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101
Phyllomedusa - 23(2), December 2024
Received 13 May 2024
Accepted 05 August 2024
Distributed December 2024
The Black Aesculapian Snake Zamenis longissimus
(Serpentes: Colubridae): characters and possible
origin of the subgrisea morphotype
Alessandro Paterna
OPHIS Museo Paleontologico e Centro Erpetologico, 64100 Teramo, Italy. E-mail: alessandro.paterna@hotmail.com.
Phyllomedusa 23(2):101–109, 2024
© 2024 Universidade de São Paulo - ESALQ
ISSN 1519-1397 (print) / ISSN 2316-9079 (online)
doi: http://dx.doi.org/10.11606/issn.2316-9079.v23i2p101-109
Abstract
The Black Aesculapian Snake, Zamenis longissimus (Serpentes: Colubridae): characters
and possible origin of the subgrisea morphotype. New data acquired on the biology of
the Aesculapian snake Zamenis longissimus shed light on a widespread specic morphotype
in this species: the subgrisea form. Through captive breeding of groups of individuals for
several generations, it was established that this morphotype is caused by a recessive
mutation. The presence and combination of several traits indicate that this form is not from
a single genetic mutation, such as melanoticism or axanthism but from a morphotype more
complex than previously considered. The expression of this form in several specimens
from dierent European and Middle Eastern countries suggests that the origin of the
morphotype is common and ancient, not random. From genetic analyses, fossil records,
and the recent observations of wild individuals, it is probable that this form originated in
the Balkan peninsula, where it is more common, and spread to central Europe during the
species expansion and recolonization in the late Pleistocene after the last glaciation.
Zamenis longissimus could therefore be considered a polymorphic species.
Keywords: Balkans, Phenotype, Polymorphism, Recessive gene, Snakes.
A serpente-negra-de-esculápio, Zamenis longissimus (Serpentes: Colubridae): caracteres e
possível origem do morfotipo subgrisea. Novos dados adquiridos sobre a biologia de Zamenis
longissimus lançam luz sobre um morfotipo especíco amplamente difundido nessa espécie: a forma
subgrisea. Por meio da criação em cativeiro de grupos de indivíduos durante várias gerações, foi
estabelecido que esse morfotipo é causado por uma mutação recessiva. A presença e a combinação
de vários caracteres indicam que essa forma não provém de uma única mutação genética, como o
melanismo ou o axantismo, mas sim de um morfotipo mais complexo do que considerado
anteriormente. A expressão dessa forma em vários exemplares de diferentes países da Europa e do
Oriente Médio sugere que a origem do morfotipo é comum e antiga, não aleatória. A partir de análises
genéticas, registros fósseis e observações recentes de indivíduos selvagens, é provável que essa
forma tenha-se originado na península dos Balcãs, onde é mais comum, e se espalhado para a Europa
Central durante a expansão e a recolonização da espécie no nal do Pleistoceno, após a última
glaciação. Zamenis longissimus poderia, portanto, ser considerada uma espécie polimórca.
Palavras-chave: Balcãs, Fenótipo, Gene recessivo, Polimorsmo, Serpentes.
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Phyllomedusa - 23(2), December 2024
Paterna
Introduction
Melanism and melanoticism are conditions in
which an individual is characterized by an excess
of melanin compared to the normal phenotype of
intraspecic individuals (Majerus 1998). This
form represents the most common and highly
variable mutation among ophidians and can
express itself in multiple forms, aecting an
individual partially or totally or being congenital
or ontogenetic; multiple melanotic forms can be
present within the same species (Senczuk et al.
2021, Fănaru et al. 2022, Jablonski et al. 2023,
Storniolo et al. 2023, Meier et al. 2024). In
snakes, mutations such as melanoticism,
melanism, amelanism, leucism, xanthism/
axanthism, and erythrism/anerythrism can
randomly occur in any individual of any species
in any location (Schulz 1996, Bruni 2017, Meier
et al. 2021, Jablonski et al. 2022), leading to the
possibility that characters may become xed
within some populations (Tokunaga and Ono
1991, Andrén 2004). Studies on melanistic/
melanotic populations of snakes are abundant in
the literature, as are reports of a single or a few
individuals (Andrén and Nilson 1981, Kuriyama
et al. 2013, Bury et al. 2020).
In this study, the “melanotic” morphotype of
the Aesculapian snake, Zamenis longissimus
(Laurenti, 1768), was examined. Previously, such
dark/black individuals have been treated as
“simple” or sporadic chromatic mutations,
involving single individuals or small populations
described in single reports from several Central
European, Balkan, and Middle Eastern countries
(Fitzinger 1826, 1832, De Betta 1853, Massalongo
1859). In these works, following Schulz (1996)
and others (Edgar and Bird 2006, Kreiner 2007),
this form is identied by the name designated by
Wern er (1 89 7) a s “ va r. subgrisea.”
Data from the literature, together with
observations published on online platforms, were
used to dene a spatial map in which this
morphotype is found. Published genetic and
phylogenetic research about populations of
Zamenis longissimus was considered to
hypothesize the most probable origin of the
morphotype and how it spread to the locations
where it is currently found. This information was
combined with a seven-year project in which
individuals of the subgrisea phenotype were kept
and bred in a controlled environment, and several
captive-bred generations were produced to
determine the genetic nature of this morphotype.
Materials and Methods
Two pairs of the subgrisea form born in
captivity were donated to OPHIS, Museo
Paleontologico e Centro Erpetologico in 2017
and 2023. The most recently received pair
consisted of two adult individuals from
Montenegro, while the other consisted of two
young specimens born in 2017 from parents
originating from two Balkan locations (male
from Croatia and female from Montenegro). The
specimens remain at OPHIS, where they have
reproduced for two generations. The adult
specimens were raised in terraria with dimensions
of 100 × 60 × 50 cm (length, height, and
depth, respectively). Their ospring were housed
in terraria appropriate to their size and moved to
larger ones during growth.
After being collected and measured, the eggs
were placed in an incubator (38 × 58 × 36 cm)
that had the temperature regulated by an
electronic thermostat and digital probes. Each
clutch was positioned in a plastic box with a
transparent lid lled with moist vermiculite as a
medium.
Photographs were obtained with Sony α6000
and Nikon Coolpix P510 digital cameras.
Comparative or geographical data were obtained
from the literature and from the GPS data provided
in the reports on the iNaturalist.org platform.
Results
During the growth of the subgrisea specimens,
as in the classic phenotype, the juvenile dorsal
pattern fades, replaced by a uniform color
ranging from solid black to dark grey with very
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Phyllomedusa - 23(2), December 2024
The Black Aesculapian Snake Zamenis longissimus
small white ecks (Figure 1A, B). The scales of
both black and grey individuals are iridescent,
and blue pigmentation may be present in the
contact areas of black and white. In some
individuals, four longitudinal dorsal lines may be
visible. The ventral coloration is black, with
white spots at the lateral margins of the ventral
scales. These white spots form a longitudinal
white stripe along the lower portion of the anks.
The chin and labial scales are white, and the
subocular black spot disappears completely in
adults. Scattered yellow spots appear on the
ventral, subcaudal, and labial scales of adults
(Figure 1A, B).
Juveniles of the subgrisea form exhibit a
dorsal pattern of spots arranged in four
longitudinal rows that distinguish all young
Zamenis longissimus (Figure 1C, D). Unlike the
more widespread phenotype, however,
longitudinal rows are dark grey on a lighter grey
background. As in adults, the belly is completely
black with small white dots located on the lateral
edges of the ventral scales. The chin and neck
are white ventrally with small symmetrical black
spots. The labial scales are white, the fourth and
fth with a black tear-shaped spot below the eye.
A black line extends along the postocular and
temporal scales. The head shields are dark grey,
almost black. The iris is dark; in some individuals,
the pupil is dicult to distinguish.
Three clutches were produced by the female
born in 2017: in 2019, 2021, and 2022. These
clutches consisted of 6, 2 and 6 fertilized eggs
(plus an infertile egg), respectively (Figure 2A).
The elongate white eggs featured irregular
concretions on the shell (Figure 2B). Egg length
ranged from 50–59 mm and diameter from 20–
24 mm; eggs weighed 9–14 g.
Following an incubation of 51–56 days at
temperatures between 26 and 28°C, the clutches
hatched completely (Figure 2B). The hatchlings
measured 30–33 cm and weighed 12–14 g. In the
2019 clutch, half of the specimens exhibited the
subgrisea form and the other half the classic
phenotype (two males and one female for each
phenotype; Figure 2B). In the 2021 clutch, both
Figure 1. Specimens from the breeding program of
Zamenis longissimus: (A) adult male subgrisea
from Montenegro; (B) adult female subgrisea;
(C) hatchling of the subgrisea morphotype;
(D) hatchling of the dominant morphotype
from subgrisea parents.
A
B
C
D
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Phyllomedusa - 23(2), December 2024
hatchlings were of the subgrisea form. In 2022,
four individuals exhibited the subgrisea form,
and two were the classic phenotype. At hatching,
the individuals of the classic phenotype from the
mating of the subgrisea specimens exhibited a
darker coloration than the hatchlings of Z.
longissimus from other localities bred by the
author and those observed by the author in the
wild in Central Europe. The darker coloration
becomes paler as the snakes grow. These
ospring also exhibit a very bright orange iris
(Figure 1D) that contrasts with the dark ground
color.
Some chromatic “anomalies” occurred
among the captive-bred specimens. One of the
snakes born in 2023 (second generation bred in
captivity) from heterozygous specimens (rst
generation in captivity) exhibits typical dorsal
Figure 2. Specimens from the breeding program of Zamenis longissimus: (A) adult female subgrisea with eggs; (B)
hatchlings from both morphotypes pipping the eggs; (C) juvenile female of the dominant morphotype
showing black ventral coloration; (D) juvenile male showing characters of both dominant and subgrisea
morphotypes.
coloration but is black ventrally (Figure 2C). A
specimen born in 2022 from the original
subgrisea pair exhibits coloration intermediate
between the two morphotypes: hypoxanthistic
with darker head shields and a greysh/bluish
background dorsal coloration. The black pattern
of this individual, if exposed to light, produces
the same iridescence typical of the dorsal scales
of subgrisea individuals (Figure 2D), possibly
caused by a variation of concentration of
iridophores and xanthophores compared to the
classic phenotype.
Discussion
For many years, several authors have reported
their observations of dark or “melanistic”
individuals of Zamenis longissimus, naming this
Paterna
AB
CD
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Phyllomedusa - 23(2), December 2024
variety/form nigra, or nigrescens (Fitzinger
1826, 1832, De Betta 1853, Massalongo 1859,
Boulenger 1913). The rst detailed information
for identifying the morphotype, the object of this
study, with those described in past literature was
by Werner (1897). This author provided precise
references to some characters, such as the dark
belly and the longitudinal white line generated
by the succession of spots located on the external
portion of each ventral scale. This particular
character was also conrmed by Angel (1946)
and Cattaneo (1975), who even specied that
this line terminates at the cloaca and is not
present on the subcaudal scales.
The subgrisea form has been documented in
France, Italy, Austria, Hungary, Croatia,
Montenegro, Greece, Romania, Bulgaria, and the
Caucasus (Werner 1897, Cattaneo 1975, Kreiner
2007, Schulz 1996, 2013). Most reports consist
of observations of single individuals, although
cases in which this form appears widespread are
known (Werner 1897, Cattaneo 2017). This latter
situation appears to be more frequent in Balkan
localities, where individuals of the classic and
subgrisea phenotypes share the same habitats.
Photos portraying these subjects appear in recent
texts (Schulz 1996, 2013, Kreiner 2007), where
details and localities are reported. Photographs
of the subgrisea morphotype of Z. longissimus
are on online platforms such as iNaturalist, with
specic localities of the observations. Both
literature and online records point out a high
concentration of subgrisea sightings in the
Balkan peninsula, and the online data conrm
the distribution area in literature records (Figure
3). Most of the specimens have been documented
in Greece, Bulgaria, Romania, Serbia, and
Croatia, with records also in Hungary and
Slovakia. The easternmost records reconrm the
presence of such morph in Russia and Turkey,
and the westernmost in Italy, France, and Spain
(Figure 3).
Figure 3. Distribution and observations of individuals of the subgrisea form. The yellow area indicates the distribution
of Zamenis longissimus. Diagonal red lines indicate the predicted area of occurrence of the subgrisea form,
based on information provided in the literature (Werner 1897, Cattaneo 1975, Kreiner 2007, Schulz 1996,
2013). Black dots correspond to recent observations of individuals of the subgrisea form from specific
localities (Cattaneo 1975, Kreiner 2007, Schulz 1996, 2013, Zadravec and Lauš 2011) and from the
iNaturalist platform (to April 2024).
The Black Aesculapian Snake Zamenis longissimus
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Phyllomedusa - 23(2), December 2024
In the literature, this morphotype has often
been treated as melanic or axanthic (Zadravec
and Lauš 2011, Cattaneo 2015, 2017). The
results obtained by reproduction in captivity
highlight the presence of several traits for which
this form cannot be considered a single chromatic
mutation. A character uniformly present in the
subgrisea specimens is the black belly. This
character is not found in the classic phenotype,
in which the chin, belly, and tail are all colored
with the same cream/yellowish shade. Pure
melanic individuals are completely black,
lacking even the small white spots between the
dorsal scales, and any axanthistic specimen
would have a white or light-grey venter, as in
subgrisea juveniles, in which labials and the
most anterior dorsal scales on the neck are white.
Dark grey specimens with uniform white venters
have been documented and are present on the
iNaturalist platform. The same concept can be
veried in the known axanthic/anerythristic
forms of other colubroids (Fankhauser and
Cumming 2008, Borteiro et al. 2021) and in the
closely related species Zamenis lineatus (Russo
et al. 2020).
A character not described in the literature is
the presence of yellow pigment, which appears
in some scales of subgrisea subjects. This
pigmentation may aect any scale on the body,
usually covering part of the scale. The yellow
coloration is more evident in larger scales, such
as the head shields, ventrals, and subcaudals but
is also found on the dorsals. Yellowing scales in
adults also occur in other species, such as the
sympatric Elaphe quatuorlineata Lacépède,
1789 (pers. obs.). The presence of yellow
pigmentation contradicts the hypothesis of
axanthism and melanism because xanthophores
are absent or rare in purely melanic colubrids
(Kuriyama et al. 2013, 2016). The absence of
iridophores was also reported in melanic
individuals of the formerly congeneric Elaphe
quadrivirgata (Boie, 1826) (Kuriyama 2013).
The white line on the external margins of the
ventral scales is present in specimens of the
classic phenotype. In the typically colored
individuals, it is present although barely visible
against the light venter.
The data obtained from breeding show that
the genetics of this morphotype are recessive.
The results shed light on the genetics of the
original pair. One of the two subgrisea parents
that generated the individuals born in 2017 was
heterozygous because among the ospring of the
second generation (obtained from the mating of
the 2017 subgrisea specimens) some of the
hatchlings exhibit the classic/dominant
phenotype. Furthermore, in the third generation
produced by individuals of the classic phenotype,
all of the hatchlings exhibited the same coloration
as the parents. Conrmation of the recessive
nature of this morphotype is noted by Cattaneo
(1975), where a pregnant subgrisea female,
captured near Rome in a limited and mixed
subgrisea colony (possibly now extinct), laid
eggs producing ospring of both forms.
Anomalies in the livery appeared in two
hatchlings of the classic phenotype (Figure 2 C,
D). These anomalies involved typical
characteristics of the subgrisea form,
demonstrating that some characters of this
morphotype may appear individually in
heterozygous specimens. This may be a case of
incomplete dominance of the alleles but would
need to be further investigated in future
generations.
Conclusion
The results obtained from breeding suggest
that the subgrisea form is a recessive mutation.
Within the groups raised in a controlled
environment, specimens manifesting partial
traits of such morphotypes were born. An
individual born in the third generation, obtained
from the mating of recessive heterozygous
specimens exhibiting the dominant classic
coloration, featured the black belly. This trait is
characteristic of the subgrisea form, which does
not exist in the classic phenotype, as darker
iridescent dorsal tones manifested in a second
individual. This would likely mean that this
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Phyllomedusa - 23(2), December 2024
morphotype expresses itself in a combination of
multiple traits and would be consequently not
linked to a single gene, representing a more
complex form than a single chromatic mutation.
The fact that such combinate traits can be
found in the same form in dierent sites greatly
distant from each other suggests that the observed
specimens in the wild may not be the result of
individual/occasional mutations, but instead
these specimens have an ancient common origin
that continues to be actively transmitted by
recessive homozygous and heterozygous
individuals within populations in which the classic
phenotype appears to be the dominant one.
Recent genetic analyses and fossil records
could help determine the origins of this form. It
is supposed that in the last glacial period, the
northern and central European populations of Z.
longissimus became extinct, and these areas
were subsequently repopulated in the Holocene,
mainly by populations surviving in Balkan
refuges (Musilová et al. 2010, Allentoft et al.
2018). Most of the observations of individuals or
small populations of the subgrisea morphotype
come from the Balkans. It is conceivable that
this form was already present in the Pleistocene
of southeastern Europe, and that it has survived
to this day in certain central European populations
that were recolonized by individuals with the
genetics of the eastern clade. Further studies
focused on dermal chromatophores could
indicate where this form would have been
advantaged and more functional during the
glacial period (King 1988, Forsman 1995, Trullas
et al. 2007, Geen and Johnston 2014, Monahan
et al. 2022). The appearance of the subgrisea
form could even be backdated because records
of this morph come from the Caucasus and
Greece (Schulz 1996, 2013, iNaturalist data), of
which populations present profound genetic
dierences from the European and Transcaucasian
ones (Musilová et al. 2007, 2010), suggesting
that these southern-oriental groups remained
isolated even longer and did not contribute to the
colonizing expansion of Central Europe
following the last glacial phase.
The subgrisea individuals and populations
have been reported from coastal areas in
Montenegro, Croatia, Italy, and Russia to
mainland forests of the central and eastern
European countries (Werner 1897, Cattaneo
1975, Kreiner 2007, Schulz 1996, 2013,
Zadravec and Lauš 2011, iNaturalist data). Such
dierences both in altitudes and biotopes suggest
that the presence of this form may not depend
exclusively on environmental factors. The
occurrence of the subgrisea form could not be
selected by a switch of an environmental nature
but would mainly depend in primis on the
genetic pool of the micropopulation in question.
Considering the analyzed evidence, the
Aesculapian snake could be considered a
polymorphic species that expresses (at least) two
forms: the dominant classic one and the
recessive subgrisea, which occurs in several
countries within the entire distribution of this
colubrid.
Acknowledgments
I thank Rainer Fesser for donating the
specimens of Zamenis longissimus of the
phenotype described here to OPHIS, and all the
iNaturalist users who shared their observations
about Z. longissmus. I thank Ross D. MacCulloch,
Jaime Bertoluci, and anonymous reviewers for
revising and improving this manuscript.
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Editor: Ross D. MacCulloch
The Black Aesculapian Snake Zamenis longissimus
