Energy storage in salamanders’ tails: the role of sex and ecology

Abstract

In vertebrates, the main tissue devoted to energy storage is the adipose tissue. In salamanders, energy reserves can also be stored in the adipose tissues of the tail. Therefore, we evaluated if energy storage in salamanders' tails is related to individual body condition, life cycle and environmental constraints. We calculated a scaled measure of tail width for 345 salamanders belonging to six Mediterranean taxa exhibiting wide phylogenetic, behavioural and ecological variation. We related this measure to the Scaled Mass Index (SMI), a body condition index which reliably predicts body fat. We found significant relationships between the SMI and scaled tail width in the terrestrial Spectacled salamander and Alpine salamanders, independently of sex. At the same time, we found that energy storage in the tail is maximum in Alpine Salamanders, which experience reduced activity periods and restricted access to resources. Conversely, we found a significant effect of sex in Imperial cave salamanders, where females store reserves in the tail to counterbalance resource investment in parental care, and in Corsican Brook Newts, where the reproductive function of males' tails may imply a greater tail width. Finally, in the biphasic Great Crested Newt, tail width was not related to SMI in both sexes.

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The Science of Nature (2021) 108:27
https://doi.org/10.1007/s00114-021-01741-1
SHORT COMMUNICATION
Energy storage insalamanders’ tails: therole ofsex andecology
GiacomoRosa1· AndreaCosta1 · JulienRenet2· AntonioRomano3,4· LucaRoner4· SebastianoSalvidio1
Received: 25 February 2021 / Revised: 7 June 2021 / Accepted: 9 June 2021
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021
Abstract
In vertebrates, the main tissue devoted to energy storage is the adipose tissue. In salamanders, energy reserves can also be
stored in the adipose tissues of the tail. Therefore, we evaluated if energy storage in salamanders’ tails is related to individual
body condition, life cycle and environmental constraints. We calculated a scaled measure of tail width for 345 salamanders
belonging to six Mediterranean taxa exhibiting wide phylogenetic, behavioural and ecological variation. We related this
measure to the Scaled Mass Index (SMI), a body condition index which reliably predicts body fat. We found significant
relationships between the SMI and scaled tail width in the terrestrial Spectacled salamander and Alpine salamanders,
independently of sex. At the same time, we found that energy storage in the tail is maximum in Alpine Salamanders, which
experience reduced activity periods and restricted access to resources. Conversely, we found a significant effect of sex in
Imperial cave salamanders, where females store reserves in the tail to counterbalance resource investment in parental care,
and in Corsican Brook Newts, where the reproductive function of males’ tails may imply a greater tail width. Finally, in the
biphasic Great Crested Newt, tail width was not related to SMI in both sexes.
Keywords Amphibians· Body condition index· Energy storage· Salamanders· Tail
Introduction
All animals need to store energy-rich compounds to survive
periods in which they will be unable to find, collect and
process trophic resources (McCue 2010). In fact, individuals
possessing large quantities of surplus energy reserves better
adapt to seasonal environmental changes, climatic variations
and, in general, increase reproductive success (Pond 2011).
In all vertebrates, from fishes to mammals, the adipose tissue
is the main tissue devoted to energy storage (Birsoy etal.
2011). This specialised tissue, composed of cells called
adipocytes, stores triacylglycerol, an energy-rich molecule
(Birsoy etal. 2011). During periods of food deprivation,
hydrolysis of triacylglycerol generates metabolic energy
which is exploited by other organs and used to maintain
homeostasis (Gregoire etal. 1998).
In most amphibians, the adipose tissue is accumulated in
the liver and in fat gonadal bodies (Zancanaro etal. 1996).
Moreover, cutaneous and subcutaneous adipose tissues have
been described in some anurans (Wygoda 1987). In salaman-
ders, the tail has been described as another organ involved in
the accumulation of adipose tissue (Maiorana 1977; Fraser
1980). Lipids stored in the tail could be used during hiberna-
tion, drought, reproduction or metamorphosis (Pond 2011).
Consequently, relative variation in tail width should reflect
changes in lipid and/or protein content (Fraser 1980; Bendik
and Gluesenkamp 2013). However, tail morphology may
vary strongly between species, depending on their ecological
traits (Gvozdik and Van Damme 2006). For instance, the tail
of aquatic salamanders is important for swimming and may
contain more muscular tissue in comparison to terrestrial
Communicated by: Oliver Hawlitschek .
Giacomo Rosa and Andrea Costa contributed equally to this work.
* Andrea Costa
andrea-costa-@hotmail.it
1 Department ofEarth, Environment andLife Sciences
(DISTAV), University ofGenova, Corso Europa 26,
16132Genova, Italy
2 Conservatoire D’espaces Naturels de Provence-Alpes-Côte
D’Azur, Pôle Biodiversité régionale, 18 avenue du Gand,
04200Sisteron, France
3 Institute ofBioeconomy – Biology, Agriculture andFood
Sciences Department (IBE), Italian National Research
Council (CNR), Via dei Taurini, 19, 00185Roma, Italy
4 MUSE-Museo Delle Scienze, Sezione Di Zoologia Dei
Vertebrati, Corso del Lavoro e della Scienza 3, 38122Trento,
Italy

The Science of Nature (2021) 108:27
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27 Page 2 of 6
species (Delvolvé etal. 1997). On the other hand, during ter-
restrial locomotion, a muscular and heavy tail may decrease
salamanders’ mobility (Gvozdik and Van Damme 2006).
Finally, tail size (i.e., length and width) may vary between
sexes, depending on their different reproductive strategies
or ecological requirements (Serra-Cobo etal. 2000; Bak-
kegard and Rhea 2012). On the basis that tail width should
reflect individual nutritional status and energy reserve, this
measure has been employed as an index of body condition
in salamanders (e.g., Nissen and Bendik 2020), although its
reliability has not been validated yet.
Here we investigated whether relative tail width is related
to body condition in salamanders and if it predicts energy
storage while assessing whether this relationship is affected
by sex or life cycle. We answered these questions by investi-
gating the relationship between a condition index, the Scaled
Mass Index (Peig and Green 2009), and a scaled measure of
tail width. Therefore, we studied six species of European
salamanders, spanning through a wide range of body sizes
(from the diminutive Spectacled Salamander, Salamandrina
perspicillata, to the medium-sized Alpine Salamander, Sal-
amandra atra), different life-cycles (terrestrial or biphasic
cycle) and reproductive strategies (i.e., mating behaviour,
presence or absence of parental care).
Materials andmethods
Study system
In our study, we included six taxa representative of the wide
range of phylogenesis, body size and ecological traits of Euro-
pean salamanders: the Imperial Cave Salamander (Speleo-
mantes imperialis (Stefani, 1969)), the Northern Spectacled
Salamander (Salamandrina perspicillata Savi, 1821), the
Alpine Salamander (Salamandra atra atra Laurenti, 1768),
the Golden Alpine Salamander (Salamandra atra aurorae
Trevisan, 1982), the Great Crested Newt (Triturus cristatus
Laurenti, 1768), and the Corsican Brook Newt (Euproctus
montanus Savi, 1838). Sample sizes, sampling details, infor-
mation on reproductive cycle, behaviour and tail shape are
given in Table1. Detailed information for each species, with
bibliographic references, are given in Online Resource 1.
Salamanders’ measurement
Only adult individuals with intact tails were measured, and
processing procedures were similar for all taxa. Pseudorepli-
cation was avoided by individual recognition based on photo
identification or by temporary removal. Captured individu-
als were weighed in the field with a digital scale (precision
0.01g). Digital images were imported in the software ImageJ
and the scale was set according to the reference ruler present
in each image. For each individual, we digitally measured the
snout-vent length (SVL) and the width of the tail (TW) imme-
diately after the cloaca region (Online Resource 2).
Data analysis
The Scaled Mass Index (SMI) is based on the relationship
between body mass and a linear predictor of body size,
accounting for allometric growth (Peig and Green 2009). In
the specific case of salamanders, MacCracken and Stebbings
(2012), by experimentally controlling animals’ diets, assessed
the reliability of the SMI as a measure of energy reserve and
predictor of fat, protein, or lean mass content.
Using individual measures of body mass and SVL, we cal-
culated SMI as follows:
where: Mi is the mass of the individual i, L0 is the mean
length value of the study population (mean SVL), Li is the
(1)
SMI
=Mi∗
[
L0
L
i]𝛽SMA
Table 1 Sampling, life-history, sample size, and tail shape information on six study taxa. FF and MM stand for females and males, respectively
Species Sampling information Life-history Samples FF/MM Tail shape
Speleomantes imperialis Villasalto (IT),
April 2017
Terrestrial; brooding females 16/13 rounded
Salamandrina perspicillata Vastogirardi (IT),
October 2012
Biphasic; terrestrial adults 80/37 rounded
Salamandra atra atra Tonadico (IT),
August 2018
Terrestrial 24/26 rounded
Salamandra atra aurorae LevicoTerme (IT),
August 2017–20
Terrestrial 42/31 rounded
Triturus cristatus Arles (FR),
March 2010
Biphasic; adults mainly aquatic 22/19 laterally compressed
Euproctus montanus Zonza (FR),
June 2017
Biphasic; amplexing adults 21/14 laterally compressed

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SVL of individual i, and βSMA is the slope of Standardized
Major Axis regression of log-transformed body mass on
body length. Since estimated βSMA values are species-spe-
cific, SMI values have been calculated separately for each
species (Peig and Green 2009). In order to relate SMI to TW,
we calculated a scaled measure of tail width (Scaled Tail
width Index; STwI), by substituting Mi with TWi in Eq.1.
Relationships between SMI and STwI have been inves-
tigated using linear regression for all species and sex sepa-
rately, assuming STwI as a predictor of SMI and consider-
ing that regression slopes significantly different from zero
indicate an effect of TW on SMI. When we found significant
slopes for both sexes within a given species, we used analy-
sis of covariance (ANCOVA) to test for differences in slopes
between sexes, using SMI as the response, and sex and STwI
as predictor variables. When slopes between sexes did not
differ within species, we used ANCOVA to test for differ-
ences in slopes between taxa. In the case of significant het-
eroscedasticity, we employed heteroscedasticity-corrected
covariance matrices. For statistical tests, significance level
was set at α = 0.05, but when the same dataset was used
for multiple pairwise comparisons, Bonferroni correction
was applied. All analyses were conducted within the R envi-
ronment (R Development Core Team 2018) with packages
“stats” (R Development Core Team 2018) and “car” (Fox
etal. 2012), while graphical visualisations have been pre-
pared with package “ggplot2” (Wickham 2011).
Results
From salamander sampling, we obtained 345 individuals
with intact tails (Table1). Taxon-specific descriptive statis-
tics are reported in Online Resource 3. The Shapiro–Wilk
test for normality was not significant for all variables tested.
Linear regression models showed that the relationship
between SMI and STwI was significant for both sexes in
three study taxa: S. perspicillata, S. atra atra and S.atra
aurorae (Table2). The slope of the regression model was
also significant for females in S. imperialis and for males in
E. montanus, while it was not significant for either sex in T.
cristatus (Table2). Furthermore, when the slope of the lin-
ear model was significantly different from zero, it assumed
positive values (Fig.1, Table2, Online Resource 4). The
Levene test was not significant for all species where both
sexes showed a significant slope (Table3). None of the three
tested taxa showed a significant difference in slope between
sexes (Fig.1; Table3). Results of the Levene test, performed
Table 2 Values of the scaling
exponent of the SMI (βSMA) for
each study taxon, parameters of
the linear regression of SMI on
STwI. * indicates a significant
slope at α = 0.05
Taxon
𝜷SMA
Linear regression parameters
Males Females
Speleomantes imperialis 2.52 Sample size 16 13
Intercept 1.89 -0.11
Slope (p-value) 0.66 (p = 0.133) 1.18 (p = 0.006)*
R-squared 0.09 0.46
Salamandrina perspicillata 3.79 Sample size 80 37
Intercept 0.73 0.63
Slope (p-value) 0.19 (p < 0.001)* 0.26 (p = 0.002)*
R-squared 0.19 0.21
Salamandra atra atra 2.57 Sample size 24 26
Intercept 3.95 3.18
Slope (p-value) 0.72 (p = 0.026)* 0.89 (p = 0.003)*
R-squared 0.17 0.28
Salamandra atra aurorae 2.55 Sample size 42 31
Intercept 3.37 5.05
Slope (p-value) 0.93 (p < 0.001)* 0.68 (p = 0.011)*
R-squared 0.34 0.17
Triturus cristatus 2.87 Sample size 22 19
Intercept 10.01 5.83
Slope (p-value) 0.14 (p = 0.70) 0.81 (p = 0.065)
R-squared 0.04 0.14
Euproctus montanus 3.08 Sample size 21 14
Intercept -0.90 1.11
Slope (p-value) 0.72 (p < 0.001)* 0.26 (p = 0.119)
R-squared 0.53 0.12

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between these taxa, are reported in Table3 and showed sig-
nificant heteroscedasticity between S. perspicillata and S. a.
atra, and between S. perspicillata and S. a. auroare, for both
SMI and STwI, while it was not significant for S. a. atra and
S. a. aurorae. The ANCOVA, after adjusting significance
values with Bonferroni correction (α = 0.016), highlighted a
significant difference in slope between S. perspicillata and S.
a. atra and between S. perspicillata and S. a. aurorae, while
no significant differences in slope were found between the
subspecies of S. atra (Table3; Online Resource 4).
Discussion
Our results reveal that, only in certain species, there was a
positive relationship between body condition and a scaled
measure of tail width, and this relationship was strongly
affected by both sex and life cycle. Based on our results, tail
width does not seem to be a reliable proxy of body condition
(e.g., Nissen and Bendik 2020).
Within the genus Speleomantes, females guard eggs and
hatchlings for long periods: in S. imperialis, post-hatch
parental care is reported for up to 52days (Lunghi etal.
2015). The observed difference between males and females
of S. imperialis in the present study is consistent with the
hypothesis that females store greater energy reserves in their
tail than males.
Also, E. montanus displayed a significant sexual differ-
ence in the relationship between body condition and scaled
tail width. The species of the genera Euproctus and Calotri-
ton display a unique mating behaviour among salamanders.
During mating, the male wraps his tail around the female’s
body, bites her tail with his jaws and uses his hind legs to
guide the spermatophores into the female’s cloaca (Brizzi
etal. 1995). Therefore, tail width is probably related to
muscular tissue in males, and originated by sexual selection
rather than adipose tissue accumulation driven by energy
storage.
For the three terrestrial salamanders, STwI was positively
related to SMI in both sexes. In these taxa, tails do not pos-
sess particular specialization: parental care is not present,
and mating does not imply the use of tail (Duellman and
Trueb 1994). In these species, variations in tail width could
be mainly linked to the amount of lipids stored.
Fig. 1 Scatterplots representing
the relationship between SMI
and STwI for six salamander
taxa divided by sex. Sexes are
coded by colors, as follows:
Red = females, blue = males

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Triturus cristatus was the only taxon for which we did
not find a relationship between STwI and SMI. In this spe-
cies, parental care is absent, and reproduction is driven by
visual and chemical stimuli (Malmgren and Enghag 2008).
Furthermore, this is the most aquatic among the studied taxa,
and its tail might contain more muscle than fat due to the
importance of the tail in aquatic locomotion for both sexes
(Online Resource 1).
Based on our findings, tail width in salamanders pro-
vides only partial information on physiological status as it
is subject to a wide range of of biological and ecological
processes, at intra and inter-specific levels. Tail width can be
related to the ecology of individuals and may be an indica-
tor of body condition for those species where the tail is not
involved in particular environmental or reproductive adapta-
tions. Therefore, we do not recommend employing the tail as
a proxy of body condition unless a validation with a quanti-
tative metric of lipid content has been previously conducted.
Supplementary Information The online version contains supplemen-
tary material available at https:// doi. org/ 10. 1007/ s00114- 021- 01741-1.
Acknowledgements Data collection of S. atra was supported by
Servizio Aree Protette e Sviluppo Sostenibile PAT (Convention PAT-
LIFE11/NAT/IT/000187 "TEN"–Trentino Ecological Network), by
MUSE and by Paneveggio–Pale di San Martino Natural Park. Paolo
Pedrini participated to fieldwork. We are grateful to Matthias Waltert
(EiC), to Oliver Hawlitschek (AE) and to three anonymous Reviewers
for their valuable comments on a previous version of this study.
Author contribution GR, AC, and SS conceived and designed the
study; all Authors collected the data; GR and AC analysed the data;
GR, AC and SS led the writing of the manuscript. All authors con-
tributed critically to the drafts and gave final approval for publication.
Data availability All datasets are available from the corresponding
author on reasonable request.
Code availability Not applicable.
Declarations
Ethics approval Permits for temporary capture were issued by: Ital-
ian Ministry of Environment (Prot. 10210/PNM of 21/05/2015) and
Sardinia Region (Det. 14951N 465 of 01/07/2015) for S. imperialis;
Italian Ministry of Environment (Prot. PNM-II-2012–0015691; PNM-
EU-2017–005370; PNM-EU-2017–005370) for S. perspicillata, S. atra
atra and S. a. aurorae, respectively; Prefecture of Haute Corse (2B–
2018–01–92–004) for E. montanus, and Prefect Bouches-du-Rhône
(2010 252–0001) for T. cristatus.
Competing interests The authors declare no competing interests.
Consent to participate Not applicable.
Table 3 Results of the Levene
test and ANCOVA performed
between sexes within the same
taxon and between taxa. *
indicates a significant p-value
at α = 0.05. + indicates a
significant p-value at α = 0.016,
after Bonferroni correction
Levels Levene test A NC OVA
Salamandrina perspicilillata SMI F1,115 = 0.008 Sex F1,113 = 15.84 p < 0.001*
p = 0.93 STwI F1,113 = 29.91 p < 0.001*
Sexes STwI F1,115 = 0.691 STwI*Sex F1,113 = 0.58 p = 0.44
p = 0.41
Salamandra atra atra SMI F1,48 = 3.495 Sex F1,46 = 2.00 p = 0.16
p = 0.07 STwI F1,46 = 17.81 p < 0.001*
Sexes STwI F1,48 = 3.402 STwI*Sex F1,46 = 0.16 p = 0.69
p = 0.07
Salamandra atra aurorae SMI F1,71 = 1.674 Sex F1,69 = 0.35 p = 0.55
p = 0.20 STwI F1,69 = 26.48 p < 0.001*
Sexes STwI F1,71 = 0.050 STwI*Sex F1,69 = 0.63 p = 0.43
p = 0.82
Salamandrina perspicilillata SMI F1,165 = 119.4 Taxon F1,163 = 155.9 p < 0.001+
p < 0.001* STwI F1,163 = 26.32 p < 0.001+
Salamandra atra atra STwI F1,165 = 22.15 STwI*Taxon F1,163 = 8.21 p = 0.004+
p < 0.001*
Salamandrina perspicilillata SMI F1,188 = 130.3 Taxon F1,186 = 192.1 p < 0.001+
p < 0.001* STwI F1,186 = 33.71 p < 0.001+
Salamandra atra aurorae STwI F1,188 = 51.56 STwI*Taxon F1,186 = 17.89 p < 0.001+
p < 0.001*
Salamandra atra atra SMI F1,121 = 1.283 Taxon F1,119 = 11.17 p < 0.001+
p = 0.26 STwI F1,119 = 42.87 p = 0.002+
Salamandra atra aurorae STwI F1,121 = 2.953 STwI*Taxon F1,119 = 0.02 p = 0.86
p = 0.09

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Consent for publication Not applicable.
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ELECTRONIC SUPPLEMENTARY MATERIAL FOR:
Energy storage in salamanders' tails: the role of sex and ecology
Journal: The Science of Nature
Giacomo Rosa1,+, Andrea Costa1,+,*, Julien Renet2, Antonio Romano3,4, Luca Roner4, Sebastiano
Salvidio1
1 University of Genova, Department of Earth, Environment and Life Sciences (DISTAV), Corso
Europa 26, I-16132 Genova, Italy
2 Conservatoire d’espaces naturels de Provence-Alpes-Côte d’Azur, Pôle Biodiversité régionale, 18
avenue du Gand, 04200 Sisteron, France
3 Italian National Research Council (CNR), Institute of Bioeconomy – Biology, Agriculture and
Food Sciences Department (IBE), Via dei Taurini, 19, 00185 Roma, Italy
4 MUSE - Museo delle Scienze, Sezione di Zoologia dei Vertebrati, Corso del Lavoro e della
Scienza 3, 38122 Trento, Italy
+ These authors contributed equally to the work.
*Correspondence. Andrea Costa, Email: andrea-costa-@hotmail.it
Online Resource 1. Detailed descriptions of adult size and morphology, life cycle, study sites,
sampling and relevant bibliographic references
Speleomantes imperialis is a fully terrestrial plethodontid salamander endemic to Sardinia
island (Italy). It is a mid-sized salamander (max 150 mm total length in females and 133 mm in
males), in which females exhibit post-hatching parental care, and inhabit both surface and
underground environments (Lanza et al. 2007; Sparreboom 2014). We sampled one underground
population of S. imperialis, capturing individuals by hand on the cave walls. Individuals with a snout
to vent length (SVL) larger than 55 mm were sexed as follows: when displaying mental glands, they
were determined as mature males, otherwise as females (Lanza et al. 2007). Individuals smaller than
55 mm were considered as subadults and not retained for the present study (Salvidio et al. 2017). We
avoided pseudoreplication by temporary removing processed individuals. Pregnant females were
excluded from the analyses.
Salamandrina perspicillata is a biphasic, diminutive salamander, endemic to central and
northern Italy (Romano et al. 2009a). It usually inhabits shady and damp forests but also occurs in
Mediterranean maquis. Adults are terrestrial and only females go to water for spawning during spring,
while the mating usually occurs in autumn during the terrestrial phase (Lanza 1983). We sampled one
population of S. perspicillata inhabiting a beech forest in central Italy. Individuals were captured by
hand when active on the forest floor and sexes were distinguished by observation of the cloaca walls
(Romano et al. 2009b), while juveniles [i.e. small sized specimens, measuring less than 7 cm (Lanza
et al. 2007), with no evident cloacal extroflection; Romano et al. 2009b; Costa et al. 2015] were
discarded for this study. We avoided pseudoreplication by temporary removing processed
individuals.
Salamandra atra atra is a mid-sized, fully terrestrial, and viviparous salamander (Lanza et al.
2007). It usually occurs in mixed coniferous and deciduous forests, alpine meadows and rocky tundra-
like habitats. This salamander is active in the warmest months, while in the rest of the year there is
no surface activity (Klewen 1988). We sampled one population of S. a. atra in a habitat composed
by open pastures and conifer forests, at 1800 m a.s.l. We adopted a temporary removal approach in

order to avoid pseudoreplication. Sexes were distinguished by analysis of external secondary sexual
characters: adult males have a prominent, swollen, cloaca, and are slenderer than females (Klewen
1988). Females that appeared pregnant, were excluded from the study. We considered as juveniles,
which we excluded in the present study, individuals without evident external secondary sexual
characters and a total length smaller than 90 mm (Klewen 1988).
Salamandra atra aurorae is one subspecies genetically well differentiated of the Alpine
salamander S. atra (Pederzoli et al. 2001). Like other Alpine Salamanders, it is a fully terrestrial,
viviparous taxon whose activity is mainly restricted to the warmest months of the year (Bonato and
Fracasso 2003). This salamander is endemic to northern Italy, occurring in a small portion of the
south-eastern Prealps, where it usually inhabits coniferous forests (Romano et al. 2018). We sampled
one population of S. a. aurorae inhabiting a conifer forest at about 1450 m a.s.l. Salamander sampling
occurred during or after rain, when salamanders were active on the forest floor, and capture was made
by hand (Romano et al. 2018). Salamander sex was assessed as in the nominal subspecies, and
pseudoreplication was avoided by individual identification, trough digital pictures of the dorsal
pattern (Bonato and Fracasso 2003). Pregnant females were excluded from the analyses.
Triturus cristatus is one of the two mainly aquatic species of our study system. It is a large-
bodied newt widely distributed in Northern, North-Western (including Great Britain), and Eastern
Europe (Sparreboom 2014; Speybroeck et al. 2016), also including isolated populations in Southern
France (Grossi 2015; Grillas et al. 2018). It usually inhabits large and deep waterbodies with rich
vegetation, where reproduction occurs usually during spring. We sampled an isolated population of
T. cristatus in a pond located in the Southern Rhône river valley, before the reproductive period.
Salamanders were captured by Ortmann funnel traps (Drechsler et al. 2010). Sexes were distinguished
on the basis of the secondary sexual characters (males have a jagged crest along the back that dips at
the rear of the abdomen during the breeding season; Raffaëlli 2007). Immatures were later identified
by the method of Hinneberg et al. (2020) and were not considered in the present study. Individuals
presenting predation marks, scars on the tails, or regenerating tails were excluded from the study.
Pseudoreplication was avoided by individual recognition, based on visual matching of ventral pattern
(Hagström 1973).
Euproctus montanus is the other mainly aquatic species considered in our study. It is a
medium-sized lungless newt, endemic to Corsica Island (France), which during the aquatic phase
usually inhabits streams located in forested areas, while during the terrestrial phase finds cover
underground (Delaugerre and Cheylan 1992; Lanza et al. 2007). Reproduction takes place in water
and is dependent on climate and altitude. It occurs in spring as well as early autumn at lower altitudes
while, conversely, during summer at higher ones (Duguet and Melki 2003). We sampled one
population of E. montanus on a stream located at an altitude of about 1100 m a.s.l., within a mixed
supra-Mediterranean vegetation, before the reproductive period. Salamanders were captured by
netting in stream pools. Sex was assessed by observation of the cloaca and by the presence of spurs
on the hind feet of males (Brizzi et al. 1995). Juveniles were determined following Brizzi et al. (1995)
and were not considered in the present study. Individuals presenting scars on the tails, predation
marks, or regenerating tails were also excluded from the study.
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Online Resource 2. Graphical representation of digital measurement
Fig. S1 Graphical representation of biometric measurements. SVL = Snout to Vent Length, TW =
Tail Width. Image partially adapted from Speybroeck et al. (2016).

Online Resource 3. Descriptive statistics of morphometric variables employed in the analyses
Fig. S2 Violin plots representing descriptive statistic of Snout Vent Length (SVL), weight and tail
width for six salamander taxa. Within each plot, from left to right: Euproctus montanus, Speleomantes
imperialis, Salamandrina perspicillata, Salamandra atra atra, Salamandra atra aurorae, Triturus
cristatus. White dots and vetical lines, within each violin plot, represent mean and SD, respectively.
Image partially adapted from Speybroeck et al. (2016).

Table S1. Descriptive statistic of Snout Vent Length (SVL; mm), tail width (mm) and weight (g) for
six salamander taxa.

Online Resource 4. Relationship between body condition and scaled tail width
Fig. S3 Scatterplot representing the relationship between Scaled Mass Index (SWI) and a scaled
measure of tail width (STwI) for six salamander taxa. Solid lines represent linear regression models
for each taxa, while filled area represent the 95% Confidence Interval of the regression line. Side
(upper and right) plots represent distribution of the two variables for each study taxon. Study taxa are
coded as follows: filled triangle = Euproctus montanus, empty square = Speleomantes imperialis,
cross = Salamandrina perspicillata, filled square = Salamandra atra atra, filled circle = Salamandra
atra aurorae, star = Triturus cristatus.