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SYSTEMATICS OF SNAKES OF THE DIPSAS OREAS COMPLEX (COLUBRIDAE: DIPSADINAE) IN WESTERN ECUADOR AND PERU, WITH REVALIDATION OF D. ELEGANS (BOULENGER) AND D. ELLIPSIFERA (BOULENGER)

J. Cadle

Published 2005 in Unknown venue

ABSTRACT

ABSTRACT The systematics and biology of colubrid snakes from western Ecuador and northern Peru in the Dipsas oreas group, comprising the nominal taxa D. oreas (Cope), D. elegans (Boulenger), and D. ellipsifera (Boulenger), are reviewed. The last two species are resurrected from the synonymy of D. oreas. These species, especially D. elegans and D. ellipsifera, have been confused in previous literature because of inadequate attention to patterns of sexual dimorphism and geographic variation. Dipsas elegans and D. ellipsifera share a distinctive color pattern that is quite different from color patterns in D. oreas. Dipsas ellipsifera differs from both D. oreas and D. elegans in having lower ventral and subcaudal counts, but sexes must be analyzed separately to see the distinctions clearly. Other subtle characters of scutellation, coloration, and dentition aid in distinguishing these species. Dipsas elegans is unusual in that males have significantly more ventral scutes than females, the reverse of the more common colubrid pattern of sexual dimorphism, in which females have more ventrals than males; neither D. oreas nor D. ellipsifera is sexually dimorphic for this character. Dipsas ellipsifera is known only from the valley of the Río Mira in extreme northwestern Ecuador (Imababura Province). Dipsas elegans is known from the western versant of the Andes in Ecuador from just north of the equator to about latitude 2°S; it is also found in the inter-Andean valley of the upper Río Guayllabamba east of Quito. Dipsas oreas is known from southern Chimborazo and Guayas Provinces south to Loja Province in southern Ecuador, thence south along the western slopes of the Andes to at least the Río Zaña (6°51′S) in northern Peru. The occurrence and distribution of D. oreas in Peru is detailed for the first time. Most localities for D. oreas are on the Andean slopes, but the species is also recorded by specimens from the lowlands in the vicinity of Guayaquil, Ecuador. The type locality of D. oreas and many other South American amphibians and reptiles obtained by the naturalist James Orton is the “elevated Valley of Quito,” which has been erroneously interpreted narrowly as the vicinity of Quito, Ecuador. Orton's own writings show that a broader interpretation encompassing virtually all of the Ecuadorian highlands was intended. The ranges of D. elegans, D. ellipsifera, and D. oreas are very likely extremely fragmented because of significant destruction of forest habitats in western Ecuador and Peru. Hemipenes of Dipsas elegans, D. ellipsifera, and D. oreas are slightly bilobed, fully capitate, and have ornamentation similar to other species of the tribe Dipsadini (Dipsas, Sibon, Sibynomorphus, and Tropidodipsas). The capitulum is ornamented with papillate calyces and the sulcus spermaticus bifurcates within the capitulum. Proximal to the capitulum a battery of enlarged spines encircles the midsection of the organ. A large basal nude pocket is present on the hemipenis in all three species. Notes on coloration, natural history, and behavior are reported for the three species of the oreas group, although most observations are for Dipsas oreas. In northern Peru, D. oreas shows extensive intrapopulational variation in coloration, which could in part be sexually dimorphic. It is unclear whether this variation pertains to other parts of the distribution. Dipsas oreas is active nocturnally in low vegetation but seeks seclusion in leaf litter or under surface objects on the ground during the day. This diel behavior pattern is also reported for several other species of Dipsas and might be common in the genus. In northern Peru, the activity of adult D. oreas is strongly seasonal and coincides with the rainy season. A peculiar aggregation of Dipsas oreas encountered at a locality in northern Peru is described. Comprising one female and six males, this is the first reported case of “aggregation behavior” in any snake of the tribe Dipsadini and one of very few observations of such behavior in Neotropical colubrids. Details of the aggregation suggest an association with mating, and the existence of communal nesting in this species suggests that aggregation might occur for oviposition as well. A key to all species of Dipsas reported or expected in western South America (Colombia, Ecuador, and Peru) is provided. This includes six species known from western Ecuador (andiana, elegans, ellipsifera, gracilis, oreas, and temporalis), two of which (gracilis, oreas) also occur in western Peru, and three additional species known or expected in Chocoan Colombia (nicholsi, sanctijohannis, and viguieri). Dipsas gracilis and D. viguieri are not distinguishable by any reported characteristics of the taxa. Brief notes are provided on the occurrence of D. gracilis in northwestern Peru. Some taxonomic issues concerning two species of the Amazonian versant, D. latifasciata and D. latifrontalis, are outlined. These species are not clearly distinguishable on the basis of characters discussed in the literature, and the assignment of these names to specimens from eastern Ecuador needs to be reviewed in conjunction with study of their holotypes.

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