systematics of snakes of the dipsas oreas complex - BioOne

Dipsas oreas Complex in Ecuador and Peru • Cadle 109
4, 5), who considered the species identification
provisional at the time. Cadle and
Myers (2003) discussed the species in resurrecting
D. andiana from its synonymy;
however, they did not specifically address
the attribution of the Peruvian specimens
to D. oreas. Some minor differences exist
between the Peruvian and Ecuadorian
specimens of D. oreas, but there is sufficient
similarity to conclude that the range
of D. oreas extends well into northern
Peru. Nonetheless, some commentary
concerning the referred Peruvian specimens
is warranted. In assessing the following
characterization of variation within Peruvian
specimens of D. oreas, it is helpful
to keep in mind that this sample is overwhelmingly
dominated by specimens from
the Río Zaña Study Site, which accounts
for 17 of the 21 Peruvian specimens; thus,
most of the variation within the ‘‘Peruvian
sample’’ of this species actually represents
intrapopulational variation within the Río
Zaña Study Site population (Table 3).
There is a weak suggestion of a geographic
cline in the number of dorsal
bands on the body in Dipsas oreas, although
samples are inadequate to analyze
the trend thoroughly and are heavily
weighted toward Peruvian specimens. Arrayed
roughly north to south, the number
of bands on the body in aggregated samples
are (ranges followed by mean SD
and sample size in parentheses):
Chimborazo Province
‘‘Western Ecuador’’:
22–30, 24.8 2.73 (N 7)
Guayas Province, Ecuador:
23–29, 25.3 2.21 (N 7)
Loja Province, Ecuador:
19–30, 24.5 7.78 (N 2)
Peru:
17–24, 19.7 1.63 (N 19)
Differences in the number of bands for
these samples is mainly accounted for by
the width of bands on the anterior body,
which generally cover 8–10 dorsal scale
rows in Peruvian specimens compared
with only 5–7 rows in Ecuadorian specimens.
Midbody and posterior bands are of
similar widths throughout the range (usually
3–5 scale rows).
Ecuadorian and Peruvian specimens of
Dipsas oreas also differ in some scutellation
and other characteristics, but these
are primarily average or frequency differences
rather than discrete character differences.
The differences between the
‘‘Ecuador’’ and ‘‘Total’’ samples of D. oreas
in Table 1 are accounted for by the incorporation
of Peruvian specimens into the
‘‘Total’’ sample summary (see also Table 3
for summary characteristics of a population
sample from Peru). Ecuadorian specimens
average higher numbers of ventral
scales; have different frequencies of loreal,
temporal, and labial scale patterns; and
differ in modal number of maxillary teeth.
All Ecuadorian specimens (N 18) examined
have a single pair of infralabials in
contact behind the mental, whereas Peruvian
specimens (N 19) have either a
single pair (N 7), two pairs (N 4), or
one infralabial contacting two on the opposite
side (N 8).
Loreal pattern 6 (Fig. 1) was observed
only in specimens from the Río Zaña
Study Site (Peru), but in this population it
occurred with high frequency (13 of 40
observations, considering each side of a
specimen as an independent observation).
A few specimens do not fit the discrete
loreal patterns outlined. For example,
UMMZ 56491 (Chimborazo/Cañar Province,
Ecuador) has, on the left side, a small
preocular that lies superior to an extension
of the prefrontal intercalated between the
preocular and the loreal scale; the prefrontal
touches the eye at little more than a
point. The right side of the same specimen
has loreal pattern 2, but a partial suture on
the posterolateral portion of the prefrontal
is suggestive of a partially formed preocular
scale. Variations such as this, and the
similar relationship between patterns 3
and 4, give credence to the idea of a developmental
relationship between patterns
1 and 2 on one hand and patterns 3 and 4
on the other. These apparent developmen-