Discovering the diversity of tadpoles in the mid-north Brazil: morphological and molecular identification, and characterization of the habitat

Abstract

Brazil stands out for presenting the highest amphibian anuran diversity in the world. However, taxonomic studies that address characteristic of larval stage of anurans are incipient, representing only 62% of known species. We assess the species diversity of tadpoles from eastern Maranhão state, mid-northern region of Brazil based on morphological and molecular identification (i.e., 16S rRNA gene fragment), and we also provide characteristics of the habitats occupied by each species. We carried out 30 field samplings during 13 months in 16 environments along an ecotonal area, over five cities inside the limits of state of Maranhão, between the Maranhão Babaçu Forest and Cerrado ecoregions. We searched for tadpoles in a variety of water bodies, and the tadpoles that reached the developmental stage between 34 to 40 Gosner were morphologically identified. The tadpoles collected herein represent 26 species belonging to five families. The external morphology enabled the identification of 24 species, while the molecular data recognized 22 unique evolutionary units. The most represented family was Hylidae (Hylinae 11 spp., Phyllomedusinae one spp.) followed by Leptodactylidae (Leptodactylinae seven spp., Leiuperinae three spp.), Microhylidae (Gastrophryninae two spp.), and Bufonidae (two spp.). Our results show that oral morphology was the most important character for identifying tadpoles based on morphology, and the specific 16S rRNA primer was suitable for molecular identification. This study pioneers the use of both morphological and molecular data to identify tadpoles in the state of Maranhão. It also provides, for the first-time, habitat characteristic for the species. Our study reveals a high number of anuran species sampled at the larval stage in the region, identifies species that require further taxonomic and systematic attention, and extends the geographic distribution of six species, three of which represent new occurrences for the state. Our results strengthen the hypothesis that the diversity of amphibians from Maranhão is underestimated and highlight the importance of herpetological inventories in poorly sampled areas, decentralizing the knowledge of biodiversity.

Keywords: Babaçu Forest of Maranhão; Biodiversity; Cerrado; Conservation; Geographic distribution; Tadpole habitats; Tadpole morphology; Tadpole oral morphology; Taxonomy.

Figure 1. View of the study area in the eastern Maranhão, mid-north region of Brazil.

(A) Map of Maranhão highlighting the location of the sampling areas in the following municipalities: São Mateus do Maranhão (1 and 2), Coroatá (3), Aldeias Altas (4), Caxias (5, 6, 7, 8), and São João do Sóter (9, 10). Sampled habitats: (B) perennial ponds; (C and D) dam; (E and F) seasonal ponds; (G) temporary stream; (H) flooded area; (I) perennial pond being sampled by PSS using a 2 mm net. Municipal and ecoregions limits follow (Dinerstein et al., 2017; IBGE, 2019).

Figure 2. Oral disks (right) and lateral view (left) of the tadpoles of eastern Maranhão, mid-north region of Brazil.

Rhinella diptycha (TL: 18.9 mm; GS: 37), Rhinella mirandaribeiroi (TL: 14.4 mm; GS: 36), Boana cf. atlantica (TL: 40.1 mm; GS: 37), Boana raniceps (TL: 53.7 mm; GS: 36), Boana multifasciata (TL: 36.4 mm; GS: 36), Dendropsophus cf. nanus (TL: 18.9 mm; GS: 37), Dendropsophus soaresi (TL: 27.8 mm; GS: 36), Osteocephalus taurinus (TL: 27.5 mm; GS: 36), Scinax fuscomarginatus (TL: 21.3 mm; GS: 36), Scinax x-signatus (TL: 36.4 mm; GS: 39), Scinax cf. similis (TL: 23 mm; GS: 36), Trachycephalus typhonius (TL: 39.3 mm; GS: 37). TL: Total length; GS: Gosner stage.

Figure 3. Oral disks (right) and lateral view (left) of the tadpoles of eastern Maranhão, mid-north region of Brazil.

Leptodactylus fuscus (TL: 31.3 mm; GS: 37), Leptodactylus macrosternum (TL: 38.5 mm; GS: 35), Leptodactylus mystaceus (TL: 30.6 mm; GS: 36), Leptodactylus natalensis (TL: 17 mm; GS: 35), Leptodactylus pustulatus (TL: 37.5 mm; GS: 39), Leptodactylus vastus (TL: 56.8 mm; GS: 38), Physalaemus cuvieri (TL: 19.4 mm; GS: 36), Physalaemus nattereri (TL: 29 mm; GS: 37), Pseudopaludicola sp. (TL: 19 mm; GS: 36), Dermatonotus muelleri (TL: 29.2mm; GS: 36), Elachistocleis cesarii (TL: 25.6mm; GS: 35), Pithecopus aff. hypochondrialis (TL: 39.5 mm; GS: 37). TL: Total length; GS: Gosner stage.

Figure 4. Maximum Likelihood tree of the mitochondrial gene rRNA 16S.

Numbers on branches indicate bootstrap support Maximum Likelihood (ML). Tadpoles sampled in this study show the acronym GFN (Guedes Field Number) and a number before the species name. All remaining specimens comprise adults from the reference database (GenBank, Appendix S5).