ISSN 1062-3590, Biology Bulletin, 2006, Vol. 33, No. 2, pp. 144–148. © Pleiades Publishing, Inc., 2006.Original Russian Text © V.V. Rozhnov, A.V. Abramov, 2006, published in Izvestiya Akademii Nauk, Seriya Biologicheskaya, 2006, No. 2, pp. 183–187.

144

Sexual size dimorphism is typical for many mam-mals. It is particularly pronounced in many carnivoresof the family Mustelidae, which is manifested as thecranial size and proportions. This phenomenon wasextensively studied in small mustelids (largely

Mus-tela

) (Ralls and Harvey, 1985; de Marinis, 1995; Abra-mov and Tumanov, 2003; etc.). Some hypothesesattribute sexual size dimorphism in mustelids to theirintraspecific social relations or trophic ecology.

The intrapopulation and geographic variation inmorphological, particularly, cranial characters of mar-bled polecat

Vormela peregusna

(Güldenstaedt, 1770)remains underexplored (Rozhnov, 1999) and their sex-ual dimorphism has not been studied. Only fragmentarydata on some cranial characters are available for theIsraeli (Dayan et al., 1989) and Bulgarian (Spassov andSpiridonov, 1993) marbled polecat populations.

The range of the species covers steppes, semi-deserts, and deserts of Southeast Europe (Balkan Pen-insula, Bulgaria, and Ukraine), Caucasus, SouthwestAsia (including Israeli, Syria, Iraq, Iran, and Afghani-stan), Central Asia, Kazakhstan, Mongolia, and China.In Russia, this species occurs in the steppes of the NorthCaucasus, Volga Region, and southern Siberia (Rozh-nov, 1999a, 1999b). Such wide palearctic rangeassumes intraspecific variation in morphological char-acters.

The goal of this work was to study sexual dimor-phism of cranial characters in marbled polecat by theexample of a homogeneous sample from Turkmenistan.

MATERIALS AND METHODS

The material of the collections of the ZoologicalInstitute of Russian Academy of Sciences (St. Peters-burg) and Zoological Museum of Moscow State Uni-versity was studied. In total, 85 skulls of adult animals

including 34 males, 28 females, and 23 individuals ofunspecified sex were analyzed. All animals were caughtin the plain regions of Turkmenistan. A series of26 measurements were measured on each skull usingcalipers accurate within 0.1 mm.

The obtained data were processed using a combina-tion of principal component analysis and discriminantanalysis (Lynch and O’Sullivan, 1993; Lynch, 1996;Reig, 1997). Principal component analysis with vari-max rotation demonstrated that uncorrelated new char-acters (principal components) can be considered as thesize (first component) and shape indices (all other com-ponents) (Bookstin, 1989). The size component here isthe allometric variation, while the shape variation is therest of variation that cannot be attributed to allometry.Discriminant analysis of the resulting size and shapecomponents allowed us to evaluate their contribution tosexual dimorphism. Sexual dimorphism index

I

SD

wascalculated as the male/female ratio of the mean charac-ter values (Holmes and Powell, 1994; Reig, 1997). Theobtained data were analyzed by multivariate statisticalmethods using Statistica 5.5 for Windows.

RESULTS AND DISCUSSION

Discriminant analysis (using all measurements) wascarried out on individuals of specified sex (

n

= 62). Theresulting discriminant function allowed the identifica-tion of males and females among individuals of unspec-ified sex. Later the obtained samples of males (

n

= 51)and females (

n

= 34) were analyzed separately. Theabsolute values of all studied cranial characters ofmales and females overlapped, while the mean valueswere significantly (

p

<0.01) higher in males than infemales (Table). The sexual dimorphism indices wereover 90% for all studied characters.

Sexual Dimorphism of Marbled Polecat

Vormela peregusna

(Carnivora: Mustelidae)

V. V. Rozhnov* and A. V. Abramov**

* Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Leninskii pr. 33, Moscow, 119071 Russia** Zoological Institute, Russian Academy of Sciences, Universitetskaya nab. 1, St. Petersburg, 199034 Russia

e-mail: rozhnov@sevin.ru

Received September 16, 2005

Abstract

—Analysis of morphometric variation in 26 cranial characters were studied in 85 individuals of mar-bled polecat

Vormela peregusna

from Turkmenistan demonstrated a low level of sexual dimorphism in the spe-cies. The properties of sexual dimorphism in marbled polecat are discussed in terms of available hypotheses ofsexual dimorphism in carnivores.

DOI:

10.1134/S1062359006020075

ZOOLOGY

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Vormela peregusna

145

1014

13

12

11

2

3

1

5

17

16

1526

25

7 624

4

89

2122

23

20

19

18

Principal component analysis demonstrated positivecoefficients of correlation between the first componentof size and all characters except postorbital width, andthis component was responsible for 37.2% of the totalvariation in the studied characters. The principal char-acters of the size component included condylobasallength, viscerocranial length, palatal length, interorbitalwidth, zygomatic width, mastoid width, and mandibu-lar length and height.

The revealed uncorrelated new characters (compo-nents) were analyzed by stepwise discriminant analy-sis. The first component contributed most to the distinc-tion between males and females together with compo-nents 13, 14, 3, 6, and 9, which were defined by theupper canine length, auditory bulla width, postorbitalwidth, upper carnassial tooth

Pm

4

, and neurocraniallength. Hence, male marbled polecats featured largerand heavier skulls with marked postorbital constriction,larger auditory bullae, and more powerful teeth. Thefemale skulls were smaller and relatively narrower byall width characters (zygomatic, palatal, and mastoid)and featured relatively short foreface and weaker teeth.

The Mahalanobis distance between the male andfemale samples was

D

2

= 13.64 for the complete set ofprincipal components. Analysis of all componentsexcluding the first one (shape variation analysis) dem-onstrated a much lower value of this coefficient (

D

2

=8.66); i.e., the absence of the size component dimin-ished the cranial distinction between the sexes. Analy-sis of all studied individuals using the complete set ofvariables (including the size variable) allowed their100% partitioning into the sexual groups, while only a92.9% partitioning was obtained in the absence of thesize component (6 specimens were misidentified).

Sexual dimorphism in marbled polecat cranial char-acters is primarily due to the difference in the total skullsize. Overall, the studied sample of marbled polecatsfrom Turkmenistan demonstrated an insignificant sex-ual dimorphism; i.e., the differences were largely allo-metric. Comparison of sexual dimorphism levels insmall mustelid species demonstrated a lower sexualdimorphism in the marbled polecat compared to othermustelids of similar size. The female/male condylo-basal length ratio was 88% in Siberian weasel

Mustelasibirica

, 84% in European polecat

M. putorius

andsteppe polecat

M. eversmanii

, and 87% in Americanmink

M. vison

(northwestern Russian population)(Abramov, 1999). Relatively low sexual dimorphismlevels were observed in European mink

M. lutreola

(91.7%; Abramov and Tumanov, 2003), pine marten

Martes martes

(91.3%), and stone marten

M. foina

(95.2%) (Reig and Ruprecht, 1989). In the Turkmeni-stan population of the marbled polecat, the sexualdimorphism index

I

SD

for the condylobasal length was97%; it was also higher in the Israeli population: 92.5%for the condylobasal length, 88.5% for the caninelength, and 94.3% for the upper carnassial tooth

Pm

4

length (Dayan et al., 1989).

Several hypotheses were proposed to explain sexualsize dimorphism in Mustelidae. According to the sexualselection hypothesis, larger male size is beneficial incompetition for a female, particularly, in the case ofpolygamous reproduction typical for small mustelids(Ralls and Harvey, 1985; Gittleman and van Valken-burgh, 1997; Weckerley, 1998). Relatively wide ros-trum, large canines, widely flaring zygomatic arches,and high mastoid width in the skull of male Europeanpolecat is attributed to the intrasexual aggressive inter-

Skull measurements taken in marbled polecat

Vormela peregusna

; 1–26, cranial characters described in Table.

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actions (de Marinis, 1995): observation during theirreproductive period demonstrated a higher reproductivesuccess of large males. The sexual selection hypothesesis also confirmed by a relatively low sexual dimorphismlevel in highly social mustelid species—Eurasian bad-ger

Meles meles

, giant otter

Pteronura brasiliensis

, andsea otter

Enhydra lutris

(Johnson et al., 2000). Euro-pean polecat and American mink demonstrate notablyless aggressive intraspecific interactions compared toEuropean mink (Rozhnov and Petrin, 1998). These dif-ferences in social behavior can underlie a lower sexualdimorphism level in European mink compared toAmerican mink and European polecat (Abramov andTumanov, 2003). On the other hand, no correlation hasbeen revealed between the sexual dimorphism level andsociality in different populations of Eurasian badger

Meles meles

and Asian badger

M. leucurus

(Abramovand Puzachenko, 2005).

The available data on the marbled polecat behaviordoes not allow the relatively low distinctions in cranialproperties between males and females to be attributedto low aggressiveness or to sociality of this species.

Another hypothesis considers sexual dimorphism ofmustelids as a result of separated ecological (trophic)niches of males and females: smaller females feed onsmaller preys, which decreases intraspecific feedingcompetition (Shubin and Shubin, 1975; Erlinge, 1979;Moors, 1980; Dayan et al., 1989; Dayan and Simber-loff, 1994). Some distinctions in the food and feedingbehavior between males and females were reported forcertain small mustelids with marked sexual dimor-phism—ermine

Mustela erminea

, least weasel

Mustelanivalis

(Moors, 1980; Erlinge, 1981), European polecat(

Lod

é, 2003), and American mink (Birks and Dun-stone, 1985). Egyptian weasel

M. subpalmata

demon-strates a much lower sexual dimorphism level com-

Cranial measurements of adult male and female

Vormela peregusna

, mm

DimensionFemales (

n

= 34) Males (

n

= 51)I

SD

x

min max

S x

min max

S

1. Condylobasal length 53.41 50.0 58.5 2.04 55.09 50.0 59.1 2.14 97.0

2. Neurocranial length 31.60 28.6 34.2 1.20 32.90 30.5 35.0 0.98 96.1

3. Viscerocranial length 26.67 24.1 30.4 1.66 27.90 24.0 32.0 2.02 95.6

4. Minimum palatal width 5.29 4.3 6.0 0.37 5.71 4.7 6.7 0.41 92.7

5. Palatal length 23.87 21.2 26.8 1.13 24.91 23.0 26.5 0.89 95.8

6. Maxillary toothrow length 16.33 15.1 17.4 0.62 17.11 16.2 18.8 0.58 95.4

7.

Pm

4

length 6.28 5.7 6.9 0.28 6.58 5.9 7.4 0.30 95.4

8. Auditory bulla length 15.49 14.3 17.6 0.65 16.00 14.3 17.4 0.69 96.8

9. Condyle to bulla length 18.98 17.4 21.0 0.78 19.45 17.4 21.5 0.88 97.6

10. Zygomatic width 31.38 28.9 33.7 1.25 32.83 29.0 37.4 2.01 95.6

11. Interorbital width 28.36 26.3 31.3 1.25 29.72 26.1 32.7 1.61 95.4

12. Mastoid width 10.61 9.4 12.4 0.63 11.19 9.7 13.0 0.83 94.8

13. Postorbital width 14.29 12.4 16.4 0.89 15.15 12.2 17.3 1.16 94.3

14. Rostrum width 12.39 11.4 13.5 0.56 13.06 11.2 15.3 0.86 94.8

15. Maximum palatal width 18.95 18.0 20.3 0.60 19.88 17.4 21.2 0.81 95.3

16. Auditory bulla width 9.05 8.0 10.3 0.57 9.37 8.1 11.1 0.62 96.6

17. M

1

width 5.17 4.9 5.5 0.14 5.43 5.0 5.9 0.21 95.2

18. Cranial height 20.45 19.6 21.5 0.53 21.44 19.9 24.0 0.83 95.4

19. Mandibular length 33.05 31.0 36.2 1.30 34.72 31.8 37.4 1.49 95.2

20. Angular length of mandiba 32.19 29.8 35.0 1.32 33.80 31.0 36.3 1.29 95.2

21. Mandibular toothrow length 20.29 19.3 21.8 0.67 21.22 19.6 22.7 0.70 95.6

22. M

1

length 6.56 6.1 7.1 0.27 6.93 6.2 7.7 0.31 94.7

23. Height of coronoid process 14.79 13.3 16.1 0.76 15.42 14.2 17.0 0.76 95.9

24. M

1

length 2.54 2.2 2.8 0.17 2.72 2.3 3.1 0.23 93.1

25. Upper canine length 3.16 3.0 3.5 0.12 3.48 2.9 4.0 0.22 90.6

26. Upper canine width 2.48 2.2 2.8 0.16 2.77 2.3 3.2 0.21 89.6

Note:

x

, mean; min, minimum; max, maximum;

S

, standard deviation; I

SD

, sexual dimorphism index, %.

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pared to closely related species

M. nivalis

(Van Zyll deJong, 1992; Abramov and Baryshnikov, 2000): it haslargely synanthropic life style and a limited diet (Hand-werk, 1993). Low sexual dimorphism level in Europeanmink can also be due to its narrow feeding preferences(almost stenophagy) compared to other sympatric spe-cies (European polecat and American mink) as well asto specific ecological niche resulting from the adapta-tion to semiaquatic life (Abramov and Tumanov, 2002,2003). Low sexual dimorphism of pine and stone mar-tens is also attributed to similar feeding strategies ofmales and females and to the same diet (Reig andRuprecht, 1989).

A relatively low sexual dimorphism level in marbledpolecat can be partially explained in terms of thishypothesis by its limited diet: in Turkmenistan itlargely feeds on great gerbil (Geptner et al., 1967;Kalustov, 1995) and, to a lesser extent, on long-clawedground squirrel, jerboas, and small gerbils (Libyan jirdand midday gerbil). The size composition of the diet isrelatively narrow, which requires no marked sexualdimorphism in this case. Food selection is limited by itspresence—even considerably different size of malesand females will not separate their trophic niches.Observations of marbled polecat hunting behaviorunder experimental conditions revealed no differencesbetween males and females in hunting types and pre-ferred preys (Ben-David et al., 1991).

Thus, the study of geographical variation in sexualdimorphism of

Vormela peregusna

, comparative analy-sis of the dimorphism in marbled polecat and othersmall mustelids in the cohabitation zone (in particular,steppe polecat), and further studies of their feeding andintraspecific behavior can shed light on the factorsunderlying this phenomenon.

ACKNOWLEDGMENTS

Thanks are due to I.Ya. Pavlinov for the help withthe collections of the Zoological Museum (MoscowState University). This work was supported by theBasic Research Program of the Presidium of the Rus-sian Academy of Sciences “Scientific Background ofBiodiversity Conservation in Russia.”

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