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Folia Biologica (Kraków), vol. 71 (2023), No 1
https://doi.org/10.3409/fb_71-1.06
e-ISSN 1734-9168
http://www.isez.pan.krakow.pl/en/folia-biologica.html
Is the blue-spotted phenotype more widespread in the eastern slow worm
Anguis colchica (Nordmann, 1840) than the western slow worm Anguis fragilis
Linnaeus, 1758 and does it correlate with the male body size?
A case study from Central Europe
, Aleksandra , Grzegorz , Katarzyna ,
, and Bartosz
Accepted March 02, 2023 Published online March 30, 2023 Issue online March 30, 2023
B S., K A., S G., K K., Z B., N B., B B. 2023. Is the blue-
spotted phenotype more widespread in the eastern slow worm Anguis colchica (Nordmann, 1840) than the
western slow worm Anguis fragilis Linnaeus 1758 and does it correlate with the male body size? A case
study from Central Europe. Folia Biologica (Kraków) 71: 45-51.
The blue-spotted phenotype in a slow worm can be considered as an alternative colour morph or a second-
ary sexual characteristic. This phenotype is known to entail an elevated predation risk; thus, its continuous
we show that blue-spotted males are characterised by a greater snout-vent length (SVL) than typical speci-
mens. Importantly, the SVL of blue-spotted males reaches the magnitude of the average female size. This
indicates that the presence of blue spots may involve a correlated positive effect on growth and body size.
The greater body size of the blue-spotted males could enhance their survival and mating success, and thus
facilitate the continued presence of a high fraction of this morph within the population. In addition, we
found that the blue-spotted phenotype is more common in the eastern than the western slow worm, and
the eastern Anguis lineage.
Key words: colour polymorphism, condition, divergence, sexual dimorphism.
-
, Aleksandra K
Aleksandra K-
*
The maintenance of co-occurring discontinuous
colour phenotypes results from an interplay of vari-
ous evolutionary processes (Forsman et al. 2008).
In general, the maintenance of such a polymorphic
-
Andren &
Nilson 1981). In reptiles, the costs of an alternative
colour phenotypes are commonly discussed in terms
of alterations in the protective properties of the co-
louration (Madsen & Stille 1988; Wüster et al. 2004;
Farallo & Forstner 2012). These negative conse-
colour phenotype, which can be related to improved
thermoregulation (melanism; Forsman 1995) and/
or sexual signalling (Ballinger & McKinney 1967;
Martin & Forsman 1999; Bastiaans et al. 2014).
Less commonly, the maintenance of a polymorphic
colouration may be driven by relaxed, instead of in-
creased, predation (Losey et al. 1997; Lancaster et al.
2014); or by non-selective factors, such as genetic
© Institute of Systematics and Evolution of Animals, PAS, Kraków, 2023
Open Access article distributed under the terms of the Creative Commons Attribution License (CC-BY)
http://creativecommons.org/licences/by/4.0
OPEN ACCESS
Short communication
pression of sexual characteristics in males is tightly
coupled to the testosterone level (e.g. Garstka et al.
1991; Sinervo et al. 2000; Ducrest et al. 2008; Sacchi
et al. 2017), while the testosterone level also impacts
the animal’s growth. In some species it may inhibit
growth; whereas in other, even closely-related spe-
cies, it enhances growth and can lead to a greater
achievable body size (Cox & John-Alder 2005).
to be characterised by a larger size compared to typi-
cal non-spotted males. Such a positive effect of the
blue-spotted morph on the male size could represent
a potential mechanism that maintains this colour
-
cial effects of size on male survival (Civantos et al.
1999), combat success and/or female choice (Capula
et al. 1998).
In this study, we investigated whether this col-
our phenotype correlates with the male body size
in a free-living slow worms. As outlined above,
a greater body size can be predicted for blue-spot-
presence of blue spots could be linked to growth and
eventual size through the positive impact of a high
testosterone level; and alternatively, the blue-spotted
pattern could be restricted to older, and therefore
larger, individuals. These two scenarios may not be
fully distinguishable as they lead to a similar pre-
diction, but two additional observations can hint
at which effect contributes to the male size. If the
blue-spotted phenotype is associated with growth,
then it should result in a body size that exceeds the
size achievable by a typical male. Given that the
biased sexual size dimorphism (SSD), such an effect
could be expected to reduce or even entirely mask
the SSD. Secondly, if the presence of a blue-spotted
pattern is solely age-dependent, then it might not be
observable in younger (smaller) individuals. As an
outcome, the range of body size variation in typical
and blue-spotted males would overlap only partially.
To gain an insight into whether the phenotype-size
relationship and the occurrence of blue-spotted in-
two slow worm populations, – one population of
and one of (Nordmann 1840)
– and scanned multiple populations of both species
for the presence of the blue-spotted phenotype.
We collected data on 13 populations of
and 18 populations of (Fig. 2, Table 1).
Two of the populations, from the San
River Valley and
densely sampled (n=104 and n=115, respectively);
whereas the samples from other populations were
Lawson
& King1996
colour polymorphism is highly context dependent,
and each example of such a polymorphism may pro-
vide a novel insight into the evolutionary processes
shaping such colour variations.
A commonly observed example of polymorphic
colouration occurs in European slow worms (genus
Anguis) – a phenotype with blue spots on the dor-
sal and lateral side of the body is widespread within
the Anguis fragilis Linnaeus, 1758 complex (Völkl
& Alfermann 2007; Terhivuo 1990; Figure 1). How-
spotted morph are poorly understood. As has been
shown experimentally, blue-spotted slow worms
are more visible to avian predators, which elevates
the predation costs (Capula et al. 1997). In females,
these costs may be balanced by positive association
between the presence of blue spots and the body size
(Sos 2011), which correlates with both improved sur-
vival (Civantos et al. 1999) and fecundity (Ferreiro
& Galán 2004). On the other hand, a greater size of
blue-spotted females can merely represent a side-
effect of the age-related expression of the blue-spot-
ted pattern, with no additive effects on growth (Sos
2011
males are unknown, but they are conceivable given
the more common occurrence of the blue-spotted
phenotype in this sex (Capula et al. 1997; Sos 2011).
morph might suggest that this colouration represents
a secondary sexual characteristic of males, which
is additionally indicated by the highest intensity of
the blue-spot expression during the mating season
(Capula 1997; Sacchi et al. 2017). The ex-
46 S. B et al.
Fig. 1. Unspotted (top) and blue-spotted (bottom) phenotypes of
anguid lizards. Photographs by Aleksandra Kolanek.
Anguis fragilis:
Prague population: NMP6V 32388, 35089/3,
74407, 74543, 74990, 75517;
Šumava population: NMP6V 31747, 32640,
34275, 35100.
populations, the slow worms, except newborns and
yearlings, were collected throughout the active sea-
son from spring to autumn. For each specimen, the
snout-vent length (SVL), sex, tail condition (intact
or broken) and colour phenotype (blue-spotted or
typical) were assessed. Because the brightness of
the blue spots can depend on the shedding cycle and
season, we encoded this variable as a categorical one
[presence/absence of spots] instead of a continuous
one. Body mass was excluded from the dataset, be-
cause it can vary considerably, e.g. in relation to the
absorptive state, and therefore it cannot be reliably
For the additional sites, the number of sampled
specimens per population was lower than the num-
smaller (from 3 to 16 specimens; see Table 1). Most
of the data for the San River Valley population was
extracted from a published source ( )
and supplemented by our original measurements
from the same locality collected in the years 2008-
2020, while morphometric data on from
2018. Data on 12 additional populations of
and 17 populations of was gathered most-
ly in 2014-2017 during earlier studies (Bury et al.
2020), as well as from museum collections (Fig. 2,
Table 1). The museum collections used in the study
are listed below.
Anguis colchica:
San River Valley population: Museum of Natural
-
tilia-0247 (5 specimens);
Štramberk population: National Museum in Prague
(NMP6V) 7415-1-3, 70591, 72822, 74103-1,2,
74119-1,2, 74121-1,2, 74132, 74132-1,2, 74153.
The blue-spotted phenotype in slow worms 47
Fig. 2. Map of the localities of the populations sampled in this study. Anguis colchica
Anguis fragilis
Data on the SVL was analysed using the General
Mixed Model that compared three groups: typical
males (N=29), blue-spotted males (N=27) and typi-
cal females (N=48). Only one blue-spotted female
was found in the analysed population of ,
which precluded it from a formal analysis and it was
-
urements of originated from two sourc-
comparable among both species (mean: 8.42 for
and 5.82 for , t=1.87, p=0.07).
We did not include these specimens in the morpho-
metric analysis due to their low number and a po-
tentially high interpopulation variability. Moreover,
morphometric measurements were not gathered for
all of the specimens from these populations.
48 S. B et al.
Table 1
List of the sampled populations of the eastern slow worm (Anguis colchica) and the western slow
worm (Anguis fragilis). N – number of specimens from the sampled population. ‘Blue-spotted’
refers to the presence (+) or absence (–) of the blue-spotted phenotype in the sample; ‘Site ID’ is
the number of the population in Figure 2.
Population N Geographic coordinates Blue-spotted Site ID
Latitude (N) Longitude (E)
Anguis colchica
4 + 1
13 + 2
Bóbrka 6 + 3
Myczkowce 12 + 4
Ustrzyki Górne 5 + 5
Czudec 15 + 6
Štramberk 15 +10
Lutcza 8 +17
6 +20
Baligród 3 +24
4 –25
10 +29
San River Valley 104 +30
Anguis fragilis
5 + 7
Šumava 4 – 8
Sulistrowiczki 6 + 9
Pszczew 6 –11
Prague 6 –12
3 –13
Piotrków Trybunalski 3 –14
7 +15
Milicz 6 –16
Lubliniec 5 –18
Ligota 5 –19
3 –21
Byków 4 +22
Bartniki 5 +23
9 +26
16 –27
6 –28
115 +31
spotted phenotype in the vs
-
type reached 26% in (27 blue-spotted
per 104 individuals), while it only reached less than
1% in (1 blue-spotted per 115 individuals)
(Chi2=30.84, df=1, p<0.001). We further observed
that, at the multi-population level, the blue-spotted
phenotype occurs more commonly in
(12 per 13 populations) than in (6 per 18
populations) (Chi2=10.78; df=1, p=0.001). Finally,
(Chi2=0.22; df=1, p=0.643), but the whole-popula-
than in (Chi2=8.54; df=1, p=0.004).
-
tween the blue-spotted phenotype in eastern slow
worms and the male body size – as expected, the blue-
spotted males appeared on average to be larger than
typical males. The data we were able to obtain did
not allow us to exclude or corroborate the contribu-
tion of the ontogenetic colour change to the observed
pattern, but it is probable that at individual’s age at
least partially explains the larger size of blue-spotted
males. However, in our study the ranges of body size
variation in both of the phenotypes in males largely
overlapped, meaning that both fully grown and old-
er individuals are present among the males without
spots. Furthermore, blue-spotted males appeared to
be not only larger than typical males, but also to ex-
ceed the size of typical males to a level comparable
to the female size (Figure 3). It is therefore conceiv-
able that additional non-age-related factors contrib-
ute to the greater SVL of the blue-spotted males. The
blue colouration in lizards often results from a high
concentration of steroid hormones (Garstka et al.
1991; Ducrest et al. 2008), including testosterone in
-
tosterone have even been shown to enhance the ex-
pression of the bluish colouration, while at the same
time, the testosterone may accelerate growth (Uller
et al. 2007; Cox et al. 2008). To fully resolve what
mechanisms underlie the observed association be-
tween colour phenotype and male body size, further
studies that are designed to assess the growth rates,
individual’s age and testosterone levels in different
colour morphs are necessary.
in can be maintained due to the positive
body size and colouration in male mating success.
es ( and our survey), we included the
source of the data as a random factor in the model,
analysed the morphometric data only for the -
chica population, because the number of blue-spot-
ted individuals in appeared to be too low
for a statistical comparison (see below). The normal-
ity of the SVL data distribution was assessed prior to
the analysis and no data transformation turned out
to be necessary. The occurrence of the blue-spotted
phenotype in both species (all populations) was ana-
lysed by comparing the number of populations for
which the blue-spotted phenotype was or was not re-
corded with a 4x4 Chi2 test. In addition, we analysed
-
the blues-spotted vs typical males of as
between and with a 4x4 Chi2
test. All analyses were conducted using the Statistica
software (ver. 13.3, StatSoft Poland).
among the tested groups (females, typical males and
blue-spotted males) (F2,100=9.33; p=0.002). A post-
-
cantly smaller than the females (p<0.001) and blue-
spotted males (p=0.015), but there were no detect-
able differences between the blue-spotted males and
the females (p=0.613). Furthermore, the range of the
body size variation overlapped largely between the
blue-spotted and typical males (Figure 3). Although it
was not possible to test the effects of the colour phe-
notype on the SVL in due to an extremely
low number of blue-spotted individuals (N=1), we
The blue-spotted phenotype in slow worms 49
Fig. 3. Body size of normally-coloured males, blue-spotted males
and typical females of Anguis colchica. Lines with an asterisk
-
– mean.
B.Z., B.N., B.B.; Data analysis and interpretation:
S.B., B.B.; Writing the article: S.B., B.B.; Critical
revision of the article: S.B., A,K., G.S., K.K., B.Z.,
B.N., B.B.; Final approval of article: S.B., A,K.,
G.S., K.K., B.Z., B.N., B.B.
Conict of Interest
Acknowledgements
We thank four anonymous reviewers for their val-
uable comments on an earlier version of the manu-
Prague) for permission to study specimens under his
care.
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