A Study of Variation in Singapore Cats

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 therefore 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. In mice with tail-kinks the cervical and upper thoracic region is also highly abnormal, with many vertebrae in the form of a b

Tex -fig. 2. AbnorrnaI vertebrae in kinky-tailed cats; a, slightly twisted sacrum with dorsal gap in third 5 acra! vertebra; b, dorsal and ventraI views of I\lsed and telescoped 1bird and fourth caudal vertebrae. Camera lucida ~irawi%qs. A. G. SEARLE 115

Text-fig. 3. Development of kinky-taiI; a, foetal tail showing abnormalities in cartilaginous skeleton; b, three-week kitten's tail (excluding first two candaIs) with abnormal vertebrae at site of kinks. Camera lucida drawings of methylene blue cartilage preparations. Cartilage shown in black, hone outlined. fragments. One complete skeleton of a very kinky-tailed cat has been studied; it shows no gross abnormalities in vertebrae other than caudal. It must be remembered, however, that tail-kinks in the mouse is a newly arisen mutant, whereas kinky-tail in the cat has been subjected to centuries ofnatm'al selection. Thus even if the genes concerned are homologous the), cannot be expected to show exactly the same effects, especially as the animals concerned are in different mammalian Orders. The mode of inheritance of kinky-tail is still uncertain; penetrance is ahnost certainly [/ieomplete, judging from the wide and continuous variation ill expression of the abnormality, ranging all the way from very slight to extreme. For this reason and because of the usual difficulty of ascertaining the paternity" of any kittens examined, no conclusive evidence has yet been obtained fi'om Singapore cats. Infornmtion has also ~een collected from controlled matings between pedigree Siamese cats in England; Some of these have kinky-tails, presumably because the breed originated in South. :East Asia. In six different sets of matings between normal-tailed Siamese, kinky- tailed offspring have been produced (about one-kinky-tall to seven normal), which Suggests recessivity, but normal overlaps might have been involved. It has not yet been possible to arrange the most informative cross, which would be between a highly kinky-tailed cat attd a normal English alley-cat. If any offspring were kinky-tailed then it would be reasonably certain that the gene concerned could manifest itself when heterozygous, since in England the kinky-tail character seems to be confined lo the Siamese breed.

ANALYS{S OF TIrE ,~INGAPORE CAT POPULATION

A Sample of 250 cats was examined in Singapore. About eighty of these were seen when alive during visits to several Malay kampongs (villages) on thc outskirts of the city; the rest were classified after death at the City Animal In~a'mavy. They were 116 Variation ilz Singapore Cats

mainly strays and unwanted animals, collected fi-om the city area or brought in to the Infirmary for destruction; very few, if any, belonged to the "show-cat" group. There were 115 male cats and 135 female; that is, 46.0~ male. Only mm of the males had beret castrated, contrasting with the s~tuation in London, where about halt' are rendered sterile. In Table 1, all the animals are classified as Par as possible fi)r coat-colour and pattern: also for degree of white-spotting. So means no :vhite-spottilag; Sa, less than 1/2 white; So, between 1/3 and 2/3 white; Sa, more than 2/3 white but not all white. Sell white and Siamese cats we,e put in the So categoKT, in some of the tabbies and tabby. tortoiseshells it was impossible to determine accurately the type of tabby pattern, which has therefbre been entered as l:. This difficulty was almost entirely due to the cats concerned having extensive white-spotting, so that only small tabby areas were avail- able for examination. For the same reason, no attempt was made to classify fo,' tabby

'fable l. Phenolypes oj'Silzgapore cats, with degree q/ white-spoltb~g

Phcnotype .S O Sl S, S: "Fotais White (W) .. ~ 2 ...... '2/ 6 :? 4" ., .... 4/ Abyssinian tabby ( t L ) .. ~ 5 4 5 3 17"1 32 9 7 6 I 1 151" Striped tabby (+) . ,3 12 9 4 1 26/ 8 5 3 2 18j Blc~tehed rabb.v (t I~) c? 0 1 0 0 1 1 Tabby ( t? ) d' 0 0 0 4 4/ 7 .o 0 0 0 3 31 Black (a) 5 7 9 4 25/ 52 9 3 10 5 9 27/ Yellow Abyssinian tabby (tLy) .. ~ 3 3 8 2 161 21 9- ,1 2 ,1 1 5/ Yellow striped tabby (2) c? 3 6 6 2 '171 2I 9 1 1 0 2 4 / Yellow blotched tabby (tUy) 0 1 0 0 1 1 Yellow (t? y) c~ 0 1 0 2 3/ 6 1 0 0 '2 3J Abyssinian tabby-tortoiseshell (+/b, t~- ) ? 2 4 "2 4 ,12 12

Striped tabby-tortoiseshell (+L;') -, o 7 8 5 2 22 22 Tabby-tortoise~heJl (§ t) .. o 0 i 1 2 4. 4 Black-tortoiseshell ( + /y a) .. ? 1 7 4 5 17 . ,17 Seal-point Siamese (cgB) . c? 1 ...... t/ 2 9 i ...... ,1t Ydlow Siamese (e~y) .... L t Blue-point Siamese (csa) .. ,s 1 ...... l 1

Totals 69 76 54 5l 250 pattern the black-tortoiseshells, in which only the small and scattered areas of yellow could he used for this purpose. The exact classification of cats carrying Siamese dilution was also dilticult; the degree of white-spotting cannot be determined accurately on them, so they were not classified for this character, A. G. SEARLE 117

Action of the silver (c e~) and dilute (d) genes is not i.ncluded in table 1. A clear-cut effect of the silver gene was noted on twelve cats, with the following phenotypes: IFc~, 7+,.-~d', 2--]-/y t ~ ~, 2 -}-/.y~. As in London, some other cats seemed to be inter- mediate between true silver tabby and normal. Four cats showed uniform dilution offur-colour, (dd), namely 1 +9, 1 ag, 2y~"G. All the cats had short hair, contrasting with the London results, where 62 out of 700 cats had medium or long hair. No examples of polydactylism, Manx tail or other skeletal mutants were tbund, apart from kinky-tail. For classificatory purposes the continuous variation shown by this character was split up arbitrarily as follows: K~, tail .with distal kink only and not much shortened, if at all; K~, more severe kinking and truncation but proximal part of tail still straight; Ka, extreme kinking affecting nearly alI the tail, which is much shortened. Results were as follows:

Without K~ K, K... Total % kinked kink Males 39 34 26 16 115 66-1 Females 48 45 32 10 135 64-4 Total 87 79 58 26 250 65.2

The,-e is no significant difference between the incidences in male and female cats.

~ENE FREQUENCIES

As shown in the previous paper Searle, 1949) we can test the hypothesis of random mating by using the sex-linked gene for yellow, since heterozygotes for this gene can be recognized. White cats and seal-point Siamese must be omitted fi'om the calculations, as we cannot tell their genetic constitution with respect to y. The remaining 242 animals were classified as follows for their constitution at they locus (expected figures in brackets) :

+/+ or -[- -t-/Y y/y or y Total Males 74 (76.8) ., 38 (35"2) 112 Females 63 (61'0) 55 (56'I) 12 (12'9) 130

Out of a total of 372 genes at they locus in this sample, there are 38 +2 7< 12 +55, ~-- 117 y genes. Thus the gene frequency for.), is 3l'4-5~ Using this value and the Hardy- Weinberg formula we obtain the figures given in brackets above as those expected on the hypothesis o[" random mating. There is a close fit widl observed values, X~- being 0-47, n =0-3 and 0'95>P >0-90. Thus the hypothesis of random mating can be accepted with Singapore's cat population, as with London's. Other gone li'equencies can now be esmnated and are given in Table 2, recessive gene frequencies being taken as the Square root of the corresponding phenotype fi'equency. The numbers of cats classifiable for the various characters have to be ascertained first; for instance, the type of 118 Variation in Singapore Cats

tabby pattern cannot be determined on solid black cats, neither is it possible to teli whether yellow cats are agouti or non-agouti.

Table 2. Phenotype m~d gene frequency estimations for Singapore cats Character No. classifiable Phenotype no. Phenotype fi'eq. Gene freq. ( o/ , oJ (%) W 250 6 2.4 1'2 -I_:0-7 l~- 156 65 -1,1-7 23"6• 1 ~ 156 89 57.1 65-1 ~:3.8 t b 156 '2 1"3 11 "3 L2"5 a 192 71] 36-5 6(3.4-2 3"5 d 244 't 1'6 12.8• ceh 12't- 12 9.7 20.84_3"6 c~ 244 ," 1-6 12,8 :k2" l ), _4 ..... 31'5 • 3"0 Whlte-spotting 240 181 75"4. .. Kinky-tail 250 163 65-2 ,.

Table 3, Cbmparisons of phenotype and gene frequency estimations for Londmz, Singapore and e~Iishima (Japan) cats

Character Phenotype frequency (%) Gene fi'equency (%) London Singapore Mishima London Singapore Mishima

;g 0-9 2'4 3.0 0.4--.0.2 1.2~-_0'7 1.5 +_0.7 tL 0-3 41"7 .. 0.2~0.3 23-6!3-4 l + 33.,1 57.1 -. 18,5 • 65. I • 3"8 lh 66-2 1 '3 .. 81-4--2-3 11.3--2"5 ~2 5t3,0 36-5 62-5 76.2 :f: ! "7 60-4~ 3"5 79-1 ::t:2-8 y ...... 10-7--1.2 31.5=k3"0 39-4~2.9 d 2"0 l'6 .. 14.2+1"3 12-B--2-1 ,o ceh 4-1 ~ 9-7 .. 20.2~2.4 3I'1 ~4-2 White-spotting 60.7 75-4 ...... Kinky-tail 0.0 69"2 81'5" .... *Komai, unpublished data

Table 4. _4 comparison of white-spotti.g in Londo~ and Singapore cats

s, s t sa Sa Total classifiable London 272 (39-4%) 282 (40-7%3 82 (tl.8%) 56 (8.t%) 692 Singapore 59 (24-6%) 76 (31.7%) 54-(22"5%) 5I (21'3%) 240

These results can now be compared (table 3) with those found elsewhere, namely by Kornai (1952) in Mishima, Japan, and by 8earle (19,}9) in London. Komai also gives data for the Japanese town of Gotemba and for Hokkaido (Komai, 1950), but for various reasons those from Mishima are the most satisfactory. I have calculated the A. G. SEARLE 119

gene fi'equencies for I1: and a in Mishima cats, also standard errors, fi-om the figures given by Komai (1952). Some striking differences in gene frequencies are immediately evident. Whereas in London (and probably throughout Europe) a high proportion of tabby loci carry the blotched (11~) allele, in Singapore and almost certainly in the rest of Eastern Asia this allele is rare; instead, the gene for striped tabby (1+) is commonest. Professor Komai (personal communication) assures me that this is also the most fi-equent allele in Japan. This seems to hold for Hong Kong too, judging by a small sample of cats I examined there. It may be significant that the few examples of a blotched tabby pattern which I have seen in Asia seem on the whole to differ fi'om the standard English pattern and to vary more. Abyssinian tabbies are common in Singapore and Hong Kong, but very rare in London. Dr. H. Spurway states that I~ appears to be present in most cats in Calcutta, while t b is quite rare; thus the gene frequencies at this locus are similar to those in Singapore. y and d also have similar frequencies, but a is probably rarer. In Eastern Asia, the gene for yellow fur-colour is three to four times as common as in London; in Japan this has meant that the tortoiseshell male occurs often enough to be the object ofcertain superstitions. The non-agouti gene is common in all three populations, although its frequency is significantly higher in London and Mishima than in Singapore. The gene for silver, however, has a significantly higher fi-equency in Singapore than in London, but is rather a difficult character to score, owing ~o inter- grades. Tables 3 and 4 show that white-spotting is not only decidedly commoner in Singapore than in London cats, but tends to be more extensive : almost three times as many Singapore cats are over two-thirds white. Pure white cats, however, are rare in all three centres. High proportions of Malayan and Japanese cats show the kinky-taiI character, which was not found at all in the London cat sample. 1-3% of London cats had short tails, however; these were presumably manifestations of the Manx character, since the off spring of Manx-normal crosses often have truncated tails (Bamber, 1927). 1 was not familiar with the kinky-tall character when classifying these cats, so a slight mani- festation of the condition might have escaped nly notice. This anomaly is widespread in East and South-East Asia. Out of 40 cats which Miss Hasnah binte Md. All kindly examined for me in the North Malayan States of Kedah, Perils, Kelantan and Trengannu, 25 (62"5%) were kinky-tail. Mr. R. Strahan (personal communication) informs me that in Hong Kong "almost exactly one-third have some sort of kink." [It. might also be mentioned here that although no polydactylous cats have yet been seen by me in Singapore, this character does occur locally, for Dr. Ivan Potunin states that it is common in some isolated kampongs in Johore.

SKULL VARIATION

Fourteen male and eighteen female cat skulls were prepared fi'om Singapore material by tire papain method; they were me~ul'ed and classified lot various characters. Seven skulls showed signs of immaturity, such as separation of bo~les, so fl~ey were only 1120 Variation in Singapore Cats measured for tooth-size. Table 5 shows that males are larger than females /br all characters measured; the difference is usually highly significant. In each sex, mean

Table 5. 3[em~ skull and tooth-sizes in Singapore cats, ill ram., with co~.'[ficie~ts qf variation and standard errors

Males Females Mean CoefL of Mean Coeff. of ,'~n. (%1 yarn. (%)

Skull length .. 89'46:t: I '03 3.6,1- 82"240:0"82 4-. 13 Condylo-hasal Iength .. 79.05-.}.:0.97 3.88 72.13-Jz0"63 3-51 Interorbital width .. 18'37• 5'69 16'24):_0'2t 5'07 Skull width . . 65"92--0"78 3"72 59-64-0"50 3.37 Left upper pm. 4 length . . 10.22~0-12 4.0fi 9.634-0'08 3.40 Left lower m. 1 length .. 7-7I 4-0-16 7.24 7-42• 3.65 LeA upper m. I length .. 3"39--0"17 I3"8 2.864-0"13 14-0 condylo-basal length is significantly less than Morrison-Scott's (1951) figure of 81-60 ram, (standard deviation 6.40) for 58 male and female skulIs from different parts of the world. This suggests that equatorial cats tend to be smaller than those from more temperate climates, which is what one would expect from Bergmann's rule. On the other hand, mean lengths of upper pm. 4 (carnassial) differ little fi'om Morrison-Scott's figure of 9"85 ram., with standard deviation 0"55. The significance of the great variation shown in the sizes of upper first molar teeth is discussed latter.

Absence of separate interparietal In some skulls the interparietal is fused with either the supraoccipital or one of the parietal bones, with obliteration of the suture. This fusion is not just an age effect, since it occurs in some young skuIls but may be absent from mature ones. Possibly interparietal-supraoccipital fusion is really a different entity from the other type. The frequency of fusions is as follows:

With Kzsion Without fusion Total % fused

Males .. 4 10 14 28.6 Females .. 11 9 20 55-0 To~al .. 15 19 3't. 44.1

Although the incidence of fusions seems much higher in females, the sex difference is not significant, X" being 1.38 and P=0"2 after applying Yates' correction for continuity.

Double bfraorbita,i. canals The canals at the fi'ont of the orbit which transmit the infraorbital nerves are normally single. In one male and one female skull, however, they were both double, with a horizontal shelf of bo~,ie dividing them, A. G. SEaRLE 121

Absence of teeth The normal dental formula of the domestic cat is: i. 3/3; c. 1/1; pm. 3/2; m. 1/1. No divergences fi'om this formula have been found in the lower jaw. In the upper jaw, however, the front premolar (morphologically the second of the original fore') and the first molar are small and tend to be absent altogether. This absence may be asymmetrical. Figures for the premolar are:

Both 1.eft only Right only Botl~ Total % presen~ absent absent ab.~ent absent

Males 11 0 f} -'2 13 t5 Females 14 0 3 2 19 26 Total .. 25 0 3 4 32 _'21-9

Thus in _79%_/. of the cat skulls one or both anterior premolars are absent. The occasional asymmetry suggests that this anomaly is mainly due to environmental factors, sometimes acting only on one side of the animal. In Bateson's (1894) data on 290 domestic cat skulls there were eight examples OF bilateral absence of this premola," and two of unilateral absence. Thus the incidence of this abnormality was 3.4%, much less than in my sample. The upper first molar lies transversely in a cramped position behind the large carnassial. Data on its occurrence are:

Both Left onl~ Right only Both To,al % present absent absent absem absent Males .. 14 0 0 0 1'4. 0 Females .. 16 0 '2 1 19 16 Total .. 30 0 2 1 33 9" 1

The difl'erence between the sexes [s not significant, P being 0"18 usin,,, Fishe,"s exact treatment.

l . i __, 1 0 5mm. Texbfig. 4. Oudhle camera hlcida drawhtg~ of cat upper first molars, .~hmvint~ dw grea, val"ia,ion in size and shape.

Those upper first molars which are p,'esent show great variation in shape and size (text-iig. 4), with a coefficient of size variation of about 14~ (table 5), which is rnuch higher than normal. Thus they show many similarities in behaviour to the small and 122 Vadation in Singapore Cats

variable third molars in certain inbred straitls of mice (Or0neberg, 1951 ; Sear/e, 1954), which may also be absent. These tooth anomalies in mice were regarded as clear-cut examples of quasi-continuous characters by Or0neberg (1952), with a physiological threshold cutting across the underlying continuous variation so as to cause discontinuity. Absence of upper first molars in the cat is doubtless another example of the same phenomenon. Again there is wide variation in adult tooth-size, presumably reflecting a variable tooth-germ size at some critical stage in development. We can postulate that at this stage tooth rudiments below a certain threshold size i?.tii to develop further, thus the tooth concerned will be absent in the adult. Two other pieces of evidence support this view. One is that male first molars, always present in this sample, are at the same time significantly larger than femaIe ones. The other is that where the first molar is unilaterally absent there is a slight (not significant) tendency for the tooth remaining to be smaller than normal (average size 2.72 ram.), as one would expect on this hypothesis, since the size of right and left teeth is usually highly correlated. Loss of upper second premolars probably represents another example of the same phenomenon of quasi-continuous variation, but their size was not measured.

DIsctJssroN

Genetical information on cat populations throughout the world is still meagre, but some details of the overall picture can already be made out. There are clearly considerable regional differences at present in the frequency of many of the known genes. Some of these genetical differences will undoubtedly remain, For they represent natural clines based on climatic and other factors. For instance, all Singapore cats examined had short hair, but 9% of London cats had medium or long hair. The gene for Persian hair is likely to remain very rare in equatorial regions, where it is presumably at a selective disadvantage, and Singapore is only 1~ 17' N. of the equator. Other differences, however, are almost certainly due to the slow spread of a mutant gene which has arisen since domestication.: The rarity of the blotched allele of tabby in Asia, compared with its high fiequency in London and probably much of Europe, may well be due to this. In his description of the British Museum collection of skins of feral cats From various parts of the world, Pocock (I951) remarks: "It is of inte,'est to note that although typical calus, with the bold blotched pattern, is as common a house-cat as any in England, it is very scarce as a ferat form, at all events outside Europe... A great majority of the feral cats, at all events of Asia, Africa and Australia, are either typical torquata (i.e. striped tabby) or red, black, partl-coloured or other mutants of that type." Thus this rarity of the blotched tabby pattern seems fairly general outside Europe, with the probable exception of North America, where most of the cat population has presumably originated fi'om faMy recent imports from Europe. In parts of Europe blotched tabbies have been common fbr at least 200 yea,'s, being the type to which Linnaeus (1758) gave the name Fells catu~, as Poc0ck (1907a) points out. Linnaeus describes this species as "corpore fasciis nigricantibus, dorsalibus longitudinalibus tribus, tateralibus spirali&us." Only blotched tabby cats have spiral markings on the A. O. SEARLE 123 flanks. No possible wiId ancestor of domestic cats shows this pattern, so it is reason- able to suppose (as Pocock does) that it arose as a mutation of the striped tabby gene subsequent to domestication. It also seems probable that its scarcity elsewhere is because it has not yet had time to establish itself, rather than to adverse environmental liactors. There are a number of blotched tabbies among the feral cats of Queensland, North Australia (Pocock, 1951), which suggests that Iropical conditions do not affect them adversely. No possible ancestral form seems to show the rich colour of sex-linked yellow in the domestic cat, ahhough some are rufescent and the mummified cat of Ancient Egypt is desc,'ibed as being "ginger-coloured, with a long dark-ringed tail." (Morrison-Scott, 1951). Present evidence suggests that the gene frequency for yellow is highest in Eastern Asia, decreasing as one passes westwards to Europe; but more data are needed before the existence of this cline can be confirmed. The ngn-agouti gene seems uni- versally common. Melanic variants are known in mm~y :wild mammals; thus the A-~a mutation-rate is probably fairly high as a rule and many non-agouti mutants may have arisen independently in the cat since domestication. The same is doubtless true of white-spotting. The higher average amount of white in the coat of Singapore cats and the lower proportion of solid black cats, when compared with some temperate countries, may be connected with the intensity of solar radiation in an equatorial climatc. Calcutta cats also have a high average grade of white-spotting (Prof~ssorJ.B.S. Haldane, personal communication). In Singapore as in London, the gene for pure white coat- colour (W) seems to be al a selective disadvantage because of associated deafness and possibly other defects. The reason for the high frequency of kinky-tailed cats in East and South-East Asia, contrasted with their rarity in other parts of the world, is a fascinating problem; the similar (but more extreme) Manx character remains uncomnmn in Britain. I have no evidence that kinky-tailed cats are in any way favoured by Man; it would indeed be surprising if they were regarded as lucky over much of their wide range, in which cats are associated with so many dift'erent peoples. If human selection was being exercised in favour of' kinky-tail one might expect to find a higher proporlion of no,mal tails among discarded kittens than among adults; the reverse was true in my sample of Singapore cats (72% of kittens with kinky-tail, 62% of'adults), but the difference is not significant. When onc considers the high proportion of feral and semi-feral cats in this area it seems very likely that the gene or genes concerned really do increase fitness, but perhaps only in a tropical environment. Heterosis may well be involved. Striped tabby is the only pattern which is reasonably common in London, Singapore and japan, supporting the "view that the domestic cat is descended from one or bolh of the wild species having this phelmty'pc, namely Felis silveslris and Fells lybica. Pocock (1951) considers the Egyptian mummilied cat to be a sub-species (bubaslis) ot'F. lybica. Whether bubaslia was ancestral to the present domesticated forms is still uncertain. Morrison-Scott (1951) fotllld the mean colldylo-basal length of 178 mummified cat skulls to be 94..75 ram. as against 81"60 mm. for present-day cats; the difference between means is 11.4-6 times its standard crror and thereforc higl?,ly significant. HumarJ 124 Karialion in Singapore Cats

selection, environmental changes etc. might conceivably have ted to this considerable decrease in skull size, but it seems more likely (as Pocock suggests) that the Egyptian cat was the result of hybridisation between a smaller North Afi'ican race of Felis lybica and the largcr Fells cha,,s nilotica. Morrison-Scott found three larger skulls among the mummified cat collection, which he decided were almost certainly Fells chaus. Present- day Felis lybica are apparently easily tamed (Lorenz, 1954), while the opposite is true of silvestris. Our domestic cats may therefore be descended from a race ofF. lybica, which later hybridised with the closely related F. silveslris. Pocock (1907b) showed that hybrids between the two "resembled in all rcspects t~airly typical domestic cats of the striped-tabby breed." The Abyssinian tabby pattern (more or less ur~iform on the body, though stripes may be seen on legs and tail) seems to be common throughout much of South and South- East Asia, but is rare in Europe. This might suggest that the domestic cat has hybridised with Fdis chaus, its nearest wild relative in this region, since this also has a uniform agouti pattern. This seems unlikely for two main reasons. The first is the size of Fells chaus: mean condylo-basal length of the skull is over 100 ram., while that for Singapore cats is less than 130 ram.; as pointed out earlier, cats in this part of the world tend. to be smaller than average and not larger as would be expected if their ancestors had hybridised with F. chaus. Second, it is doubtful whether the patterns are really identical; in caaua the kitten is apparently striped on the flartks but these stripes become more or. less suppressed in the adult (Pocock, 1951). In the Abyssinian tabby, however, young and adult have the same pattern. Thus it seems more probable that this tabby allele (t ~ ) arose by mutation of striped tabby (t +) somewhere in Asia (or possibly Africa, t'rom which I have no data yet). The domestic cat, like all Felida~, has a highly speciatised carnivorous dentition, with large and weiI-developed carnassials. The only tooth posterior to these is the small transversely placed upper first molar. This is sometimes absent and has clearly lost any fimction it had originally. Thus it is a vestigial structure as well as being a quasi- continuous variant, having~a high coefficient of variation. It is probable that these characteristics are shown by many vestigial structures, another example being third molars in the mouse. When a structure loses its original function, homeostatic control will be relaxed and it will tend to vary widely in size and other properties. Possibly some of the variants will be at a selective advantage because they develop by chance some new fimction; the old structure may then be converted to a new use: some reptilian jaw-bones to mammalian ear-ossicles for example. Alternatively, the structm'e will generally tend gradually to diminish in size while remaining variable. At a certain stage in its evolutionary degradation, a threshold effect is likely to operate whereby a proportion of variants at the lower limit of the range fail to reach a critical threshold size during embryonic development and as a result fail to grow further, being resorbed instead. Thus the vestigial character would show quasi-continuous variation. With fi.lrther gradual decrease in .mean size more and more of the variants would fall belovr the threshold, until eventually it would seldom be reached; the character concerned might then be called "aDvistie" or "supernumerary". An alternative explanation for A. G, S~*RLE 125

the sporadic absence of a vestigial structure would be that a gene abolishing the structure altogether was spreading through the population. Asymmetrical tooth absence would be difficult to explain on this hypothesis, which seems less likely than a continuation of the usual evolutionary process of gradual size reduction due to the actions of many ciifferent genes. It may: be profitable to discuss briefly the probable origin and natm'e ofpolymorphism in the cat. It seems likely that two main factors encouraged the spread of newly m'isen coat-colour and pattern nmtants. First, natural selection against poorly camouflaged animals would be relaxed when cats became associated with man and food was easier to obtain. Clearly colour and pattern are not important for sexual recognition in this species. In the wild, many cat subspecies are scrub or desert animals, living where food is scarce and camouflage of great importance, so that colour mutations making the animal more conspicuous would have no chance of spreading. Second, human selection would generally favour the novel phenotype; it certainly does at present. At most loci, potymorphism seems to be of the "balanced" type. The balance may be between adverse natural seleclion and favourable human selection, as seems likely at the lJ'*Iocus. Or the character may be favoured by human select{on when rare but at a disadvantage when common, with natural selection playing little part. This may well be the situation with agouti versus non-agouti and yellow versus black. True heterosis may possibly be involved occasionally, perhaps with kinky-tail. The high frequency of blotched tabby genes in London cats (81"4%) almost suggests that this Js an example of transient polymorphism, due to a selective advantage of th~s gene over other tabby alleles, so that the,,,, may eventually be ousted completely from some areas. It is difficult to telI at present how far human selection is responsible for the high fi'cquency of this gent and how far natural selection, although comparisons of young and adult phenotypes in London siiggesI that blotched tabby is not preferred over striped whcn selection of kittens is made. Much more evidence must be collected fi-om various sources, however, before lhese tentative conclusions can bc reinforced or refuted.

,~UMMARY

1. Results are given of a genetical survey of Singapore domestic cats; as in London, figures for yellow agree with the hypothesis of random mating. 2. The blotched tabby gene is much rarer titan in London, while that t-oi Abyssinian tabby is much commoner. As in Japan, the yellow gone is much commoner than iu London; there is also a higher average grade of white-spotting. No long-haired cats were found in the Singapore sample, 3. 69-2% of Singapore cats sh.ow tl:m kinky-tail character, in which the tail is shortened and has one or more kinks; this abnormality was ~m~ seel~ in any London cats. Associat- ed de&'ets ofcaudaI vertebrae, including fi~sions and major distortions, arc described. 4.. Skull variation is also analysed. 22% of skulls lack one or both upper fiont premolars, while 9% lack upper first molars. The latter teeth are small and very variable; they appear to be examples ()fquasi-continuous variation, It is suggested that this may be a fairly common l)henomenon among vestigial structures, ., 126 I:"arialion in Silzgapore Cats

5. The pr,3bablc meaning of the many gene fi'equency differences found and the light they throw oft the origin and evolution of tiae domestic cat are discussed. It is thought probable that the blotched tabby gene arose as a mutation in the European domestic cal and is still in Lhe process of spreading into other areas.

I am gratclhl to the veterinary staffat the Animal Infirmary, Singapore, for giving me every facilit} to examine cats brought there; also to Che Hassan bit-t A. Bakar for helping me to examine kampong cats. I should also like to thank Mr. Ronald Strahan, olc the University of Hong Kong, for kindly providing me with a sample of cats fi-om thai area, and Miss Hasnah binte Md. All for obtaining additionaI data for me fi'om North Malaya.

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Black and ,,vl~ite 1,:illml wi~h slight dislal kink. Abyssinian tabby v,'iah high-grade ldnky-tail: of si'Jix'al lype. Black cat with severe hook-like kiul~..