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SYSTEMATICS OF SNAKES OF THE DIPSAS OREAS COMPLEX

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Bull. Mus. Comp. Zool., 158(3): 67–136, July, 2005 67SYSTEMATICS OF SNAKES OF THEDIPSAS OREASCOMPLEX(COLUBRIDAE: DIPSADINAE) IN WESTERN ECUADOR AND PERU,WITH REVALIDATION OFD. ELEGANS(BOULENGER) ANDD. ELLIPSIFERA(BOULENGER)JOHN E. CADLE1CONTENTSAbstract--------------------------------------------------------------------67Resumen------------------------------------------------------------------68Introduction------------------------------------------------------------69Methods-------------------------------------------------------------------70Localities: The Rı´o Zan˜ a Study Site--------------70Systematic Characters, with SpecialReference to Dipsas----------------------------------71The Dipsas oreas Complex: Resurrection ofD. elegans and D. ellipsifera-----------------------74Dipsas ellipsifera (Boulenger)-----------------------------77Dipsas elegans (Boulenger)---------------------------------88Dipsas oreas (Cope)----------------------------------------------97Notes on the Holotype-------------------------------------98Diagnosis-------------------------------------------------------------98Description---------------------------------------------------------100Hemipenis-----------------------------------------------------------108Geographic Variation in Dipsas oreas andthe Identity of Peruvian Specimens-------108Distribution and Type Locality-----------------------112Natural History: Habitats, Activity Patterns,Eggs, and Hatchlings--------------------------------116Aggregation Behavior in Dipsas oreas----------120Taxonomic and Geographical Notes onDipsas gracilis, D. latifasciatus, andD. latifrontalis------------------------------------------------122Dipsas gracilis----------------------------------------------------123Dipsas latifasciatus and D. latifrontalis inEastern Ecuador and Peru----------------------126Key to Species of Dipsas in Western SouthAmerica------------------------------------------------------------127Acknowledgments--------------------------------------------------129Specimens Examined and Locality Records----130Literature Cited-----------------------------------------------------1321Department of Herpetology, Chicago ZoologicalSociety, 3300 Golf Road, Brookfield, Illinois 60513.Associate, Department of Herpetology, Museum ofComparative Zoology.ABSTRACT. The systematics and biology of colubridsnakes from western Ecuador and northern Peru inthe Dipsas oreas group, comprising the nominal taxaD. oreas (Cope), D. elegans (Boulenger), and D. el-lipsifera (Boulenger), are reviewed. The last two spe-cies are resurrected from the synonymy of D. oreas.These species, especially D. elegans and D. ellipsi-fera, have been confused in previous literature be-cause of inadequate attention to patterns of sexualdimorphism and geographic variation. Dipsas elegansand D. ellipsifera share a distinctive color pattern thatis quite different from color patterns in D. oreas. Dip-sas ellipsifera differs from both D. oreas and D. ele-gans in having lower ventral and subcaudal counts,but sexes must be analyzed separately to see the dis-tinctions clearly. Other subtle characters of scutella-tion, coloration, and dentition aid in distinguishingthese species. Dipsas elegans is unusual in that maleshave significantly more ventral scutes than females,the reverse of the more common colubrid pattern ofsexual dimorphism, in which females have more ven-trals than males; neither D. oreas nor D. ellipsifera issexually dimorphic for this character.Dipsas ellipsifera is known only from the valley ofthe Rı´o Mira in extreme northwestern Ecuador (Im-ababura Province). Dipsas elegans is known from thewestern versant of the Andes in Ecuador from justnorth of the equator to about latitude 28S; it is alsofound in the inter-Andean valley of the upper Rı´oGuayllabamba east of Quito. Dipsas oreas is knownfrom southern Chimborazo and Guayas Provincessouth to Loja Province in southern Ecuador, thencesouth along the western slopes of the Andes to atleast the Rı´o Zan˜a (68519S) in northern Peru. Theoccurrence and distribution of D. oreas in Peru isdetailed for the first time. Most localities for D. oreasare on the Andean slopes, but the species is also re-corded by specimens from the lowlands in the vicinityof Guayaquil, Ecuador. The type locality of D. oreasand many other South American amphibians and rep-tiles obtained by the naturalist James Orton is the‘‘elevated Valley of Quito,’’ which has been errone-68 Bulletin Museum of Comparative Zoology, Vol. 158, No. 3ously interpreted narrowly as the vicinity of Quito,Ecuador. Orton’s own writings show that a broaderinterpretation encompassing virtually all of the Ec-uadorian highlands was intended. The ranges of D.elegans, D. ellipsifera, and D. oreas are very likelyextremely fragmented because of significant destruc-tion of forest habitats in western Ecuador and Peru.Hemipenes of Dipsas elegans, D. ellipsifera, andD. oreas are slightly bilobed, fully capitate, and haveornamentation similar to other species of the tribeDipsadini (Dipsas, Sibon, Sibynomorphus, and Tro-pidodipsas). The capitulum is ornamented with pa-pillate calyces and the sulcus spermaticus bifurcateswithin the capitulum. Proximal to the capitulum abattery of enlarged spines encircles the midsection ofthe organ. A large basal nude pocket is present onthe hemipenis in all three species.Notes on coloration, natural history, and behaviorare reported for the three species of the oreas group,although most observations are for Dipsas oreas. Innorthern Peru, D. oreas shows extensive intrapopu-lational variation in coloration, which could in part besexually dimorphic. It is unclear whether this varia-tion pertains to other parts of the distribution. Dipsasoreas is active nocturnally in low vegetation but seeksseclusion in leaf litter or under surface objects on theground during the day. This diel behavior pattern isalso reported for several other species of Dipsas andmight be common in the genus. In northern Peru,the activity of adult D. oreas is strongly seasonal andcoincides with the rainy season. A peculiar aggrega-tion of Dipsas oreas encountered at a locality innorthern Peru is described. Comprising one femaleand six males, this is the first reported case of ‘‘ag-gregation behavior’’ in any snake of the tribe Dipsa-dini and one of very few observations of such behav-ior in Neotropical colubrids. Details of the aggrega-tion suggest an association with mating, and the


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