Aging Steppe Polecats {Mustela Eversmanni) and Polecats (Mustela Putorius) by Canine Cementum Layers and Skull Characters

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Digitale Literatur/Digital Literature

Zeitschrift/Journal: Wissenschaftliche Mitteilungen Niederösterreichisches Landesmuseum

Jahr/Year: 2001

Band/Volume: 14

Autor(en)/Author(s): Ansorge Hermann, Suchentrunk Franz

Artikel/Article: Aging polecats (Mustela putorius) and steppe polecats (Mustela eversmanni) by canine cementum layers and skull characters. (N.F. 436) 79-106 ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

Wiss. Mitt. Niederösterr. Landesmuseum 14 79-106 St. Polten 2001

Aging steppe polecats {Mustela eversmanni) and polecats (Mustela putorius) by canine cementum layers and skull characters

HERMANN ANSORGE & FRANZ SUCHENTRUNK

Keywords: Mustela eversmanni, Mustelaputorius, steppe polecat, polecat, aging, cementum annuii, skull Schlüsselwörter: Mustela putorius, Mustela eversmanni, Waldiltis, Steppeniltis, Altersbestimmung, Zahnzement-Jahresringe, Schädel

Summary

Based on skulls from Austria and eastern Germany, the possibilities of aging polecats and steppe polecats are considered and compared. Both species display discrete cementum annuii in thin sections of the upper canines. These annuii presumably result from annual growth breaks and are considered reliable age indi- cators. Particularly polecats from the eastern German study population that was subjected to a quite high hunting pressure showed a remarkable male-biased pro- portion of juveniles. A high concordance (92%) was found between age estimates by general skull morphology ("relative age classes") and true age as estimated by cementum annuii. Based on general age criteria of skulls, twelve qualitative (nonmetric) skull characters were compared separately with the respective age in years as obtained from the annuii counts. Each of the twelve skull characters showed age-related changes. But no one allowed assessing age in years because of large overlaps of character states across age classes. Only five skull characters proved useful to reliably separate juveniles from older individuals, in a combined consideration. Most animals in their second year of life could be recognized by their respective skull characters. But precise aging of older animals was only possible by cementum annuii. There was a general concordance of age-related changes across skull characters. But some characters showed sex-specific differences in changes with age. This fact has to be considered in either species when carrying out age estimates based on skull morphology. ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

80 HERMANN ANSORGE & FRANZ SUCHENTRUNK

Zusammenfassung

Anhand von Schädelmaterial aus Österreich und Ostdeutschland werden Mög- lichkeiten der Altersermittlung für den Steppen- und den Waldiltis erarbeitet und verglichen. Beide Arten zeigen im Zahnzement von Dünnschnitten der oberen Canini gut erkennbare Wachstumsunterbrechungen, die Jahreslinien darstellen. Das so ermittelte Alter wird als korrekte Bezugsgröße angenommen. Die Altersstruktur ist besonders bei den Waldiltissen Ostdeutschlands, die einem höheren Jagddruck ausgesetzt waren, stark in den jüngeren Bereich gestaucht und auffällig zugunsten der Männchen verschoben. Eine Schätzung in „relative Altersklassen" nach allge- meinen Schädelmerkmalen ergibt eine recht hohe Übereinstimmung mit den Er- gebnissen der Zahnschnitte (92%). Zwölf Schädelmerkmale werden einzeln nach ihrer Ausprägung numerisch bewertet. Sie weisen zwar alle eine altersabhängige Entwicklung auf, erlauben aber wegen der großen Überlappungsbereiche nicht eine eindeutige Zuordnung in Altersklassen. Nur fünf Merkmale sind bei gemeinsamer Betrachtung geeignet, um Jungtiere sicher von älteren zu unterscheiden. Die mei- sten der Tiere im zweiten Lebensjahr können aber auch noch gut ihrer Altersklasse zugeordnet werden. Für eine weitere Altersaufteilung älterer Tiere müssen die Jah- reslinien im Zahnzement herangezogen werden. Die Möglichkeiten der Alterser- mittlung anhand der Schädelmerkmale von Waldiltis und Steppeniltis stimmen grundsätzlich überein. Zwischen den Geschlechtern bestehen in wenigen altersab- hängigen Merkmalen aber sichere Unterschiede, dies ist bei einer Altersschätzung zu berücksichtigen.

1. Introduction

The correct age determination of dead specimens is a prerequisite for studies on diverse aspects of the biology of mammal species. Information on the age of individuals is not only essential for constructing models of population structure, life expectancy, mortality rates etc. (see e.g. CAUGHLEY 1980). Reliable age estimates of individuals are necessary for diverse ecological and evolutionary studies, such as testing hypothesis of variation of body size and weight. Furthermore, age estimates are essential for evaluating the meaning of ontogenetic and static allometry in systematic comparisons, to interprete changes in diverse physiological parameters, to understand characteristics of the reproduction biology, pathological developments or findings of intoxication or contamination (see e.g. REMPE 1970, KRÜGER 1996, KRUUK et al 1997, POWELL & KING 1997, PERTOLDI et al 1998, KRUS- KA & SCHREIBER 1999). Often a more detailed age classification of specimens is desired than merely a separation into juvenile and adult categories. Diverse methods have been developed to estimate the real age of dead individuals as precise as possible (see e.g. MORRIS 1972). ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

Aging polecats and steppe polecats 81

For polecats (Mustela putorius L., 1758), various schemes of age estimation have been based on the development of diverse skull characteristics (HABERMEHL & RÖTTCHER 1967, REMPE 1970, BUCHALCZYK & RUPRECHT 1977, STUBBE 1989). However, an accurate assessment of a polecat's age can only be achieved by counting the annual growth lines in bones or teeth (KLEVEZAL & KJLEINENBERG 1967, GRUE & JENSEN 1974, FANCY 1980, KLEVEZAL 1988, 1996). In polecats, KLEVEZAL & KLEINENBERG (1967) described periostal lines in the lower jaw, and GRUE & JEN- SEN (1974) found incremental cementum lines, that were considered to reflect the real age of the animals (see also table 10 in KLEVEZAL 1996). Such growth lines (annuii) of polecats have been studied in population ecological contexts by WEBER (1987) and ANSORGE (1994). As to our knowledge no comparison of aging polecats by skull characteristics and tooth annuii has been untertaken so far.

In steppe polecats (Mustela eversmanni Lesson, 1827), characteristics of skull development were used to separate juveniles and adults (HEPTNER & NAUMOV 1974, WOLSAN 1993a); annual layers in mandibles were mentioned only in the context of aging individuals from Kasachstan (GVOZDEV & STRAUTMAN 1982).

Here, we report for the first time on age determination of steppe polecats based on cementum annuii counts in tooth sections. In addition, in order to check the reliability of morphological criteria of skulls for aging steppe polecats and polecats, we compare age estimates as derived from various skull characteristics with the respective cementum annuii counts in the same individuals.

2. Material and methods

2.1 Specimens studied

We studied 51 skulls of steppe polecats and 249 skulls of polecats. Most of the individuals were trapped or shot by hunters. Only few were collected as road-kills. All steppe polecats were from eastern Austria (provinces of Lower Austria and Burgenland), mainly killed after 1990. Among the polecats, 194 individuals were from Upper Lusatia in the southeast of eastern Germany; all were collected after 1980. Twenty-seven polecats were from eastern Austria (provinces of Lower Au- stria and Burgenland), largely from the overlap zone of both species; another eigh- teen were from southern or central Austria (provinces of Styria and Carinthia), and ten from northwestern Austria (Upper Austria). The bulk of the Austrian polecats was collected in various years of the 20th century; only few individuals were collected by the end of the 19th century. While most steppe polecats were collected during late summer, polecats were collected almost exclusively between autumn and spring. The Austrian skulls are either in the mammal collection of the Natural ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

82 HERMANN ANSORGE & FRANZ SUCHENTRUNK

History Museum Vienna (NMW) or in the study collection of the Institute of Wild- life Ecology at the Veterinary Medicine University of Vienna. The skulls from Upper Lusatia are from the mammal collection of the State Museum for Natural Sciences Görlitz (MNG).

Species diagnoses were read from specimens lables and acknowledged by the authors or based on skin and skull characters (see HEPTNER & NAUMOV 1974, WOL- SAN 1993b) in case of the recently collected specimens that were dissected by the authors.

2.2 Aging methods

Each specimen was aged independently by counts of cementum annuii and skull characteristics.

2.2.1 Tooth sections and annuii counts

All skulls were aged according to cementum annuii counts (e.g., GRUE & JEN- SEN 1974, KLEVEZAL 1996). Longitudinal sections (50 - 100 |im ) of upper canine roots were produced with a low-speed precision saw (Isomet - Buehler) and annuii (i.e., narrow dense lines) were counted in unstained sections under reflected light (lateral illumination) with a dissecting microscope (DRISCOLL, JONES & NICHY 1985, ANSORGE 1995). All annuii counts were made by one author (HA), who is well experienced in interpretation of incremental dental lines of diverse mustelid species (e.g., ANSORGE 1992, ANSORGE & GROSSE 1997, ANSORGE et al. 1997, ANSORGE & JESCHKE 1999). The real age in years of single specimens was inferred directly from the number of incremental lines in the longitudinal sections. According to GRUE & JENSEN (1979) incremental cementum lines are formed between October and December. Since we did not know the actual birth dates of single animals, we accepted the 1st of June as fixed date for counting the years of age of individuals (WEBER 1987); this fixed date was based on the periods .of the breeding season of the two species given in the literature (see discussion section).

2.2.2 Skull characteristics

All specimens were assigned to one of four "relative age classes" (RAC) according to their general skull characteristics (RGTTCHER 1965, REMPE 1970, BUCHALC- ZYK & RUPRECHT 1977, STUBBE 1989), and also in reference to the "relative age classes" described for beech martens {Martes martes) by REIG & RUPRECHT (1989).

The four relative age classes are as follows (see figures 1 and 2 for typical skulls of each RAC): ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

Aging polecats and steppe polecats 83

Figure 1: Typical skulls of relative age classes (RAC) 1 - 4 of polecats (for RAC definitions see text)

Figure 2: Typical skulls of relative age classes (RAC) 1 - 4 of steppe polecats (for RAC definitions see text) ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

84 HERMANN ANSORGE & FRANZ SUCHENTRUNK.

RAC 1 animal within first year of life RAC 2 animal within second year RAC 3 animal within third, forth, or fifth year RAC 4 animal within sixth year or older This classification was based on the compound consideration of the following criteria: • development of skull shape • general degree of ossification of skull sutures, especially the nasal sutures • dental abrasion • development of the sagittal crest, the postorbital constriction, and the ectorbital processes • structuring of the surface of the cranial vault

Based on these RAC criteria twelve skull characters with multiple character states were considered separately for age estimation. These characters were esta- blished according to our experience with aging skulls of diverse mustelid species and following HABERMEHL & RÖTTCHER (1967), REMPE (1970), BUCHALCZYK & RU- PRECHT (1977), STUBBE (1989); they are listed along with the respective character states in Table 1. Several of the character states that were occasionally difficult to score are displayed in the Figures 3-5.

Figure 3a: Character states of male polecat skulls: a) unossified squamoso-zygomatic sutures (C4/1), cranial vault vaulted (C2/1), processus mastoidei little developed (C9/1) ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

Aging polecats and steppe polecats 85

Figure 3b: Squamoso-zygomatic sutures still partly visible (C4/2), straight cranial vault (C2/2), moderately developed processus mastoidei (C9/2)

Figure 3c: Completely ossified squamoso-zygomatic sutures (C4/3), depressed cranial vault (C2/3), distinctly developed processus mastoidei (C9/3) ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

86 HERMANN ANSORGE & FRANZ SUCHENTRUNK

Figure 4a: Character states of male step- Figure 4b: Male polecat: partly visible pe polecats: unossified nasal sutures nasal sutures (C3/2), moderately de- (C3/1 ), little developed postorbital con- veloped postorbital constriction (C7/2), striction (C7/1), blunt Processus ector- moderately developed Pr. ectorbitales bitales (C8/1), partly visible maxillary (C8/2), and completely ossified s. ma- sutures (C12/1) xillares(C12/2)

Figure 4c: Female steppe polecat: com- Figure 5a: Male polecat: a) rough/po- pletely ossified nasal sutures (C3/3), di- rous surface of cranial vault (C1/1), stinct postorbital constriction and pr. ec- Crista sagittalis absent (C5/1) torbitales (C7/3, C8/3), completely ossified maxillary sutures (C12/2). ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

Aging polecats and steppe polecats 87

Figure 5b: Male polecat: even surface Figure 5c: Female polecat: fine-struc- of cranial vault (Cl/2), little developed tured cranial vault (Cl/3), distinct C. sa- C. sagittalis (C5/2) gittalis (C5/3)

2.2.3 Comparison of skull characters, relative age classes, and annuii counts

In order to evaluate the usefulness of the diverse morphological criteria for age estimation in either species, we calculated the frequencies of relative age classes and character states for the age in years as assessed by the annuii counts, separately for sexes and species.

Sex-related differences of the values of character states of single characters (see Table 1) were tested separately for species and age in years by chi2 or Fisher's exact tests, based on dichotomized character states (value 1 vs. non-1, i.e. 2—4 aggregated). Lumping of values 2-3 or 2-4 of character states was necessary to obtain sufficient cases per cell of the contingency table. Significance levels were based on the Sequential Bonferroni procedure with a=0.05 to account for multiple testing (RICE 1989).

2.2.4 Within-observer variation

We checked for within-observer variation ("measurement error") of RAC determination, classifications of each of the twelve skull characters, and annuii counts by repeating the classifications and counts in random samples of 30 male and 30 female polecats and in 30 steppe polecats of both sexes, respectively. These repeats were performed after sufficient time breaks (at least one week), so that me- mory on skull features or annuii counts of certain skulls was unlikely. ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

HERMANN ANSORGE & FRANZ SUCHENTRUNK

Character Character description Character states Number (numeration)

Cl surface of cranial vault rough or porous (1) even (2) with fine structures (3)

C2 cranial vault vaulted (1) straight (2) depressed (3)

C3 ossification of nasal sutures sutures not ossified (1) sutures still (partly) visible (2) sutures completely ossified (3)

C4 ossification of squamoso-zygomatic sutures not ossified (1) sutures sutures still (partly) visible (2) sutures completely ossified (3)

C5 crista sagittalis not present (1) little developed (2) distinct (3)

C6 crista occipitalis little developed (1) moderately developed (2) distinct (3)

C7 postorbital constriction little developed (1) moderately developed (2) distinct (3)

C8 processus ectorbitales blunt (1) moderately developed (pointed) (2) distinct (3)

C9 processus mastoidei little development (1) moderately developed (2) distinct (3)

CIO abrasion of incisivi no abrasion (1) little (2) moderate (3) strong (4)

Cll abrasion of P4 no abrasion (1) little (2) moderate (3) strong (4)

C12 ossification of maxillary sutures still visible/ partly visible (1) (s. maxillo-intermaxiHaris, s. maxillo- completely ossified (2) frontalis, s. maxillo-palatina) ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

Aging polecats and steppe polecats 89

Table 1: Skull characters, description of chartacter states and associated numeration of character states. Values of character states increase with ontogenetic development

3. Results

3.1 Tooth sections and age determination

All 300 skulls of steppe polecats and polecats could be aged by cementum annuii counts in upper canines. Only one (3.3%) of all annuii count repeats in steppe polecats and two (3.3%) in polecats produced a mismatch with the respective first count results, yielding an overall rate of annuii misinterpretations of 3.3%. First annuii are visible in polecats after their first winter (Figure 6 a and b; and see GRUE & JENSEN 1979). Presently, the lines were distinctly developed, similarly to those in Mustela vison or Martes foina. They were easier to identify than those in otters (Lutra lutra). Like in the Martes species and in Mustela vison, single lines were clearly discernible from the top of the root all along the whole root region. In older animals, however, they were sufficiently differentiated only in the apical root region, except for the tip.

Figure 6a: Longitudinal section of upper canine. Steppe polecat, one cementum annulus ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

90 HERMANN ANSORGE & FRANZ SUCHENTRUNK

Figure 6b: Polecat: two cementum annuii

The microscopic picture showed a dark zone of "summer cementum" of variable breadth, right after the transition from dentine to cementum. This zone of "summer cementum" is followed by a dense zone of cementocyte-free "winter cementum". All following zones of "summer cementum" are more regular than that of the first year (Figure 6). We did not notice any marked species- or sex-specific differences in the nature of formation of the annuii. However, as in other mustelid species (personal experience of HA; and GRUE & JENSEN 1979), in either species studied presently we found few individuals with little developed incremental lines and generally little structuring of the cementum.

3.2 Age structure of the samples

The age structure of the samples are presented in Tables 2-4, separately for the species and regions. The sufficient sample size of polecats from Upper Lusatia allowed us to construct an age pyramid for this population (Figure 7). It is quite depressed with one animal reaching an age of five years. Few male polecats but no female exceeded an age of two years. Males predominated; they made up 75% of the sample (i.e., 3 males : 1 female). In the Austrian polecats, we found a more tapering age pyramid, with the oldest animal being seven years of age. The age structure of the steppe polecat sample was similar to that one of the Austrian polecat sample, but with a slightly higher mortality prior to the third year. Two steppe ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

Aging polecats and steppe polecats 91

polecats reached an age of eight years. While there was a male-biased sex distribu- tion (63.6% males; i.e., 1.75 : 1) in the Austrian polecat sample, steppe polecats showed a more even sex ratio with 56.4 % males (1.33 : 1).

Age

0,5 6

18,4

52,6

60 50 40 30 20 10 0 10 20 30 40 50 60

Figure 7: Sex and age structure of polecats (n = 194) from Upper Lusatia. Age determination was based on cementum annuii counts in first upper canines

Table 2: Age and sex structure of the steppe polecat material from eastern Austria (n = 51)

Year Total Males Females Number % Number % Number %

1. 28 54.9 11 26.2 15 35.7 2. 14 27.5 10 23.8 3. 3 5.9 2 4.8 1 2.4 4. 1 2 1 2.4 5. 2 3.9 1 2.4 6. 7. 1 2 8. 2 3.9 1 2.4 ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

92 HERMANN ANSORGE & FRANZ SUCHENTRUNK.

Table 3: Age and sex structure of the polecat material from Upper Lusatia (n =194)

Year Total Males Females Number % Number % Number %

1. 138 71.1 100 52.6 35 18.4 2. 47 24.2 35 18.4 12 6.3 3. 6 3.1 5 2.6 4. 2 1 2 1.1 5. 1 0.5 1 0.5

Table 4: Age and sex structure of the polecat material from Austria (n = 55)

Year Total Males Females Number % Number % Number %

1. 32 58.2 14 42.4 8 24.2 2. 10 18.2 3 9.1 1 3 3. 8 14.5 3 9.1 4. 1 1.8 1 3 5. 3 5.5 2 6.1 6. 7. 1 1.8 1 3

3.3 Age estimation according to skull characteristics

All 300 skulls were allocated to one of the four relative age classes (RAC) described above. Only 3.3% mismatches were obtained by repeted RAC assessments of skulls. Table 5 shows the frequencies of correspondence between RACs and real age as assessed by cementum annuii counts. The overall frequency of wrong age estimation by RACs was only eight percent. A somewhat higher frequency of wrong age estimates by RAC was found in steppe polecats of RAC 2, and particularly of RAC 3 and RAC 4. ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

Aging polecats and steppe polecats 93

Table 5: Age estimation of polecats and steppe polecats by grouping skulls in relative age classes (RAC) compared to age determination by cementimi layers (age in years)

Polecat males Agel Age 2 Age 3-5 Age>5 RAC1 113(99%) 1 RAC 2 1 37 (93 %) 2 RAC 3 9(100%) RAC 4 1 (100 %)

Polecat females Agel Age 2 Age 3-5 Age>5 RAC1 42 (98 %) 1 RAC 2 1 12(92%) RAC 3 3(100%) RAC 4

Steppe polecats Agel Age 2 Age 3-5 Age>5 RAC1 27 (93 %) 2 RAC 2 1 5 (71 %) 1 RAC 3 6 3 (30 %) 1 RAC 4 1 2 2 (40 %)

3.4 Comparison of skull characters and cementum annuii counts

In general, all skull characters showed age-related changes (i.e., changes in relation to annuii counts). These changes were most distinct in the surface of the cranial vault (Cl), the ossification of the nasal sutures (C3), the ossification of the squamoso-zygomatic suture (C4), the sagittal crest (C5), and the ossification of the maxillary sutures (C12). The frequency distributions of the character states of C1, C3, C4, and C5 are shown in the Figures 8-11, separately for years of life as ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

94 HERMANN ANSORGE & FRANZ SUCHENTRUNK determined by cementum annuii. The detailed frequencies of character states of all characters are listed in the Appendices 1 - 4. The discrimination of single years of age was not possible by single skull characters. Even juveniles could not always be reliably separated from adults by single characters. The frequencies of character states of diverse characters showed a variable amplitude across age of years.

In both species and sexes, a rough, porous, or even surface of the cranial vault (Cl) was present only in animals not older than two years; but within this age category a considerable number of specimens showed already a fine structured surface (character state 3) (Figure 8). Also, the degree of the ossification of the nasal sutures (C3) did not enable a secure separation of juveniles from older animals. Only animals that displayed completely unossified nasal sutures were not older than one year (Figure 9). Not completely ossified squamoso-zygomatic sutures could persist until the end of the third year (Figure 10). Similarly, a crista sagittalis could be absent until the end of the third year. On the other hand a pronounced crista sagittalis could already occur in the first year (Figure 11). Maxilla- ry sutures were only visible in the first year of life in both species and sexes. But a variable number of animals had already ossified sutures within the first year. All further skull characters were even less reliably related to the annuii numbers. In particular, dental abrasion (CIO, Cl 1) varied strongly across age; i.e., old animals could have still little abrasion, whereas moderate abrasion could occur already within the first year of life. In general, both sexes showed the above described patterns of age-related variation of skull characters. But among less than one year old polecats, character states of the cranial vault (C2), the crista sagittalis (C5), the postorbital constriction (C7), and the mastoid processes (C9) had lower character state values (1-4; see table 1) in females than in males (C2: p=0.00002; C5: p=0.000001; C7: p=0.00061; C9: p=0.000001; all chi2-tests with d.f.=l). In steppe polecats only trends for higher character state values in males than females were found in the respective skull characters. We could not test differences of character state values between the two species because of the different distributions of collection seasons (see material and methods section) that would have introduced a bias of the skull development particularly in animals within their first year of life. ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

Aging polecats and steppe polecats 95

100

a- 9> •State 1 20 •State 2 •State 3 2-3 3-4 4-5 5-6 6-7 Age (years) Figure 8: Relative frequencies of character states of skull character Cl (surface of cranial vault, see Table I) in all studied male polecats, separately for individuals of different age in years. Age determination by cementum annuii counts of first upper canines 100

•State 1 •State 2 •State 3 4-5 5-6 6-7 Age (years) Figure 9: Relative frequencies of character states of skull character C3 (ossification of nasal sutures, see Table I ) in all studied male polecats, separately for individuals of different age in years. Age determination by cementum annuii counts of first upper canines ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

96 HERMANN ANSORGE & FRANZ SUCHENTRUNK

100

>» 60 u Q) 40

•State 1 20 •State 2 •State 3 0-1 1-2 2-3 3-4 4-5 5-6 6-7 Age (years) Figure 10: Relative frequencies of character states of skull character C4 (ossification of squamoso-zygomatic sutures, see Table 1 ) in all studied male polecats, separately for individuals of different age in years. Age determination by cementum annuii counts of first upper canines

100

«State 1 20 •State 2 astate 3 1-2 2-3 3-4 Age (years) Figure 11 : Relative frequencies of character states of skull character C5 (development of christa sagittalis, see Table I) in all studied male polecats, separately for individuals of different age in years. Age determination by cementum annuii counts of first upper canines ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

Aging polecats and steppe polecats 97

4. Discussion

All polecats and steppe polecats exhibited unambiguous cementum annuii in the root portion of the upper canines. These structures were similar in their characteristics to those found earlier in various other mustelid species, such as badger {Mêles mêles), pine marten {Martes martes), stone marten {Martes faina), otter {Lutra lutra), mink {Mustela vison) (see e.g. GRUE & JENSEN 1979, ANSORGE 1995). DAPSON (1980) critisized that age determination by cementum annuii, among other annuii, frequently suffered from the lack of age-known material. The reliability of the presently used method of age determination, however, was proved for several mustelid species by age-known individuals (unpubl. data by HA for Mustela nivalis, Martes faina, Lutra lutra), and also for one polecat of known age, born and raised in captivity. Unfortunately we did not have more age-known animals at our disposal to test the annual background of the cementum lines. But this method was also validated for other age-known carnivore species (GRAU et al 1970, GRUE & JENSEN 1973, GRUE & KING 1984, THOMÉ & GEIGER 1997). Therefore, we accepted it as valid method of age determination in the presently studied polecats and steppe polecats.

GRUE & JENSEN (1979) and WEBER (1987) have studied cementum annuii by microtome sections of decalcified polecat canines. Our presently used technique, however, was less labourious and produced well distinguishable annuii (ANSORGE 1995). Repeated counts by one author resulted in very high aging reliability. Ne- vertheless, we think that certain experience of aging dental incremental lines is necessary to produce reliable results. Cementum annuii counts made by different observers might be associated with a higher rate of inaccuracy, as our preliminary tests with otter canines do suggest.

The determination of age of years by annuii counts is feasible if the date of death of the animal is known and the concerned species has a restricted breeding period (see e.g., GRUE & JENSEN 1979). In most of our specimens we were aware of the respective death dates; but both species have quite a long period of reproduction (c. March - September for polecats, and c. March - July for steppe polecats, cf., HEPTNER & NAUMOV 1974, MEAD et al. 1990, WOLSAN 1993 a, b). As a consequence of these long breeding seasons, the age determination of single specimens in terms of number of years may vary by one year, depending on the actual (but unknown) date of birth (WEBER 1987, STUBBE 1989). For example, if an animal with one disctinct cementum annulus, dies within the breeding period, its real age (first or second year of life) will depend on the birth date in the previous year. But we did not have any information on the actual birth dates nor the length of the breeding periods in the presently studied ranges. We followed WEBER (1987) in determining the 1st of June as the "average date of birth" that was relevant for ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

98 HERMANN ANSORGE & FRANZ SUCHENTRUNK

assigning age in years as calculated from annuii counts. We are aware that this procedure might result in species-specific biases of correct age determinations, if there are marked differences between the breeding periods of the two species.

The age structure of the polecat sample from Upper Lusatia suggested a high mortality rate of animals within their first year of life. The fraction of juveniles appeared to be smaller both in the Austrian polecats and the steppe polecats. Fur- thermore, despite clearly smaller sample sizes, the steppe polecats and Austrian polecats reached older ages than the polecats from Upper Lusatia. This might be a consequence of a higher hunting pressure over a longer period of time in the latter region (ANSORGE 1994). A comparison of the age structure of the polecat samples from Upper Lusatia with respective data for Swiss polecats collected over a similar period of time (WEBER 1987) by a G-test did not yield any significant diffe- rence of percentages of animals in three age classes (i.e., first year, second year, and over two years old). Similar age structures were also found for Polish polecats by BUCHALCZYK & RUPRECHT (1977) and for polecats form the province of Sach- sen-Anhalt in eastern Germany (STUBBE 1989). But we should be aware of the likelehood of more or less pronounced differences between age and sex structures of samples and the real age and sex compositions of the corresponding living populations. Among mustelids, such strong discrepancies were discussed by KRUUK et al. (1997) and proved for otters by ANSORGE et al.(1997). Male biases in samples of various mustelid species were described by BUSKIRK & LINDSTEDT (1989) and interpreted as resulting from sex-specific home range sizes and higher locomotory activity in males. Such mechanisms might explain the high percentage of males in all our samples.

Generally, polecats show a very high size variability between and within sexes (BUCHALCZYK & RUPRECHT 1977). Ontogenetic changes occur over long develop- mental periods (HEPTNER & NAUMOV 1974). According to BUCHALCZYK & RUPRECHT (1977) skull development shows region-specific patterns. We found also a high variability in various skull characters that were used earlier by diverse authors for age estimation. But only five characters appeared to be associated more or less tightly with age as determined by cementum annuii.

In accordance with findings in polecats from diverse European provenences (WOLSAN 1993), our data indicated marked changes in the surface of the cranial vault (Cl) already within the first year of life in both sexes. Although ossification of the nasal sutures (C3) was used by several authors to separate juveniles from older animals (RÖTTCHER 1965, HABERMEHL 1985, WOLSAN 1993), our findings indicated that the ossification process of these sutures extends until the end of the third year of life. Hence, we conclude that the state of ossification of the nasal sutures is not valid to single out juveniles. Basically the same is true for ossificati- ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

Aging polecats and steppe polecats 99

on of the squamoso-zygomatic sutures (C4). Contrary to the large time amplitude of ossification of the latter sutures, ossification of the maxillary sutures (C12) was already completed in both species and sexes within the first year of life (see also REMPE 1970). Thus, this character separates most of the juveniles from older animals but it does not allow a more refined differentiation within the non-juveniles. REMPE (1970) used this character to identify indivdiuals older than ten months of age.

The development of the crista sagittalis was used earlier for distinguishing beech and stone martens (RÖTTCHER 1965), and was later on used for sex differentiation and age estimation of various mustelid species (HEPTNER & NAUMOV 1974, HABER- MEHL 1985). The merging position of the two anterior crests in relation to the postorbital constriction and the length of the sagittal crista were considered important for aging polecats by RÖTTCHER (1965) and HABERMEHL (1985). We did not test separately these characters but they were integrated in the evaluation of the crista sagittalis characteristics (C5). Our comparisons of the formation of the sagittal crista with cementum annuii in both species suggest that it is only useful to separate animals older than two years from younger ones; this holds also for females, in spite of the generally reduced development.

As the sagittal crista, the degree of the postorbital constriction (C7) is considered in connection with the development of the chewing muscles (BÄHRENS 1960, BUCHALCZYK & RUPRECHT 1977). The postorbital constriction is also used as differential diagnositc character for polecats and steppe polecats (WOLSAN 1993 b, but see HEPTNER & NAUMOV 1974). Our findings suggest a fairly high variability of this character within and across years of age, in both males and females. This high variability might in part be due to ontogenetic and static allometry. It does not recommend the exclusive use of the postorbital constriction as a differential dia- gnostic character for the two species (see also BUCHALCZYK & RUPRECHT 1977). The patterns of dental abrasion showed high variability across the years of age of individuals in either species. Therefore this character complex should not be used for aging individuals of either species (see also WEBER 1987).

We see that no single skull character studied presently does enable reliable aging of specimens of either species. However, a combined consideration of the surface of the cranial vault (Cl), the ossification of the nasal sutures (C3), the squamoso-zygomatic suture (C4), and the maxillary sutures (C12), as well as the development of the sagittal crest (5) enables at least a separation between juveniles (i.e., animals less than one year old) from older animals. Also, most of the animals within their second year of life can be separated from older ones by these skull characters. Detailed age results can be only achieved by cementum annuii counts, particularly for two years old animals or older ones. ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

100 HERMANN ANSORGE & FRANZ SUCHENTRUNK

Acknowledgements: We are grateful to Dr. FRIEDERIKE SpiTZENBERGERfor allowing us to study skulls from the mammal collection of the Natural History Museum Vienna and Dr. BARBARA HERZIG for help with the material, ANITA HAIDEN (Vienna) for preparing several skulls, DI. L. CECIL (Leithaprodersdorf), G. EBERL (Klagenfurt), J. KOBER (Ungern- dorf), and Ing. H. POLSTER (St. Andrà) for presenting some dead polecats and steppe polecats.

References

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KLEVEZAL, G. A. (1996): Recording structures of mammals. Determination of age and reconstruction of life history. - A.A. Balkema, Rotterdam. 274 pp KLEVEZAL, G. A. & KLEINENBERG, S.E. (1967): Age determination of mammals by layered structure in teeth and bone, (in Russ.). - Nauka Moskva KRUSKA, D. & SCHREIBER, A. (1999): Comparative morphometrical and biochemical-genetic investiga- tions in wild and ranch mink (Mustela vison : Carnivora : Mammalia). - Acta Theriol. 44: 377-392 KRUUK, H., CONROY, J.W.H. & WEBB, A. (1997): Concentrations of mercury in otters (Lutra lutra L) in Scotland in relation to rainfall. - Env. Pollut. 96: 13-18 KRUUK, H., JONES, C, MCLAREN, G.W., GORMAN, M.L. & CONROY, J.W.H. (1997): Changes in age composition in populations of the Eurasian otter Lutra lutra in Scotland. - J. Zool., Lond. 243: 853-857 KRÜGER, H.-H. (1996): Altersspezifische Reproduktionsraten bei Baummardern (Martes martes) und Steinmardern (Martes faina). - Z. Säugetierk. 61, Suppl. 31 MEAD, R.A., NEIRINCKX, S.& CZEKALA, N.M. (1990): Reproductive cycle of the steppe polecat (Muste- la eversmanni). J. Reprod. Fertil. 88: 353-60 MORRIS, P. (1972): A review of mammalian age determination methods. - Mammal. Rev. 2: 69-104 PERTOLDI, C, MADSEN, A. B., RANDI, E., BRAUN, A. & LOESCHCKE, V. (1998): Variation of skull morpho- metry of Eurasian otters (Lutra lutra) in Denmark and Germany. - Ann. Zool. Fenn. 35: 87-94 POWELL, R. A. & KING, CM. (1997): Variation in body size, sexual dimorphism and age-specific survival in stoats, Mustela erminea (Mammalia: Carnivora), with fluctuating food supplies. - Biological Conservation 62: 165-194 REIG, S.& RUPRECHT, A.L. (1989): Skull Variability oï Martes martes and Martes faina from Poland. - Acta Theriol. 34: 595-624 REMPE, U. (1970): Morphometrische Untersuchungen an Iltisschädeln zur Klärung der Verwandschaft von Steppeniltis, Waldiltis und Frettchen. Analyse eines "Grenzfalles" zwischen Unterart und Art. - Z. wiss. Zool. 180: 185-367 RICE, W.S. (1989): Analyzing tables of statistical tests. - Evolution 43: 223-225 ROTTCHER, D. (1965): Beiträge zur Altersbestimmung bei Nerz, Steinmarder und Iltis. - Dissertation, Universität Gießen STUBBE, M. (1989): Iltis Mustela putorius L. - in: STUBBE, H.: Buch der Hege. Berlin: 503-513 THOMÉ, H. & GEIGER, G. (1997): Vergleich zweier Methoden zur Altersbeurteilung an Zähnen alters- bekannter wildlebender Fleischfresser. - Anat. Histol. Embryol. 26: 81-84 WEBER, D. (1987): Zur Biologie des Iltisses (Mustela putorius L.) und den Ursachen seines Rückgan- ges in der Schweiz. - Dissertation, Univ. Basel WOLSAN, M. (1993 a): Mustela eversmanni Lesson, 1827 - Steppeniltis. In NIETHAMMER, J. & KRAPP, F. (eds.): Handbuch der Säugetiere Europas. Bd. 5, II., Aula-Verlag Wiesbaden 770-816: WOLSAN, M. (1993 b): Mustela putorius Linnaeus, 1758 - Waldiltis. In: NIETHAMMER, J. & KRAPP, F. (eds.).- Handbuch der Säugetiere Europas, Bd. 5, II, Aula-Verlag Wiesbaden: 699-769 ZINKE, O. & ANSORGE, H. (1998): Remarks to age determination criteria in the otter (Lutra lutra). - Proceedings 14th Mustelid Coll 1997 Ârhus, NERI Technical Report No. 262: 26-27 ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

102 HERMANN ANSORGE & FRANZ SUCHENTRUNK

Authors' addresses:

Dr. Hermann ANSORGE Staatliches Museum f. Naturkunde Görlitz PF 300154 D-02806 Görlitz Deutschland

E-mail: [email protected]

Dr. Franz SUCHENTRUNK Research Inst, of Wildlife Ecology Veterinary Medicine University Vienna Savoyenstr. 1 A-l 160 Vienna, Austria

E-mail : franz. suchentrunk@vu-wien. ac. at

Appendix 1 : Relative frequencies (%) of character states of single skull characters in male polecats of different age in years. Age 1 = first year, Age 2 = second year etc. For skull characters and character states see Table 1. n = total number of skulls (can be lower for single characters) ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

Aging polecats and steppe polecats 103

Skull character / Character state Age 1 Age 2 Age 3 Age 4 Age 5 Age 7 n=112 n=38 n=8 n=2 n=l n=l Cl/1 36.6 2.7 Cl/2 42.9 32.4 Cl/3 20.5 64.9 100 100 100 100

C2/1 19 C2/2 77 75.7 25 100 100 C2/3 3.8 24.3 75 100

C3/1 26.8 C3/2 58 42.1 37.5 C3/3 15.2 57.9 62.5 100 100 100 C4/1 13.9 C4/2 43.5 C4/3 42.6 100 100 100 100 100

C5/1 39.3 C5/2 50.9 55.3 25 C5/3 9.8 44.7 75 100 100 100

C6/1 8.3 C6/2 82.6 70.3 100 C6/3 9.2 29.7 100 100 100

C7/1 29.5 2.6 C7/2 62.5 71.1 37.5 100 C7/3 8 26.3 62.5 100 100

C8/1 18.8 C8/ 2 62.5 42.1 12.5 C8/3 18.8 57.9 87.5 100 100 100

C9/1 10.9 C9/2 76.4 78.4 25 50 100 C9/3 12.7 21.6 75 50 100

C10/1 30.9 3 C10/2 68.2 69.7 100 50 100 CIO/3 0.9 27.3 50 100 CIO/4

Cll/1 46.8 2.6 Cll/2 53.2 73.3 75 50 100 Cll/3 23.7 25 50 Cll/4 100

C12/1 57.1 C12/2 42.9 100 100 100 100 100 ©Amt der Niederösterreichischen Landesregierung,, download unter www.biologiezentrum.at

104 HERMANN ANSORGE & FRANZ SUCHENTRUNK

Skull character/ Agel Age 2 Age 4 Age 5 Appendix 2: Relati- Character state ve frequencies (%) n=43 n=13 n=l n=2 of character states of Cl/1 55.8 7.7 single skull charac- Cl/2 44.2 23.1 ters in female pole- Cl/3 69.2 100 cats of different age in years. Age 1 = first C2/1 53.5 7.7 50 C2/2 46.5 84.6 50 year, Age 2 = second C2/3 69.2 year etc. For skull characters and cha- C3/1 9.5 racter states see Ta- C3/2 83.3 46.2 ble 1. n = number of C3/3 7.1 53.8 100 skulls (can be lower C4/1 9.5 for single characters) C4/2 54.8 7.7 C4/3 35.7 92.3 100

C5/1 83.3 30.8 C5/2 16.7 53.8 100 C5/3 15.4

C6/1 23.3 7.7 C6/2 76.7 84.6 100 C6/3 7.7

C7/1 59.5 7.7 C7/2 38.1 76.9 100 C7 3 2.4 15.4

C8/1 31 7.7 C8/2 64.3 38.5 50 C8/3 4.8 53.8 50

C9/1 46.5 15.4 C9/2 53.5 84.6 100 C9/3

CIO/I 42.5 8.3 CIO/2 57.5 75 CIO/3 16.7 100 CIO/4 100

Cll/1 62.8 8.3 Cll/2 34.9 50 Cll/3 2.3 41.7 100 100 Cll/4

Aging polecats and steppe polecats 105

Skull character/ Age 1 Age 2 Age 3 Age 4 Appendix 3: Relative Character state frequencies (%) of n=10 n=10 n=3 n=l character states of Cl/1 40 single skull charac- Cl/2 60 10 ters in male steppe Cl/3 90 100 100 polecats of different age in years. Age 1 = C2/1 22.2 C2/2 77.8 50 66.7 first year, Age 2 = se- C2/3 50 33.3 100 cond year etc. For skull characters and C3/1 88.9 character states see C3/2 11.1 40 C3/3 60 100 Table 1

C4/1 100 C4/2 60 33.3 C4/3 40 66.7 100

C5/1 90 20 C5/2 10 50 C5/3 30 100 100

C6/1 40 C6/2 60 50 33.3 C6/3 50 66.7 100

C7/1 20 C7/2 80 30 66.7 C7/3 70 33.3 100

C8/1 50 C8/2 50 40 33.3 C8/3 60 66.7 100

C9/1 33.3 C9/2 66.7 70 66.7 C9/3 30 33.3 100

C10/1 37.5 11.1 C10/2 62.5 66.7 100 100 C10/3 22.2 CIO/4

Cll/1 100 20 Cll/2 80 100 100 Cll/3 Cll/4

106 HERMANN ANSORGE & FRANZ SUCHENTRUNK

Skull character/ Agel Age 3 Age S Age 8 Appendix 4: Relative Character state frequencies (%) of n=16 n=l n=l n=l character states of Cl/1 92.9 single skull charac- Cl/2 7.1 ters in female steppe Cl/3 100 100 100 polecats of different age in years. Age 1 = C2/1 76.9 C2/2 23.1 100 100 first year, Age 2 = se- C2/3 100 cond year etc. For skull characters and C3/1 68.8 character states see C3/2 31.3 100 C3/3 100 100 Table 1

C4/1 33.3 C4/2 66.7 C4/3 100 100 100

C5/1 71.4 C5/2 28.6 C5/3 100 100 100

C6/1 15.4 C6/2 84.6 C6/3 100 100 100

C7/1 37.5 C7/2 56.3 C7/3 6.3 100 100 100

C8/1 25 C8/2 56.3 C8/3 18.8 100 100 100

C9/1 69.2 C9/2 30.8 100 C9/3 100 100

CIO/I 31.3 C10/2 68.8 100 100 CIO/3 100 CIO/4

Cll/1 87.5 Cll/2 12.5 100 100 Cll/3 100 Cll/4

C12/1 87.5 C12/2 12.5 100 100 100