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148
Folia Zool. – 65 (2): 148–156 (2016)
Introduction
The common hamster Cricetus cricetus (Linnaeus,
1758) is a widespread Palaearctic rodent of prominent
external appearance. Its range stretches across
5500 km of steppes and farmland from the Low
Countries of western Europe to the River Yenisei in
Siberia. As one can expect for a wide-ranging small
mammal, a considerable interpopulation variation
was documented in the common hamster, formalised
in recognition of about nine subspecies (Niethammer
1982, Berdyugin & Bolshakov 1998). Several
studies meticulously elaborated patterns of regional
variation in molecular markers (Neumann et al. 2005,
Banaszek et al. 2010, Schröder et al. 2013), colour
polymorphism (Gershenson 1945, 1946, Vorontsov
1982, Schröder et al. 2013), and morphometric traits
(Ognev 1924, Stefen 2013). The western part of the
range is genetically structured at different scales. The
estimated times of divergence between phylogroups
vary between 10 kya and about 150 kya (Neumann
et al. 2005), i.e. the phylogeographic architecture is
largely the outcome of the Last Glacial Maximum
(LGM). Size varies among regions but with no obvious
trend (Berdyugin & Bolshakov 1998). In addition,
morphometric dimensions of hamsters were reported
to contrast at different time scales, both centennial
(Stefen 2013) and millennial (Smirnov & Popov
1979). Colour polymorphism attracted particular
interest. While the hamster is one of the most colourful
European mammals (Niethammer 1982), it is also
quite variable in this respect. A wide range of colour
variants have been reported (Kayser & Stubbe 2000),
in addition to very high local proportions of black
hamsters in central (Niethammer 1982) and eastern
Europe (Vorontsov 1982, Berdyugin & Bolshakov
1998).
Studies regarding the intraspecic diversity in the
common hamster have intensied over the last
years, being motivated by the necessity to establish
signicant units for conservation management. Gone
are the times when hamsters were considered a major
pest to agriculture with bounties paid for destroyed
animals (Weissenborn 1839) or when they were killed
in hundreds of thousands annually to meet the demands
Low phenotypic variation in eastern common
hamsters Cricetus cricetus
Boris KRYŠTUFEK1, Aleksandr A. POZDNYAKOV2, Danijel IVAJNŠIČ3 and Franc JANŽEKOVIČ3*
1 Slovenian Museum of Natural History, Prešernova 20, SI-1000 Ljubljana, Slovenia
2 Siberian Zoological Museum, Institute of Systematics and Ecology of Animals, Siberian Branch of Russian
Academy of Sciences, Frunze str. 11, Novosibirsk 630091, Russia
3 Faculty of Natural Sciences and Mathematics, University of Maribor, Koroška cesta 160, SI-2000 Maribor,
Slovenia; e-mail: franc.janzekovic@um.si
Received 2 March 2016; Accepted 18 March 2016
Abstract. We studied 468 museum specimens of the common hamster (387 skins and 204 skulls) collected in Belarus, Ukraine, Russia
and Kazakhstan. Besides a standard tricolour type which prevailed, we identified six colour variants: stavropolicus with reduced white
spots, and a bicolour entirely devoid of spots, white, piebald, dark-black (atypical melanistic) and intense dark (melanistic). The overall
proportion of variant hamsters was estimated at 4.3 %. Colour variants were significantly more diverse and more frequent in Europe.
The presence of melanistic hamsters was positively associated with high temperatures and high levels of precipitation. Cranial traits
were largely invariant and the only significant trend was a slight increase in zygomatic width with longitude. We found no evidence
of geographically contiguous clusters of populations which would be homogeneous enough or distinct from other similar clusters to
be formally recognized as a distinct subspecies. The western segment of the common hamster’s range (to the west of the Carpathian
Mts.) is the most diverse genetically and morphologically while the populations to the east of the Carpathians are rather uniform. This
homogeneity is further intensified on the eastern side of the Urals.
Key words: colour polymorphism, geographic variability, melanism, Russia, Siberia, subspecies, Ukraine
* Corresponding Author
149
of the fur trade (Gershenson 1945, Popov 1960,
Sludskiy et al. 1977). Today, the hamster is probably
the fastest declining European mammal (Surov et al.
2015) and is classied as a species of conservation
concern in many parts of its range (Weinhold 2008).
The decline rst became evident in the west (Libois &
Rosoux 1982) and has by now reached eastern Europe
(Rusin et al. 2013).
We address spatial variability in phenotypical traits
in the common hamsters in the east, i.e. in Ukraine,
Belarus, Russia, and Kazakhstan. Contrary to western
Europe (Schröder et al. 2013, Stefen 2013), this issue
attracted little attention in eastern Europe and western
Asia beyond traditional taxonomic studies (e.g.
Ognev 1924, Vinogradov et al. 1936) and frequency
assessments of “melanistic” hamsters in presumably
dimorphic populations (Gershenson 1945). There
are several good reasons for exploring geographic
variability more in detail. The hamster is a polytypic
species and the range covered in our study is believed
to be occupied by seven distinct subspecies (Berdyugin
& Bolshakov 1998). Recognition of morphologically
diagnosable subspecies presumes discontinuities in
variation (e.g. Corbet 1978) and therefore signals the
existence of substantial morphological variability. We
searched for patterns in spatial variability in various
morphometric traits in the common hamster and
tested whether the gaps in a continuous variability
are genuine. Variability may be either a legacy of
evolutionary history or a short term response to
environment, or both. A pattern in size variation in
particular may demonstrate adaptation to ecological
variation. Namely, optimal body size maximizes the
potential for growth and reproduction and changes
with varying climatic conditions and with quality
of diet (Porter et al. 2000). Furthermore, colour
dimorphism was frequently explained by variability
in climatic conditions (Berdyugin & Bolshakov
1998), although the predictions were never tested.
Hamsters from eastern Europe are not of interest
merely on their own. Populations in Ukraine and
southern Russia were probably the main source for
repeated westward recolonizations during the LGM
(Neumann et al. 2005). Understanding phenotypic
variation in the east can therefore also shed light on
the patterns uncovered further west.
For these reasons we looked for a pattern of
variability in the common hamster and tested whether
such a pattern, if at all present, is associated with
climatic variables. We were particularly interested
Fig. 1. Locations of common hamster samples used in this study. Samples were pooled into six populations (shaded dark grey): 1 – Ukraine
and Crimea, 2 – south-central Russia and adjacent north-western Kazakhstan, 3 – Ciscaucasia, 4 – Cis-Urals, 5 – Trans-Urals, 6 – Siberia
(top inset). Bottom inset shows distribution of two colour variants (traits): intense black hamsters (black squares), and the presence of white
chest spot (circles). The tentative range of the common hamster is shaded light grey. The Urals delimit Europe (west) from Asia (east).
150
in geographic contiguity of discrete clusters of
populations which would be identiable by a
particular trait. Such populations, if uncovered, might
be suitable targets for conservation management.
Material and Methods
We studied 468 museum specimens (387 skins
and 204 skulls) housed in the following collections
(abc): BMNH – Natural History Museum, London
(formerly British Museum (Natural History)), U.K.
(12); NMW – Natural History Museum, Vienna,
Austria (3); SZM – Siberian Zoological Museum,
Institute of Systematics and Ecology of Animals,
Russian Academy of Sciences, Siberian Branch,
Novosibirsk, Russia (132); ZFMK – Zoologisches
Forschungsinstitut und Museum Alexander Koenig,
Bonn, Germany (3); ZIN – Zoological Institute and
Zoological Museum, Russian Academy of Sciences,
St. Petersburg, Russia (318). For further details on
samples see supplementary information. Among
voucher specimens we distinguished between standard
museum skins and pelts. The former were done as
round skins, more rarely as carded skins or at skins
(Hangay & Dingley 1985), retained ears, lips, paws
and the tail, had attached label with information on the
site, date, collector, sex and external measurements,
and were frequently accompanied by a skull. Pelts,
on the other hand, resulted from case skinning for the
fur market by hamster trappers. Pelts therefore lacked
parts which add no value to the fur (paws etc.) and
detailed information, and were never accompanied by
a skull. We presumed that museum skins originated
from randomly collected hamsters and that pelts were
selected for a museum collection from larger random
samples due to unusual colouration. For example,
among the 15 pelts in ZIN, 13 were colour variants.
Hamsters were collected in Belarus (1), Ukraine
(37), Russia (336), and Kazakhstan (94). The year of
collection was recorded for 447 individuals (= 95.5 %)
and ranged from 1836 to 2009. Half of specimens were
sampled between 1927 and 1956 (median year = 1932).
We divided samples into those of European and Asiatic
origins with the Ural Mts. set as the delimiting point
(Fig. 1). There were 224 hamsters from Europe and 220
from Asia; the remaining individuals (4) lacked detailed
information on geographic origin. Next, we pooled
individuals from a landscape of geomorphological and
climatic continuity into six groups hereafter referred
to as “populations”. These populations were (Fig. 1):
1 – Ukraine and Crimea, 2 – south-central Russia and
adjacent north-western Kazakhstan, 3 – Ciscaucasia, 4
– Cis-Urals, 5 – Trans-Urals, 6 – Siberia.
Scoring data
Each skin was photographed in lateral and ventral
views. We recorded any deviations from the standard
tri-colour pattern (gured in Niethammer 1982).
Furthermore we measured four fur traits (to the
nearest millimetre): SpL – chest spot length, SpW –
chest spot width, StL – chin streak length, and CuL
– cuff length (for denitions see Schröder et al. 2013).
The length of the head and body (HB) was obtained
from the specimen tags. When HB was not recorded,
it was estimated from the museum skin to the nearest
centimetre (cf. Schröder et al. 2013). We calculated
three indices (I) to quantify relative sizes of white fur
traits: SpotI = HB–1 × √100 × (SpL × SpW); StreakI
= (StL/HB) × 100; CuffI = (CuL/HB) × 100 (Schröder
et al. 2013). Similar to the results of Schröder et al.
(2013), the StreakI and the CuffI varied independently
of sex in our samples as well.
Three linear measurements were scored from each
skull using a Vernier calliper adjusted to the nearest
0.1 mm: CbL – condylobasal length, ZyW – zygomatic
width, and MxT – length of maxillary tooth-row (on
alveoli) (Stefen 2013). The relative width of the skulls
Table 1. Factor loadings obtained from the principal components
analysis of 19 z-standardized climatic variables. Only character
loadings > 0.7 are shown.
Climatic variable CPC1 CPC2
BIO1 Annual mean T 0.859
BIO2 Mean diurnal T range
BIO3 Isothermality
BIO4 T seasonality (CV) 0.840
BIO5 Max. T of warmest month 0.923
BIO6 Min. T of warmest month 0.938
BIO7 T annual range –0.944
BIO8 Mean T of wettest month
BIO9 Mean T of driest month 0.747
BIO10 Mean T of warmest month 0.801
BIO11 Mean T of coldest month 0.934
BIO12 Annual P 0.740
BIO13 P of wettest month –0.863
BIO14 P of driest month 0.928
BIO15 P seasonality (CV)
BIO16 P of wettest quarter –0.865
BIO17 P of driest quarter 0.916
BIO18 P of warmest quarter –0.919
BIO19 P of coldest quarter 0.901
Eigenvalue 9.71 5.40
Variance (%) 51.3 28.6
151
were expressed as a quotient ZyWI = (ZyW/CbL) ×
100. Two age classes (juvenile vs. adult) were assessed
on the basis of the overall size (Sludskiy et al. 1977),
skull shape, and molar wear (Vohralík 1975, Stefen
2013). Only adults were used in craniometric analyses
to minimize the effect of ontogenetic growth.
Spatial and environmental patterns in morphometric
datasets
Pooling samples into populations can obscure the
conguration of spatial variation in morphometric
data, specically by producing an articial stepwise
pattern where a smooth cline actually occurs. To avoid
this trap, we used a single specimen in regression
analysis as the sampling unit.
For each locality we obtained latitudinal and
longitudinal coordinates using ArcGIS 9.3 (ESRI
2010) base maps (coordinate system WGS84).
Climatic variables (BIO; taken for the 1950-2000
period; WorldClim database available at http://www.
worldclim.org/) represented annual trends (e.g. mean
annual temperature, annual precipitation), seasonality
(e.g. annual range in temperature and precipitation)
and extreme or limiting environmental factors (e.g.
temperature of the coldest and warmest month, and
precipitation of the wet and dry quarters) (Table 1).
Additionally, a geospatial bioclimatic database was
developed using ArcGIS Spatial Analyst tools (ESRI
2010) by attributing all variables to the location points
representing each sample.
Because climatic variables may be correlated, we
performed a Principal Components Analysis (PCA)
on these data. To prevent dominance in the PCA by
large values at the expense of small ones, data were
z-standardized using the formula: z = (x − μ) σ−1,
where x is an individual raw score, μ is the mean of
the population and σ is the standard deviation of the
population. Note that z-scores can be dened without
assumptions of normality. The rst two Climatic
Principal Components (CPCs) had eigenvalues > 5
and explained 80 % of the variance in the original
dataset. The eigenvector matrices showed that CPC1
was primarily loaded with high eigenvectors for
temperature variables and for precipitation. CPC2
was loaded with high positive eigenvectors for
temperature of the warmest period and high negative
values for precipitation in the wettest and warmest
period (Table 1).
Statistical tests
Measurements and indices were transformed to
logarithms in order to decrease differences in
variance between variables. The normal distribution
and homogeneity of the variances were tested by
Kolmogorov-Smirnov and Bartlett tests, respectively.
No substantial departures (p > 0.05) from normality
and/or homoscedasticity were found in our data
sets which legitimized the application of parametric
Fig. 2. Colour variation in common hamsters from Russia and
Ukraine: a – standard tricolour from Pokrovka in Kurganskaja
oblast’, western Siberia (ZIN 16275); b – stavropolicus type from
Vladikavkaz, North Ossetia-Alania, European Russia (BMNH
26.2.2.20); c – bicolour type from Kislovka in Tomskaja oblast’,
western Siberia (SZM 3106); d – black (atypical melanistic) hamster
from Novaja Chertoryja in Zhitomirskaja oblast’, Ukraine (ZIN
23559). Light patches: I – cheek, II – neck, III – axillary, IV – thigh.
Fig. 3. Variation in piebald hamsters from Bashkortostan,
European Russia. The underlying colour is standard tricolour (a –
Mesjagutovskij rajon; ZIN 25263) and intense black in two pelts
from Ufa (b – ZIN 25257, c – 25265). Shown are dorsal (a-c) and
ventral side (a’, b’).
152
statistical tests. Variation in continuous variables
and association between morphometric traits and
environmental variables (geographic coordinates
and CPCs) was assessed using analysis of variance
(one-way ANOVA and factorial ANOVA) and
regression analyses (simple and multiple regressions).
Differences in proportions between samples were
compared using χ2 test. Statistical analyses were
performed using STATISTICA (StatSoft, Version 5.5,
Tulso, OK, U.S.A. 1999).
Results
Colour
A signicant majority of the hamsters we examined
were of standard tricolour type (cf. Niethammer
1982) with brownish buff upper parts and a black
belly and with contrasting light patches on the contact
between the brown and black areas. These patches
were, in anterior-to-posterior direction, the cheek,
neck, axillary, and thigh patches (Fig. 2a). Obvious
deviations from the standard pattern were observed
in 29 skins, 13 of which were pelts. The average
frequency of colour variants was therefore estimated
at 4.3 %. Only one single variant was recorded to
the east of the Urals, and the difference between the
proportions of variant hamsters on the each side of the
mountain chain (8.1 % in Europe vs. 0.6 % in Asia)
was highly signicant (p < 0.0001).
An adult female from western Siberia lacked all light
spots (Fig. 2c) and is classied as a bicolour type. Two
adults from North Ossetia-Alania were intermediate
between the tri- and the bicolour types in lacking the
thigh spot entirely and showing a reduction in the
remaining blotches (Fig. 2b); these hamsters were
classied as stavropolicus morphotype (the name is
based on “subspecies” C. c. stavropolicus Satunin,
1907). One of these individuals was darkened (Fig.
2b) while the other was normally bright.
Three pelts from Bashkortostan collected between
1928 and 1930 had prominent irregular white patches
and were classied as piebald. The underlying colour
was either a standard tricolour (Fig. 3a) or black
(Fig. 3b, c). A further two pelts were white (both
from Bashkortostan), and 19 skins (incl. 8 pelts)
were intense black throughout except for white paws,
ears and snout (“melanistic” sensu Kayser & Stubbe
2000). The majority of melanistic hamsters were from
Bashkortostan (10 skins), following by Ukraine (5),
Nizhniy Novgorod (2), and Ciscaucasia (1) (Fig. 1). A
further three skins, one each from Ukraine (Fig. 2d),
Ciscaucasia (Adygea), and Kazakhstan (no locality)
were blackish but retained rufous tints dorsally, on
the rump, and the head (“atypical melanistic” sensu
Kayser & Stubbe 2000). Not a single black individual
was accounted for in samples collected to the east of
the Urals and the difference between the two major
regions was signicant (p < 0.001). ANOVA retrieved
signicantly higher CPC1 scores for localities which
contained melanistic hamsters (F = 17.746, df = 1, 136,
p = 0.00005) as compared to sites where this variant
was not recorded in our study. Melanistic hamsters
were therefore associated with high temperatures and
high precipitation.
A thigh spot was present in 336 hamsters (= 86.8
%), and this proportion did not differ signicantly
(p = 0.396) between the populations in Europe (87.7
%) and Asia (86 %). A white chest spot was rare,
recorded in 15 skins (3.9 %) and the majority of such
hamsters (n = 8) were from the middle Volga region
(Fig. 1). Although the spot was signicantly more
frequent (p = 0.04) to the west of the Urals (6.5 %
in Europe vs. 1.1 % in Asia), a single incidence was
observed at the very eastern edge of the species’ range
in the Krasnoturanskij district. The chest spot was on
average small (SpotI = 4.92 ± 2.181) and frequently
diffused (8 skins).
Indices for two white fur traits, the StreakI and the
CuffI, loosely correlated (r = 0.14, p = 0.02). A streak
Table 2. Descriptive statistics (mean ± standard deviation) for two indices expressing relative size of white fur traits (StreakI – chin streak
index, CuffI – white cuff index), three skull measurements (CbL – condylobasal length of skull, ZyW – zygomatic width, MxT – length of
maxillary tooth-row), and relative width of skull (ZyWI) in six populations (Pop.) of common hamsters. Measurements are in millimetres,
indices are given as percentages. For denition of populations see text and Fig. 1. Sample sizes (n) are given separately for pelt trains/
cranial variables. Sexes are pooled.
Population n StreakI CuffI CbL ZyW Mxt ZyWI
1 Ukraine 27/10 10.8 ± 3.55 3.2 ± 0.29 47.6 ± 0.89 27.0 ± 0.65 7.97 ± 0.11 57.0 ± 5.1
2 S-cent. Russia 49/27 13.5 ± 3.84 4.6 ± 0.21 48.8 ± 0.55 28.0 ± 0.39 8.22 ± 0.07 57.3 ± 3.0
3 Ciscaucasia 20/13 13.6 ± 4.59 4.4 ± 0.38 46.9 ± 0.79 26.2 ± 0.52 8.28 ± 0.10 56.2 ± 4.2
4 Cis-Urals 52/17 11.8 ± 3.30 4.2 ± 0.22 49.3 ± 0.69 29.0 ± 0.49 8.31 ± 0.08 58.4 ± 3.8
5 Trans-Urals 47/10 11.8 ± 4.08 3.9 ± 0.23 50.1 ± 0.90 28.8 ± 0.69 8.20 ± 0.11 57.0 ± 5.4
6 Siberia 111/55 9.0 ± 5.82 4.3 ± 0.14 49.0 ± 0.38 28.3 ± 0.28 9.20 ± 0.05 57.5 ± 2.2
153
was more frequently absent (StreakI = 0) in Asia (15.8
%) than in Europe (0.7 %) and the difference was
highly signicant (p < 0.0001). There was signicant
heterogeneity in StreakI among the populations (F
= 8.622, df = 5, 298, p < 0.0001). The StreakI was
the shortest in Siberia and the longest in Cisaucasia
and in south-central Russia (Table 2). Forward
stepwise regression on climatic variables (CPCs) and
geographic coordinates yielded signicant results (F
= 7.266, df = 3, 291, p = 0.0001) but regression t
was very low (6 %). Beta and F-to-enter values were
signicant (at p < 0.05) for both climatic variables and
CPC2 had the highest explanatory power. Therefore,
the chin streak tended to be longer in regions of hot
warm season and low precipitation.
The Cuff was absent in 4.1 % of individuals but
we found no difference between the two main
regions. There was signicant heterogeneity among
populations (F = 4.375, df = 5, 299, p = 0.0008) with
Ukrainian hamsters having the shortest CuffI (Table
2). Forward stepwise regression on coordinates and
CPCs resulted in a signicant model (F = 11.760, df
= 4, 315, p < 0.00001). Of the three environmental
variables included in the regression model, Beta and
F-to-enter values were by far the highest for latitude.
Only a small fraction of variance (5 %) was explained
by latitude alone.
Cranial data
Factorial ANOVA (population and sex as factors)
retrieved no signicant variation in any of the three
linear parameters and in the quotient. The two factors
were not in interaction. Regression of variables
onto geographic coordinates and the two climatic
variables retrieved signicant associations only for
both measures of skull width, ZyW (F = 9.877, df = 1,
158, p = 0.002) and ZyWI (F = 7.242, df = 1, 159, p
= 0.008). In both models, the longitude was the only
variable with a reasonably high Beta and F-to-enter
values. The correlation between zygomatic width and
longitude was positive, i.e. hamsters tend towards
wider skulls in the east, the t however was very low
(5.5 % for ZyW and 4.2 % for ZyWI).
Discussion
Our results conrmed signicant regional variation
in colour types and colour traits among hamsters
occupying eastern Europe and western Asia. Colour
variants were signicantly more diverse and more
frequent in Europe. Similarly, two white fur traits
(the white chin streak and the chest spot) were more
frequently present in Europe. Furthermore, the
StreakI attained the lowest mean in Siberia, and the
CuffI showed signicant deviations only in European
populations. Differences between means were slight
however, the overlap in ranges was wide and spatial
trends were weak. Interpopulation differentiation in
the two indices is more the statistical phenomenon
than the evidence of the existence of discrete colour
types. Cranial measurements proved even more inert
than colour traits and only zygomatic width showed a
slight trend of west-to-east increase. There was nothing
in our results to evidence discrete morphotypes.
Obviously we found no evidence of geographically
contiguous clusters of populations which would be
homogeneous enough on one hand and distinct from
other similar clusters on the other to be formally
recognized as a distinct subspecies. Our results
therefore offered little hope for meeting the established
“75 % rule” threshold as a guideline for good practice
in delimiting subspecies (e.g. Amadon 1949). Instead,
we repeatedly came across slight differentiation with
no proof of discontinuity. Division of the common
hamster into subspecies therefore does not create
entities which would be “recognizably different”
(Corbet 1978), i.e. would allow for the allocation
of each specimen, or a majority of them, into the
actual subspecies. Since this criterion was not met in
our study we conclude that division of the common
hamster into a subspecies is not congruent with the
pattern in morphological variability (or lack of it)
and thus obscures reality. Our conclusion matches
that already expressed by Novikov (1935) and Popov
(1960) who believed that the number of subspecies in
the common hamster is grossly exaggerated.
Colour polymorphism is the most prominent feature of
individual and population variability in the common
hamster. The list of variants includes black (atypical
melanistic and melanistic), piebald, white, albino,
yellow (avistic), red, sand, and “iron grey” coloured
hamsters (Petzsch 1936, Kayser & Stubbe 2000).
Yellow, red, sand, and iron grey were not represented in
our material. The only variant we encountered in Siberia
(bicolour) has thus far not been detected in Europe.
Colour variants were frequently detected in very low
proportions, e.g. < 0.1 % in Germany and 0.3-1.0 %
in Austria (reviewed in Kayser & Stubbe 2000). We
tentatively estimated the overall proportion of colour
variants at 4.3 % what is remarkably close to 3.08 %
as the average percentage of “melanistic” hamsters in
Ukraine and European Russia estimated from nearly
two million skins (Gershenson 1946). Local proportions
of black hamsters, usually reported as melanistic, attain
values of up to 50 % in Thuringia (Zimmermann 1969)
154
and > 80 % in Ukraine and Bashkortostan (Berdyugin
& Bolshakov 1998). The last two regions also emerged
on our map (Fig. 1) as areas with a relatively abundant
presence of black hamsters. The phenomenon however
was inadequately documented in the museum material
available to us. For example, all black hamsters from
Bashkortostan were pelts while the museum skins (n =
41) were of a standard tricolour type.
Considering the overall low proportion of variants it
is not surprising that the main source of information
on colour polymorphism in different periods of the
20th century was the fur market which was supplied by
hundreds of thousands hamster pelts annually. Kayser
& Stubbe (2000) had at their disposal records of more
than 73 thousand hamsters trapped between 1915 and
1980 in the Harz Mts., Germany, and Gershenson
(1946) was dealing with summary statistics based
on 1.97 million hamster skins collected in Ukraine
and Russia between 1931 and 1939. Museum
collections, with up to a few hundred skins at the
best, are dwarfed when compared to samples which
were a by-product of commercial trapping. While we
accept the limitations of our material in studying the
phenomenon, we nevertheless stress the importance
of museum vouchers as reality checks. In the records
of hamster trappers the colour variants frequently
lack clear description (Kayser & Stubbe 2000)
what may oversimplify reality. Gershenson (1945)
regarded hamsters in eastern Europe as “dimorphic
with respect to an easily classiable trait” (i.e.
melanistic vs. tricolour). As concluded by Kayser
& Stubbe (2000) and shown also in our study, a
standard tricolour pattern may be connected to the
melanistic extreme through a gradation in darkening,
across a slightly darker, with remnants of the normal
colouration (dark stavropolicus in Fig. 2b) and a
much darkened “atypical melanistic” which still
retains a rusty wash to a various degree (Fig. 2d). The
category “melanistic” as used in Gershenson (1945,
1946) most probably contains a diversity of dark and
black variants which may not necessarily share the
same genetic background. Due to the fact that only a
few dozens of pelts from a huge fur market have been
saved as museum vouchers, an enormous wealth of
information has been irretrievably lost. This concern
does not hold only for black hamsters but may have
wider connotations. Popov (1960) wrote of three white
skins from Bashkortostan which were deposited in
ZIN, and were evidently the only ones ever recorded
in the region. We examined these vouchers and found
that one of them (ZIN 51959) is not a hamster, but a
white russet souslik Spermophilus major.
Skull dimensions were surprisingly stable throughout
the entire region especially when considering the wide
range of climatic diversity, with a range in annual
mean temperature of 12.8 °C (from –0.9 °C to 11.9 °C)
and the annual precipitation varying from a low 160
mm to a moderately high 875 mm. Also surprisingly,
we detected no secondary sexual dimorphism in
size, although this phenomenon is widespread in the
species, being reported from various populations
(Popov 1960, Vohralík 1975, Sludskiy et al. 1977,
Niethammer 1982). Cranial samples available to us
were small, which possibly posed undesirable bias on
statistical tests by creating a type II error. Similarly, as
previously stressed in the account on colour variants,
museum samples are hardly sufcient to allow testing
of variation in natural populations. The times when
collecting hamsters was easy are over, and the gaps
in museum collections will most likely never be
lled. Considering a general decay in natural history
collections in many European countries (Andreone
2015, Kryštufek et al. 2015a) it will already be an
achievement to save the existing museum vouchers
for future generations.
Our results, in concert with published information,
make it possible to propose a wider picture of
morphological variability across the entire range of
the common hamster. The most divergent are the
westernmost populations (to the west of the River
Rheine) which are characterized by smaller size
(Niethammer 1982), a high incidence of large chest
spot, a longer chin streak and a white cuff on the
forepaws (Schröder et al. 2013). Henceforth, this
morphotype is referred to as the Western. Its cranial
uniqueness was further conrmed in a multivariate
analysis of linear skull dimensions (Stefen 2013).
Hamsters from the area between central Europe and
the eastern margin of their range on the banks of the
River Yenisei are of fairly uniform size (cf. Table
2 and data in Niethammer 1982). The chest spot is
rarely present and is small or diffused and the cuff
and chin streak are shorter (Eastern morphotype).
Populations from the Upper Rheine in Germany
show intermediate characteristics (Schröder et al.
2013). Although the hamsters occupying vast areas
of central and eastern Europe and western Siberia
are fairly uniform, some regional variations are also
obvious. Asiatic populations were the least variable in
nearly all studied traits. Proportion of colour variants
seems to be higher in eastern Europe than in central
Europe (Kayser & Stubbe 2000). Furthermore, the
prevalence of the tricolour type is locally punctuated
by a high proportion of black hamsters, again coming
155
from central and eastern Europe (Gershenson
1945, Niethammer 1982). Part of this variation was
perhaps due to local environment. It was stressed
in the past (Gershenson 1945, 1946, Popov 1960,
Vorontsov 1982) and shown in our study, that
melanistic hamsters are associated with high (> 500
mm) annual precipitation. This can at least partly
explain their absence from Siberia, where the average
precipitation is < 300 mm annually (Gvozdetskiy &
Mikhaylov 1963). The reality however may be more
complex since the proportion of melanistic hamsters
(Berdyugin & Bolshakov 1998) and of other colour
variants (Kayser & Stubbe 2000) also correlates
with population densities. One of the possibilities
for the interplay between the population context and
deviations from the standard colour type may be
population stress (Potapov et al. 1998).
The overall pattern of morphological variability is
only partly concordant with the genetic architecture of
the common hamster (Banaszek et al. 2010), possibly
due to different rates of molecular and morphological
evolution (cf. Kryštufek et al. 2012, 2015b). Namely,
of the three evolutionary lineages in Banaszek et al.
(2010), the North lineage includes both morphotypes
and the transitional populations, while the remaining
lineages, the Pannonian and the East lineages, contain
only the Eastern morphotype. The most diverse is the
western segment of the species’ range (to the west of the
Carpathian Mts.) which contains two of the three genetic
lineages, and both main morphotypes. Populations
occurring to the east of the Carpathians are rather
uniform, containing a single phylogeographic lines and
only one morphotype. The morphological uniformity is
further exacerbated on the eastern side of the Urals.
Acknowledgements
For access to specimens we thank (abc) Nataliya Abramson
and Alexandra N. Davydova (ZIN), Rainer Hutterer (ZFMK),
Paula Jenkins and Roberto Portela Miguez (BMNH), and Frank
Zachos (NMW). Visit of B.K. to BMNH received support from the
SYNTHESYS Project http://www.synthesys.info/ which is financed
by the European Community Research Infrastructure Action under
the FP7 Integrating Activities Programme. Fig. 2b was used with
permission from the Natural History Museum, London. Rainer
Hutterer and Vladimír Vohralík provided valuable comments on
an earlier draft and Karolyn Close improved English and style.
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Supplementary online material
Supplementary information – list of specimens (URL: http://www.ivb.cz/folia_zoologica/supplemetarymaterials/krystufek_et_al._supplementary_
information.docx).