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The genus Rhinella Fitzinger, 1826 comprises 92 species distributed in North, Central, and South America (Frost, 2022). In Paraguay, eight species are known to occur (Brusquetti & Lavilla, 2006; Pereyra et al., 2021a, 2021b): R. azarai (Gallardo, 1965), R. bergi (Céspedez, 2000), R. diptycha (Cope, 1862), R. dorbignyi (Duméril and Bibron, 1841), R. icterica (Spix, 1824), R. major (Müller and Hellmich, 1936), R. ornata (Spix, 1824), and R. scitula (Caramaschi & Niemeyer, 2003). Rhinella icterica is a large robust toad (females can reach up to 190 mm), with heavily developed cephalic crests (Cei, 1980; Kwet & Di-Bernardo, 1999), and is a member of the Rhinella marina Group (Pereyra et al., 2021a). The distribution of the species covers southern, northeastern, and a portion of central Brazil (Rio Grande do Sul north to Bahia, Minas Gerais, and Goiás); Misiones province, Argentina, and isolated populations in eastern Paraguay (Frost, 2022).
Rhinella icterica was first cited for Paraguay in Frost (1985), and then in Aquino et al. (1996), however, no reference material was provided in either. The presence of the species was formally confirmed in Brusquetti & Lavilla (2006) based on two specimens deposited in the Museo Nacional de Historia Natural del Paraguay: MNHNPy 6338 from Parque Nacional Cerro Corá, Amambay department, and MNHNPy 9328 from Reserva Natural de Bosque Mbaracayú, Puesto Aguara Ñú, Canindeyú department. These localities correspond to the southern limits of the Cerrado ecoregion sensuDinerstein et al. (1995). Subsequently, Maciel et al. (2007) described R. cerradensis, a large species of the R. marina Group morphologically similar to R. icterica, R. marina, R. poeppigii, R. diptycha, and R. jimi but distinguishable by the well-developed cranial crests and parotoid gland, shape of the head and body sizes (Maciel et al., 2007).
Rhinella cerradensis is known from northeastern to central-western Brazil, in the Cerrado ecoregion (Maciel et al., 2007; Maciel et al., 2010; Santana et al., 2010), with a population in the Municipality of Dourados, State of Mato Grosso do Sul, close to the records of R. icterica from Paraguay. Although the presence of R. cerradensis in Paraguay is plausible, the taxonomic identity of the specimens from eastern Paraguay has never been reassessed and the name R. icterica has been maintained until now (Motte et al., 2009; Weiler et al., 2013; Cacciali et al., 2015; Motte et al., 2019; Cabral et al., 2020).
Considering the geographic localization of the records of R. icterica from Paraguay and the morphological similarities between R. icterica and R. cerradensis, we re-analyzed both specimens to clarify their identity. Based on the diagnostic characters proposed by Maciel et al. (2007), we compared the Paraguayan specimens with others of R. icterica and R. cerradensis housed in the Amphibian Collection Célio F. B. Haddad (CFBH), Departamento de Zoologia, I.B., Universidade Estadual Paulista, Rio Claro, São Paulo, Brazil.
Both specimens from Paraguay (MNHNPy 6338, 9328) present the character states that diagnose R. cerradensis from R. icterica: less developed preocular crest (Figs. 1A-D), tympanum without folded skin (present in R. icterica,Figs. 1A-D), smaller parotoid glands (Figs. 1E-H), and narrower head (Figs. 1E-H). According to these comparisons, we confirm the presence of R. cerradensis in eastern Paraguay in small incursions of Cerrado ecoregion in the departments of Amambay and Canindeyú (Fig. 2) extending the species distribution 130 km W (Amambay record), 220 km S (Canindeyú record) from the nearest records in Mato Grosso do Sul (Santana et al., 2010). With the reassignment of these two specimens to R. cerradensis, there is no evidence for the occurrence of R. icterica in Paraguay, and thus it must be excluded from the herpetofauna of the country.
Figure 1 Lateral view of Rhinella cerradensis specimens (A) MNHNPy 6338, Parque Nacional Cerro Corá, Amambay department; Paraguay, white arrows showing the pre-ocular crest and the tympanum without folded skin; (B) MNHNPy 9328, Reserva Natural de Bosque Mbaracayú, Puesto Aguara Ñú, Canindeyú department, Paraguay; (C) CFBH 20517, Jaborandi, Bahia state, Brazil; and (D) R. icterica specimen, CFBH 37279, Tanguá, Rio de Janeiro state, Brazil, white arrows showing the pre-ocular crest and the tympanum with folded skin. Dorsal view of R. cerradensis specimens (E) MNHNPy 6338, white arrow showing the parotoid gland; (F) MNHNPy 9328; (G) CFBH 20517; and (H) R. icterica specimen CFBH 37279, white arrow showing the parotoid gland. / Figura 1. Vista lateral de Rhinella cerradensis (A) MNHNPy 6338 del Parque Nacional Cerro Corá, Departamento de Amambay, Paraguay, las flechas blancas señalan la cresta pre-ocular y tímpano sin pliegue; (B) MNHNPy 9328 de la Reserva Natural de Bosque Mbaracayú, Puesto Aguara Ñú, Departamento de Canindeyú, Paraguay; (C) CFBH 20517, Jaborandi, Bahia, Brasil; (D) R. icterica CFBH 37279, Tanguá, Rio de Janeiro, Brasil, las flechas blancas señalan la cresta pre-ocular y tímpano con pliegue. Vista dorsal de R. cerradensis (E) MNHNPy 6338, flecha blanca señala la glándula parotoidea; (F) MNHNPy 9328; (G) CFBH 20517; y de Rhinella icterica (H) CFBH 37279, flecha blanca señala la glándula parotoidea.
Figure 2 Distribution map of Rhinella cerradensis (black dots); type locality, Brasília, Distrito Federal (white dot); new records from the Cerrado ecoregion in Paraguay (stars). / Figura 2. Mapa de distribución de Rhinella cerradensis (círculos negros), localidad tipo Brasilia, Distrito Federal (círculo blanco), nuevos registros de la ecorregión del Cerrado en Paraguay (estrellas).
Vera Candioti et al. (2016) and Ferraro et al. (2018) comment on the presence of a population of large toads morphologically similar to R. cerradensis assigned as R. cf. cerradensis in Corrientes, Argentina. It is also important to mention that in a phylogenetic analysis of the genus Rhinella (Pereyra et al., 2021a) specimens from Misiones, Argentina, and Rivera, Uruguay assigned as R. aff. cerradensis clustered in a different lineage than R. cerradensis sensu stricto. Nonetheless, the authors abstained from making taxonomic decisions considering the evidence of nuclear and/or mitochondrial introgressions and phenotypic plasticity, among others, as promoters of the morphological diversity of the group.
Since no molecular data are available for the specimens from eastern Paraguay, we cannot be unfailingly certain if they are R. cerradensis or are more related to the populations of Argentina and Uruguay. However, once the former species appears to be restricted to the Cerrado and the records of R. aff. cerradensis in Argentina and Uruguay correspond to the Southern Cone Mesopotamian savanna and Uruguayan savanna (Dinerstein et al., 1995) we assign the specimens from eastern Paraguay to R. cerradensis.
