Chromatic variation in populations of Xenodon merremi (Serpentes: Dipsadidae) in Paraguay

Abstract

Xenodon merremi is a polychromatic species distributed in South America. Among its wide range of color patterns, the most common pattern resembles a pitviper of the genus Bothrops. In this work is recorded the different patterns found in Paraguayan populations of X. merremi. Four patterns can be observed: marked pattern, slightly marked pattern, smooth, and banded pattern. The marked pattern is the most common pattern (mimetic with pitvipers), and all juveniles bear this coloration. Only adults show variation in their coloration.

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Acta Herpetologica 5(1): 107-112, 2010
Chromatic variation in populations of Xenodon merremi
(Serpentes: Dipsadidae) in Paraguay
P C
Departamento de Paleontología, Facultad de Ciencias, Universidad de la República. Iguá 4225 CP
11400, Montevideo, Uruguay. Instituto de Investigación Biológica del Paraguay, del Escudo 2044, Asun-
ción, Paraguay. E-mail: pier_cacciali@yahoo.com
Submitted on: 2009, 10th June; revised on 2010, 25th March; accepted on 2010, 9th April.
Abstract. Xenodon merremi is a polychromatic species distributed in South America.
Among its wide range of color patterns, the most common pattern resembles a pit-
viper of the genus Bothrops. In this work is recorded the dierent patterns found in
Paraguayan populations of X. merremi. Four patterns can be observed: marked pat-
tern, slightly marked pattern, smooth, and banded pattern. e marked pattern is the
most common pattern (mimetic with pitvipers), and all juveniles bear this coloration.
Only adults show variation in their coloration.
Keywords. Xenodon merremi, Paraguay, chromatic variation.
Xenodon merremi is a colubrid snake widely distributed from Ecuador and the Guia-
nas, to northern and central Argentina, and Uruguay (Cerreira et al., 2005; Tipton, 2005).
roughout its distribution, X. merremi occurs in both natural and anthropogenic areas
(Cabrera, 2004; Scrocchi et al., 2006) and feeds largely on toads (Carreira, 2002).
Several works have made reference to the variable polychromatic coloration of X.
merremi (under the genus Waglerophis) even in local areas (Giraudo, 2001; Cabrera, 2004;
Scrocchi et al., 2006). e typical coloration of X. merremi is a pattern with semicircular
brownish lateral marks with wavy edges and skirted by white thin margins, this pattern
being mimetic with pitvipers of the genus Bothrops (Giraudo, 2001; Cabrera, 2004; Carrei-
ra et al., 2005; Scrocchi et al., 2006). Additionally, Brodie and Brodie (2004) also pointed
out that the species can show coloration mimetic of coral snakes (see plate 1338 in Camp-
bell and Lamar, 2004).
Included in the range of variation reported in X. merremi are specimens with black
marks (not brownish); specimens with the body completely yellowish, brown, or even
almost completely blackish; as well as a specimen with partial albinism (Scrocchi et al.,
2006). Giraudo (2001) identied six dierent patterns: A (uniformly immaculate), B (with
rings on the back), C (with small semicircular marks on the sides, with a vertebral stripe),

108 P. Cacciali
D (the typical pattern with smooth marks), E (the typical pattern with clear center marks),
and F (with one undulated stripe on each side). Giraudo (2001) stated that there is no
concordance between coloration variation and distribution, but there is an ontogenet-
ic pattern: juveniles are always marked with patterns D or E), whilst adults are variable.
Ontogenetic changes were also recorded by Norman (1994).
In this work is presented a summary of the coloration patterns recorded in Paraguay,
together with the frequency of each pattern.
Paraguay with an area of 406,752 km2 is located in the center of South America,
and divided approximately in half by the Paraguay River. Western Paraguay (commonly
referred to as “e Chaco”) makes up 60% of the territory, whereas the remaining 40% is
represented by the eastern or Oriental Region. Biogeographically, Paraguay is divided into
seven ecoregions (Fig. 1). X. merremi is distributed almost throughout the whole country.
For this study, a sample of 60 Paraguayan specimens (18 juveniles and 42 adults,
Appendix 1) preserved in the Museo Nacional de Historia Natural del Paraguay (MNH-
NP) was analysed. Specimens shorter than 25 cm were considered juveniles.
Four dierent patterns were recognized in this sample: marked (normal pattern),
slightly marked, smooth, and banded. All juveniles analysed were of the normal marked
pattern, only adults exhibited variation. ere follows a brief denition of each of the
observed patterns, with comments on their frequency in the sample.
Fig. 1. Ecoregional distribution of Paraguay.

109Chromatic variation in populations of Xenodon merremi in Paraguay
Marked pattern: this is the “typical” pattern of the species, with series of marks on the
sides (Fig. 2A). Marks can reach the vertebral zone, joining with its couple of the other
side. Although dierent color patterns were observed, all are here grouped as “marked”
individuals. All juveniles were shown to exhibit this pattern in addition to 22 of the adults
(52.4% of the adults in the sample).
No difference was observed between specimens from the western and Oriental
Regions (Fig. 3A).
Slightly marked pattern: “slightly-marked” individuals tend to lose the body markings
(Fig. 2B), though typically traces of marks remain near the vertebral zone. Eleven adults
bore this pattern corresponding to 26.2% of the sample. No juveniles in the sample exhib-
ited this pattern. Specimens with “slightly marked pattern” are present in a wide variety of
environments, and have been recorded from all the Paraguayan ecoregions except for the
Pantanal (Fig. 3B).
Smooth: specimens with smooth coloration, lack contrasting pattern (Fig. 2C) and are
usually uniformly yellowish or brownish. Six adults were recorded with this coloration,
representing 14.3% of the adults examined.
Specimens with smooth coloration were collected from the Dry Chaco and Wet
Chaco, and were recorded in the Oriental Region only in the Departments of Central and
Ñeembucú, where the predominant habitat is similar to that of wet Chaco (Fig. 3C).
Fig. 2. Body color patterns of Paraguayan populations of Xenodon merremi. A: marked pattern, B: slightly
marked pattern, C: smooth coloration, and D: banded pattern.

110 P. Cacciali
Banded pattern: the “banded pattern” consists of a series of black bands or rings along
the body, against a grey background (Fig. 2D). Specimen MNHNP 2601 additionally
shows vertebral constriction in some bands, and is quite similar in shape to the typical
“marked” pattern. Only three adults in the sample showed this pattern, corresponding to
7.1% of the total adults.
e three specimens were collected from three widely-dispersed localities: Cerro Corá
National Park (Cerrado ecoregion, Departamento Amambay), Colonia Walter Insfrán
(Alto Paraná Atlantic Forest ecoregion, Departamento Caaguazú), and the surroundings
of Loma Plata (Dry Chaco ecoregion, Departamento Boquerón) (Fig. 3D).
Fig. 3. Distribution of examined specimens, according to the color pattern. Black dots are adults, and
open squares are juveniles. Note that there are juveniles only in “A”. A: marked pattern, B: slightly marked
pattern, C: smooth coloration, and D: banded pattern.

111Chromatic variation in populations of Xenodon merremi in Paraguay
Results show that like other previous works (Norman, 1994; Giraudo, 2001), juvenile
coloration is always consisting in well dened marks, whereas adults can show dierent
patterns of coloration. is results conrms that coloration probably change ontogeneti-
cally in this species.
e commonest adult pattern in the Paraguayan sample was the marked pattern,
which accounted for 52.7% of the adult specimens. Giraudo (2001) dened two dierent
kinds of “normal” patterns, to dierentiate them from the other marked patterns. Never-
theless, in Paraguay, the marked specimens only exhibit the normal marked coloration (Fig.
2A), and not the wide range described by Giraudo (2001, Fig. 42). ese ndings suggest
that more than half of all Paraguayan specimens retain juvenile coloration into adulthood.
In the Dry Chaco, it is possible to nd all the dierent patterns. Probably also in the
Wet Chaco; but examined specimens with banded pattern was not presents in the Wet
Chaco. An important fact is that in the Cerrado, occur three of the four dierent patterns,
being absent only the smooth coloration. In the Table 1, is presented a list of number of
individuals of each color pattern in each ecoregion. Any specimen came from Pantanal.
More sampling eort is required to get a clearer picture of the distributional patterns
of the dierent color types. Given the small sample size the current observed distribution
of the pattern types in Paraguay may be a result of dierent sampling eorts in dierent
locations. Bearing this mind it should be noted that the smooth type could yet prove to
have a wider distribution in Paraguay than it currently appears.
ACKNOWLEDGEMENTS
anks to Martha Motte (MNHNP) for allowing access to the specimens under her care.
To Norman Scott for providing information of United States Museums records. To David Gill and
Paul Smith for corrections to the english version. Also to three referees whose suggestions helped
improve the work. To Mónica Rumbo for the patience and help. is work was done within the
framework of the esis Project “Biogeography of the Reptiles of Paraguay” that is being carried out
by the author.
Table 1. Patterns frequencies in each ecoregion. PA (Pantanal), DC (Dry Chaco), WC (Wet Chaco), CE
(Cerrado), AF (Alto Paraná Atlantic Forest), CP (Central Paraguay), MG (Mesopotamian Grasslands).
ere are 12 additional sampled specimens without specic locality data.
PA DC WC CE AF CP MG Total
Pattern A 0 8 3 1 7 10 3 32
Pattern B 0 3 0 1 2 2 0 8
Pattern C 0 3 1 0 0 1 0 5
Pattern D 0 1 0 1 1 0 0 3
Total 0 15 4 3 10 13 3 48

112 P. Cacciali
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Cornell University, New York.
Cabrera, M.R. (2004): Las Serpientes de Argentina Central. Publicaciones de la Universi-
dad Nacional de Córdoba, Córdoba.
Campbell, J.A., Lamar, W.W. (2004): e Venomous Reptiles of the Western Hemisphere.
Cornell University, New York.
Carreira, S. (2002): Alimentación de los odios de Uruguay. Monografías de Herpetología
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Carreira, S., Meneghel, M., Achaval, F. (2005): Reptiles de Uruguay. Universidad de la
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Giraudo, A. (2001): Serpientes de la Selva Paranaense y del Chaco Húmedo. Literature of
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Norman, D. (1994): Anbios y Reptiles del Chaco Paraguayo, Tomo I. San José, Costa Rica.
Scrocchi, G., Moreta, J.C., Kretzschmar, S. (2006): Serpientes del Noroeste Argentino. Fun-
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APPENDIX 1
Examined specimens
A. Marked pattern (including juveniles): Paraguay (MNHNP 2611, 9256, 9429, 9431, 9432,
9516, 9554, 9583). Alto Paraguay: Fortín Madrejón (MNHNP 2657). Amambay: Parque Nacion-
al Cerro Corá (MNHNP 2660). Boquerón: 15.6 km S of Filadela (MNHNP 10033); 26 km N of
Filadela (MNHNP 9736); Parque Nacional Teniente Enciso (MNHNP 6524); Filadela (MNH-
NP 2610, 8495); Neuland (MNHNP 9992); Route IX, Km 519 (MNHNP 6825). Caazapá: Parabel
(MNHNP 8808). Central: Asunción (MNHNP 3180, 6520); Guarambaré (MNHNP 2664); Luque
(MNHNP 6288-90); San Lorenzo (MNHNP 7461, 9939). Concepción: Horqueta (MNHNP 2609).
Cordillera: Altos (MNHNP 10309). Itapúa: Isla Yacyretá (MNHNP 9568). Misiones: Yabebyry
(MNHNP 3779-80). Ñeembucú: Estancia Yacaré (MNHNP 4556, 6679). Paraguari: Acahay (MNH-
NP 3540); Coronel C. Barrientos (MNHNP 3781); Parque Nacional Ybycui (MNHNP 2661-3);
Yaguarón (MNHNP 2658). Presidente Hayes: Estancia Bella Vista (MNHNP 10610).
B. Slightly marked pattern: Paraguay (MNHNP 9456, 9593, 9594). Alto Paraguay: Fortín
Madrejón (MNHNP 2679). Amambay: Parque Nacional Cerro Corá (MNHNP 9193). Boquerón:
Parque Nacional Teniente Enciso (MNHNP 2656); Filadela (MNHNP 3839); Central: Luque
(MNHNP 6286); San Lorenzo (MNHNP 9172). Guairá: 13 km W of Villarrica (MNHNP 6518).
Itapúa: Coast of the Paraná (MNHNP 4213).
C. Smooth coloration: Paraguay (MNHNP 9566). Alto Paraguay: Estancia Tres Marías
(MNHNP 9197); Laguna León (MNHNP 11041). Boquerón: Route IX, Km 508 (MNHNP 2655);
Central: San Lorenzo (MNHNP 7053). Ñeembucú: Estancia Yacaré (MNHNP 4585).
D. Banded pattern: Amambay: Parque Nacional Cerro Corá (MNHNP 2659). Boquerón: 9
km S of Loma Plata (MNHNP 9996). Caaguazú: Colonia Walter Insfrán (MNHNP 2601).