Introduction

In the mid-1970s, expeditions financed by the Museu de Zoologia da Universidade de São Paulo and the Smithsonian Institution allowed a better understanding of the amphibian species of the Rivers Purus and Madeira in Brazil (Heyer 1976). Heyer (1977) described two new genera (Phyllonastes and Phyzelaphryne) and two new species (Hyla pauiniensis and Phyzelaphryne miriamae), the former of which was included in the Hyla parviceps group sensu Duellman & Crump (1974). Discoveries in southwestern Brazilian Amazonia continued into the 1980s, making it a period of great advancement in the knowledge of this region's herpetofauna. Soon after, William Duellman and Linda Trueb, working in the Madre de Dios region of Peru, described two species: Hyla allenorum and Hyla koechlini (Duellman & Trueb 1989). In their review of the family Hylidae, Faivovich et al. (2005) resurrected the genus Dendropsophus to include the Hyla species with 30 chromosomes, organised in nine groups (columbianus, garagonensis, labialis, leucophyllatus, marmoratus, microcephalus, minimus, minutus and parviceps). Fifteen species were assigned to the Dendropsophus parviceps group, including Dendropsophus allenorum (Duellman & Trueb, 1989), Dendropsophus bokermanni (Goin, 1960), Dendropsophus brevifrons (Duellman & Crump, 1974), Dendropsophus gaucheri (Lescure & Marty, 2001), Dendropsophus giesleri (Mertens, 1950), Dendropsophus grandisonae (Goin, 1966), Dendropsophus koechlini (Duellman & Trueb, 1989), Dendropsophus luteocellatus (Roux, 1927), Dendropsophus microps (Peters, 1872), D. parviceps (Boulenger, 1882), Dendropsophus pauiniensis (Heyer, 1977), Dendropsophus ruschii (Weygoldt & Peixoto, 1987), Dendropsophus schubarti (Bokermann, 1963), Dendropsophus subocularis (Dunn, 1934), and Dendropsophus timbeba (Martins & Cardoso, 1987).

Fig. 1.

Dorsal (A), lateral (B) and ventral (C) view of the Dendropsophus pauiniensis holotype MZUSP 49892.

Among them, the taxa D. pauiniensis and D. koechlini share remarkable morphological similarities. Inasmuch, Orrico et al. (2021) recovered D. koechlini and D. pauiniensis as sister species. The scarcity of data on D. pauiniensis after its description and, on the other hand, the apparent abundance of information on D. koechlini led me to investigate whether these two taxa could be conspecific. The present study aims to summarise the phenotypic variation of these species to clarify their taxonomic status.

Material and Methods

I analysed material deposited in the herpetological collection of the Universidade Federal do Acre (UFAC-RB) in Rio Branco and Museu Nacional (MNRJ), Rio de Janeiro (see Appendix S1.). I also examined the holotype of D. pauiniensis deposited in the herpetology collection of the Museu de Zoologia da Universidade de São Paulo (MZUSP) to compare the presumed diagnostic characters employed by Heyer (1977) with the holotype of D. koechlini given the diagnostic characters employed by Duellman & Trueb (1989). For snout-vent length (SVL) measurements, I used a digital calliper graduated to 0.01 mm precision. Furthermore, I analysed images of the type series of D. koechlini from Digital Archives Collection of the Division of Herpetology of the Biodiversity Institute of the University of Kansas ( https://collections.biodiversity.ku.edu/KUHerps/).

Table 1.

Colouration of thighs in specimens of Dendropsophus pauiniensis.

Results

In the description of the taxon Dendropsophus koechlini, the authors mention the skin texture as finely shagreen on dorsum and skin coarsely granular on chest, belly, and proximal posteroventral surfaces of thighs. In addition, the presence of a completely black thigh on both the anterior and posterior surfaces is a diagnostic feature. Furthermore, they mention that the dorsal markings of D. koechlini are chevrons, while those of D. pauiniensis have a more transverse orientation. Moreover, when reporting colour variation, Duellman & Trueb (1989) wrote: “Most specimens have uniformly black anterior and posterior surfaces of the thighs; however, a few specimens have a single pale (orange in life) spot on the anterior and/or posterior surface of one or both thighs. Eight individuals have spots on the anterior and posterior surfaces of each thigh. Of 420 surfaces (anterior and posterior surfaces of two thighs of 105 specimens), pale spots are present on 21 (5%)”.

In the description of colour in preservative, the authors highlight the presence of a light band in the frontal region for D. koechlini. The colour of the thighs is also described as “dark anterior face with a large light spot (bright golden yellow in life), dark, uniform, almost black posterior thigh”.

When examining the D. pauiniensis holotype (Fig. 1), I confirmed that the granular texture of the skin and colouration pattern fully match the description of D. koechlini, and that the SVL of both taxa overlap (males 20.2-20.3 mm and females 23.0-24.0 mm in D. pauiniensis vs. males 17.5-23.8 mm and females 23.9-28.1 mm in D. koechlini). Furthermore, the two taxa occur in southwestern Amazonia and occupy the same type of habitat (open forests and forest edge). The texture of the dorsum is variable in both taxa, being finely granular and even containing tubercles. The presence of spots on the thighs is variable in both taxa, and such spots may be absent, present only on one side, present on both thighs and may also occur on the back of the thigh (Figs. 2-4). The presence of chevrons on the dorsum is highly variable. Both the holotype of D. pauiniensis (Fig. 1A) and D. koechlini (Fig. 5A) have chevrons and irregular marks in dorsum. The chevrons are more common in males and sometimes incomplete or faded in a given individual. This character also depends on activity and time of the day. Chevrons are absent in paratype KU 205694 (Fig. 5B), regular in paratype KU 205725 (Fig. 5C, D), and transverse in paratype KU 207569, depicted in the frontispiece (Fig. 5E). Populations from Jenaro Herrera in Northern Peru also show thighs with both conditions: spotted (male treated as D. bokermanni in Fig. 28) or uniform (female in Fig. 35) by Guerrero et al. (2011). Given their complete morphological overlap, with intra-taxon variation in traits previously considered diagnostic, I consider D. koechlini a junior synonym of D. pauiniensis.

Taxonomic account

Dendrosophus pauiniensis (Heyer, 1977)

Hyla pauiniensis (Heyer, 1977), Pap. Avulsos Zool. 31: 145.

Holotype: MZUSP 49892, Type locality: “Boca do Pauini, Amazonas, Brazil”.

Hyla leali nec (Bokermann, 1964) Souza & Cardoso (2002) Hyla minuta nec (Peters, 1872) Souza & Cardoso (2002) Hyla koechlini (Duellman & Trueb, 1989), Herpetologica 45: 5. Holotype: KU 205692, Type locality: Reserva Cuzco Amazónico on the Río Madre de Dios, approximately 15 km east of Puerto Maldonado, Department of Madre de Dios, Peru. New Synonymy. Hyla koechlini Rodríguez & Duellman (1994) 29: plate 3G; De la Riva et al. (2000) 33; Bartlett & Bartlett (2003) 65: plate 47; Duellman (2005).

Dendrosophus koechlini Souza (2009) 34; Moravec et al. (2011) 49: Fig. 2C; Motta et al. (2012) 20: Fig. 1J, K; Orlofske et al. (2012) 256: Fig. 4A, B; Waldez et al. (2013) 305: Fig. 3J; Ramalho et al. (2016).

Fig. 2.

Phenotypic variation in Dendropsophus pauiniensis. UFAC-RB 9564 male (A, B), UFAC-RB 9613 male (C, D), UFAC-RB 9614 female (E, F), UFAC-RB 9627 male (G, H).

Fig. 3.

Phenotypic variation in Dendropsophus pauiniensis. UFAC-RB 9640 male (A, B), UFAC-RB 9642 male (C, D), UFAC-RB 9648 male (E, F) and UFAC-RB 9637 female (G, H). Note the presence of partially (B) and completely (G) black-bordered yellow spots in both thigh and shank respectively, indicated by yellow arrow, and absence of yellow spot in thighs (D) indicated by red arrow.

Distribution

Known from the Madre de Dios Region in Peru, Beni, La Paz, and Santa Cruz departments in Bolivia. In Brazil, D. pauiniensis occurs in the states of Acre and Amazonas, and in the adjacent region of Leticia, Colombia (Frost 2021). Ramalho et al. (2016) reported D. koechlini = D. pauiniensis from the lakes Cametá, Santana, and Flor do Ouro along the River Purus, the latter being only 54 km in a straight line from the type locality of D. pauiniensis. Lynch (2005) has reported this species for Colombia as D. koechlini, but I am wary that it corresponds to Dendropsophus frosti as those reported by von May & Venegas (2010) and Motta et al. (2012).

Fig. 4.

Dendropsophus pauiniensis specimens from the mouth of the River Chandless-Chá, Santa Rosa do Purus, Acre, Brazil. Male calling in shrubby vegetation over water (A, C), female with oocytes (B). Photos Moisés Barbosa de Souza.

Discussion

Several recent investigations have contributed to our knowledge of the Amazonian frog genus Dendropsophus, yet this group remains taxonomically challenging (see De la Riva & Duellman 1997, Duellman 2005). For instance, the synonymising of D. allenorum with D. timbeba suggested by Souza (2009) and confirmed by Orrico et al. (2013), supports that this genus' taxonomy is not trivial and has sometimes been chaotic. The D. parviceps group has received considerable attention recently, with the description of D. frosti (Motta et al. 2012), Dendropsophus counani (Fouquet et al. 2015), Dendropsophus kamagarini and Dendropsophus kubricki (Rivadeneira et al. 2018). The allocation of Dendropsophus yaracuyanus (Mijares-Urrutia & Rivero 2000) by Orrico et al. (2021) into the D. parviceps group supports the need to meticulously revise species descriptions based on morphological characters that are key to defining species groups. Furthermore, it is increasingly clear that the group is primarily composed of lowland species but also includes species from regions with higher elevation (Mijares-Urrutia & Rivero 2000, Orrico et al. 2021).

Fig. 5.

Some specimens of type series of Dendropsophus koechlini from Cusco Amazónico, Madre de Dios, Peru: holotype KU 205692 (A), paratypes KU 205694 (B), KU 205725 (C, D), KU 207569 (E). Yellow arrow shows irregular transversal bar on the dorsum. Red arrow shows the chevron. Photos William E. Duellman/Kansas University Digital Archive.

After the most complete phylogeny of the genus Dendropsophus by Orrico et al. (2021), which retrieved the Dendropsophus garagonensis group of Faivovich et al. (2005) as a clade into D. parviceps group, the latter group now contains 20 species. However, none of the samples representing D. koechlini and D. pauiniensis came from topotypic material (samples MNCN/ ADN34662 La Paz, Bolivia and TG2531 Tarauacá, Acre, Brazil, respectively). Therefore, we are still likely missing the true diversity within that group. We note that this comprehensive phylogenetic analysis found a paratype of D. pauiniensis (MZUSP 49893) to correspond to D. koechlini (Orrico et al. 2021; Supplementary material 16, Appendix 4).

Fig. 6.

Representatives of Dendropsophus parviceps group with distinct colouration and mark on thighs and shanks. Dendropsophus bokermanni uncollected (A). Dendropsophus giesleri uncollected (B). Dendropsophus kamagarini UFAC-RB 9629 (C). Dendropsophus kubricki PRMS 0799 (D). Dendropsophus timbeba UFAC-RB 9533 (E).

Conclusion

Taxonomic assessments of Amazonian frogs require careful consideration of phenotypic variation (Melo-Sampaio et al. 2018). Melo-Sampaio & Souza (2015) warned that a frequency of erroneous identifications in the genera Dendropsophus and Scinax might compromise many conclusions drawn from ecological studies. The interpretation of some morphological characters in the taxonomy of hylids needs to be deepened. In addition to the taxa synonymised here, other taxa described from southwestern Amazonia should be reassessed with new material available. This effort will allow a more complete and accurate understanding of Amazonian amphibian biodiversity. Another case in the D. parviceps group requiring additional assessment is that of Hyla rondoniae, currently a junior synonym of D. bokermanni. The need to examine type material collected long time ago in the face of recent and ongoing biodiversity surveys highlights the critical role of zoological collections hosted in museums worldwide. Regarding taxonomy, access to collections and databases is essential and irreplaceable.