Patterns of geographic varation in Zamenis

Patterns of geographic varation in Zamenis longissimus
and Z. lineatus (Reptilia: Colubridae): a landmark-based approach
Massimo Capula1, Sophia VALENTI1, Luca LUISELLI2, Anna Loy3
Museo Civico di Zoologia, Via U. Aldrovandi 18, I-00197 Roma, Italy
Centro di Studi Ambientali Demetra s.r.l., Roma, Italy
3
Dipartimento di Scienze e Tecnologie dell’Ambiente e del Territorio, Università degli Studi
del Molise, C.da Fonte Lappone, I-86090 Pesche (IS), Italy
1
2
Riassunto.La variazione della forma e delle dimensioni delle squame cefaliche dei Colubridi Zamenis longissimus e Z. lineatus è stata analizzata utilizzando la morfometria geometrica basata sui landmark al fine di definire le relazioni fenetiche
inter- e intraspecifiche. Sono state registrate le coordinate di 35 punti omologhi
sulle squame cefaliche delle emiconfigurazioni di 128 esemplari adulti (Zamenis longissimus, n = 91; Z. lineatus, n = 37). Le configurazioni originali sono
state trasformate e sovrapposte attraverso GPA, e i residui analizzati con metodi multivariati di ordinamento e classificazione. La variazione di taglia è stata
analizzata confrontando le dimensioni dei centroidi delle configurazioni. Le
due specie risultano significativamente diverse sia nella forma sia nelle dimensioni delle squame cefaliche. Le griglie di deformazione associate alle differenze
nello spazio multivariato indicano come altamente diagnostica la forma delle
squame sopraoculari e parietali. L’analisi della variabilità intraspecifica evidenzia
un maggiore polimorfismo di Zamenis longissimus – specie caratterizzata da un
ampio areale – rispetto a Zamenis lineatus, specie che invece presenta un areale
relativamente ristretto. Vengono inoltre presentati nuovi dati sulla distribuzione
e la simpatria delle due specie in Italia.
Keywords. Zamenis lineatus, Zamenis longissimus, geographic variation, cephalic scales,
head shape, distribution, Italy.
In Italy Zamenis longissimus (Laurenti, 1768) and Z. lineatus (Camerano, 1891) seem to be
vicariant species. Zamenis longissimus is said to inhabit northern and central Italy (Razzetti
and Zanghellini, 2006). Zamenis lineatus is endemic to the southern Italian Peninsula and
Sicily (Lenk and Wüster, 1999; Arnold and Ovenden, 2002). The occurrence of Z. lineatus
/ Z. longissimus was also reported for Sardinia, but according to Razzetti and Zanghellini
(2006) both locality records and species attribution need to be confirmed. The two species
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are anatomically and ecologically similar (Capula et al., 2006) and are recognizable using
some morphological and molecular characters (see Lenk et al., 2001).
To assess the pattern of geographic variation in Zamenis longissimus and Z. lineatus,
landmark based geometric morphometrics of the cephalic scales was investigated in
several populations. Sixteen samples of Zamenis longissimus (16 localities from southern,
central and northern Italy, Switzerland, Croatia, Greece, Turkey) and four samples of
Z. lineatus (4 localities from southern Italy: Campania, Basilicata, Calabria, Sicily) were
analyzed. Geometric morphometric analyses were run on a total of 128 specimens (Zamenis
longissimus, n = 91; Z. lineatus, n = 37) preserved in the collections of some Italian natural
history museums (Museo di Storia Naturale, Sezione di Zoologia, “La Specola”, Università
di Firenze; Museo Civico di Zoologia di Roma; Museo di Zoologia “Pietro Doderlein”,
Università di Palermo). Each animal was placed under a binocular microscope provided
with a digital camera connected to a PC. Thirty-five X-Y coordinates were recorded on
digital images of the half configuration of the cephalic scales through TpsDig (Rohlf,
2004a). Configurations of landmarks were rotated, translated and superimposed through
GPA using the program TpsRelw (Rohlf, 2003). Partial Warps and centroid sizes were
extracted through TpsRelw and then analyzed through ANOVA and MANOVA in order
to summarize and visualize patterns of variation. Based on (1) geographic origin of the
studied individuals, (2) original data by the authors (M.C., L.L), and (3) literature data, the
distribution of both species in Italy was also analyzed and discussed.
Interspecific variation. Based on shape variation expressed by Relative Warps of partial warp
scores, the two species are clearly recognizable and multivariate discrimination is highly
significant (Wilks’ lambda = 0.028; F = 12.21; P< 0.00001). Shape differences between
species are mostly related to the variation of specific cephalic scales. Transformation grids
(Bookstein, 1991), produced through TpsRegr on CV scores (Rohlf, 2004b), indicate that
major differences are in the shape of internasal, sopraocular, prefrontal and frontal scales
(Fig. 1). In particular, the shape of the frontal and parietal scales appears to be highly
diagnostic between the two species. The shape of the head of Z. lineatus is at one extreme of
variation, with a rostral and nasal region narrower with respect to the central portion of the
head, while Z. longissimus is at the other extreme, showing wider rostral and nasal regions.
Intraspecific variation. In Zamenis lineatus both the analysis of relative warps 1 and 2
(accounting for 33.53% and 15.35% of variance respectively) and the Canonical Variates
Analysis on partial warps scores (Wilks’ lambda: 0.00123, F (38.4)= 2.839518, P< 0.1591)
indicate that (i) the samples are very similar to each other, and (ii) there is very low variation.
On the other hand Zamenis longissimus, which has a geographic range much larger than that
of Z. lineatus, is characterized by higher interpopulation variability, as shown by CVA on
the first 42 relative warp scores (Wilks’ lambda= 0.00004 F (252.74.4)= 1.324262, P<
0.0769) (Fig. 2).
Distribution. Our results indicate that the distribution of both species in Italy should be
revised. Contrary to the opinion by Lenk and Wüster (1999), Zamenis longissimus does
occur in Campania. According to our data, this region of southern Italy is inhabited both
by Z. lineatus and Z. longissimus. Hence Campania can be considered as a parapatric contact
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area for the two species. This is probably true also for Apulia (southern Italy), where we
recorded the occurrence of Zamenis longissimus for the first time, for Latium (central Italy),
where the two species occur sympatrically in the southernmost part of the region (see Capula
et al., 2008; Corsetti e Romano, 2008; Corti et al., in press), and for Molise (central Italy),
where both species were found to occur in the western part of the region (Capula et al.,
2010). Based on these data, it can be noted that (i) contrary to the literature data provided
to date, Zamenis longissimus does occur in some areas of southern Italy (e.g. Apulia), (ii)
the range of Zamenis lineatus is wider than that known to date and extends north towards
Molise and Latium (central Italy), and (iii) Z. lineatus and Z. longissimus co-occur at least
in some areas of central (Latium, Molise) and southern Italy (Campania, Apulia) (see Fig.
3). Finally, the occurrence and autochthony of Z. longissimus and/or Z. lineatus in Sardinia
need to be confirmed.
Fig. 1. Distribution of Relative Warps 1 and 2 in samples of Z. lineatus (black circles)
and Z. longissimus (open squares). Deformation grids related to the extremes of
variation along CV1 and CV2 are shown upper right (Z. lineatus) and bottom (Z.
longissimus).
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Fig. 2. Canonical Variates Analysis on partial warps scores in Italian samples of Z. longissimus
(Liguria, Toscana, Abruzzo, Lazio) and in Z. lineatus (Campania, Calabria, Sicilia).
Fig. 3. Distribution of Zamenis longissimus (tan) and Z. lineatus (light blue) in Italy. In
some areas of central (L= Latium; M = Molise) and southern Italy (C= Campania;
A = Apulia) both species occur (area of overlap, dark green). The occurrence and
autochthony of Z. lineatus and/or Z. longissimus in Sardinia (?) need to be confirmed.
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