Herpetologica, 61(2), 2005, 178–198 Ó 2005 by The Herpetologists’ League, Inc. A NEW, CRYPTIC SPECIES OF PHYSALAEMUS (ANURA: LEPTODACTYLIDAE) FROM WESTERN ECUADOR WITH COMMENTS ON THE CALL STRUCTURE OF THE P. PUSTULOSUS SPECIES GROUP SANTIAGO R. RON 1,2,3 ,LUIS A. COLOMA 2 , AND DAVID C. CANNATELLA 1 1 Section of Integrative Biology and Texas Memorial Museum, The University of Texas, Austin, TX 78712, USA 2 Museo de Zoologı´a, Centro de Biodiversidad y Ambiente, Escuela de Biologı´a, Pontificia Universidad Cato´lica del Ecuador, Av. 12 de Octubre y Roca, Aptdo. 17-01-2184, Quito, Ecuador ABSTRACT: We describe a new species of leptodactylid frog of the genus Physalaemus from the lowlands of western Ecuador. It belongs to the P. pustulosus species group and differs from other group members in its smaller size, skin texture, tadpole characters, and advertisement call. The new species has wide variation in size and color pattern both at the intra- and inter-population levels. This variation matches that observed in P. montubio and P. randi, and render difficult its diagnosis on the basis of morphological features. A phylogenetic analysis of morphological characters shows that the new species belongs to a clade distributed west of the Andes in Ecuador and northern Peru, sister to (P. petersi þ P. pustulosus). A phylogeny based on mtDNA shows that P. montubio and P. randi form a clade sister to (P. coloradorum þ P. sp. nov.). The calls of these three species have two components with different acoustic features that arguably match the frequency sensitivity of the ear of conspecific females, in a manner similar to the complex calls of P. pustulosus. The new species occurs in two predominantly dry regions, the Lowland Deciduous Costa Forest, and the Lowland Semideciduous Costa Forest. Key words: Anura; Advertisement call; Ecuador; Leptodactylidae; Morphology; New species; Phylogeny; Physalaemus guayaco; Physalaemus montubio; Physalaemus pustulatus; Physalaemus pustulosus group; Physalaemus randi; Sensory exploitation hypothesis; Tadpole ECUADOR has one of the highest amphibian species richnesses, with a total of 441 de- scribed species (updated from Coloma and Quiguango, 2000–2003). Within Ecuador, the biogeographic regions with the highest re- gional diversities are the montane forests of the Andean slopes. Conversely, the most depauperate amphibian communities are those from the driest habitats in Ecuador, the Dry Costa Shrub and the Deciduous and Semideciduous Costa forest (S. R. Ron, un- published; vegetation types as defined in Sierra et al., 1999). Although covering an area of approximately 33,700 km 2 (Sierra et al., 1999) only 25 amphibian species have been recorded in these dry habitats. At least 19 of those amphibians have significant portions of their distribution ranges in adjacent habitat types, especially the Chocoan Tropical Rainforest. The remaining species have distributions re- stricted (or nearly so) to dry habitats and are therefore unique elements of the amphibian fauna. These species are Ceratophrys stolz- manni, Leptodactylus labrosus, Physalaemus pustulatus, Colostethus infraguttatus, C. ela- chyhistus, and Rana bwana. Surveys carried out in 2002 and 2003 at the Deciduous and Semideciduous Costa forest have resulted in additions to this short list. Two species of Physalaemus belonging to the P. pustulosus species group have been described recently (Ron et al., 2004). Herein, we de- scribe an additional species of the same group from the lowlands of western Ecuador. During fieldwork in 2002, specimens of the new species initially were misidentified as P. montubio because of similarities of their calls and external morphology. However, analyses of mitochondrial DNA and a careful examina- tion of the morphology of adults made evident the distinctiveness of this new species from other members of the P. pustulosus group. METHODS Morphological terminology and abbrevia- tions follow Lynch and Duellman (1997) for adults and Altig and McDiarmid (1999) for tadpoles. Osteological characters used in the diagnosis were examined in clear-and-stained 3 Correspondence : e-mail, sron@mail.utexas.edu 178