 2 with no predators, 4 with a strong predator, and 4 with a weak predator and let them do their thing for 14 months) the chameleons have the benefit of being able to tone down their bright colors for survival while at the same time being able to turn up the dial as soon as a female walks by. The guppies could not, so in the ponds where predation was strong the guppies had to sacrifice flashiness for practicality. Where as the males in the no or weak predation ponds had become significantly more colorful, and had developed spots/patterns which contrasted against their environment, for increased visibility for females.

As far as where each locale color palette comes from, that's harder to say. I don't think it has anything to do with the color of the water or the trees, but let's assume that they started off as green (since most continental African chameleons are green). Once they had colonized the island of Madagascar I think it was probably just a question of where color variations started to pop up. If one chameleon in one area turned out a little more teal than blue and more females found that attractive (females are attracted to "different" and "new") then that male had more offspring. Those offspring were selectively more and more teal until they were turquoise, and so on and so forth. Where as the same process probably began somewhere else with a different palette, until the different locales began taking form. For example.

Sorry for the wordiness.

 

[drcrossfire]

Darwin actually never said "Survival of the Fittest" (A common misconception) ... but did make reference to natural selection by adaptation. Those that adapt, survive.

...that being said...

I am curious as to what has driven the coloration difference we can use to identify the different locales.

Sexual selection does explain parts of it, I ponder if there are any specific reasons for coloration differences geographically. Maybe there are certain plants/predators found in certain regions that may drift the coloration in a region.

Id be curious to hear from someone who's been there to know if they noticed an specific changes in flora or fauna which may cause certain advantages of colors.

 

[Ulrich]

Funny, I was looking for an answer to the question why men have beards. I found three answers: Rival Dominance, Sexual Attraction, Environment. Maybe in certain areas certain colors leave a bigger impact in terms of all three factors?

 

[Olimpia]

If we take the guppy example and carry it over to chameleons it makes sense that if your goal is to impress the ladies, and the male who does so is the most prolific, you want to stand out from your environment as much as possible so a female can spot you from several trees away. So if you live in a forest with lots of red flowers, it's probably in your best interest not to look like another red flower (not that I think this is what's going on). The colors unique to each locale probably have very little to do with environmental cues and more to do with other selective pressures.

Most likely, due to physical or man-made barriers, these things were left to run their course in more isolated population pockets (since chameleons aren't particularly inclined to migrate great distances), where they only overlap along the edges of two populations. Especially in islands the differences tend to be greater.

Also, an added thought on sexual selection - bright colors are more than just nice to look at, they signify health. A bland, greyish chameleon looks like it's on death's door for a reason. Where as a super vibrant, saturated male tells a female "look, I am in great health, this is because I am a successful hunter and have excellent genes. We'd make healthy babies together." Therefore, the brightest males will pretty much always be the more prolific breeders. And that in turn keeps selecting for brighter and better colors in subsequent generations.