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CC BY-NC-ND (4.0) https://doi.org/10.22201/ib.20078706e.2023.94.4969
Revista Mexicana de Biodiversidad
Revista Mexicana de Biodiversidad 94 (2023): e944969
Ecology
Morphological differentiation of Ambystoma dumerilii
populations in captivity and wildlife conditions
Diferenciación morfológica en poblaciones de Ambystoma dumerilii
en condiciones de cautiverio y vida libre
Berenice Ramírez-López a, Ireri Suazo-Ortuño a,
Luis H. Escalera-Vázquez b, Omar Domínguez-Domínguez b,
Yurixhi Maldonado-López c, *
a Universidad Michoacana de San Nicolás de Hidalgo, Instituto de Investigaciones sobre los Recursos Naturales, Avenida Juanito Itzícuaro s/n,
Nueva Esperanza, 58330 Morelia, Michoacán, Mexico
b Universidad Michoacana de San Nicolás de Hidalgo, Facultad de Biología, Calle Gral. Francisco J. Múgica s/n A-1, Felícitas del Río, 58030
Morelia, Michoacán, Mexico
c Universidad Michoacana de San Nicolás de Hidalgo, Cátedra Conacyt-Instituto de Investigaciones sobre los Recursos Naturales, Avenida Juanito
Itzícuaro s/n, Nueva Esperanza, 58330 Morelia, Michoacán, Mexico
*Corresponding author: yurixhimaldonado@gmail.com (Y. Maldonado-López)
Received: 2 February 2022; accepted: 9 May 2023
Abstract
Ambystoma dumerilii, known as “achoque”, is a microendemic salamander from Lake Pátzcuaro, considered as a
critically endangered species according to the IUCN (2020). The main threats are high levels of water contamination,
high levels of eutrophication in addition to the fact that invasive species can be found within the “achoque” habitat. For
these reasons, an important conservation effort has been the maintenance of “achoque” in captivity. However, captivity
is known to be a stressor derived from non-optimal conditions that can have important physiological consequences
that are reflected in body conditions. Therefore, our objective was to evaluate the condition of A. dumerilii individuals
through a morphological analysis using different parameters such as morphological character sizes, geometric
morphometrics, fluctuating asymmetry and allometry, in individuals from Lake Pátzcuaro and captivity. We found that
almost all the traits have a negative allometric relationship with the body size in individuals from both conditions. Our
results showed that individuals from the lake presented greater sizes, slimmer bodies and higher levels of fluctuating
asymmetry than captive individuals, all results are consistent in the context of performance with greater potential
adaptations to increase swimming performance than individuals from captivity.
Keywords: Ambystoma; Achoque; Allometric patterns; Fluctuating asymmetry; Geometric morphometrics; Habitat
perturbation
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Introduction
The family Ambystomatidae is composed of the genus
Ambystoma, with 35 species distributed from southern
Canada and Alaska to the southern limit of the Mexican
highlands (Casas-Andreu et al., 2004). In Mexico, there are
17 species of which 15 are classified in some risk category
according to the NOM-059-Semarnat-2010 (Ortega,
1999). Specifically, A. dumerilii, known as “achoque”,
is a micro-endemic salamander from Lake Pátzcuaro,
whose population is close to extinction (Zambrano et al.,
2011), and even considered a critically endangered
species according to the IUCN (2020), as well as being
under special protection by Semarnat (2010). Like other
members of the Ambystomatidae family, this species is
very sensitive to anthropogenic activities (Soto-Rojas et al.,
2017). For example, in Ambystoma ordinarium an increase
in the frequency of morphological abnormalities related
to habitat degradation has been described (Soto-Rojas
et al., 2017). In the same species, a high parasitic infection
was found associated with disturbed streams (Ramírez-
Hernández et al., 2019). The conditions of Lake Pátzcuaro
have deteriorated due to the high disturbance derived
from anthropogenic factors such as changes in land use,
contamination by wastewater, herbicides and pesticides
(Zambrano et al., 2011). It is in a eutrophic state due to
high levels of nitrogen and phosphorous, it has decreased
in depth by 6 m since 1939 and has sedimentation rates
of around 100,000 m3 each year (Ramírez-Herrejón et al.,
2014; Tomasini-Ortiz et al., 2016). According to Aguilar-
Miguel (2005) Ambystoma dumerilii has a restricted area
of occupancy of less than 10 km2.
The endemic nature of A. dumerilii and the critical
status of the habitat has led to breeding this species in
captivity as a conservation strategy (Huacuz-Elías,
2002; IUCN SSC Amphibian Specialist Group, 2020).
Therefore, the maintenance of “achoques” is vital to
enhance conservation efforts. However, captive amphibian
populations can present morphological and physiological
problems associated with long-term stress derived from
non-optimal conditions (Assis et al., 2015; Michaels et al.,
2014; Titon et al., 2017). One of the main problems is the
adaptability of organisms to captive conditions, since there
are species of salamanders that have highly specialized
microclimate and microhabitat requirements, therefore
replicating these conditions in captivity is complicated, as
is the case of Ambystoma cingulatum. The maintenance
of the appropriate temperature for organisms is also
important to avoid infectious diseases caused by bacteria,
parasites and fungi. If the water quality is poor due to
inadequate filtering and continuous replacement, it can
contain dissolved substances such as ammonia, urea or
toxins (de Vosjoli, 1999). An inadequate diet with low
nutritional intake also has negative effects on development
(Slight et al., 2015).
Regardless of the stress source, amphibian response
underlies shaping an organism’s phenotype (Denver, 2009).
A permanent stress source induces an overproduction of
glucocorticoids, the stress hormones, that negatively affect
amphibian growth and induce changes in their morphology
(Davis & Maerz, 2010; Davis & Maney, 2018; Davis
et al., 2020; Gangenova et al., 2020), leading to permanent
alterations in morphology (Brunson et al., 2001; Matthews,
2002; Hu et al., 2008). Morphological changes in
Resumen
Ambystoma dumerilii, conocido como “achoque”, es una salamandra microendémica del lago de Pátzcuaro,
considerada como en peligro crítico. Las principales amenazas son los altos niveles de contaminación del agua y
de eutrofización, además de las especies invasoras dentro del hábitat del achoque. Por estas razones, un importante
esfuerzo de conservación se ha enfocado en la crianza del achoque en cautiverio. Sin embargo, el cautiverio es un
estresor derivado de las condiciones no óptimas que pueden tener importantes consecuencias fisiológicas que se
reflejan en las condiciones corporales. Por tanto, nuestro objetivo fue evaluar la condición de individuos de A. dumerilii
a través del análisis de la morfología utilizando diferentes parámetros como tallas, morfometría geométrica, asimetría
fluctuante y alometría, en individuos del lago de Pátzcuaro y en cautiverio. Encontramos que casi todos los rasgos
tienen una relación alométrica negativa con el tamaño corporal en individuos de ambas condiciones. Nuestros
resultados mostraron que los individuos del lago presentaron mayores tamaños en los caracteres morfológicos, cuerpos
más delgados y mayores niveles de asimetría fluctuante que los individuos en cautiverio, todos estos resultados son
consistentes en el contexto del desempeño con mayores adaptaciones potenciales para aumentar el rendimiento del
nado que los individuos en cautiverio.
Palabras clave: Ambystoma; Achoque; Patrones alométricos; Asimetría fluctuante; Morfometría geométrica;
Perturbación del hábitat
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amphibians occur during their ontogenetic development,
from the larval phase to the adult stage (Shi et al., 1996;
Steinicke et al., 2015). Hence, amphibians of the same
species show different morphological forms, depending
on the degree of stress suffered during their development
(Tejedo et al., 2010). Morphological changes derived
from environmental stress involve different morphological
parameters, such as size and shape of morphological traits,
allometric patterns, and fluctuating asymmetry.
Environmental stress decreases growth with smaller size
at metamorphosis (Cayuela et al., 2017; Delgado-Acevedo
& Restrepo, 2008; Iglesias-Carrasco et al., 2017). Changes
in morphology (Denver et al., 1998; Relyea & Hoverman,
2003) and the shape and size of morphological traits also
vary in predictable ways in response to environmental
stress (Morrison et al., 2004; Phillips et al., 2006). For
example, amphibians can develop smaller hindlimbs in
individuals present in fragmented habitats (Delgado-
Acevedo & Restrepo, 2008; Steinicke et al., 2015).
Variation in morphological traits often scales with
overall body size, defined as morphological allometry
(Fairbairn, 1997, Shaffer, 1984). However, the degree
of such correspondence can range from nearly perfect
covariance of a trait with body size (i.e., isometry) to highly
uncorrelated, where specific morphological traits change at
a different rate than the body size (i.e., allometry). Positive
allometry occurs when morphological characters have
greater growth than body size, while negative allometry is
associated with lower growth of morphological characters
than body size (Fairbairn, 1997; Fox et al., 2015). Changes
in allometric patterns can influence amphibian fitness
(Delgado-Acevedo & Restrepo, 2008; Tejedo et al., 2010).
For example, in salamanders, the scaling relationships of
head shape with body size have been related to larval diet
and predation risk (Shaffery & Relyea, 2015; Van Buskirk,
2011). In addition, positive allometric relationships
between head and body size improve the vocal efficiency
of frogs in a sexual selection context (Riva-Tonini
et al., 2020).
Stressful conditions induce changes during development
that result in morphological asymmetry (Lens et al., 2002;
Wright & Zamudio, 2002), such as fluctuating asymmetry
(FA) that measure slight (Zhelev et al., 2014), random
deviations of bilateral symmetrical traits, reflecting
developmental instability of the organisms. In disturbed
or high stress environments, metamorphosis and growth
can be accelerated (Lowe et al., 2006), leading to higher
FA (Møller & Manning, 2003). For example, Pelophylax
ridibundus and Pseudepidalea viridis showed higher FA in
sites with high levels of anthropogenic disturbance (Zhelev
et al., 2014). In a similar study, Pelophylax ridibundus in
highly contaminated sites, presented high levels of FA
where they evaluated the levels of FA in 10 morphological
traits while individuals in uncontaminated sites presented
FA in 3 morphological characters (Zhelev et al.,
2015, 2019).
Understanding how amphibians respond phenotypically
to environmental changes resulting from habitat disturbance
is an important challenge to detecting the degree of
susceptibility to new stressful environments and then
proposing conservation strategies (Lomolino et al., 2001).
Amphibians show morphological plasticity to adjust to a
changing environment such as predator presence, habitat
quality, competitors, and stressful conditions (Johansson
et al., 2010; Relyea, 2001; Relyea & Hoverman, 2003;
Stoler & Relyea, 2013). Due to the deterioration of Lake
Pátzcuaro and the stress induced in captivity, we expected
to find physiological stress in individuals of A. dumerilii
that can be reflected in their morphological traits.
Therefore, our objective was to evaluate the condition
of A. dumerilii individuals through the analysis of the
morphology of A. dumerilii, using different parameters
such as morphological character sizes, geometric
morphometrics, fluctuating asymmetry and allometry,
in individuals from Lake Pátzcuaro and captivity. We
hypothesized that the anthropogenic disturbance present in
the lake and the maintenance of sub-optimal conditions in
captivity would cause stress on the organisms, therefore, we
expect to detect this using FA, geometric morphometrics
and allometry patterns, with an increase under the most
stressful condition. Our results will allow us to know the
conditions of organisms in both populations, as well as
provide useful information for future conservation and
management plans of this species in its habitat, and for
the improvement of captivity conditions.
Materials and methods
We analyzed 107 individuals, 60 individuals from the
lake (males and females) and 47 from captivity (males
and females). All salamanders sampled were individuals
classified as adults with a minimum snout-vent length
(SVL) of 60 mm (Anderson & Worthington, 1971).
The captive salamanders were sampled at a
management unit for wildlife conservation and sustainable
use. At this center, A. dumerilii is bred in captivity.
Captive individuals were born and raised in captivity. The
salamanders are kept in a covered area that protects them
from direct sunlight. Between 6 to 8 individuals are kept
in oval recycled plastic tubs of approximately 180 L, with
artificial shelters, natural aquatic plants and hiding places
made of PVC. The containers are shallow, allowing them
to move around mainly using their limbs. Temperatures
were maintained around 17 °C ± 1°C. The “achoques”
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were fed with a mixed diet of brine shrimp, fish fillets,
tubifex (Tubificidae) and acociles (Procambarus sp.). The
pH oscillated between 7.5 and 7.8.
The wild specimens were sampled in Lake Pátzcuaro
that is located in the western portion of the Transmexican
Volcanic Belt (09°32’-19°42’ N, 101°32’-101°42’ W.)
Sampling was carried out monthly from March 2019 to
December 2020, using 180 metallic cylinder traps with
a conical inlet, set at the bottom of the lake. To identify
the “achoques” collected in the lake, we used a microchip
marking system, to avoid resampling. The microchip
marking system was initiated in 2018.
For all salamanders, we registered snout-vent length
(SVL, mm) and total length (mm), using a digital caliper.
The sex of each individual was determined based on the
cloacal bulge. We used the SVL as a standard measure
of body size (Gangenova et al., 2020). To analyze all
morphological traits, we obtained a digital image from the
dorsal part of each organism with a high-resolution camera
(Sony α350), ensuring that all pictures were taken with
the same objective and at the same distance (30 cm) with
a scale. All pictures had a resolution of 14.2 megapixels.
All images were used for the morphometric measurements,
FA and allometry (Alarcón-Ríos et al., 2017; Soto-Rojas
et al., 2017).
To determine differences in body shape between
individuals from captivity and lake conditions, we used
the photographs to measure the following morphometric
traits: eye to eye distance (EED), head width (HW), head
length (HL), body width (BW), total length (TL), tail
width (TW), tail length (TLe), femur length right and
left (FLR, FLL), tibia-fibula length right and left (TFLR,
TFLL), radius-ulna length right and left (RULR, RULL),
humerus length right and left (HLR, HLL) (Fig. 1A). The
sizes were measured with the Image J 1.44 software. To
analyze differences in morphological characters between
both conditions, we used a one-way ANOVA test the
lake and captivity effect. Individuals from the lake and
captivity were considered as independent variables and
morphological characters as dependent ones.
For allometric relationships between body size and
all morphological traits, we used the SLV as standard
measure of body size. We compared captivity and lake
conditions with normalized data to remove allometric
effects, following the method developed by Lleonart
et al. (2000). The theoretical equation adjusts the shape
considering allometry and scales all individuals to the
same size, and the absolute values of morphometric
characters are standardized as follows: (Yi* = Yi (SVL0/
SVLi)b. Where Yi*: size-adjusted proportion character
of specimen i; Yi: body character; SVL0: mean value
of SVL; SVLi: SVL of specimen i; b: within-habitat
treatment regression slope of log (Y) against log (SVL).
We transformed all variables to log. We evaluated the
effect of lake and captivity on SVL and its allometric
relationship with morphological characters, applying an
ordinary least squares regression between snout-vent
length (x-axis: mm) and size of morphological characters
(y-axis: mm) for individuals from the lake and captivity.
We calculated the allometric slope for each regression. For
those variables in which a correlation was identified, we
applied an analysis of covariance (ANCOVA) to test the
difference in regression slopes between individuals from
the lake and captivity.
With the digital image obtained for each individual, we
measured FA of abdomen and head (Fig. 1B). Fluctuating
asymmetry was calculated as the absolute value of the
difference among the distances from the middle to the left
and right margins of the body part (|Ai - Bi|), divided by
the average distance (Ai + Bi / 2), to correct for the fact
that asymmetry may be size-dependent. Additionally, 10
individuals were blindly re-measured, without reference to
previous measurements to control the measurement error
in FA. We then evaluated the degree of significance of FA
relative to measurement error using two-way mixed-model
ANOVA. The significance of the interaction (individual
× body part × side) indicated that variation in FA was
greater than expected by measurement error: (F9,25 = 22.4;
p < 0.002).
Fluctuating asymmetry is found when the right-minus-
left (R-minus-L) differences are normally distributed with
a mean value = 0, unlike directional asymmetry that is
found when the R-minus-L differences are also normally
distributed, but with a mean significantly different from
0, and antisymmetry, characterized by a platykurtic or
bimodal distribution of R-minus-L differences about
a mean of 0 (Palmer & Strobeck, 1986). To determine
whether our data fitted only FA and no other types of
asymmetry, we performed a Student’s t test and Lilliefors’
normality test to evaluate whether mean values of signed
R-minus-L values differed significantly from 0. We
found that R-minus-L measurements did not differ from
0 (t = 1.1; p > 0.05), and therefore, we discarded the
presence of directional asymmetry in our data. In the
same way, we also reject the presence of antisymmetry
because our data (R-minus-L) exhibited a normal
distribution (p > 0.05). Once determined that our data
fitted only in FA criterium, we used an analysis of variance
(ANOVA) to determine the differences in FA levels
between individuals that occur in the lake and captivity
condition. In all cases, the normality was tested after
suitable transformations.
Differences in body morphology between individuals
that occur in the lake and captivity conditions, were
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analyzed using geometric morphometric techniques (Vega-
Trejo et al., 2014). Each individual was photographed
separately. We used grid lines as guides in order to obtain
the maximum vertical image. In each image, 22 landmarks
type II landmarks were placed along the corporal shape
of the salamanders and 2 additional landmarks over the
centimeter as size reference to record the coordinates
(x, y) of the 22 landmarks in each salamander image
(Cuevas-Reyes et al., 2018) (Fig. 2). The type of
landmarks used are classified as homologous type II
landmarks, since they represented pairs of points in the
places with greater curvature from the body shape (sensu
Bookstein, 1997). For the application of landmarks, the
TPS software package was used (Rohlf, 2015). Then, a
Procrustes superimposition analysis was performed using
the Integrated Morphometrics Package (IMP series: http://
www.canisius.edu/~sheets/morphsoft.html) to align the
landmark coordinates and eliminate size effect (Vega-
Trejo et al., 2014). This Procrustes superimposition
analysis rescales, translates, and rotates (using a least-
squares criterion) the raw landmark coordinates in order
to eliminate any non-shape variation (Bookstein, 1997;
Klingenberg, 2003). The mean configuration of all
individuals for this condition was considered as reference
of shape variables (Procrustes distances) and calculated
by a superimposition coordinates analysis (Cuevas-
Reyes et al., 2018). We applied a principal component
analysis (PCA) to determine shape differences between
lake and captivity conditions (Cuevas-Reyes et al.,
2018). The PCA test produces ordination plots indicating
the differences in the shape of the salamanders. These
analyses were performed in MorphoJ software v1.07a
(Klingenberg, 2011).
Results
We found differences in morphological characters
between both populations, with individuals from the lake
with a larger head width, head length, total length, tail
width, tail length, femur length of left side, tibia-fibula
length of left side, radius-ulna length of right and left sides,
humerus length of right and left sides, radius-ulna length
of left and right side and SVL than individuals raised in
captivity. In the case of body width, femur length right,
tibia-fibula length right we did not find any differences
(Table 1).
Figure 1. Individual of Ambystoma dumerilii with A) body measurements, B) traits measured for fluctuating asymmetry assessment.
B. Ramírez-López et al. / Revista Mexicana de Biodiversidad 94 (2023): e944969 6
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We observed significant allometric relationships
in most of the traits in individuals of A. dumerilii from
the lake and captivity. We found that almost all traits
showed a negative allometric relationship with body size
in individuals from the lake. In the case of tail width,
radius-ulna length of left side, fibula length of left size
showed an isometric relationship with body size in captive
individuals. Femur length of left size showed a positive
relationship (Table 2).
ANCOVA analyses showed significant differences
between slopes in some allometric relationships of both
habitat conditions. In individuals from the lake, the
slopes of the allometric equations between body size and
humerus length of right size and radius-ulna length of right
side were significantly higher than in individuals from
captivity (HLR: F = 77.6; p = 0.0001. RULR: F = 105.9;
p = 0.0001). In the rest of traits, the slopes of the allometric
equations were higher in individuals from captivity
(HW: F = 10.68; p = 0.0001. HL: F = 4.1; p = 0.0001.
BW: F = 112.7; p = 0.0001. TL: F = 47.6; p = 0.0001.
TW: F = 62.23; p = 0.0001. TLe: F = 115.5; p = 0.0001.
FLR: F = 41.02; p = 0.0001. TFLR: F = 28.7; p = 0.0001.
FLL: F = 53.29; p = 0.0001. TFLL: F = 40.89; p = 0.0001).
We found differences in FA between salamanders
from the lake and those from captive conditions. Our
results show higher FA in the body (F = 27.9, d. f. = 1,
p = 0.0001) and head (F = 47.1, d. f. = 1, p = 0.067)
of individuals sampled in the lake.
Based on a coordinate superimposition analysis, we
found differences in body shape between individuals of
the lake and captivity (Fig. 3A), where the PC1 and PC2
explained 58.8% and 13.3%, respectively. Two well-
segregated groups were formed between lake and captive
individuals in our PCA (Fig. 3A). The wireframe graph
based on Procrustes coordinates showed that body shape
of individuals from the lake were slimmer than individuals
from captivity (Fig. 3B). This difference in body shape
between individuals from captivity and lake is supported
by discriminant analysis, where both distances (values) of
Mahalanobis (3.95) and Procrustes (0.046) were significant
(p = 0.0001).
Discussion
Anthropogenic threats have led to the deterioration of
the “achoque” (Zambrano et al., 2011), leading it to live
under stressful conditions. The conservation alternative,
captivity, necessary to face the imminent extinction of this
endangered species, also represents stressful conditions
derived from non-optimal environment (Michaels et al.,
2014). Morphological changes in amphibians occur
during their ontogenetic development, from the larval
phase to the adult stage (Shi et al., 1996; Steinicke et al.,
2015), hence amphibians of the same species can show
different morphological forms, depending on the degree
of stress suffered during their development (Tejedo et al.,
2010). Our results showed that individuals from the lake
are larger, have higher FA and the slopes of allometric
correlations of almost all traits were lower, suggesting
that SVL increases faster according to morphological
characters than those individuals in captivity. Conversely,
individuals from captivity present shorter morphological
traits and narrower bodies than individuals from the lake.
In our study, individuals from the lake are larger than
individuals from captivity. This result is the opposite to what
would be expected if we hypothesize that the conditions
in the lake were more stressful than those in captivity,
and that amphibian exposure to environmental stressors
Figure 2. Individual of Ambystoma dumerilii with 22
morphological landmarks around the body shape and 2 more as
reference size to measure geometrical morphology.
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Table 1
ANOVA of morphological characters in individuals of A. dumerilii from captivity and wildlife. Eye to eye distance (EED), head
width (HW), head length (HL), body width (BW), total length (TL), tail width (TW), tail length (TLe), femur length right and left
(FLR, FLL), tibia-fibula length right and left (TFLR, TFLL), radius-ulna length right and left (RULR, RULL), humerus length right
and left (HLR, HLL). Numbers in bold indicate statistically significant differences.
Character Lake Captivity d. f. Fp
HW 4.678 ± 0.389 4.033 ± 0.228 1 102.17 0.0001
HL 4.496 ± 0.494 3.47 ± 0.528 1 106.96 0.0001
BW 3.529 ± 0.388 3.624 ± 0.357 1 1.6966 0.1956
TL 24.9 ± 1.747 21.4 ± 1.002 1 142.14 0.0001
TW 1.418 ± 0.183 1.3064 ± 0.178 1 9.9329 0.0021
TLe 10.532 ± 1.445 8.482 ± 0.995 1 68.819 0.0001
FLR 1.465 ± 0.279 1.406 ± 0.227 1 1.3783 0.2431
FLL 1.4567 ± 0.259 1.332 ± 0.206 1 7.1695 0.0086
TFLR 1.3385 ± 0.272 1.2991 ± 0.2219 1 0.6458 0.4234
TFLL 1.4035 ± 0.278 1.2977 ± 0.182 1 4.084 0.04584
HLR 1.553 ± 0.206 1.3826 ± 0.225 1 7.9356 0.0069
HLL 1.555 ± 0.203 1.3028 ± 0.231 1 17.071 0.0001
RULR 1.515 ± 0.155 1.2717 ± 0.165 1 29.847 0.0001
RULL 1.499 ± 0.211 1.248 ± 0.177 1 23.017 0.0001
SVL 14.32 ± 1.393 13.01 ± 2.386 1 12.47 0.0001
Table 2
Allometric patterns of morphological characters in individuals of A. dumerilii from the lake and captivity in relation to standard body
size SLV. Eye to eye distance (EED), head width (HW), head length (HL), body width (BW), total length (TL), tail width (TW),
tail length (TLe), femur length right and left (FLR, FLL), tibia-fibula length right and left (TFLR, TFLL), radius-ulna Length right
and left (RULR, RULL), humerus length right and left (HLR, HLL) . Numbers in bold indicate statistically significant differences.
Character
(Log)
Lake Captivity
Slope b (95% CI) r2pSlope b (95% CI) r2p
HW 0.6 (0.39, 0.8) 0.36 0.0001 0.73 (0.05, 0.81) 0.88 0.0001
HL 0.58 (0.3, 0.85) 0.23 0.0001 0.71 (0.49, 0.9) 0.49 0.0001
BW 0.86 (0.59, 1.1) 0.41 0.0001 0.97 (0.83, 1.1) 0.82 0.0001
TL 0.89 (0.72 1.05) 0.67 0.0001 1 (0.91, 1.04) 0.95 0.0001
TW 0.73 (0.41, 1.05) 0.26 0.0001 0.86 (0.67, 1.05) 0.65 0.0001
TLe 0.83 (0.49, 1.16) 0.3 0.0001 0.95 (0.79, 1.1) 0.75 0.0001
FLR 0.53 (0.07, 1) 0.08 0.025 1 (0.85, 1.27) 0.69 0.0001
FLL 0.44 (-0.04, 0.9) 0.06 0.06 1.12 (1.05, 1.49) 0.75 0.0001
TFLR 0.9 (0.36, 1.4) 0.16 0.002 0.91(0.66, 1.15) 0.55 0.0001
TFLL 0.8 (0.29, 1.3) 0.15 0.002 1 (0.79, 1.19) 0.68 0.0001
HLL 0.68 (0.24, 1.1) 0.35 0.004 0.94 (0.62, 1.2) 0.71 0.0001
HLR 0.91 (0.4, 1.4) 0.44 0.001 0.82 (0.51, 1.12) 0.44 0.0001
RULR 0.86 (0.49, 1.22) 0.58 0.0001 0.59 (0.34, 0.84) 0.38 0.0001
RULL 0.78 (0.3, 1.25) 0.38 0.001 0.83 (0.57, 1.09) 0.55 0.0001
EED 0.3 (-0.08, 0.7) 0.04 0.12 0.67 (0.57, 0.77) 0.83 0.0001
B. Ramírez-López et al. / Revista Mexicana de Biodiversidad 94 (2023): e944969 8
https://doi.org/10.22201/ib.20078706e.2023.94.4969
decreased the growth rate of the main morphological
traits (Delgado-Acevedo & Restrepo, 2008; Tejedo et al.,
2010). However, A. dumerilii does not show a decrease
in size, since the larger sizes and higher FA occur in
individuals from the lake. To explain the relationship
between growth and FA, it has been hypothesized that
a favorable environment, such as greater availability of
food items with a higher nutrient content (Milligan et al.,
2008), allows for rapid growth of organisms, prompting
higher developmental instability and FA levels (Lempa
et al., 2000; Martel et al., 1999). The main reason is that
there are trade-offs between growth rate and life-history
traits such as developmental stability (Sibly & Calow,
1984), and within species, different genotypes in specific
environments need to change from optimizing growth
rate to optimizing developmental quality. Therefore, we
can expect higher FA in individuals of A. dumerilii that
reach an optimal growth rate for their development in lake
conditions, showing that fluctuating asymmetry might not
be an unequivocal indicator of environmentally induced
stress, since other factors can be involved, such as genetic
stress or growth rate (Milligan et al., 2008; Velickovic &
Perisic, 2006).
An important factor may be the resource availability
that can lead to larger body size (Jessop et al., 2006; Wu
et al., 2006). Ambystoma dumerilii in the natural habitat
has a high degree of trophic specialization, and consumes
mainly crayfish (Cambarellus sp.), an abundant resource in
Lake Pátzcuaro (Huacuz-Elías, 2008), although sometimes
it consumes other crustaceans, insects, worms, small fish
and tadpoles too (Aguilar-Miguel, 2005; Velarde-Mendoza,
2012; Semarnat, 2018). In captivity, A. dumerilii had a
mixed diet of fish fillet, earthworm, tubifex and acociles.
According to some authors a mixed diet results in a slower
growth rate than a bloodworm-only diet, and it seems
that for captive aquatic species such as A. dumerilii, an
invariant but good-quality diet is a better option, indicating
that mixed diets being best is not universally true (Slight
et al., 2015).
Morphology of amphibians is directly related to
movement, locomotion ability and individual performance
(Aubret & Shine, 2008; Ijspeert & Cabelguen, 2006;
Irschick & Garland, 2001). In our study, it was expected that
individuals from the lake presented traits that are correlated
with the fast-swimming performance in salamanders,
necessary to escape from predation but also to capture
prey (Urban, 2010; Van Buskirk & Schmidt, 2000). For
example, tail morphology is known to have an impact on
the locomotor performance while swimming (Van Buskirk
& Schmidt, 2000; Vorndran et al., 2002), large tails are
adaptations for rapid acceleration (Duellman & Trueb,
1986), and are associated to the response to chemical
predator cues (Van Buskirk & McCollum, 2000). In our
study, we found larger and wider tails in individuals from
the lake, suggesting that these individuals have developed
a greater capacity of movement. A larger tail surface area
can also generate greater thrust, so a greater stride can
be achieved (Aubret & Shine, 2008). The morphology of
Ambystoma is adapted to have larger tails but also larger
heads. In Ambystoma larvae head size is associated with a
greater acceleration ability, high acceleration bursts, and
high swimming velocity (Hoff et al., 1989), as well as head
width is positively related to propulsive performance and
may serve an important stabilizing function (Fitzpatrick
et al., 2003). In adult salamanders, head size is associated
with food intake and level of aggression (Adams, 2000,
2004; Adams & Rohlf, 2000).
Figure 3. A) Principal components analysis on Procrustes
coordinates of individuals from captivity and lake conditions that
represents the variation in body shape between both conditions.
Black circles indicate individuals from captivity, and gray circles
to those from lake. B) Wireframe graph of mean body shape of
individuals from captivity and lake conditions. Black contour
represents the mean body shape of individuals from captivity,
and gray contour to that of lake individuals.
B. Ramírez-López et al. / Revista Mexicana de Biodiversidad 94 (2023): e944969 9
https://doi.org/10.22201/ib.20078706e.2023.94.4969
Aquatic species have elongated bodies because these
species may use their whole trunk for swimming using
a posterior traveling wave along their bodies (Deban &
Schilling, 2009). Aquatic salamanders have an undulatory
swimming gait with limbs tucked against the body (Frolich
& Biewener, 1992). However, this species also uses its
limbs for aquatic walking on the substrate (Azizi &
Horton, 2004). In the case of A. dumerilii it can move
towards the water column, however, by being considered
epibenthic, it can swim or use its limbs (Aguilar-Miguel
& Casas-Andreu, 2005; Montes-Calderón et al., 2011).
Our results show that lacustrine organisms have larger
limbs, as in other species of the genus Ambystoma where
it has been reported that A. ordinarium have a daily
displacement between 4 and 20 m (Aguilar-Miguel &
Casas-Andreu, 2005; Montes-Calderón et al., 2011), while
A. maculatum has a range of 3.3 to 29.4 m (Duellman &
Trueb, 1994), which coincides with the displacements of
other salamanders with an average distance of 10 m so that
A. dumerilii could show a similar behavior (Duellman &
Trueb, 1994). On the other hand, in captivity, individuals
of A. dumerilii may not develop traits associated with
swimming, as do individuals from the lake due to the
effect of the size of the enclosure, and the limitations of
artificial conditions (Álvarez & Nicieza, 2002; Altwegg &
Reyer, 2003; Relyea & Hoverman, 2003), where there are
no competitors or predators of other species. Therefore, it
is not easy to replicate natural abiotic conditions (Essner
& Suffian, 2010). In this way, Ambystoma salamanders
perceive captivity as “mildly stressful” (Davis & Maerz,
2011), however they show smaller sizes due to suboptimal
environments and present less swimming capacity due
to the limited space available for movement, greater
susceptibility to hunger, and higher mortality when
raised in conditions where resources are limited (Álvarez
& Nicieza, 2002; Altwegg & Reyer, 2003; Relyea &
Hoverman, 2003).
Variation in morphological traits scales with body
size, ranging from the perfect covariance of a trait with
body size (isometry) to highly uncorrelated, where
morphological traits grow more or less slowly than
body size (Fairbairn, 1997). The ontogenetic allometry
is the source of morphological variation during the
growth process (Murta-Fonseca et al., 2020). In our
study, the allometric relationships between SVL and
morphological traits were highly consistent, with most of
the morphological characters showing negative allometric
patterns or hypoallometry in many traits and the slopes
of allometric correlation of many traits were lower in
salamanders from the lake than captivity. We suggest
that stressful conditions in the lake, such as disturbance
derived from anthropogenic factors, change in land use,
contamination by wastewater, herbicides and pesticides
(Zambrano et al., 2011), promote lower development rates
of these traits than body growth.
It is important to mention that although we did not
measure individual fitness and performance, all variations
in phenotypic traits such as body size and body proportions,
could affect performance. Our results are consistent
in the context of performance, since individuals in the
lake with slimmer bodies, reduced limbs, and higher FA
suggest potential adaptations toward increased swimming
performance and the opposite for those in captivity.
Amphibians with smaller body sizes are associated with
reduced survival (Altwegg & Reyer, 2003), and may
dehydrate quicker when compared with larger individuals
(Gray & Smith, 2005). It is important to ask if individuals in
captivity are functionally similar to their wild counterparts
(Calisi & Bentley, 2009).
Suboptimal environmental conditions can lead to stress
that affects the health of the organisms and modifies their
morphology, as well as their behavioral and physiological
performance (Denver, 1997). The captivity conditions are
designed to replicate the wild environmental parameters,
in order to maintain animals in good long-term health
and potentially improve their fitness, and on occasions
promote their reintroduction into suitable environments
(Davis & Maerz, 2011), therefore our study could help to
rethink the conditions in which the organisms are found,
since negative allometric patterns were found in relation
to the extremities, which plays an important role for
their fitness.
Since different populations of the same species are
not found under the same conditions, the inclusion of
morphological diversity data in biodiversity conservation
seems to be an important developing strategy for reducing
biodiversity losses under global change (Des Roches
et al., 2018).
Acknowledgements
This study was supported by The Mohamed bin Zayed
Species Conservation Fund, with the project number:
182518929, “Evaluating populations of the Michoacan
axolot (A. dumerilii) in Lake Pátzcuaro for the recovery
of local management and fisheries”, and Chester Zoo with
the project “Conservation and long-term management of
the “achoque” (Ambystoma dumerilii) and its habitat”.
We thank the Regional Center for Fisheries Research
in Pátzcuaro for the facilities, and two anonymous
reviewers whose comments helped us to improve
the manuscript.
B. Ramírez-López et al. / Revista Mexicana de Biodiversidad 94 (2023): e944969 10
https://doi.org/10.22201/ib.20078706e.2023.94.4969
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