A review of the elusive bicolored iris Snouted Treefrogs (Anura: Hylidae:Scinax uruguayus group)

Abstract

The genus Scinax currently includes more than 120 species, recovered in two major clades, the S. catharinae and the S. ruber clades. The latter comprises 75 species, most of which remain unassigned to any species groups, while 12 are included in the S. rostratus and S. uruguayus groups. In this paper we present a taxonomic review of the two species currently included in the S. uruguayus group, discussing some putative phenotypic synapomorphies of this group. Although S. pinima and S. uruguayus have been considered as distinct species, this has been based on scant evidence, and several authors doubted of their distinctiveness. Our study of available specimens of S. pinima and S. uruguayus corroborates that both are valid and diagnosable species based on phenotypic evidence. Furthermore, our results show that S. pinima previously known only from its type locality, has a much widespread distribution than previously thought (including the Brazilian states of Paraná, Santa Catarina, and Rio Grande do Sul), which, added to the biological information presented here allows to suggest the removal of this species from the "Data Deficient" IUCN Red List category to "Least Concern". Also, we describe a new species formerly reported as S. aff. pinima and S. uruguayus from NE Argentina and some localities from the Brazilian State of Rio Grande do Sul. All species are diagnosed and characterized using adult and larval morphology, osteology, vocalizations, cytogenetics, and natural history.

Fig 1

Dorsal (left) and ventral (right) views of the body. (A) Scinax fontanarrosai sp. n. (LGE 4451, holotype), (B) S. pinima (WCAB 46238, holotype; now MZUSP 73668), and (C) S. uruguayus (FMNH 10567, holotype). Scale bars = 50 mm.

Fig 2. Scinax fontanarrosai sp. n., holotype (LGE 4451).

(A) Head in lateral view. (B) Left hand in dorsal view. (C) Left hand in ventral view. (D) Left foot in ventral view. Scale bars = 2 mm.

Fig 3. Adult external morphological characters.

Scinax fontanarrosai sp. n. (left), S. pinima (central), and S. uruguayus (right). (A) Head in dorsal view. (B) Color pattern of the bicolored iris. (C) Dorsal views of right hand and foot showing the color pattern of the discs in life. (D) Color pattern of the posterior surface of thighs in life.

Fig 4. Color pattern of Scinax fontanarrosai sp. n. in life.

(A–C) Dorsolateral, (D–F) dorsal, and (G–I) ventral views.

Fig 5. Skeletal morphology of Scinax fontanarrosai sp. n. (LGE 2040, male).

Skull (A) dorsal, (B) ventral, and (C) lateral views. Mandible (D) dorsal view. Hyoid (E) ventral view. Larynx (F) ventral, (G) lateral, and (H) posterior views. Pectoral girdle (I) ventral view. Humerus (J) ventral view. Manus and radioulna (K) dorsal view. Vertebral column and pelvic girdle (L) dorsal and ventral views, respectively from left to right. Femur and tibiofibula, respectively from left to right (M) dorsal view. Pes (N) dorsal view. Scale bars = 1 mm.

Fig 6. Osteological characters.

(A) Dorsal view of the skull showing the level of proximity of the medial margins of the frontoparietals. (B) Shape of vomers. (C) Ventral view of the skull showing the short medial ramus of pterygoid. (D) Dorsal view of the sacral vertebra showing the medially expanded iliosacral sesamoids. Scinax fontanarrosai sp. n. (LGE 2040; left), S. pinima (UFMG 20185; central), and S. uruguayus (LGE 4569; right). Scale bars = 1 mm.

Fig 7. Tadpoles in different views and oral discs.

(A) Scinax fontanarrosai sp. n. (LGE 8529, stage 31), (B) S. pinima (UFMG 2262, stage 28), and (C) S. uruguayus (MNHN 9884, stage 36). The two plates in the specimen of S. uruguayus (MNHN 9884) are covered by the folded oral disc. Scale bars = 5 mm (upper) and 1 mm (lower).

Fig 8. Audiospectrograms (above) and oscillograms (bellow) of the advertisement calls.

(A) Scinax fontanarrosai sp. n. (LGE 4451), (B) S. pinima (UFMG 20184), and (C) S. uruguayus (MNHN 9877). Left: A series of calls. Right: A single call.

Fig 9. Chromosome morphology of Scinax fontanarrosai sp. n. (LGE 4472).

(A) Conventional staining. (B) C-banding technique. (C) Ag-NORs. Arrows indicate the NOR bearing chromosome pair. Scale bar = 10 μm.

Fig 10. Partial map of the South American Ecoregions showing the known geographical distribution of the species of the Scinax uruguayus group.

Scinax fontanarrosai sp. n. (light blue circles; white star: type locality), S. pinima (yellow circles; yellow star: type locality), and S. uruguayus (red circles; black star: type locality). Abbreviations: ARG = Argentina, BRA = Brazil, PRY = Paraguay, and URY = Uruguay. Brazilian states: MG = Minas gerais, PR = Paraná, RS = Rio Grande do Sul, SC = Santa Catarina, and SP = São Paulo. Argentinian provinces: CR = Corrientes and MN = Misiones.

Fig 11. Calling males, defensive behavior, and egg clutches.

Males of (A–B) Scinax fontanarrosai sp. n. and (C–D) S. uruguayus calling at breeding sites. Male of (E) S. fontanarrosai sp. n. and a juvenile of (F) S. uruguayus performing the passive defensive “crouching down” behavior. (G) and (H) egg clutches of S. uruguayus. Note the dark brown to black animal pole and a dark cream vegetal pole in G.

Fig 12. Color pattern of Scinax pinima in life.

(A–C) Dorsolateral, (D–E) dorsal, and (F) ventral views. Photo (A) courtesy of J Pombal Jr.

Fig 13. Color pattern of Scinax uruguayus in life.

(A–C) Dorsolateral, (D–F) dorsal, and (G–I) ventral views.