by Greg Mayer
A while back Jerry posted a video of lion cubs at the Tulsa Zoo, and noted that they have spots, remarking
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.
Sean B. Carroll mentioned coloration and spots and stripes and patterns in his books “Endless Forms Most Beautiful” and “The Making of the Fittest”.
Added to the question “how do you tell if a feature of an organism is an adaptation?” is “When is it a relaxation of natural selection due to phenotype changes?”
Are sexual selection pressures classed as adaptation, or not?
I have to wait for baby tapirs? That’s just mean.
Just google ‘brazilian tapir’ and you’ll get a couple of babies right off the bat – you don’t even have to go to images.
Weren’t some of the now-extinct lion subspecies spotted? At least drawings I saw of them when I was a kid had spots, but that may or may not reflect reality in any way.
I mentioned spotted lions very briefly in my earlier comment on the Tulsa Zoo lion cubs. The short answer is that it’s not clear that spotted lions (adult ones) ever existed. I’ll post more on them later.
GCM
Ah, tapirs, and baby tapirs especially. I can tell a funny little zoo story that’s not relevant to the post but is just a funny little zoo story. One summer afternoon I went to clean up the tapir/llama yard while my fellow keeper Ellen went to the administration building to do something. It was a big yard, and I just cruised around dreamily with my wheelbarrow and rake and shovel, picking up llama pellets. After awhile I got a radio call from Ellen asking me if I was in the llama yard. I confirmed and she said ‘Oh, good.’ I went on dreamily raking up piles of pellets – then suddenly noticed a whole flock of people including administrators and people from the education department lined up along the fence gazing at me. Eh? What’s so interesting?! Ellen was there too – I think she waved and looked excited. ‘What’s going on?!’ I shouted. I forget if she got on the radio, or pointed, or shouted – but anyway, the pregnant Brazilian tapir had just given birth and she and the darling little spotted baby were cruising around a few yards from me, and I hadn’t noticed. When I confirmed I was in the yard Ellen naturally thought I meant ‘Yes I’m here I know all about it isn’t it exciting.’ But noooooo.
I did once see one of the llamas give birth though, so that’s all right.
So, you failed to spot them?
Haw.
She certainly was very cute and spotted, while her parents were just a dull dark grey.
It’s not a major point, but since Hugh Cott is long dead, wouldn’t it be more correct to say that Jerry Coyne agrees with Hugh Cott? (assuming, of course, that he does? (Which I suppose is an open question.))
I mean, it doesn’t quite sound right for me to say that Watson and Crick agree with me that DNA is a double helix.
There’s probably a simple answer to this question so – I hope someone can respond. Given Jerry’s chapter on ‘The Geography of Life’ how do we explain the existent of a species of tapir in the America’s and another one in Asia? How closely are they related? Did their common ancestor exist somewhere in Asia and did their intermediates in North America die out or what? This might be a dumb question!
Stay tuned– I’ll post on tapir zoogeography later.
GCM
Thanks – look forward to it!