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What is the proposed selection pressure that leads to the distinctive coloration of Orca whales? I can find nothing in the literature.

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    $\begingroup$ Hello. I want to remind you that natural selection is not the only process important to evolutionary processes. There are probably several posts that discuss that. You will find a paragraph in the first answer on this post for example. $\endgroup$ – Remi.b Apr 3 '15 at 5:25
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    $\begingroup$ Adding to Remi.b's comment, not every trait is adaptive. We've most recently discussed this here in this answer to a question about rose thorns. $\endgroup$ – Corvus Apr 3 '15 at 5:30
  • $\begingroup$ Assuming the pattern of color would be adaptive (to a certain degree), here are few guesses. It sounds likely to me that such coloration would have evolved in reaction to recognition and signalling. Eventually due to sexual selection or to kin recognition. It may also be under selection for camouflage. Indeed orcas are black on the back and white on the belly and preys seeing from above would see a black background and those seeing from below would see a lighter background. $\endgroup$ – Remi.b Apr 3 '15 at 5:30
  • $\begingroup$ Clarification: I am familiar with concepts such as genetic drift and non-adaptive mutations. Given that the Orca is an apex predator, I could certainly believe that coloration doesn't confer much interspecies competitive advantage. If I were pressed to guess, I would actually guess sexual selection. I was just hoping someone actually had a theory (i.e. with some evidence) on which evolutionary process governs it. $\endgroup$ – medley56 Apr 3 '15 at 5:52
  • $\begingroup$ Also, @Remi.b, I totally agree, countershading makes perfect sense. I guess was referring more to the black and white eye spots and the other well-known splotchy patterns. $\endgroup$ – medley56 Apr 3 '15 at 5:55
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You can find a discussion of this topic in the literature:

Mitchell, Edward. 1970. Pigmentation pattern evolution in delphinid cetaceans: an essay in adaptive coloration. Canadian journal of Zoology 48(4): 717-740.

Perrin, W.F., 1972. Color patterns of spinner porpoises (Stenella cf. S. longirostris) of the eastern Pacific and Hawaii, with comments on delphinid pigmentation. Fish. Bull, 70(3), 983-1003

Caro, T., Beeman, K., Stankowich, T. and Whitehead, H., 2011. The functional significance of colouration in cetaceans. Evolutionary Ecology, 25(6), pp.1231-1245. http://web.csulb.edu/~tstankow/Caroetal2011.pdf

And related helpful article:

Evans, W.E., Yablokov, A.V. and Bowles, A.E., 1982. Geographic variation in the color pattern of killer whales (Orcinus orca). Report of the International Whaling Commission, 32, pp.687-694. http://www.kasatka.com/kirsten/ColorVariation.pdf

I'll let you explore these and their citations.

Remember, Google Scholar is your friend.

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  • $\begingroup$ It would actually be better if you summarized the main points of the articles. $\endgroup$ – kmm Jan 27 '16 at 22:25
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    $\begingroup$ @kmm I was simply addressing the second part of the question: demonstrating sources in the literature. We don't have to handhold through the entire learning process... $\endgroup$ – theforestecologist Jan 27 '16 at 22:26

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