Evolutionary convergence in conspicuous colouration between Arctic fox (Alopex lagopus) and Tibetan wild ass (Equus kiang)
The Arctic fox (Alopex lagopus) and Tibetan wild ass do not live together, but both in a sense inhabit ‘tundra’.
Their patterns of colouration are remarkably similar, considering that one is much smaller-bodied than the other, and a carnivore instead of a herbivore.
In both cases, the pale of the ventral surfaces has extended so high on the sides of the animal that the whole effect is flag-like, i.e. the colouration is conspicuous. The pale has particularly crept up on the hindquarters (between haunch and tail), on the area just posterior to the shoulders, and on the neck (but not the face).
The main difference, apart from the far bushier tail of the fox, seems to be that the Arctic fox retains dark legs/feet, whereas the Tibetan wild ass has pale legs/feet.
http://www.skolaiimages.com/stock/albums/alaska/anwr/pbay_arcticfox_002.jpg
http://4.bp.blogspot.com/-QlhXs1WZmro/Tpp0Mxgsa5I/AAAAAAAABUE/fSNLJoxBn6E/s1600/D2H_1524.jpg
http://static.zoonar.com/img/www_repository2/54/38/f4/10_9acc6df8ce0dac743bc0f3cb1d99ab03.jpg
The Arctic fox is coloured for inconspicuousness in winter (all-white) but conspicuousness in summer.
Why would the Arctic fox want to be conspicuous in summer but inconspicuous in winter?
In the case of Arctic/boreal mustelids, the situation may also be more complex than it seems. Several weasel-like species turn white in winter but their summer coats are hard to interpret because they, a bit like the Arctic fox, have conspicuous aspects (e.g. even the winter white coats have dark tail-tips). In the case of the wolverine, the main pattern is a perverse one in which the animal remains dark, so dark that it stands out from a snowy background in what I interpret to be a form of aposematism (which incidentally it shares with the musk-ox in a way).
Stoat (Mustela erminea):
When the white (winter-coat) stoat is in a non-snowy situation, the whole animal stands out in a way consistent with aposematism rather than crypsis; and that the dark distal part of the tail would be unmistakably conspicuous even against an all-snow background. In the summer coat, the animal stands out like a beacon when it adopts a bipedal stance. This, exposing what could be assumed to be a merely countershaded ventral surface but is too abruptly demarcated to conform to that model even when the animal slinks along quadrupedally.
http://en.wikipedia.org/wiki/Stoat#mediaviewer/File:Mustela_erminea_winter_cropped.jpg
http://en.wikipedia.org/wiki/Stoat#mediaviewer/File:Mustela_erminea_upright.jpg
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