systematics of snakes of the dipsas oreas complex - BioOne

122 Bulletin Museum of Comparative Zoology, Vol. 158, No. 3
and attempting to paint a scenario of what
seems to occur. At the Río Zaña site, eggs
of D. oreas with well developed embryos
were discovered in mid-June in a well-secluded,
relatively cool location deep within
a crevice (details reported above). The advanced
developmental stages of two embryos
suggest that the eggs were laid some
time prior to their discovery in mid-June.
This observation, combined with the observed
aggregation of several adult males
and an adult female in late January, suggests
that a mating period in late January
may not be unreasonable. Moreover, the
condition of the oviducts in the female and
the vasa deferentia in the males suggest
that these individuals were reproductively
competent. The delay between the presumed
mating period and egg laying would
give ample time for fertilization and yolking
of the ova.
In a related colubrid, Sibynomorphus
ventrimaculatus, mating apparently takes
place several months (perhaps as many as
seven) before vitellogenesis commences
and egg-laying occurs (Cechin and Oliveira,
2003). A similar sequence in Dipsas
oreas would explain the small follicles in
the female described above well before
the inferred oviposition season. The strong
seasonal activity pattern of D. oreas at the
Río Zaña Study Site, as well as the few
observations on eggs and hatchings, imply
that reproduction is strongly seasonal in
this species, at least in the southern part
of its range. Other species of Dipsas that
inhabit less seasonal environments of
Amazonia or the Atlantic Forest of southeastern
Brazil are apparently aseasonal in
their reproductive patterns (Zug et al.
[1979] for D. catesbyi; Porto and Fernandes
[1996] for D. neivai), and some other
members of the Dipsadini have extended
periods of oviposition (e.g., two species of
Sibynomorphus; Laporta-Ferreira et al.,
1986).
Aggregation behavior is best known in
north temperate species of natricine colubrids
and viperids, although scattered observations
of scolecophidians, elapids, and
other groups of colubrids suggest that aggregation
behavior is taxonomically widespread.
Aggregations have previously been
reported in three other species of Neotropical
colubrids. An aggregation of
Rhadinaea calligaster (Myers, 1974: 221)
in a pile of decomposing thatch consisted
of six females and a male. Females were
apparently attracted to the site for oviposition
because a communal nest was in the
same pile of debris. The other cases involve
aggregations for mating functions in
snakes of the clade Colubrinae (sensu Cadle,
1984c, 1985): Drymobius margaritiferus
(Campbell, 1998: 213) and Chironius
flavolineatus (Feio et al., 1999). The observations
reported here for Dipsas oreas
constitute the first report of aggregation
behavior in any species of Dipsadini (Dipsas,
Sibon, Tropidodipsas, Sibynomorphus)
and one of only three cases of mating
aggregations in Neotropical colubrids.
Because communal nests are now known
in two distantly related members of the
larger Neotropical clade Dipsadinae (sensu
Cadle, 1984b; Zaher, 1999), D. oreas and
Rhadinaea calligaster, aggregation behavior
for oviposition may be widespread
within this group if particular oviposition
sites offer favorable conditions for egg development.
TAXONOMIC AND GEOGRAPHICAL
NOTES ON DIPSAS GRACILIS,
D. LATIFASCIATUS, AND
D. LATIFRONTALIS
While studying the systematics of species
in the Dipsas oreas complex and others
in western Ecuador and Peru (e.g., Cadle
and Myers, 2003) I had occasion to
examine specimens of other species reported
from the eastern and western versants
of the Andes in this region. In a few
cases, the specimens examined amplified
distributional knowledge of species or
raised questions concerning systematic
and nomenclatural issues. I here comment
on these points for three species. Dipsas
gracilis has been well known from the
western lowlands of Ecuador, but new in-