VOLUME 56 MAY 1959 NVMBER 2 A STUDY OF VARIATION IN SINGAPORE CATS Bv A. G. SEARLE Deparlmetzt of Zoology, University o,f Malaya, Singapore* (Received 3iay 30ltz, 1957) ~[NTIRODUGTION The domestic cat can, for several reasons, be regarded as very suitable material for work on population genetics. It is polymorphic for coat colour, pattern, and various other :characters; moreover the genetics of this variation is fairly well understood. It is common in large cities throughout the world, where it is usually divided into two social groups with little mrtual intercourse. Show-cats comprise the smaller group; 'the}' are ,carefully bred and selected by, fancier's for exhibition purposes and are therefore much subject to human interference. The other larger and more heterogeneous group can .be called "alley-cats", including ordinary house-cats and feral or gear-feral "strays". These m'e commonly regarded as domesticated, yet they are much less dependent on man .than most animals of this category; so the?, can, in my opinion, be treated in man?, ways as natural populations. London alley-cats, for instance, appear to mate at random (Searle, 194-9), which suggests that human influence on their choice of mates is negligible. Human selection is exercised almost entirely by keeping some kittens and discarding others. Those discarded may be kiIled or just left by the wayside to fend for them- selves, adding to the feral group if they survive. In much of Europe, but less commonly in Asia, human selection also operates by sterilising a high proportion of aduh males and some females too. Any differential effect which these selective forces may have, tending to change the frequency of a particuIar variant, can be ganged by making appropriate tests. This paper and a previous ot~.e on London's cats (Searle, 1949) are part of what is hoped will be a series, studying fiom an evolutionary aspect cat populations in different parts of the world. Its purpose wilt be to find out (i) to what extent there are regional differences in gene fiequencies and in quantitative characters, (ii) how far these are due to natural selection, artificial selection, local nmtations or other causes, (iii) what light :these facts throw on the evolution of the domestic cat and on evolutionary phenomena in general. Thc present paper deals particularly with a sample of the alley-cat polgulation of Singapore, analysing its polymorphism with respect to known genes. It also gives data on a number of quantitative skull characters, which are likely to show geographical .variation, and considers a tooth character (loss of upper first molars) which turns out to be an example o1" quasi-continuous variation. Details are given of the interesting "kinky-tail '~ abnormality, which is apparently common throughout South-East Asia, but is very rare in Europe. Oene fi-equencv estimates for Singapore are compared with .figures for Japan and London; some striking differences are found and the meaning of these is discussed. * Now at M.R.C. Radiubiological Research Unit, A.E.R.E,, Harwcll, U.te. I12 Variation in Singapore Cats C',LASSIFIGATION A r&mnd of present-day knowledge of cat genetics was given by Searle (1949). In the present investigation, cats were classified for the following coat colour and pattern characters, the gene symbol used being given after the character concerned: (i) Full colour (+) versus white (W) (ii) Black (-t-) versus sex-linked yellow (5')- Tortoiseshells arc -+-/y and there- fore normally female. (iii) Agouti (+) ve,sus non-agouti (a). (iv) Abyssinian (uniform) tabby pattern (1L ) versus striped tabby (+) versus blotched tabby (tb). (v) Intense (@) versus dilute (d). (vi) Intense (+) versus silver (coh) tersus Siamese dilution (cS). The latter acting on different coIour combinations gives the various Siamese breeds: seal-point, chocolate-point, blue-point etc. The original seal-point Siamese is supposed to contain a dominant gene for chocolate-black (Tjebbes, 1924), with symbol B. (vii) White-spotting against its absence (-4-). This character shows continuous variation; probabIy severaI genes are involved. Any peculiarities in the following structures were also noted: (i) Feet, where polydactylism is dominant (Danforth, 1947) and split-hand probably an incomplete dominant (Searle, 1953). (ii) Tail, where the Manx character (external absence of tail) is incompletely dominant. The "kinky-tail" abnormality is described below. (iii) Hair. Long (Persian) hair is recessive (]3amber, 1927); so is the English rex character (Searle & Jude, 1956). KINKY-TAiL Darwin (I868) remarks that throughout "the Malayan Archipelago, Siam, Pegu and Burmah all the cats have truncated tails about half the proper length, often with a sort of knot at the end." It is interesting to note that in the same year he presented to the British Museum (Natural History) a cat skin showing this very character and coming fiom the Malay Archipelago. Since then, several other biologists have commented on this abnormality, Pocock (1951) saying "... there are two admitted breeds characterised by the abbreviation of the tail. One of these, in which the organ is reduced to about the length of the hind foot and is fiequently 'kinked' or bent, is common in Malaya, whence it was many years ago introduced into Madagascar. The other is the so-called 'Manx' breed, in which the tail is at most a mere stump, about one inch long." Berg (1913) discusses tail-shortening in tile Japanese, .Javanese and Manx cats, distinguishing three grades of abnormality. In the first there is only slight shortening, ~fl'ecting the distal caudal vertebrae. In the second grade truncation is more pronounced; both proximal and distal w:rtebrac ~,re involved. In the third, with extreme shortening, distal caudal A. G. SEaRL~ 113 vertebrae are absent, while proximal ones are reduced in number. Bcrg lbund all three grades in Javanese cats, but only grade 3 ill Manx cals. The situation in Singapore eals is essentially the same as that described by Berg for javanese oncs; this tail abnormality is clearly widespread in South-East Asia. I propose to call it "kinky-tail:', as it is nearly aIways associated with one or more pronounced kil~ks which usually cannot be straightened out. There is great variation in the amount of lail-shortening: there may be merely a slight distal kink with no appreciable trunca- tio~t, or the tail may be contracted to a tight spiral about one-third its normal length. In the most extreme example seen it was reduced to a small knob, but was stil[ visible ejxternally, unlike the Manx condition. Plate ] shows examples of different grades o~'abnormality. A spiral arrangement of the tail is common where there sre several kinks (text-fig. I a); it may be either eIockwise or antlclockwise. Text-fig. I. Appcarancc of kink?'-tail in the cat; a, skinned tails showing typical twisting and truncation; b, alizarin transparencies of distal parts ofkil~kV-tails, with atmormal vertebrae a~ the kinks; c, skeit:t.on of tail with scvcr(: hook-likc kink~ involving abnormalities ~o six caudal vertebrae; the saCrtllll is asymmetrical. Camera lucida drawhags. Kinky-tail is associated with marked abnormalities ill caudal vertebrae. These have J been studied i1~ sil~l by means o[' alizarin h'ansparencies of the adt!~!t bony skeleton and i14 Varialion lit Silzgapore Cals methylene blue preparations of the young cartilaginous one. Individual vertebrae have been exami~ed after enzymatic maceration of the tail with papain. The number of caudal vertebrae is usually reduced, and in extreme exampIes may be only seven or eight instead of the normal 22. Alizarin preparations (text-fig. I b) sho,~v that each ldnk is tile site of distorted vertebrae. Up to six or seven elements may be affected where the kink is severe, as iu text-fig. Ic, where the tall is bent through I80 ~ to form a hook. Distal kinks are often associated with irregular, roughly wedge-shaped fragments of centra; the epiphyses at each end, instead of being parallel, may be almost perpendicular to each other. In more proximal kinks the neural arch and zygapophyses of affected vertebrae are also bent and distorted, while the transverse process is often reduced on the inner side of the kink. Fusions between adjacent vertebrae are fhirly common at kinks; they are usualiy decidedly skew (text-lig. 2b) and result in rile partial elimination of one of" the two vertebrae. Fusions of distal cat, dal vertebrae give rise to very irregular structures. Anomalies are generally much commoner distaily, but in one cat with extreme kinky-tail (text-fig. 2a) even the sacrum was slightly twisted and the third sacral vertebra showed,~lyssymphysis of the neurat arch. The kinky-tail anomaly is preformed in cartilage and has been traced back to a late t'oetal stage, as shown in text-fig. 3a. Here endochondral ossification has just begun in the normal vertebrae, but there is no sign of it in the abnormal wedge-shaped element. There is an asymmetrical proliferation of cartilage at the tip of the tail. Methylene blue preparations of newborn and three-week kittens show that ossification of these abnormal elements takes place at the outer side of the kink first, in a very asymmetric manner (text-fig. 3b). Kinky-tail in the cat shows similarities with certain genes causing tail abnormalities in tile mouse; for example, "taiI-kinks" (Griineberg, 1955). In this mutant the tail is shortened "fi-om about 0-8 down to about 0-5 of its normal length or less" and also has up to ten kinks, especially distally, which cannot as a rule be straightened out. Mot-e- over, the abnormal caudal vertebrae at kinks are often wedge-shaped, as in kinky- tailed cats; but there ai:e no bony fusions.