Caturday felid: how the king cheetah got his stripes

by Greg Mayer and Jerry Coyne

Our felid for today is actually five felids: a mackerel (striped) tabby, a blotched tabby, a spotted cheetah, a king cheetah and a black-footed cat. In a new paper in Science by Christopher Kaelin and colleagues, the physiological basis of these pattern variations in both domestic cats and cheetahs is shown to be due to mutations at the Transmembrane aminopeptidase Q locus (Taqpep for short ) that alter the function of its encoded protein, which they call Tabulin.

Allelic variation at Tabby [mackerel (TaM) is dominant to blotched (Tab)] controls the arrangement of dark- and light-colored areas. Diagrams indicate how the distribution of black or brown eumelanin versus yellow or pale pheomelanin within individual hairs underlies the macroscopic color patterns, although in reality cat hairs frequently exhibit multiple pheomelanic bands.

It has long been known that the dark areas in a tabby’s coat are places where the hairs are colored mostly by eumelanin (a darker pigment), while the hairs of the lighter areas have more phaeomelanin (a lighter pigment). In both areas, the individual hairs have bands of color (look closely at your cat’s hairs: you’ll see that few are unicolored– most are banded in some way). In mackerel tabbies, the dark and light areas are arranged in a periodic pattern, creating tiger-like stripes. This is the pattern found in the wild cats that are the domestic cat’s progenitors, and is still one of, if not the, most common patterns in domestic cats.

It has also long been known that the blotched tabby condition is due to recessive alleles at an autosomal (i.e., non sex-chromosomal) locus, called Ta, so that having two copies of the mutant allele b makes the tabby blotched. What Kaelin and colleagues have done is show that the Ta locus is in fact the gene Taqpep. In domestic cats, blotched tabbies have one (or more) of three single nucleotide mutations that alter the Tabulin protein’s function. If you have one copy of the dominant (M) allele, you’re mackerel (see diagram above).

One of the coauthors of the paper is Ann van Dyk, who, back in 1986, with R.J. van Aarde, first definitively demonstrated that king cheetahs, at one time thought to be a different species and the object of much cryptozoological speculation, were in fact a color-pattern variant of the common cheetah, with the same mode of inheritance as the blotched tabby: an autosomal recessive gene.

In the new paper Kaelin et al. extend their work to cheetahs, sequencing their Taqpep genes, and found that in king cheetahs there is a single base pair insertion in the gene that causes a frameshift, a type of mutation that alters every amino acid encoded downstream in the gene from the site of the insertion. Thus the king and blotched patterns result from alterations of a homologous gene, but the mutations themselves are not identical, being caused by a single nucleotide substitution in domestic cats but by an insertion in cheetahs.

Black-haired areas are larger, more irregular, and associated with dorsal stripes in the king cheetah.

Kaelin et al. also sequenced the Taqpep locus in 29 other species of wild cats, assessing any nonsynonymous substitution (i.e., those that change the amino-acid sequence of the protein produced by the gene) for how likely they were to alter protein function. All the cats had “normal” genes, except for the black-footed cat (Felis nigripes), which had five substitutions that were collectively judged as being very likely to alter the protein’s function. Interestingly, the black-footed cat has a pattern similar to domestic cats with a “swirled” pattern associated with the mutation T139N of the Taqpep locus:

Black-footed cat (Felis nigripes); note swirled pattern. Photo by Pierre de Chabannes pour http://www.photozoo.org.

Kaelin et al. note that blotched tabbies rarely appear in early illustrations of cats, but that by the 18th century they had become more common. They also note that there is a fairly large region (244kb of nucleotides) around the Taqpep locus that is invariant in blotched tabbies, while it has usual levels of variability in mackerel tabbies. This is the exact pattern, both historically and genetically, that we would expect if the blotched pattern had been favored by (presumably artificial) selection over the last few hundred years.

When an allele is favored by selection, closely linked forms of genes will also increase in frequency (a phenomenon known as “hitchhiking”), leading to higher frequency or fixation for a whole block of genetic material. Recombination will eventually break up the association of the favored and hitchhiking alleles, and new mutations will increase variability; but this dissociatio takes time, and until it happens the region of low variability persists as a record of the selection (which in this case may still be ongoing).

[Note by GCM: While the paper, at five pages, is long by Science's standards, there are still 27 pages of online supplements, and it is difficult to follow the authors' train of argument and evidence since it requires constant switching between the paper and the appendices to fully appreciate what they've done (not to mention it would be impossible to do so if you were reading the journal or a reprint, rather than an online version). More justice would have been done to the authors' work, and to their readers, had a substantially longer paper been published (which, of course, could not have appeared in Science). I mention this not to criticize the authors, but to decry the increasing practice of putting essential parts of a paper into relatively inaccessible and, I fear, ephemeral, appendices.]

_______________________________________________________________

Kaelin, C. B., X. Xu, L. Z. Hong, V. A. David, K. A. McGowan, A. Schmidt-Küntzel, M. E. Roelke, J. Pino, J. Pontius, G. M. Cooper, H. Manuel, W. F. Swanson, L. Marker, C. K. Harper, A. van Dyk, B. Yue, J. C. Mullikin, W. C. Warren, E. Eizirik, L. Kos, S. J. O’Brien, G. S. Barsh, and M. Menotti-Raymond. 2012. Specifying and sustaining pigmentation patterns in domestic and wild cats. Science 337:1536-1541. abstract

van Aarde, R.J. and A. van Dyk. 1986. Inheritance of the king coat colour pattern in cheetahs Acinonyx jubatus. Journal of Zoology 209: 573-578. pdf

13 Comments

  1. Posted September 29, 2012 at 9:00 am | Permalink

    ghghgnbnb

    The evolution of a WEIT post — or a comment from one of the study subjects?

    I’m glad to see that there’s work being done on felid coat patterns. Baihu is basically a mackerel tabby, but he’s got dorsal stripes; some of his stripes separate into spots; and his belly fur is spotted like a lion cub. He’s almost a “I’ll have a little bit of each” cat.

    b&

    • whyevolutionistrue
      Posted September 29, 2012 at 9:10 am | Permalink

      We had some technical posting issues this morning, and the gibberish Ben quotes was in an earlier version of the post before we could overcome them, and the gibberish is now gone.
      GCM

      • Posted September 29, 2012 at 9:16 am | Permalink

        [T]he gibberish is now gone.

        But not forgotten!

        …or…erm…something…mumble…carry…on….

        b&

      • Posted September 29, 2012 at 2:55 pm | Permalink

        Oh. Not arsenic based DNA, then?

        /@

  2. marksolock
    Posted September 29, 2012 at 10:20 am | Permalink

    Reblogged this on Mark Solock Blog.

    • Git
      Posted September 29, 2012 at 12:41 pm | Permalink

      I approve of this post. Science plus Kittehs. Doubly awesome.

  3. jcm
    Posted September 29, 2012 at 1:18 pm | Permalink

    For those interested I haz access to the paper published in Sciece. It is available at http://goo.gl/m8zZs

    • jcm
      Posted September 29, 2012 at 1:19 pm | Permalink

      Err. It should be Science

  4. MadScientist
    Posted September 29, 2012 at 2:24 pm | Permalink

    I challenge the creationists to show how god did it.

  5. Posted September 29, 2012 at 2:58 pm | Permalink

    Fascinating!

    /@

  6. Posted September 30, 2012 at 6:48 am | Permalink

    Very interesting to understand more about this – I have a spotted/striped tabby and a blotched (“target” pattern) tabby; both were rescued strays so I know nothing about their ancestry.

    What about the clouded leopard (Neofelis nebulosa)? It has the ultimate wild cat “blotched” pattern but they all look like that – they don’t have a “spotted” version.

    I’d love to see someone write a science book (not a breeding book) about cat genetics.

  7. Avis
    Posted September 30, 2012 at 12:28 pm | Permalink

    Interesting post! Yesterday I met a male tortie / calico!


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