by Greg Mayer
Many species of cats show this pattern in the cubs, even if the pattern disappears with growth. It almost certainly reflects (as discussed in WEIT), an atavistic trait: the persistence in a descendant of traits that were adaptive only in an ancestor. I suspect that the ancestor of lions had spots as adults, and that’s why they show up, briefly, in lion cubs.
I posted a comment to the effect that Hugh Cott, the great student of adaptive coloration, agreed with Jerry, although I wasn’t so sure:
Hugh Cott, in his classic “Adaptive Coloration in Animals” (Methuen, 1940) agreed with Jerry on this: “Among mammals and birds, first liveries acquired by the young– whether this happens before or after birth– often differ widely from the full dress of their parents. But it must not be assumed that such differences are necessarily adaptive. Lion cubs have spotted coats, and their tails are ringed…[Cott gives some more cat examples]… Since the kittens of all these animals…are born in sheltered dens or holes, carefully hidden or guarded by the mother, the spotted pattern can hardly be explained as protective.”(p. 21). I’m not so sure, though. Lions are not sheltered in dens or burrows, but rather are kept in thickets and kopjes, and may be on their own for a day at a time (George Schaller, “The Serengeti Lion” [Chicago, 1972], so the spots might be protective coloration for keeping the young hidden before they become formidable individually. (Protective coloration in the young is well known in mammals– whitetailed and mule deer, and tapirs, being good examples: their young bear dots and vermiculations that blend with sun- or moon-dappled forest floors.)
Since then, Jerry and I have conducted an off-blog discussion on this, and he has particularly challenged me with regard to tapirs. While tapirs (and lions!) present many interesting aspects of natural history, the general question is one one of fundamental conceptual importance for evolutionary biology: how do you tell if a feature of an organism is an adaptation? So I’m going to pursue this question over a few posts. To set the scene, let’s introduce tapirs. The best web source of info on them is the IUCN‘s Tapir Specialist Group.
Tapirs, along with horses and rhinoceroses, are odd-toed ungulates, members of the mammalian order Perissodactyla, which is the less species-rich of the two great extant orders of hoofed mammals. (Most hoofed mammals, such as deer, antelope, cattle, sheep, pigs, etc., are even-toed, members of the Artiodactyla.) There are four species, all of which have short trunks. Three are in the Neotropics (Tapirus bairdii, T. pinchaque, and T. terrestris), found from southern Mexico to northern Argentina. As adults, they are all more or less uniformly colored, brown to gray to black. The Malay tapir (T. indicus) of southeast Asia, however, is strikingly particolored.
I’ll show some baby tapirs in the next post.