evaluation of anatomical characters and the question of

1Institut fur Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universitat, Jena, Germany;2Natural History Museum, Bern, Switzerland; 3Institut fur Okologie, Friedrich-Schiller-Universitat, Jena, Germany

Evaluation of anatomical characters and the question of hybridization with domesticcats in the wildcat population of Thuringia, Germany

Matthias Kruger1, Stefan T. Hertwig

2, Gottfried Jetschke3 and Martin S. Fischer

1

AbstractGermany�s large population of wildcats (Felis silvestris silvestris) can be clearly distinguished from domestic cats on the basis of morphologicalcharacters. However, an examination of 71 specimens from Thuringia also illustrates the risks involved in using only a few such characters. Themost reliable tool for identification in the field are three pelage characters (distinctness of tail bands, stripes on the nape and stripes on theshoulder). Only two morphological characters (intestine length and cranial volume) are unambiguous and demonstrate no overlap in distributionbetween domestic cats and wildcats. A linear discriminant analysis with forward selection of variables showed that only five skull variables arenecessary to distinguish all four groups (subspecies · sex). Additionally, the high degree of correlation between most of the 49 variables examined(as indicated by Pearson�s r correlation matrix) speaks against the utility of measuring such high numbers of characters in the future. Principalcomponent analysis (PCA) enabled the subspecies to be separated clearly. The first PCA axis was highly correlated with variables characterizingoverall body size, thus separating male and female into wildcats and domestic cats. Even when the chief differentiating characters are missing, thePCA still resulted in a good separation of subspecies. None of the genetically determined hybrids could have been deciphered unambiguouslyusing the morphological characters still intact after a road death. Hybridization seems to occur whenever wildcats change their ecological functionand become field cats. The impulse to hybridize seems to come much more from the wildcat side than the side of feral cats, and deforestationrepresents the major threat to the wildcat.

Key words: Wildcat – morphometry – hybridization

Introduction

The long discussion surrounding subspecies of Felis silvestrisand the existence of a �pure� European wildcat culminated in

the question posed by Daniels and Corbett (2003): �when is awildcat a wild cat?�. The authors argue that �protection shouldmove away from efforts to affect a definition based on type,accepting that extensive introgression has already occurred� (p.216) given that �in Scotland the collection and classification ofthe type specimen for the wildcat took place in 1904, at least2000 years after the two forms (wildcat and domestic cat) had

been in sympatry� (p. 213). Their principal idea is that a speciesconcept based purely on typology and morphology should beabandoned in favour of a functional definition in the future

protection of wildcats. Because Daniels and Corbett do notlimit their suggestion to the local Scottish population, theirunderlying observation on the high degree of hybridization of

the wildcat population needs to be tested elsewhere before theirradical recommendation can be accepted, particularly in lightof its far reaching consequences given the large amount ofresources being invested in the protection of the European

wildcat. In other words, can future conservation effortslegitimately be based on a functional species definition.Recent results from Driscoll et al. (2007) shed new light on a

long-standing discussion concerning splitting events within F.silvestris. The species first occurred in Europe at least 350 000–450 000 years ago (Garcia et al. 1997), and split into the

European forest wildcat and the African ⁄Asian steppe wildcat

lineage around 200 000 years ago (Heptner and Sludskii 1972;Yamaguchi et al. 2004a). The exact timing of these splitting

events is contested, Randi and Ragni (1991) proposing on thebasis of allozyme electrophoresis data that they took place asrecently as 50 000 or 20 000 years ago, respectively. Yamag-uchi et al. (2004a) dated the split between F. silvestris silvestris

and F. silvestris lybica to 50 000 years ago as the wildcatspread from Europe to Asia and later to Africa. Driscoll et al.(2007) has made clear using a molecular clock approach that

the African and Asian wildcats including the domestic cat forma strongly supported clade which diverged from the Europeanwildcat between 173.000 and 230.00 years ago. The last

common ancestor of the F. silvestris lybica ⁄F. silvestris ornataclade and hence of domestic cats lived between 107 000 and155 000 years ago. The domestication of the cat probably tookplace several times as is illustrated by the presence of five

matrilineal mitochondrial DNA lineages in modern domesticcats. However, the dating method in Driscoll et al. failed toreveal a plausibly hypothesized age for cat domestication.

The prevailing hypothesis that the first domestication ofthe cat occurred in Egypt between 3000 and 1600 bc (e.g.Kratochvil and Kratochvil 1976; Kitchener 1991) was falsified

by the discovery of cats introduced to Cyprus by Neolithicsettlers as early as 7300–7200 years bc (Vigne et al. 2004). Thedomestic cat came to France (Lepetz and Yvinec 2002) and the

British Isles (Grant 1984) with the Romans, but it has onlybeen abundant in larger parts of Europe since 400–500 ad. Weare not aware of any published references concerning theintroduction of domestic cats to Germany as it is recognized

today.Our current knowledge of the hybridization of the wildcat

and the domestic cat in Europe is based on a number of

morphological and molecular studies (Beaumont et al. 2001;

Corresponding author: Martin S. Fischer ([email protected])

Authors� email addresses: Matthias Kruger (kruegermatthias@

t-online.de), Gottfried Jetschke ([email protected]), Stefan T. Hertwig

([email protected])

� 2009 Blackwell Verlag GmbHAccepted on 17 April 2009

J Zool Syst Evol Res doi: 10.1111/j.1439-0469.2009.00537.x

J Zool Syst Evol Res (2009) 47(3), 268–282

Daniels et al. 1998; Daniels and Corbett 2003; Eckert 2003;French et al. 1988; Hertwig et al., 2009, this volume; Hubbardet al. 1992; Kitchener et al. 2005; Lecis et al. 2006; MacDonald

et al. 2004; Oliveira et al. 2008; Parent 1974; Pierpaoli et al. 2003;Stahl and Artois 1994). Because numerous morphological charac-ters or combinations thereof are also used to pre-classify samples in

genetic studies (e.g. Randi et al. 2001; Pierpaoli et al. 2003), theyare an important tool for future studies. Guidelines for selectingmorphological characters are provided by the exemplary study byDaniels et al. (1998), in which 26 pelage variables (n = 187),

intestine length (ITL, n = 57), limb bone variables (n = 53), and43 variables from 51 skulls of 333 cats from Scotland weremeasured. The authors� principal result was that neither pelage norcranial variables alone were useful in identifying wildcats, hybridsand domestic cats with certainty. By contrast, Ragni and Possenti(1996) have shown that it is possible to differentiate domestic cats

and European wildcats reliably using only pelage variables.Puzachenko (2002) investigated differences between Europeanand African wildcats on the basis of 42 cranial characters, 11 of

which he indicated to be both discriminative and to have lowintragroup variability. Yamaguchi et al. (2004b) used 31 measure-ments of the skull and mandible and five derived indices to identifypossible differences in the three recent subspecies of F. silvestris.

Most recently, Kitchener et al. (2005) studied 20 pelage variables in135 specimens of �presumed wild-living cats from Scotland� invarious collections �to develop and test a reliable definition of the

Scottish wildcat�.The morphological identification of individuals with hybrid

origin, however, remains difficult because of the long-term

sympatry and interbreeding of domestic cats and wildcats andis usually based on the presence of a mixture of charactersassumed to be typical for both forms. In most studies,

characters are claimed to be intermediate or indicative withoutknowledge of their variability, first within the subspecies andthen between wildcats and domestic cats. However, thepractice of classifying as hybrids all those individuals whose

characters are not unambiguously identifiable as either wildcator domestic cat (e.g. Kock and Altmann 1999) is flawed from

the start. Characters that do not clearly separate wildcats fromdomestic cats should be excluded from the analysis becausethey do not represent a basis on which to declare a specimen a

hybrid: overlapping character states do not equal �overlappingsubspecies�. And as there are no diagnostic, non-overlappingcharacters which identify hybrids, differential diagnosis is

necessary.Although a number of previous studies have shown a good

level of concordance between the outcomes of morphologicaland genetic methods of identifying domestic cats and wild

cats, no evaluation of the morphological characters used hastaken place (Randi et al. 2001; Pierpaoli et al. 2003). The aimof this study, therefore, is, through a comparison with the

results of our parallel molecular study (Hertwig et al.), toidentify the diagnostic value of anatomical characters on thebasis of the Thuringian wildcat population (Gorner 2000;

Klaus 1993). A total of 49 morphometric traits weremeasured, including 40 skull traits (36 direct measurementsand four indices), seven limb skeleton variables, body weight

and ITL. Using a range of statistical methods, we aim toprovide a reliable, practical diagnostic method based on thelowest possible number of characters, and to provide second-ary criteria for those cases where key characters (e.g. ITL) are

missing. Our complementary approach has the additionaladvantage to provide the basis to reduce the measuring effortnecessary to distinguish domestic cats from wildcats with

special regard to age-related changes and sexual dimorphismin subsequent studies. Finally, we discuss whether or not theThuringian and German wildcat populations are threatened

by crossbreeding with domestic cats, and explore the potentialcauses of hybridization.

Materials and Methods

Specimens and measurements

Morphological examinations were conducted on the 58 specimensfrom Thuringia in the collections of the Phyletisches Museum Jena(Appendix S1, Fig. 1), the central collecting institution for wildcats in

THÜRIGER

A38A38

UMWELT UND GEOLOGIELANDESANSTALT FÜR

Fig. 1. Map of the Free State ofThuringia showing the distributionof dead wildcats (Felis silvestris) asof May 2006. Courtesy of Thurin-ger Landesanstalt fur Umwelt undGeologie

On German wildcats, morphology 269

J Zool Syst Evol Res (2009) 47(3), 268–282� 2009 Blackwell Verlag GmbH

Thuringia. We feel confident that this number is sufficient given thatRagni and Possenti (1996) showed growth curves of number ofphenotypes versus sample size that approximate an asymptotic form inwildcats starting from about 12 specimens.

Depending on the condition of the carcasses, we tested a suite of 40cranial, eight skeletal, 20 pelage characters, and ITL as well as bodyweight suggested by previous authors (see above) to distinguishbetween wildcats and domestic cats (Table 1). Pelage characters werenot included in the statistical analysis.

All measurements were taken by M.K., with pelage characteristicsidentified by M.K. and M.S.F. Intestinal length from the pyloric toanal sphincters was measured to the nearest millimetre by Muller(2005), who also checked the pigmentation of the palate. Weight (tothe nearest 10 g) was recorded, and total length and tail length weremeasured (to the nearest mm) as far as the condition of carcassesallowed. Cranial measurements were taken to the nearest 0.5 mm inaccordance with previous authors (Driesch 1976; French et al. 1988;Piechocki 1990; Yamaguchi et al. 2004b; Kitchener et al. 2005 andothers). Cranial volume (CRV) was estimated using mustard-seedgrains (2–3 mm). Age was estimated by counting the cementum layersof the upper canine and ⁄ or by epiphyseal ossification followingPiechocki and Stiefel (1988).

Elementary statistics

The measurements within each population and between wildcats anddomestic cats were evaluated using the coefficient of variation (CV)and the coefficient of difference (CD) (Mayr et al. 1953). CV iscalculated as CV = (SD ⁄M) · 100%, expressing the standard devia-tion (SD) as a percentage of the mean (M). According to Mayr et al.(1953), �CV is particularly useful when comparable samples of the samespecies from different localities are investigated� (p. 135). CD isobtained by dividing the absolute difference between the means by thesum of both SD: CDBA = |MB – MA| ⁄ (SDA + SDB) and measures,roughly speaking, the degree of separation between two distributions.The error of misclassification between the two groups A and B is 10%for CDBA = 1.28, 5% for CDBA = 1.64 and 1% for CDBA = 2.33(exact values for the special case of equal standard deviationsSDA = SDB).

Statistical analyses

All statistical analysis was carried out using aabel 2.3 (Gigawiz Co.,Houston, TX, USA, 2007), jmp 6 (SAS Co., Cary, NC, USA, 2006),pc-ord and spss 15 (SPSS Co., Chicago, IL, USA, 2006). A nominal

Table 1. Characters in descending order according to their coefficient of difference (CD) together with their coefficient of variance (CV)

ITLCRVCRITILC1LHFLP4LFELPMLCLEHULP4LULLTALC1RBCWFMBOCBPPUMABZYBCRLPCBRAHORDMCWPMUFALCMLISIPADPABWGTMDMNMAPCDCSWCMUCBLSKLNMIFRBABDROBIFDMPWORISNLPMI

intestine lengthcranial volumecranial index = greatest length of scull : cranial volume

coefficient of difference coefficient of variation0 5 10 15 20 25 30 35

wc

dc

0 1 20.5 1.5 2.52.42.11.81.21.11.11.11.11.01.00.90.90.80.80.70.70.60.60.60.50.50.50.50.40.40.30.30.30.30.30.30.30.30.30.30.20.20.20.20.20.20.20.10.10.10.10.10.10.1

8.735.234.675.927.425.443.6

6.564.3712.16.235.457.226.389.443.254.244.264.055.037.339.564.3910.37.8110.23.855.454.685.317.355.4523.88.935.636.6328.33.5

5.285.425.556.065.196.885.858.536.666.645.06

tibia lengthlength C1

hind foot lengthgreatest length of P4

fernur lengthlength between mandibular P3 and M1

length of enamel C1

humerus lengthgreatest breadth of P4

ulna lengthtail lengthrood of C1

greatest width of the braincasegreatest breadth of the foramen magnumgreatest breadth of the occipital condyleslength between P2 and P4

mastoid breadthzygomatic breadthhead trunk lengthleast breadth of the postorbital constrictionheight of ramusleast breadth between the orbitsmaximum width of mandibular condyleslength between P2 and M1

facial lengthlength betweeen C1 and M1

breadth between the infraorbital foramina : lateral length of snoutmaximum distance between pogonium and angular processgreatest palatal breadthweightdepth of the mandible behind M1

maximum length of the nasalsmaximum distance between pogonium and coronoid processwidth of cranial suturelength between C1 and M1

condylobasal lengthgreatest length of skullminimum length of nasalsfrontal breadthanteriorposterior diameter of the auditory bullarostrum breadthbreadth between the infraorbital foraminamaximum width of mandibular P4

least breadth of the postorbital constriction : least breadth between the orbitslateral length of snoutgreatest palatal breadth : length between P2 and M1

5.66.327.215.678.196.46

6.25.788.485.468.165.198.561.33.76.3

5.585.154.865.698.7

4.927.826.785.185.659.56.4

5.136.335.0418.411.211.66.0430.46.426.334.9212.66.9

8.617.146.125.2

8.796.5

4.47

270 Kruger, Hertwig, Jetschke and Fischer


alpha value of 0.05 was assumed for all tests. It was not possible tomeasure all traits in all individuals. To incorporate as much of theavailable information as possible into the statistical analysis, missingtraits were estimated on the basis of the group median within the samesubspecies and sex group (the median was chosen to avoid anyinfluence of extremes). Individuals with more than six missing traitswere then excluded from the analysis, leaving 46 individuals with 2254entries in total, 4.5% of them represented by a median. However, CRV[and therefore, cranial index (CRI) in accordance with Schauenberg]was not available for 16 specimens and ITL was not available for 11specimens. Therefore, a subgroup of 30 cats for which data wasavailable on 42–49 traits (with only 2.6% estimated as median values)was used for the main analysis, while the whole sample of 46individuals was only examined for 42–46 traits (i.e. excluding CRV,CRI and ITL), to test which other variables might be important forclassification.

The correlation matrix of Pearson�s r coefficients was displayed as aheatmap to check which variables are highly correlated and could,therefore, be partially omitted for future measurements. A principalcomponent analysis (PCA) was performed both for the set of 42–49variables and for the subset of 33–40 skull variables to obtain anoverview of how the four target groups (wild ⁄ domestic · male ⁄ female)could be separated in a low-dimensional projection.

On the basis of these four pre-defined groups, a linear discriminantanalysis with forward selection was performed to determine whichvariables (and in which order) are necessary for accurate classification.The quality of this discrimination was tested by a jackknife procedure.

Results

Evaluation of single characters

Comments on specific characters are provided elsewhere forthe sake of simplicity and minimum redundancy.

Pelage characters

We tested all 20 pelage characters discussed in Kitchener et al.(2005), of which the following were considered by the authorsto be valuable in wildcat identification (numbering according

to the table in which they appear):(7) Extent of dorsal line(8) Shape of tail tip

(10) Distinctness of tail bands(15) Broken stripes on flanks and hindquarters(17) Spots on flanks and hindquarters(18) Stripes on nape

(19) Stripes on shoulder.Characters 15 and 17 were of no indicative value in our

sample. The dorsal line stops at the base of the tail (#7) in 20

wildcat specimens, and continues on to the tail in five. The tailtip (#8) is blunt in all wildcat specimens, but also in a fewdomestic cats. Tail bands (#10) are distinct in all wildcat

specimens (Fig. 2). In three cases, however, we observeddouble bands that did not encircle the whole tail. Four to fivestripes on the nape (#18) and stripes on the shoulder (#19) are

also distinguishing features for wildcats (Fig. 3). In the Italiansample, the dorsal line (#22 in Ragni and Possenti 1996) wasvaluable, but not the tail bands. Our sample is also different inthat the gular areola is variable in wildcats. The only character

on which all studies agree are the 4–5 stripes on the nape.An additional character not mentioned by Kitchener et al.

(2005) is the colouring of the hind paw (Schwangart 1943).

However, Piechocki (1990) doubted the utility of this trait andour sample shows variable paw colouring of the populations.

Metric characters

Coefficient of difference and coefficient of variance

Table 1 presents all characters in descending order accordingto CD and also gives CV values. With regard to length-relatedtraits, CV usually varies between four and 10 in mammals, asin our sample. The few characters outside this range [width of

cranial suture (CSW), body weight] are age-related characters.CV is also a sensitive indicator of homogeneity of samples andsuggests that our sample is indeed homogenous. The CD of

only two chief differentiating characters (ITL and CRV) andone ratio (CRI) exceed the critical value of 1.28 considered byMayr et al. (1953) to correspond to the 90% standard of

subspecific difference. There is no overlap in the distributionsof ITL and CRV between the populations.As in previous samples (Schauenberg 1977; Piechocki 1990),

ITL is the most reliable character in differentiating wildcatsand domestic cats (CD = 2.4). The clear gap between ITLdistributions in our samples is even wider than previouslyobserved (Braunschweig 1963). The intestine of the domestic

cat is more than 40% longer than that of the wildcat (mean2080 mm, SD 111 mm to mean 1440 mm, SD 126 mm). Thelongest wildcat intestine (1680 mm) was still considerably

shorter than the shortest one of a domestic cat (1880 mm).Body mass (WGT) is clearly gender-specific but is of no

other diagnostic value (CD 0.29) because it varies so much

within each sex (e.g. two males of equal head trunk lengthdisplayed a 31% difference in body weight). It also depends onmany external factors which change daily. The validity of head

wc

10 mo.

4 mo. 127 mo. 15mo. 71 mo.

49 mo. 17 mo. 74 mo.

dc

m

fFig. 2. Tail patterning of Thurin-gian wildcats arranged in ascend-ing age from left to right. Tails ofdomestic cats of one and sevenyears of age are shown for com-parison



trunk length (CRL) is limited by the lack of a standard

measuring procedure for the nuchal curvature. Additionally,measurements are affected by the condition of the carcasses.Finally, there is an overlap of 58% between CRL distribution

in wildcats and domestic cats, and a CD of only 0.48. Almostthe same is true for tail length (TAL) with an overlap of 35%(CD 0.84). Tail length is shorter than 50% of CRL in only

three specimens. The tail of wildcats is 5% longer on averagethan that of domestic cats (male wildcat 57%, male domesticcat 52%, female wildcat 61%, female domestic cat 56%). Hind

foot length (HFL) is only diagnostic when specimens showextreme values. Lengths higher than 130 mm are definitelywildcats, lower than 115 mm domestic cats. Although Krat-ochvil (1976a) and Piechocki (1990) accepted this character as

highly significant, we found a 39.5% overlap between thegroups in our sample. Still, its CD value of 1.1 indicates HFLto be the fifth most diagnostic character.

Although we lack the necessary specimen numbers to discusspostcranial characters in depth, some trends can be identified.Femur (FIL) and tibia (TIL) length are diagnostic only when

they are plotted in age and sex classes. Wildcats display femurlength above 130 mm for subadult and adult males and 120 forsubadult and adult females, whereas domestic males rangebelow 111 mm. TIL is 135 and 125 mm for male and female

wildcats, respectively. The CD for TIL is very close to the

critical value of 1.28, and the character ranks third. The tibiaof the Scottish wildcat is more than 10% shorter than that ofthe individuals in this study (Daniels et al. 1998).

Cranial characters

We restrict our specific comments here to the cranial charac-ters that are most informative and most often used. Thetaxonomic value of the other, less frequently used traits can beinferred from Table 1.

The greatest length of the skull (SKL) and the condylobasallength (CBL) have no taxonomic significance because theirdistributions overlap by 67% (CD 0.22) and 57% (CD 0.23),

respectively. There is also high sexual dimorphism inboth characters as male specimens are always significantlylarger than females in the both the wildcat and the domestic

cat.CRV consistently separated the two groups in our sample

(CD 2.1). Wildcats always exceed 34 cm3 (mean 37.3 cm3, SD

1.9 cm3) in contrast to domestic cats (mean 29.3 cm3, SD1.8 cm3). Schauenberg (1969) and Piechocki (1990) evenmeasured a slightly higher minimum value of 35 cm3 for thewildcat. A gap of 13.8% separates the two groups.

Fig. 3. Coat patterning of Thurin-gian wildcats. Top left: male wild-cat, 49 months old, Toba ⁄Helbetal07.06.1996; top right: female wild-cat, 75 months old, Weberstedt29.08.1996. Bottom left: maledomestic cat, 71 months old, All-menhausen 14.04.2004. Bottomright: female domestic cat,71 months old, Ebenau/Creutzburg29.04.1998



The oft-used CRI (greatest length : CRV), while apparentlydiagnostic, is less reliable than pure CRV (CD 1.8). Schauen-berg (1969), who introduced this index, stated that it is always

greater than 2.75 in domestic cats and below this in wildcats.However, the maximum value reached by one of the wildcatsin our sample was 2.73.

Zygomatic breadth (ZYB) has two limitations. First, there isa broad overlap in the range of distributions (56.6%, CD 0.49)and second, this factor is strongly age-related (Fig. 4).

The lengths of upper and lower tooth rows (C to M1),

(CMU and CML), both fail completely to distinguishwildcats from domestic cats (CD 0.24 and 0.34 respectively)because of the extensive overlap in their distributions (72.1%

and 89.7% respectively) and also because 20% of thedomestic cats we sampled displayed longer tooth rows thanwildcats. Our results, with the variable showing 86% overlap

(CD 0.34), also contradict the conclusion reached byPuzachenko (2002) that the length of P2 ) M1 (PMU) inthe upper and lower dentition is a significant diagnostic

character. The Thuringian wildcats have almost identicalvalues to the sample of Harz wildcats (Piechocki 1990), whilevalues from the Western Carpathian population are 3%higher (Sladek et al. 1972).

Canine length (C1L), which has only been used by Puz-achenko (2002) thus far, represents one of the most diagnosticof the easily accessible characters (CD 1.1), but is still

hampered by a 27.5% overlap in population distributions.The canine also has to be taken out of its alveole. One factorswhich counters these disadvantages is that C1L remains useful

even in older specimens because worn enamel crowns arecompensated by tooth cement in the apical region of the roots.Neither the length of canine enamel (CLE; 36.4% overlap, CD1.0) nor that of canine root (C1R; 37.7%, CD 0.73) were as

informative as total C1L.

Correlation between traits

Pearson�s r correlation matrix of the 49 characters for the 30individual set in Table 1 showed both expected and surprising

correlations (see Fig. 5). An examination of the Pearsoncorrelation coefficients for all possible pairs of traits revealsthat 13 (of 1176) exceed an absolute value of 0.9 (with a

maximum of 0.989), with another 83 coefficients havingabsolute values of between 0.8 and 0.9. However, 49 pairs ofvariables are essentially uncorrelated, with absolute values of rsmaller than 0.1. Among the nine non-skull variables TIL,

Fig. 4. Dorsal view of the skullcontours in wildcats and domesticcats. Top right: male wildcats, topleft: female wildcats, bottom right:male domestic cats, bottom left:female domestic cats; green: 0–6months, blue: 7–10 months, black:11–24 months, red: <24 months.Dorsal view of the skull contours inmale wildcats and domestic cats,right: wildcats, left: domestic cats,blue: 7–10 months, black: 11–24months, red: <24 months



FEL, ULL and HUL were highly correlated with r exceeding0.85, while HFL, TAL and CRL had correlation coefficients of

around 0.75. Body weight (WGT) was slightly positivelycorrelated, while ITL showed weak negative correlations (andalmost no correlation to WGT).

Among the cranial variables, SKL is identical (0.97) to CBL,and highly correlated (absolute values of r = 0.8–0.9) to eachof facial length, lateral length of snout (SNL), rostrum breadth(ROB), distances between pogonium and coronoid or angular

process (PCD and PAD), depth of mandible behind M1,maximum width of mandibular P4 (MPW) and length of C1 toM1 (CML). The variability of SKL is due more to size

differences in the anterior half of the skull than in theposterior. Additional strong correlations (>0.7) of SKL exists

with each of ABD, MAB, ZYB, IFD, RAH, MCW and CMU.Obviously, changes in skull shape are generally size-related insome fashion, albeit with some unexpected non-correlations

(e.g. PMI, CRI, PCB, ISI, CLE, BCW and FMB). The highintercorrelation of the characters defining skull shape contra-dict the alleged disadvantages of size-dependent characters

with regard to their low specificity (Reig et al. 2001, p. 130).Contrary to what these authors claim, the same size score incats is not due to different combinations of shape changes(except for the orbitonasal region; characters 27–30).

The length of the tooth row (C1 – M1) (CMU) correlatesstrongly with snout length (SNL), as might be expected, andalso with each subunit of tooth measurement (e.g. CML,

PMU, PPU). CRV, however, does not correlate strongly withany of width of cranial suture, SKL or weight (WGT), but doeswith several postcranial measurements (TAL, HFL, HUL,

ULL, FEL and TIL), tooth characters (PPL, P4L, P4B, C1L,CLE and C1R), and even intestinal length (ITL). No causalfunctional explanations for these latter correlations are imme-

diately apparent.All limb measurements correlate almost perfectly (r = 0.85–

0.98), meaning that there does not appear to be any need infuture studies to measure more than one limb segment. We

suggest that the preferred segment should be TIL because it ismostly conserved and easily accessible.

Principal component analysis

A brief look at the two PCA graphs shows that wildcats and

domestic cats can be clearly separated, with each groupdisplaying one of the hybrids at its border (Fig. 6a). The sexesdo show some overlap within each group, but this appears to

be an age-related phenomenon.The PCA for the 30 individuals possessing data for all 42–49

characters (Fig. 6b) underlines the highly intercorrelatednature of the characters described previously. The first five

axes cumulatively explain 54%, 64%, 71%, 75% and 79% ofthe total variance. The scatterplot of PCA axes 1 and 2(hereafter, PC_1 and PC_2) separated both subspecies unam-

biguously and showed only minor partial overlap betweenmale and female cats within each group. By contrast, scatter-plots of PCA axes higher than 2 always showed a distinct

overlap between at least two groups (subspecies or sex).Almost the same results were obtained for the subset of only 40skull variables, with the gap between groups becoming evenlarger when ITL was included as a 41st character (Fig. 6c).

PC_1 was highly correlated with variables characterizingoverall body size. As a result, this axis also tended to separatemales and females (because of the slight sexual dimorphism in

the species), especially in the wildcat. The highest contribu-tions to PC_1 were made by the skull variables PAD, RAH,PCD, CML, PML, ZYB and MAB, and the non-skull

variables ULL, FEL, HUL, TIL and HFL. PC_2 representeda complex cranial shape factor; the highest contributions herewere made by CRI, CSW, and CRV, but also by ITL. This axis

tended to reflect the quality of the few discriminating traitsidentified above. The PCA clearly separated the two subspe-cies, largely because domestic cats showed a substantiallyhigher value on PC_2. Partial overlap between the sexes only

occurred for domestic cats and was mainly age-related, witholder individuals tending to have larger values for both of thefirst two PCA axes (see labels in Fig. 6b–d). This seems to be a

general phenomenon. Older cats are larger than younger ones,

Table 2. Most important variables for discriminant analysis (indescending order) for different combinations of individuals and traits,both for four groups (subspecies · sex) and two groups (sex only)

Traits included % Misclassified

30 Individuals ⁄ 49 variables4 Groups (subsp. · sex)ITL 23C1L 17CRI 10HFL 10CSW 3

2 Groups (subspecies)ITL 0HFL 0

46 Individuals ⁄ 46 variables (excluding CRV, CRI, ITL)4 Groups (subsp. · sex)C1L 22CSW 17TIL 17SNL 13P4L 13ABD 7

2 Groups (subspecies)TIL 7SKL 0

30 Individuals ⁄ 40 skull variables4 Groups (subsp. · sex)CRV 33C1L 13CML 13MPW 7CSW 0

2 Groups (subspecies)CRV 0

46 Individuals ⁄ 38 skull variables (excluding CRV, CRI, ITL)4 Groups (subsp. · sex)C1L 22CSW 17P4L 17PMU 15RAH 11ROB 9

2 groups (subspecies)C1L 4CML 9PML 0

CRV, cranial volume; ITL, intestine length; C1L, canine length; CRI,cranial index; HFL, hind foot length; CSW, width of cranial suture;TIL, tibia length; SNL, snout length; ABD, anterior posterior diameterof the auditory bulla; SKL, skull length; RAH, height of ramus; P4L,greatest length of P4; ROB, rostrum breadth; MPW, maximum widthof mandibular P4; CML, length of lower tooth row.



but the shape of their skull also changes. The PCA of skullvariables alone gave similar loads, but greatly reduced thecontribution of SKL and CBL to PC_1.

Because CRV was not measured in 16 individuals (approx-imately one third of 46), we used all 46 individuals andreplaced the missing trait values (always fewer than six) by thecorresponding group median. The PCA analysis for this group,

using 42–46 variables but excluding CRV, CRI and ITL, stillresulted in a generally clear separation of the subspecies, albeitwith a small overlap between them (Fig. 6d). This underlines

the fact that CRV (or, to virtually the same degree, CRI) wasthe most diagnostic cranial variable in terms of separating thetwo subspecies. On the other hand, using the median of the

corresponding group to estimate the missing values for someindividuals appears to be an acceptable means (up to a certainproportion of individuals) of avoiding having to throw out

otherwise incomplete variables and individuals, and allows theanalysis to be based on the most comprehensive data setpossible.

Discriminant analysis

Although the first two PCA axes resulted in the best separation

of the two subspecies and, to a lesser degree, of the sexes, PCArequires the measurement of 49 variables, which entails bothsignificant effort and the danger of missing data. As a result,

we attempted to find smaller subsets of variables that would besufficient to distinguish between wild and domestic cats and sooptimize the cost-benefit ratio. A linear discriminant analysiswith forward selection of variables showed that CRV, C1L,

CML, MPW and CSW (in this order) were sufficient amongthe 33–40 skull variables to discriminate all four groups(subspecies · sex) without any classification error (Wilk�sLambda = 0.010, F = 15.8, p < 0.0001). The canonical plotis given in Fig. 7a. CRV and C1L made the largest contribu-tion to the first canonical axis, with CML being most

important for canonical axis 2. When non-skeleton variableswere included in the analysis, ITL became the most importantvariable, with HFL ranking fourth (Fig. 7b; Wilk�s Lamb-

da = 0.0038, F = 24.1, p < 0.0001).With 42–46 characters, excluding CRV, CRI and ITL, a

higher number of variables was needed to achieve sufficientseparation between the four groups. In decreasing order of

contribution, these were C1L, CSW, TIL, SNL, P4L, ABDand C1R (Wilk�s Lambda = 0.018, F = 17.2, p < 0.0001).Even so, three individuals were still misclassified. If the

analysis was restricted to skull variables only (excludingCRV and CRI), the variables needed to achieve goodseparation were C1L, CSW, P4L, PMU, RAH and ROB

(Wilk�s Lambda = 0.037, F = 12.2, p < 0.0001), albeit withfour misclassifications (see Fig. 7c).To distinguish between wild and domestic cats only (i.e.

ignoring gender), linear discriminant analysis showed that,among skull variables, CRV alone could classify both subspe-cies without error (Wilk�s Lambda = 0.189, F = 112,p < 0.0001). If non-skeleton characters were included, ITL

performed even better than CRV. In the absence of CRV andCRI, given that values for these traits are often unavailable,C1L, CML, PML were sufficient to discriminate between both

subspecies without any misclassifications (Wilk�s Lambda =0.226, F = 45.7, p < 0.0001), whereas TIL and SKL werenecessary for error-free differentiation if non-skull variables

were included (and ITL was omitted; Wilk�s Lambda = 0.150,F = 116, p < 0.0001). The importance of the respectivevariables in the different constellations examined is summa-rized in Table 2.

Identification of hybrids

Morphological identification of the four genetically deter-mined hybrids was rendered difficult by the fact that 14characters, including the highly diagnostic ones, were missing

SK

LC

BL

FAL

SN

LP

MU

PP

UP

4LP

4BA

BD

MA

BO

CB

FM

BB

CW

ZY

BF

RB

OR

DPA

BR

OB

PC

BIF

DN

MI

NM

AC

SW

PC

DPA

DP

ML

MD

MR

AH

MC

WM

PW

CM

UC

ML

C1L

CL

EC

1RC

RV

CR

IIS

IP

MI

OR

IW

GT

CR

LTA

LH

FL

HU

LU

LL

FE

LT

ILIT

L

SKLCBLFALSNLPMUPPUP4LP4BABDMABOCBFMBBCWZYBFRBORDPABROBPCBIFDNMI

NMACSWPCDPADPMLMDMRAH

MCWMPWCMUCMLC1LCLEC1RCRVCRIISI

PMIORI

WGTCRLTALHFLHULULLFELTILITL

Pea

rso

n's

r

–1.0

–0.8

–0.6

–0.4

–0.2

0.0

0.2

0.4

0.6

0.8

1.0

Heatmap of 49 traits (30 individuals)

Fig. 5. Matrix of Pearson�s pair-wise correlation coefficients r, dis-played as heatmap for 49 traits from30 individuals (circles: positive val-ues of r, squares: negative values;size proportional to absolute value)



in one hybrid 7985 (collection number, see Appendix S1). Inline with our exclusion of individuals with six or more missingcharacters, this hybrid is not included in our analyses. CRVand CRI were also unavailable for both of the other two (male)

hybrids, and ITL was unavailable for 5104. This lack of themost informative characters rendered the morphologically-based identification of the individuals almost impossible.

Unfortunately, a similar lack of data will often be the casefor road kills, the most common source of specimens.Nevertheless, our analyses always classified hybrid 8006 as a

wildcat, and hybrid 5104 as a wildcat if only skull variables,excluding CRV and CRI, were used, and as a domestic catotherwise.

To visualize the character state (wildcat, domestic cat, noneor both) of each variable in the hybrids, we used a star diagramfollowing Precht et al. (2005) (Fig. 8). Individual 7985 showsthe patterning typical of wild coloured domestic cats (Fig. 8),

but with 63% of the linear measurements being typical ofwildcat, 17% of domestic cat, and 20% being intermediate.The higher-ranking variables for this individual all tended to

indicate wildcat affinities. The male hybrids display extremelydifferent character distributions from one another. In terms ofcoat patterning and 91% of the measured variables, individual

5104 would be unambiguously classified as a wildcat, whilegenetically it is a clear hybrid. The morphological status ofindividual 8006 is less decisive: 23% of the variables indicate

(a)

Fig. 6. Scatterplot of first two standardized PCA axes PC_1 and PC_2 for all 58 individuals based on all 7–49 traits (a), for 30 individuals basedon 42–49 skull traits (b), and for 30 individuals based 33–40 skull traits (c) and for 46 individuals based on 42–46 traits (d), but excluding CRV,CRI and ITL. Outlines correspond to the four groups wild ⁄male, wild ⁄ female (grey, violet), domestic ⁄male, and domestic ⁄ female (brown, pink).Hybrids are in green. Labelling is ID ⁄ subspecies ⁄ sex ⁄ age in months



wildcat-like values, 35% intermediate and 42% domestic cat.This hybrid also more strongly resembles a domestic cat in

appearance (Fig. 8). Finally, individual 5097 shows 64%

wildcat characters, 16% of intermediate and 20% of domesticcat.

Discussion

One of the foci of recent morphological research on wildcats isthe undeniable need �for a defining characteristic that can be

applied reliably by practical people under difficult conditionsand before the trigger is pulled or the trap sprung� (Reig et al.

Fig. 6. (Continued)

Fig. 7. Canonical plot of first two canonical variables for a lineardiscriminant analysis of four predefined groups (wild ⁄male, wild ⁄female, domestic ⁄male, domestic ⁄ female) based on all 33–40 skulltraits of 30 individuals (a), on 42–49 traits of 30 individuals (b) and on42–46 traits, except CRV, CRI and ITL for 46 individuals. Circlescorrespond to 50% contour lines of a normal distribution of eachgroup



Collection number 8006 5104 7985 5097ITL Intestine length d whm wm dmCRV Cranial volume wTIL Tibia length d w w w

w w ww w ww w ww w ww d w

C1L Length C1

HFL Hind foot lengthP4L Greatest length of P4 dFEL Femur length dPML Length between mandibular P3 and M1CLE Length of enamel C1 w wHUL Humerus lengthP4B Greatest breadth of P4 w w w

w w

ULL Ulna lengthTAL Tail length w w d wC1R Rootle von C1 dBCW Greatest width of the braincase d w wFMB Greatest breadth of the foramen magnum dOCB Greatest breadth of the occipital condyles d

w w w

w w w

w w ww w w

w d dw dw w

dd

PPU Length between P2 and P4 d wMAB Mastoid breadth d wZYB Zygomatic breadth d w wCRL Head trunk length dPCB Least breadth of the postorbital constriction dRAH Height of ramus

wORD Least breadth between the orbits d

0

0,5

1ITL

CRVTILC1L

HFLP4L

FEL

PML

CLE

HUL

P4B

ULL

TAL

C1R

BCW

FMBWGT

MDM

NMA

PCD

CSW

CMU

CBL

SKL

NMI

FRBABD

ROBIFD

MPWSNL

MCW Maximum width of mandibular condyles w dPMU Length between P2 and M1 d wFAL Facial length wCML Length between C1and M1 w

ww

w ww ww w wPAD Maximum distance between pogonion and angular process

PAB Greatest palatal breadthWGT Weight w

w dw w w

MDM Depth of the mandible behind M1 w23% w42% d

NMA Maximum length of the nasalsPCD Maximum distance between pogonium and coronoid processcoll. nr. 8006 Bad Salzungen 02.12 2003 d

35% intermediär CSW Width of cranial suture d w dCMU Length between C1and M1

w w dw w w

d wCBL Condylobasal length w w wSKL Greatest length of skull w w wNMI Minimum length of the nasals wFRB Frontal breadth d

w ww d d

ABD Anteriorposterior diameter of the auditory bulla d wROB Rostrum breadth w w dIFD Breadth between the infraorbital foramina d wMPW Maximum width of mandibular P4 wSNL Lateral length of snout w

w d dd w

OCB

PPUMAB

ZYBCRLPCBRAHORDMCW

PMUFAL

CMLPAD

PAB

0,5

1ITL CRVTIL

C1LHFL

P4LFEL

PML

CLE

CBL

SKL

NMI

FRBABD

ROBIFD

MPWSNL

hm wm dm

91% w7% dcoll. nr. 5104 Rathsfeld / Kyff. Jun. 19932% intermediär

hf wf df

0

HUL

P4B

ULL

TAL

C1R

BCW

FMB

OCBPPU

MABZYB

CRLPCBRAHORDMCWPMU

FALCML

PADPAB

WGT

MDM

NMA

PCD

CSW

CMU

CBL

0

0,5

1ITL CRVTIL

C1LHFL

P4LFEL

PML

CLE

HUL

P4B

ULL

TAL

C1R

BCW

FMB

OCBPAB

WGT

MDM

NMA

PCD

CSW

CMU

CBL

SKL

NMI

FRBABD

ROBIFD

MPWSNL

PPUMAB

ZYBCRLPCBRAHORDMCW

PMUFAL

CMLPAD

0,5

1ITL

CRVTILC1L

HFLP4L

FEL

PML

CLE

HUL

P4BCMU

CBL

SKL

NMI

FRBABD

ROBIFD

MPWSNL

hf wf df

64% w20% dcoll. nr. 5097 Sondershausen Nov.199616% intermediär

63% w17% dcoll. nr. 7985 Hohengandern 14.04.200520% intermediär

0 ULL

TAL

C1R

BCW

FMB

OCBPPU

MABZYB

CRLPCBRAHORDMCW

PMUFAL

CMLPAD

PAB

WGT

MDM

NMA

PCD

CSW

Fig. 8. Star diagram following Precht et al. (2005). Genetically identified hybrids are shown in green. For comparison, median values of theappropriate wildcats male (grey) and female (violet), as well as domestic cats male (brown) and female (pink) are presented. Variables are figuredclockwise after decreasing coefficients of difference (CD). Measurements are scaled between 0 and 1



2001, p. 131). The high degree of introgression of the domesticcat into the Scottish wildcat population has led to differentapproaches to developing a morphologically based method for

identifying the Scottish wildcat, if it still exists (MacDonaldet al. 2004). Our complementary approach of independentmolecular and morphological analyses enabled us to cross-

check and compare the content of information in the differentcharacter sets.

Identification of wildcats

Pelage charactersIn addition to the linear measurements discussed below, a set

of qualitative pelage characters exists that diagnoses wildcatsunambiguously. Three of the 20 pelage characters discussed byKitchener et al. (2005) were diagnostic in our sample: tail

bands (No. 10), 4–5 stripes on the nape (No. 18) and stripes onthe shoulder (No. 19). Nuchal stripes are arguably thecharacter of choice, given the work of Ragni and Possenti

(1996), who found that the tail bands were more variable in theItalian population and also less pronounced in older speci-mens, and older males in particular. In our sample, the threepelage characters 10, 18 and 19 match perfectly with the

genetically identified wildcat group), and each in isolation canalso distinguish wildcats from domestic cats, but not ofhybrids. Two of the four hybrids 5104 and 5097 have wildcat

and the other two (8006 and 7985) domestic cat pelagecharacters. Even in the Scottish sample, the absence of one ofthese characters will definitively identify a domestic cat. If we

score these three characters alone according to the schemepresented in Kitchener et al. (2005), a score of >3 will identifya wildcat with certainty. We therefore propose that these three

characters be taken as the best means of identifying wildcats inthe future, and should prevent the trigger from being pulled –at least under good light and weather conditions.

Biometric charactersIn agreement with Schauenberg (1969), we found that only twomeasurements, ITL and CRV, enable wildcats and domestic

cats to be distinguished with absolute certainty. Unfortunately,like many of the other most reliable differentiating characters,these are post mortem characters. Because the maximum

length of skull was less robust than CRV in distinguishing thesubspecies, the CRI was likewise less reliable than CRV. Noother variables than the two measurements and the indexpossessed a CD score greater than 1.2. The latter phenomenon

indicating that the chance of wrongly identifying a randomspecimen is as high as 11.5%. A CD of 1.8 results in a 3.6%chance and for the CRV (CD = 2, the error is only 1.8%). As

such, it is surprising that most of these latter characterscontinue to be used in recent studies in the light of theirenormous variability and inability to reliably assign a subspe-

cies.

Craniometric characters

Postnatal changes in the shape of the skull differ in the wildcatand domestic cat (Fig. 4). The higher CRV of the wildcat islikely due to the more vaulted frontal portion of the skull,where the frontal bone is more in the plane of the skullcap. At

the same time, the postorbital processes in the wildcat projectalmost at right angles to the sagittal plane. Both traits givethe wildcat its typical facial expression. In our opinion, this

facial difference between the subspecies explains the lack of

correlation between the characters associated with overall skullshape (characters 27–30) in the total correlation matrix. Thesmaller CRV of the domestic cat compared to the domestic cat

is often ascribed to the results of domestication. However, thisneed not be the case, given that comparatively smaller CRValso characterize the subspecies of Felis silvestris native to

North Africa (F. silvestris lybica) and South Asia (F. silvestrisornate) (Hemmer 1972). The more parsimonious explanation isthat CRV have increased in the wildcat in conjunction with thenorthern distribution of this form.

Evaluation of charactersA linear discriminant analysis with forward selection of

variables showed that CRV together with C1L, CML, MPW,PML and CSW (in this order) was sufficient to discriminate allfour groups (subspecies · sex) with no classification errors. As

such, correct classification does not require any non-skullskeleton variables. If the non-skeleton variables ITL and WGTwere included in the analysis, ITL became the most important

variable. In the absence of both CRV and ITL, discriminationbecomes extremely difficult. We are convinced that discrimi-nant analysis should precede PCA, and hope that the traitsidentified in this study will be as reliable in other populations.

We also question the use of derived variables (see Yamaguchiet al. 2004a,b) based on largely unassigned variables. Usingfewer but more reliable traits results in the unambiguous separa-

tion of domestic cat from wildcat. Unfortunately, there do notappear to be any traits that can identify hybrids as such.We found no correlation between ITL and either body mass

or CRL, and therefore cannot support Daniels et al. (1998) intheir argument that wildcats are presumably �less able tosustain the higher energy costs associated with carrying a

longer gut�. Future research in this area should focus ondetermining whether the length difference over the entireintestine accrues from differences in specific regions of theintestinal tract.

Hybridization of wildcats and domestic cats

The diagnostic value of morphological characters and mor-phometric data in distinguishing domestic cats from wildcats,and particularly in the difficult task of identifying hybrids, is the

subject of intense discussion (Suminski 1962a,b, 1977; Krat-ochvil and Kratochvil 1970, 1976; Kratochvil 1973, 1975,1976a,b, 1977; Schauenberg 1977, Ragni and Randi 1986;Puzachenko 1996; Ragni and Possenti 1996; Daniels et al.

1998; Reig et al. 2001; Kitchener et al. 2005). The successfulidentification of hybrids is intimately linked to the validity ofpostulated diagnostic characters for the parent taxa. Pheno-

typically identifying hybrids on the strength of the observationof a set of characteristics halfway between those of wild catsand domestic cats is very likely to be wrong for heuristic

reasons. In the light of the broad overlap in the distribution ofmost biometric characters (Fig. 8) and the heterogeneousdistribution of qualitative characters, it is not to pinpoint

hybrids on the basis of anatomical characters alone (Kratochviland Kratochvil 1970, 1976, Kratochvil 1973, 1975, 1976a,b,1977; Piechocki 1990).The parallel morphological and genetic analyses of our

sample resulted in the correct identification of individuals aswildcats or domestic cats. However, as far as the fourindividuals genetically identified as potential hybrids were

concerned, the picture was less clear. The examination of three



hybrids (8006, 5104, 5097) yielded intermediate parametervalues, with each specimen displaying also diagnostic charac-ters typical of both wildcats and domestic cats. Morphological

characters would especially not allow the recognition ofspecimen 5104 as a hybrid, because 91% of the charactersindicated wildcat affinity. Only one of the genetically identified

hybrids (7985) has been identified by morphological traitsbecause it presents a �contradiction� between pelage charactersand relevant other characters.Despite several studies that argue against extensive amal-

gamation having taken place between wildcats and domesti-cated cats (Eckert 2003; Fernandez et al. 1992; Hertwig et al.2009; Kratochvil 1973, 1975, 1976a,b, 1977; Kratochvil and

Kratochvil 1970, 1976; Ragni and Randi 1986; Randi et al.2001; Randi and Ragni 1991; Piechocki 1990; Pierpaoli et al.2003), there is no doubt that hybridization in Europe has

occurred during the extended coexistence of both forms.Ancient hybridization likely caused an introgression of genesfrom wildcat populations into the domestic cat population

and vice versa. However, this relatively rare but probablyrepeated introgression of alleles, and especially of thematernally inherited mitochondrial genes that can be tracedback for a long time (Hertwig et al. 2009; Randi et al. 2001),

apparently had no significant influence on the ecological andmorphological separation of both sympatric forms of F.silvestris. Cases of historical admixture between the otherwise

disjoint genetic lineages could only be detected by thecombined use of various genetic markers (Beaumont et al.2001; Hille et al. 2000; Lecis et al. 2006; Oliveira et al. 2008;

Pierpaoli et al. 2003; Vaha and Primmer 2006; Vila et al.2003; Wiseman et al. 2000; Yamaguchi et al. 2004a, b) andshould be studied more in detail based on the oldest

specimens in museum collections. In addition to the tracesof repeated past introgression events a certain percentage ofhybrids arising from occasional recent interbreeding at mostsome generations ago seem to exist in all populations of

European wildcats, albeit with strong regional variation evenwithin Germany (Hertwig et al. 2009).The reasons behind the extensive hybridization of F. silvestris

with feral cats observed in certain regions of Europe and thecontinued separation of the two forms in others are the subjectof a long-standing and controversial debate (Ragni and Randi

1986; French et al. 1988; Piechocki 1990; Fernandez et al.1992; Hubbard et al. 1992; McOrist and Kitchener 1994;Beaumont et al. 2001; Randi et al. 2001; Daniels and Corbett2003; Eckert 2003; Pierpaoli et al. 2003; MacDonald et al.

2004; Biro et al. 2005; Kitchener et al. 2005). In Thuringia, theareas inhabited by F. silvestris silvestris are restricted andisolated from each other by cultivated landscape, but still

provide sufficiently structured closed forests to house small,viable wildcat populations. Within the borders of the HainichNationalpark in Thuringia, for instance, a population esti-

mated at about 50 specimens favours old forests dominated byFagus silvatica and adjacent military training areas (T Molich,personal communication). Studies on the biology of this

population, including radio telemetry tracking (Molichand Klaus 2003), and on populations from other localities(Naidenko and Hupe 2002) showed a low level of overlapbetween the territories of domestic cats and wildcats because

the latter spends most of its time in the forest, in contrast toferal domestic cats. Although a study in northern Switzerlandusing foto traps could demonstrate that feral cats can intrude

far into the forests and come indeed repeatedly into contact

with wildcats (D. Weber, personal communication). Ourresults, however, support rather the hypothesis that the wildcatin Thuringia represents a scattered but distinct population that

is clearly separated both morphologically and genetically fromdomestic cats.

Factors which promote the reproductive interaction of wild

cats and free-ranging domestic cats include the small popula-tion densities of wildcats compared to free-ranging domesticcats and extensive deforestation which has created a mosaic-like landscape structure dominated by agriculture, settlements

and small patches of forest (see Lecis et al. 2006 and Oliveiraet al. 2008 for a further discussion). Because these factors alsoapply to most other European countries, they do not explain

the differences observed on a regional scale. The questionremains, therefore, of why such a high percentage of feral cats,particularly those in Scotland and Hungary, show �admixing

genotypes, which probably originated through a protractedprocess of hybridization and introgression� (Pierpaoli et al.2003, p. 2594). Especially the surprising high percentage of

hybrids in the western population in Germany and its influenceon the morphological and genetic integrity of the wildcat inthis region needs further investigation effort.

Comparison of these populations with the situation of the

wildcat in Thuringia points to the existence of areas ofcontiguous and appropriately structured forest as being acrucial factor in hybridization levels. Radical deforestation in

Scotland and perhaps also in the native wildcat localities inHungary has forced the forest cat to become a field cat relianton the same resources as feral cats. Arguably it is only the loss

of its primary ecological niche that causes the wildcat to startto interbreed with feral or even domestic cats. The theory thatdomestic cats derive from the steppe wildcat lineage (Yamag-

uchi et al. 2004a) lends force to the idea of ecologicalseparation. The major threat to the European wildcat, then,is the fragmentation of forest and not the diffusion of free-ranging domestic cats (contra Pierpaoli et al. 2003).

Acknowledgements

The authors are grateful to Dr Siegfried Klaus (Thuringer Landesan-stalt fur Umwelt und Geologie, Jena) for many years of successfulcooperation and the reliable provision of carcasses together with theprecise locality in which they were found. Thomas Molich (Bund furUmwelt und Naturschutz Deutschland, Landesverband Thuringen e.V., Projektleiter Rettungsnetz Wildkatze) provided us with basicinsights into the Thuringian wildcat population and also supplied uswith roadkill. The authors thank Dr Dietrich Heidecke (ZoologischesInstitut der MLU, Halle ⁄Saale) for allowing us access to thecollections and for morphometric data on four domestic cats. Theauthors finally wish to thank Dr Franz Muller (Vorderau MuseumFulda) for his standardized measurement of intestine length.

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Supporting Information

Additional Supporting Information may be found in the onlineversion of this article:

Appendix S1. Measurements.

Appendix S2. Biometric data were worked on by wild- anddomestic cat in the Phyletic museum, Jena.

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evaluation of anatomical characters and the question of

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