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The genus Trachycephalus Tschudi, 1838 currently includes 18 valid species distributed throughout Mexico, Central, and South America (Blotto et al., 2020; Frost, 2020). At this time, 14 Trachycephalus species are known to occur in Brazil (Segalla et al., 2019; Blotto et al., 2020), and seven of them are found in the Amazonia: Trachycephalus coriaceus (Peters, 1867), T. cunauaruGordo, Toledo, Suárez, Kawashita-Ribeiro, Ávila, Morais, and Nunes, 2013, T. hadroceps (Duellman and Hoogmoed, 1992), T. helioi Nunes, Suárez, Gordo, and Pombal, 2013, T. resinifictrix (Goeldi, 1907), T. typhonius (Linnaeus, 1758), and T. venezolanus (Mertens, 1950). Of these species, only T. typhonius is widely distributed in South America, while the six remaining are Amazonian species (La Marca et al., 2010; Gordo et al., 2013; Nunes et al., 2013; Meneghelli et al., 2017; Meneghelli and Calderon 2017; Carvalho et al., 2018).
As most species within this genus, the milk frog Trachycephalus coriaceus have a paired, lateral vocal sac, a putative morphological synapomorphy of the genus (Faivovich et al., 2005); the exceptions are T. hadroceps and T. helioi, which have a single, subgular vocal sac (Nunes et al., 2013). Besides, this species can be easily diagnosed from its congeners by having (1) a dark bronze or golden iris without radial lines, (2) a pair of black blotches where the forearm inserts into the body, and (3) dorsum and flanks covered by brown shades or distinct brown rectangular blotches that extends from the upper eyelids to the lower sacral region (Duellman, 2005).
The current known geographic distribution of Trachycephalus coriaceus in the Amazonia is characterized by extensive gaps, with sparse records throughout Guyana, Surinam, French Guyana, Colombia, Ecuador, Peru, Bolivia, and Brazil (e.g., Peters, 1867; De la Riva, 1994; Gottsberger and Gruber, 2001; Duellman, 2005; Cole et al., 2013). In Brazil, T. coriaceus was already reported to occur in the States of Acre, Amapá, Amazonas, and Rondônia (Zimmerman and Rodrigues, 1990; Bernarde et al., 2011; Benício and Lima, 2017; Meneghelli et al., 2017). Herein, we report a new record of T. coriaceus for the Brazilian southern Amazonia, Pará state. Additionally, we provide an updated geographic distribution map for this species based on literature data (e.g., Gottsberger and Gruber, 2001; Bernarde et al., 2011; Cole et al., 2013; Benício and Lima, 2017; Meneghelli et al., 2017) and in our fieldwork (Supplementary material).
On November 8th of 2016, during a nocturnal survey inside a dense ombrophilous forest in the right bank of the Teles Pires River, municipality of Jacareacanga, southern of Pará state (9°15' S, and 56°47' W, 194 m. a. s. l), we collected one specimen of Trachycephalus coriaceus (Fig. 1a). The individual was fortuity found after it drop-down from a tree in front of the researcher. The collected specimen was euthanized using 5 % lidocaine, fixed in 10 % formalin, and then permanently stored in 70 % alcohol. We collected the specimen under permit ICMBio 54493-12 and deposited it at Coleção Zoológica da Universidade Federal de Mato Grosso do Sul (ZUFMS-AMP08782; Snout-vent length: 63.3 mm).
Figure 1 Trachycephalus coriaceus (ZUFMS-AMP08782) collected in Jacareacanga, Pará state (a), and Trachycephalus cunauaru (Field series: AAGARDA12670) recorded in Paranaíta, Mato Grosso state (b), Brazil.
The record of Trachycephalus coriaceus to the municipality of Jacareacanga is the first for Pará state and extends its geographic distribution nearly 760 km southeast from the nearest record in the municipality of Manaus, Amazonas state (Zimmerman and Rodrigues, 1990), 790 km eastward from the municipality of Porto Velho, Rondônia state (Meneghelli et al., 2017), and 920 km northeast from the Puerto Almacén, Santa Cruz, Bolivia (De La Riva, 1994). This record also extends the range of T. coriaceus nearly 1480 km southward from the type locality, Suriname (Peters, 1867) (Fig. 2). This was the only observation of T. coriaceus so far after 12 field expeditions of 15 days each in the study area, between 2015 and 2019. In contrast, we observed the congener T. cunauaru (Fig. 1b) in reproductive behavior during different expeditions in the same area.
Figure 2 Geographic distribution map of Trachycephalus coriaceus in South America. Asterisk: new record for the Pará state; Star: type locality in Suriname. White circles: literature records.
We believe that the highly disjointed geographic distribution of T. coriaceus likely emerges from an interaction between the i) extensive knowledge gaps throughout the Amazonia (e.g., Mayer et al., 2019; Cracraft et al., 2020), and ii) the explosive reproductive behavior of T. coriaceus, since that the individuals of this species remain inactive most of the year and become active by just a few days (Duellman, 2005), which hamper its records during field surveys.
The Tapajos endemism center is one of the most jeopardized Amazonian regions by anthropogenic pressures (Braz et al., 2016). The Teles Pires River is located at the South of Tapajos endemism center and struggles with extensive damming by hydroelectric plants established along with it (e.g., ANA, 2020). As a consequence of this activity, the river becomes highly fragmented, the large artificial lakes provoke irreversible losses of natural habitats and drives the climate changes by the emission of methane gas (Fearnside, 2000). Even though fishes are the most obviously impacted groups by hydroelectric power plants (Pelicice et al., 2015), deleterious effects of this activity on amphibians are also well demonstrated (Brandão and Araújo, 2008; Silva et al., 2018). The effectiveness of public policies is diminished given the current situation of knowledge gaps regards the Amazonian amphibians. The new record of T. coriaceus from a highly threatened Amazonian region represents a small but essential step toward the great challenge of understanding the Amazonia biota and provides information for future conservation actions.
