Can you see that monkey up there?

March 12, 2011 • 2:25 pm

by Greg Mayer

Among the first phenomena to be interpreted in a Darwinian manner after the publication of the Origin of Species was adaptive coloration, most famously Batesian mimicry (wherein a palatable organism mimics a noxious organism); Jerry has recently posted  on mimicry in insects and in birds. Matthew has brought to our attention a paper by J.M. Kamila and B.J. Bradley, in press in the Journal of Zoology, on another aspect of adaptive coloration: obliterative, or countershading, and in particular how it applies to primates. The Capuchin below is not countershaded.

Capuchin monkey, Guanacaste, Costa Rica, by David M. Jensen, from Wikipedia

Countershading, which is familiar to fishermen and military planespotters, consists of having the illuminated surface of an object darkened, and the unilluminated surface lightened, so as to “counteract the effect of shade and light”, producing “upon a rounded surface the illusionary appearance of flatness” (Cott, 1957:36). As such, it is one of the chief methods by which animals (as well as war planes, at least old ones) achieve concealment, and is very common. Kamila and Bradley, in their paper, ask: If primates spend a lot of time standing up on two legs (like we do), are they less likely to exhibit dorso-ventral countershading? Intuitively, it seems entirely plausible, and, after measuring the reflectance of the front and back of skins of 113 species of primates, they find that, indeed, the more bipedal a primate is, the less strongly it is countershaded.  So now we know why our backs and chests/bellies are about the same color– we’re too bipedal!

My experience is that monkeys in trees are hard to see, regardless of whether they are countershaded. The three common Costa Rican species shown in the pictures here, all of which I know in the wild, are hard to spot, even though they are not countershaded. The large white scrotum of the male mantled howler, below, known as “huevos”, do make the males somewhat more conspicuous, but this is almost certainly a sexually selected feature.

Mantled howler, Prov. Alajuela, Costa Rica, by Tim Ross, from Wikipedia.

The fourth Costa Rican monkey species (not pictured here), the squirrel monkey, is countershaded.

[Jerry’s note: I’ve added the picture below, which shows the countershading of a squirrel monkey: it’s darker on the illuminated dorsal (back) side and lighter on the ventral (belly) side:]

Of about 30 species of monkeys in the Guianas, Venezuela, and Colombia, many of which are very strikingly patterned, only a handful might be considered countershaded (Eisenberg, 1989).  Perhaps not surprisingly, Kamila and Bradley found that the effect of bipedal tendencies, while significant, was small. They did find that body size made a difference (bigger, less predation-prone primates are less countershaded), but that group size does not (although it was almost significant). Overall, the factors they considered explained only 14% of the variation in countershading in primates.

Spider monkey, Golfo Dulce, Costa Rica, by Steven G. Johnson, from Wikipedia.

Somewhat surprisingly, adaptive coloration was very controversial (critics considering resemblances of mimics and models, and the concealing effects of color patterns, to be coincidental) in Darwin’s time, and continued to be so for decades afterwards. It was not until 1940, that Hugh Cott, one of the 20th century’s most influential herpetologists, put the controversy to rest in his classic Adaptive Coloration in Animals. We’ll conclude with some video, taken by my wife, of monkeys leaping from tree to tree near Tortuguero, Costa Rica. It was a typical lowland Costa Rican day, quite warm, which enables me to label this video as “hot monkey action” (let’s see how many hits that phrase brings in!)


Cott, H.B. 1940. Adaptive Coloration in Animals. Methuen, London.

Eisenberg, J.F. 1989. Mammals of the Neotropics. Vol. 1. The Northern Neotropics. University of Chicago Press, Chicago.

Kamilar, J.M. and B.J. Bradley. 2011. Countershading is related to positional behavior in primates. Journal of Zoology 283:227-233.

Caturday felid– No.3, the snow leopard

November 13, 2010 • 4:15 pm

by Greg Mayer

As an extra bonus felid for today, and continuing the theme of cat coat patterns as camouflage, here’s the snow leopard (Panthera uncia).

You can’t see the snow leopard or it’s pattern very well, but, of course, that’s the point. Its head is to the right.

(BTW, is anyone getting the Monty Python reference?)

The evolution of cat coat patterns

October 27, 2010 • 8:35 am

Why are some species of kittehs plain, while others have spots, stripes, or more elaborate patterns? A provisional answer comes from a new paper by William Allen et al., “Why the leopard got his spots: relating pattern development to ecology in felids”, in the Proceedings of the Royal Society.  The paper’s title, of course, comes from Rudyard Kipling’s Just So Stories.  And the short answer is this: the coats of wild cats help camouflage them, and what pattern evolves depends on where the species lives.

The simple answer comes from a rather elaborate analysis.  The authors set up the paper with what I think is a good specimen of clear scientific writing.  It’s not Joyce, of course, but these guys know how to write. I love the alliteration of “flanks of felids” and the breeziness of “pounce or quick rush.”

The patterns displayed on the flanks of felids are intriguing in their variety. Previous studies of the adaptive function of cat coat patterns have indicated that they are likely to be for camouflage rather than communication or physiological reasons [1,2]. The primary hunting strategy of felids is to stalk prey until they are close enough to capture them with a pounce or quick rush [3,4]. As hunts are more successful when an attack is initiated from shorter distances [5,6], cats benefit from remaining undetected for as long as possible and camouflage helps achieve this. Many smaller cats are also likely to be camouflaged for protection from predation [7].

The authors first note that others before them have suggested—and supported with some data—the idea that spotted or stripey cats live in forested habitats, and plain cats in open habitats.  But they quantify this “complexity” by doing a developmental analysis of coat patterns on pictures taken from the internet.  I won’t go into the details, but they match the photographs with patterns generated from a mathematical model in which pattern results from the interaction of two diffusible chemicals along gradients of the body.  Given a model that matches an existing pattern (they used 35 species of felids), they could then encompass “pattern” in the mathematical constants involved in generating it.  They could then correlate these constants with various aspect of cat ecology: where they live, preferred times of activity, how big they are, what they eat, and how social they are.

Here’s an example of a cat that came out “plain” in their analysis: the caracal (Caracal caracal), from Africa and the Middle East:

Nine of the 35 species were considered “plain.” Here’s a cat considered “patterned and complex”: the gorgeous clouded leopard (Neofelis nebulosa), from southeast Asia:

Sixteen species were considered patterned, with four of these, including the clouded leopard, as “always complex.”  The other ten were considered “variable”,” since there was polymorphism: individuals within a species can look quite different.

The results?

  • Pattern itself, whether complex or not, was significantly associated with habitat, with more patterned cats in more “closed” habitats (forest, jungle, etc.).  Plain cats are found in open habitats like grasslands, deserts, and mountains.
  • More irregular patterns, like the cloud leopard, are significantly associated with tropical forests and other “closed” environments.
  • “The more time cats spent in trees, the more likely they were to be patterned.”
  • Pattern polymorphism, as in the melanism of “black panthers,” was significantly associated with living in temperate forests that vary seasonally and also with habitat generalism. This supports the idea that “disruptive selection,” that is, selection for different patterns in different places, maintains the intra-specific variation in coat color.
  • There were a few “outliers,” or exceptions—cats that had patterns not fitting into the habitat correlations given above.  One is the very rare bay cat (Catopuma badia; I’ve posted on it before), which is plain though it lives in tropical rainforest:

And another outlier is the black footed cat of Africa (Felis nigripes), which is patterned though it lives in open habitat (savannah, grassland, and semi-desert):

The authors note that the tiger is the only wild cat with vertical stripes, and the common notion that this camouflages them in grassland is unfounded: tigers don’t live in grasslands.

The conclusion, then, is that the patterns of cat coats reflect, in large degree, selection for camouflage in their natural habitats. This camouflage almost certainly evolved to hide them from prey, and, in smaller cats, predators as well.

I love the inclusion of a Kipling quote in their conclusion (reference “45” is to the Just So Stories):

These findings support the hypothesis that felid flank patterns function as background matching camouflage. Evolution has generally paired plain cats with relatively uniformly coloured, textured and illuminated environments, and patterned cats with environments ‘full of trees and bushes and stripy, speckly, patchy-blatchy shadows’ [45].

Now the sample size—35 species—is not large, and some of the associations were barely significant from a statistical standpoint.  This could reflect the low power of tests in small samples. Nevertheless, the study offers a good working hypothesis for the evolution of pattern not just in cats, but other species that “need” to be cryptic.  What remains to understand are those outliers like the bay cat, and also the existence of developmental change of pattern, in which some species are patterned when young and lose the patterns when they get older.  Lions, which are spotted as cubs, are a good example of this:

This change might not be adaptive per se, but simply be an atavism: a holdover from an ancestral spotted pattern that still persists in the young.


Allen, W. L., I. C. Cuthill, N. E. Scott-Samuel and R. Baddeley. 2010.  Why the leopard got his spots: relating pattern development to ecology in felids.  Proc. Roy. Soc. B online: doi: 10.1098/rspb.2010.1734

Caturday Felid- spotted lions

June 5, 2010 • 9:08 am

by Greg Mayer

Spotted lions, semi-mythical beasts and the subject of cryptozoological inquiry, have been discussed here at WEIT before, but the spotted lions here are not mythical at all, because they are cubs.

Badu and Zuka, born April 16, 2010 at the Racine Zoo.

Lion cubs, as we’ve also discussed before here at WEIT, are born spotted, and retain some spots for up to two years or so, but eventually lose them as they mature. The controversy about spotted lions is whether adult spotted lions (only a single individual has ever been collected) form a distinct species or subspecies, or just a (very) rare pattern variation. There’s a bit of a controversy about the cubs’ spotting as well– Jerry, agreeing with the foremost student of animal coloration, Hugh B. Cott, thinks the spots are atavistic, while I think they are likely adaptively concealing.

These two cubs, Badu and Zuka, were born April 16, 2010 at the Racine (Wisconsin) Zoo. They are the younger siblings of lions that were Caturday felids last year. In the next photo, you can also see the spotting on the hindquarters and tail.

Badu and Zuka, born April 16, 2010 at the Racine Zoo.

Albino squirrel update

March 29, 2010 • 10:39 am

by Greg Mayer

Observant reader Chris Helzer saw an albino squirrel outside the National Museum of Natural History a few days after I did, and got a much better picture of it, which he has kindly allowed me to post here.

Albino gray squirrel outside the USNM, Washington, DC, 28 March 2010.

This is probably the same squirrel I saw, and it seems to be on the same tree. In Chris’s much better picture you can see the pink eye, showing that it is a true albino, not merely albinistic.

UPDATE. I came across this posting at The Chicken or the Egg blog about white squirrels at the Museum of Comparative Zoology, my (and Jerry’s) alma mater. It seems that white squirrels have an affinity for natural history museums. Note that the MCZ white squirrel is albinistic, not true albino (it has a dark eye). Chicken also links to this wonderful site, the White Squirrel Research Institute, devoted to the white squirrels of Brevard, North Carolina. The Brevard squirrels, like the MCZ ones, are also albinistic rather than albino.

Caturday felid: the King Cheetah

March 27, 2010 • 8:42 am

by Greg Mayer

Of interest to both ecological geneticists studying vertebrate polymorphisms and cryptozoologists is the king cheetah.

King Cheetah, by Jurvetson. Source

The king cheetah, known only from southern Africa, is a striking pattern variation of the common cheetah (Acinonyx jubatus). Instead of being spotted, the dark markings of the king cheetah coalesce into stripes and vermiculations, especially along the dorsal midline. King cheetahs are to common cheetahs as blotched tabbies are to spotted tabbies, not just in the similarity of the patterns, but in their genetic relationship: the king pattern is a variation within populations of the same species, and both patterns can occur in the same litter.

Common cheetahs, by Picture Taker 2, source

In 1927, R.I. Pocock of the British Museum named the king cheetah as a new species, Acinonyx rex, the holotype being a specimen at the Queen Victoria Memorial Library and Museum in Rhodesia (now Zimbabwe). In 1932 the zoologist Angel Cabrera suggested that the king cheetah was merely a coat pattern variant of the common cheetah. For many decades after that the question of the status of the king cheetah was unresolved, as few specimens were known, and genetic experiments on cheetahs not possible. Cryptozoologists became interested in the king cheetah as a ‘semi-cryptid’– a not quite undiscovered species of large mammal, but at least a mysterious one.

In the 1970s more king cheetahs turned up, and methods of captive breeding of cheetahs, developed for conservation purposes, had advanced to the point where it was possible to investigate the question. In 1986, R.J. van Arde and Ann van Dyk of Pretoria University and the National Zoo in Pretoria, South Africa, showed that the king coat pattern was due to a recessive mutation at a single autosomal locus, thus vindicating Cabrera’s hypothesis from 50 years earlier. King cheetahs are now found in several animal parks in South Africa, and can be easily seen and photographed.

The story of the king cheetah shows that even when a new species is described and named according to the best practices, including insuring a publicly available holotype, it doesn’t guarantee that the species so named is new. It might be a new species, but it might also be a geographic or within-population variation of a known species (the latter in the case of the king cheetah), or in some cases nothing new at all (as when the describer is unaware that a description had been published previously).

Polymorphism in vertebrates

March 26, 2010 • 1:04 pm

by Greg Mayer

Darwin’s theory of evolution (and ours), unlike that of Lamarck, is variational, rather than transformational: the process of evolution is a change in frequency of different variants within a population, not a transformation of the individuals.  Darwin thus made the origin, nature, and inheritance of variation key problems for biology; indeed, for much of the 20th century, evolution and genetics were often taught as a single course at universities.

One of the most distinctive sorts of variation is polymorphism, in which two or more discontinuous forms are found in a single species (this is distinct from sexual or age related variation). Darwin himself pioneered the study of polymorphisms. Such discontinuous variation often has a simple genetic basis, with allelic variation at one genetic locus accounting for all (or most) of the variability.The color polymorphism in peppered moths (Biston betularia) is a well known and well studied case involving industrial melanism, in which light and dark forms are adapted to polluted and unpolluted environments, respectively. A well known case of polymorphism in vertebrates are the two color phases of Cuban sparrow hawk (Falco sparverius sparverioides). This case is not well studied, though, and we know nothing about the genetics, nor the adaptive significance (if any) of the polymorphism.

Light and rufous phase male Cuban sparrow hawks (Falco sparverius sparverioides).

A polymorphism in vertebrates that many Americans and Canadians are familiar with are the melanistic and gray forms of the gray squirrel (Sciurus carolinensis). The most frequent color form is gray, but blackish or dark brownish individuals are widely distributed, and in places quite frequent. I have seen them in Illinois (Cook County), Wisconsin (Racine and Kenosha Cos.) and Michigan (Ingham Co.), and also on the campus of Princeton University. (I was told at Princeton that, during football season, black squirrels are captured, and orange stripes applied to them, so that they resemble diminutive arboreal tigers, the tiger being Princeton’s mascot.)

A demonic gray squirrel (locally known as 'yard dogs'), Annapolis, MD, 23 June 2008.

A much less common color morph is the leucistic or albinistic form, which is whitish, cream or yellowish. They are famously common in Olney, Illinois (due to an introduction of two albinistic individuals to an area previously lacking any gray squirrels at all), and also occur regularly in Stevens Point, Wisconsin, but I had never seen one before my recent trip to Washington, DC, where I saw one on the tree right across from the steps on the Mall entrance to the USNM.  (The picture was taken through a bus window.)

Leucistic or albinistic gray squirrel, Washington, DC, 16 March 2010.

Vertebrate polymorphisms are often less well understood than those of invertebrates, because their generally greater size and longer generation times make experimental study more difficult. Melanism in squirrels, for example, has been related to thermoregulation and fire frequency, but no thoroughly compelling explanation has been found. One exception to this is coat color variation in mice of the genus Peromyscus, where coat color seems to be an adaptation for camouflage in varying environments.

Light and dark forms of Peromyscus polionotus from sandy and dark soils (P. p. leucocephalus on the left, P. p. polionotus on the right, I think).

In the 1930s, F.B. Sumner conducted classic field and lab studies on light colored mice living on sandy soils and dark mice on dark soils. Unlike the melanistic and albinistic squirrels, which are variant individuals within a populations, there is an element of geographic variation in the mice, which live in distinct, though adjacent, places. Sumner’s studies showed that there were several (not just one) genetic loci involved in coat color, and the color forms intergrade where their habitats meet and they interbreed. Hopi Hoekstra of the Museum of Comparative Zoology is currently conducting exciting studies of some of the same species studied by Sumner.

Although the mice occur in distinct modal forms (white vs. brown), the intergradation where they meet shows an underlying continuous variation. The frogs below show that although we can pick out distinctly different individuals, the range of pattern from plain to mottled to striped makes it difficult to recognize a small number of discrete color morphs, and the variation approaches a continuous dictribution. Such continuous variations were thought by Darwin, and most biologists today as well, to be important raw material for the evolutionary process.

Leotpdactylus albilabris from Isla Vieques.

Caturday felid: the Spotted Lion

January 30, 2010 • 1:22 pm

by Greg Mayer

One of the most enigmatic of the felids is the spotted lion. Indeed, it’s so enigmatic that it might, in some senses, be said to not even exist.

As you may recall from Jerry’s earlier posting of a video of lion cubs, lions are born with spots, which disappear as they mature. Jerry and I disputed whether such patterns in young animals are atavistic or adaptive, but my concern today is not with whether spots are adaptive, but whether there are spotted lions at all.

The photograph above is the best evidence we have for the existence of spotted lions. (The skin’s total length is 8 ft. 8 in., so it’s not a cub!). I’ve previously noted that photographs are not the best evidence for documenting the existence of a previously unknown species of animal, but in this case we have the benefit of the fact that the specimen in the photograph was examined by Reginald Pocock of the British Museum (Natural History) in the 1930s. Here is some of what Pocock, a world authority on cats, had to say, about the specimen loaned to him by Kenneth Gandar Dower (subscription required):

…it is a remarkable specimen owing to the distinctness of the spots in a beast of its size.

It is a male. … From it’s size I guessed it to be about three years old, a year or more short of full size.

…the peculiarity of the skin lies in the distinctness of its pattern of spots, consisting of large “jaguarine” rosettes arranged in obliquely vertical lines and extending over the flanks, shoulders and thighs up to the darker spinal area where they disappear.

As is well known, lion-cubs at birth generally, but not always, show a pattern of spots or stripes supposed, probably correctly, to be the remnants of an ancestral pattern transmitted from the time when lions were denizens of forests or jungles. In nearly all cases this juvenile pattern vanishes at three or four months on the body, but persists longer on the belly and legs and may sometimes be visible on those parts at maturity, especially apparently in sone lionesses from East Africa. Mr. Gandar Dower’s lion-skin is quite exceptional in this respect.

Pocock went on to indicate the absence of this pattern in a large series of adult specimens at the British Museum and the United States National Museum, but noted one account and one photograph that indicated at least an approach to being spotted. He also examined a skull provided by Gandar Dower, which may have come from this specimen, or from a female shot at the same time; the skulls were not kept when the animals were skinned, but one was retrieved later. Pocock concluded

…it is clear that no precise conclusion can be formed regarding this interesting beast until skins and skulls of adults have been collected.

As noted above, the skin was brought to Pocock by Kenneth Gandar Dower. Gandar Dower had read accounts of the spotted lion and mounted an expedition to East Africa to try to find one, but was unsuccessful, save for the skin and skull which he obtained from Michael Trent, a farmer in the Aberdare Mountains of Kenya, who had shot a pair of spotted lions a few years earlier. Gandar Dower recounted his expedition in a book, The Spotted Lion. Bernard Heuvelmans summarized Gandar Dower’s investigations, and recounted later stories of the spotted lion in his On the Track of Unknown Animals.

So what is the spotted lion? There are several possibilities. First, it might represent a distinct population that lives in the Aberdare Mountains of Kenya. In this case, it might be a species distinct from other lions, or it could be a geographical race or subspecies of the familiar lion. Second, it could just be a rare individual variation, in the same way that populations of house cats have spotted, striped, particolored, solid, etc. patterns occurring in individuals that are part of the same breeding population (and, indeed, part of the same litter). Finally, it could be a hybrid, perhaps between a lion and a leopard. Pocock, however, was well familiar with interspecific hybrids in large cats, and did not mention this possibility; also, interspecific hybridization in large cats is known (almost?) exclusively among captive animals. So, a hybrid origin does not seem likely to me.

If the first possibility is true, then there would indeed be something we can rightfully call the spotted lion. If the second is true, while there would then be known to exist lions with spots, there would not be a distinct natural population. And if the third is true, then there aren’t spotted lions at all– only lion-leopard hybrids that have spots. Further study of the skin or supposed skull, especially using modern techniques, might have allowed at least some of the possibilities to be eliminated, but unfortunately, Pocock apparently did not retain them at the British Museum, and I am unaware of their current whereabouts.  (I had thought they were at the British Museum until reading Pocock’s full account, in which he notes the specimens were left for him to examine, but makes no mention of them being donated to the collection.) To solve this problem, we thus must, as Pocock did over 70 years ago, await the collection of more specimens.


Gandar Dower, K. 1937. The Spotted Lion. Little Brown, Boston.

Heuvelmans, B. 1959. On the Track of Unknown Animals. Hill and Wang, New York.

Pocock, R.I. 1937. Note on the spotted lion of the Aberdares. pp. 317-321 in Gandar Dower, 1937.

Poison dart frogs: poison, yes; dart, not so much

August 21, 2009 • 10:07 pm

by Greg Mayer

The brightly colored, poisonous frogs of the family Dendrobatidae are usually called poison dart frogs, but the name is a bit of a misnomer. While they do have toxic alkaloids in their skins, only three species are definitely known to be used for poisoning blowgun darts– Phyllobates aurotaenia, Phyllobates bicolor, and Phyllobates terribilis— all by the Noanama and Embera Choco Indians of western Colombia. The most toxic of these, and the most toxic of all dendrobatids, is the very bright yellow, and appropriately named, Phyllobates terribilis.

Phyllobates terribilis, photo by Wilfried Berns, via Wikipedia

The foremost students of these frogs have been Chuck Myers of the American Museum of Natural History, and his colleague John Daly. During a visit to the Museum some years ago, Chuck kindly showed me the terribilis he kept in his office, but I did not take any pictures, hence the Wiki photo. Their studies have shown that there is considerable individual, geographic, and interspecific variation in the poisons present in the frogs, and that individual frogs may contain multiple toxic compounds. Some of this variation results from the fact that the frogs obtain the alkaloids, at least in part, by uptake from arthropod prey.

The American Museum has made all the back issues of its scientific publications available as pdf’s, and many of  Myers and Daly’s papers, including quality color plates, are available there.  I would recommend

1976. Preliminary evaluation of skin toxins and vocalizations in taxonomic and evolutionary studies of poison-dart frogs (Dendrobatidae). Bulletin of the AMNH 157:175-262;

1978. A dangerously toxic new frog (Phyllobates) used by Emberá Indians of western Colombia, with discussion of blowgun fabrication and dart poisoning. Bulletin of the AMNH 161:309-365 (with Borys Malkin);

1995. Discovery of the Costa Rican poison frog Dendrobates granuliferus in sympatry with Dendrobates pumilio, and comments on taxonomic use of skin alkaloids. AM Novitates 3144:1-21 (with H.M. Garrafo, A. Wisnieski, and J.F. Cover).

Rational exuberance

August 21, 2009 • 11:40 am

by Greg Mayer

Continuing with the frog theme, here are two representatives of Dendrobates pumilio, the strawberry poison dart frog, from Costa Rica.

Dendrobates pumilio from Estacion Biologica La Suerte, Costa Rica
Dendrobates pumilio from Estacion Biologica La Suerte, Costa Rica
Dendrobates pumilio from Estacion Biologica El Zota, Costa Rica.
Dendrobates pumilio from Estacion Biologica El Zota, Costa Rica.

As the word “poison” in their vernacular name indicates, these frogs are toxic, and their bright coloration is aposematic: it advertises the toxicity of the frog, and protects them from predators. They may often be seen wandering boldly about the rain forest floor in daylight. These two individuals show much of the range of color variation in the species:  red backs with more or less darker speckling, and blue on the extremities ranging from the whole limb to just a hint on the toes and vent.

In northwestern Panama, however, in the region of Bocas del Toro, there are many color morphs– yellows, blues, blacks, greens– some of which are cryptic (i.e. camouflaged), rather than aposematic. In a paper last year (abstract only), Ian Wang and Brad Shaffer of UC-Davis studied the within-species phylogeny of these color morphs, and found that apparently cryptic forms had arisen multiple times. They proposed that this convergence in coloration might be driven by selection. But they admit much more work must be done:

The dramatic level of color polymorphism in the Bocas del Toro populations of D. pumilio remains difficult to explain, especially because our phylogeographic study of color evolution indicates a complex history of color changes.