Introduction
Anurans exhibit great diversity in life histories, reproductive modes, and trophic relationships. They are abundant in most ecosystems, acting mainly in the transfer of energy through food webs, nutrient cycling, and bioturbation, the latter consisting of organisms that directly or indirectly control the availability of resources for other organisms (Cortés-Gomez et al. Reference Cortés-Gomez, Ruiz-Agudelo, Valencia-Aguilar and Ladle2015). These organisms are used as environmental bioindicators, reflecting local disturbances (Heyer et al. Reference Heyer, Rand, Cruz and Peixoto1998), and are considered key components of ecosystem functions. Most anuran species have an aquatic pre-metamorphic stage, the tadpole, which represents a connection between terrestrial and aquatic environments. Tadpoles exhibit a wide diversity of feeding and behavioral strategies and are considered key components in the biology and ecology of both anurans and ecosystems (Cortés-Gomez et al. Reference Cortés-Gomez, Ruiz-Agudelo, Valencia-Aguilar and Ladle2015; Schulze et al. Reference Schulze, Jansen and Köhler2015).
Unfortunately, these animals are critically endangered, as several populations have declined and even species extinctions have occurred worldwide (Alton and Franklin Reference Alton and Franklin2017; Carrasco et al. Reference Carrasco, Souza and Santos2021; Luedtke et al. Reference Luedtke, Chanson and Neam2023). Due to aspects of their biology and ecology, anurans host a high diversity of helminth parasites. Among trematodes, these vertebrate hosts can act as both definitive and intermediate hosts (Aho Reference Aho, Esch, Bush and Aho1990; Campião et al. Reference Campião, Morais, Dias, Aguiar, Toledo, Tavares and Silva2014; Queiroz et al. Reference Queiroz, Pontes, Neto, Campião and Anjos2020a, Reference Queiroz, López-Hernández, Locke, Pinto and Anjos2020b). Trematodes are characterised by some of the most complex life cycles in nature, involving one or more intermediate and definitive hosts, a wide variety of behavioural patterns in free-living and parasitic stages to infect hosts, and, in most cases, trophic relationships for transmission to the definitive host (Esch et al. Reference Esch, Barger and Fellis2002; Sukhdeo and Sukhdeo Reference Sukhdeo and Sukhdeo2004).
Among the helminth parasites of amphibians, digenean trematodes have received considerable attention over the past 20 years. Among the main factors of concern are their documented role in the decline of amphibian populations (Szuroczki and Richardson, Reference Szuroczki and Richardson2009) and their usefulness as indicators of ecosystem health (Morley Reference Morley2012; Pinto and Melo Reference Pinto and Melo2013). Nevertheless, much of this attention has focused on studies of parasite–host interactions, mostly those involving human and domestic animal parasites (Bolek et al. Reference Bolek, Detwiler, Stigge, Toledo and Fried2019; Pinto and Melo Reference Pinto and Melo2013). In fact, regarding the trematode fauna found in wild animals, there remains a scarcity of studies, especially in the Neotropical region, where basic information is even more limited.
South America harbors more than 4,000 identified anuran species (AmphibiaWeb 2025), of which just under 250 have been reported to host approximately 80 species of adult digeneans (Aguiar et al. Reference Aguiar, Morais, Silva, Anjos, Foster and Silva2021; Alcantara et al. Reference Alcantara, Ebert, Ferreira-Silva, Forti, Morais, Pérez-Ponce de Léon and Silva2024; Campião et al. Reference Campião, Morais, Dias, Aguiar, Toledo, Tavares and Silva2014; Chero et al. Reference Chero, Cruces, Iannacone, Sáez, Alvariño, Luque and Morales2016, Reference Chero, Cruces, Cacique, Ponce, Iannacone, Alvariño, Sanchez and Silva2023; Fernandes and Kohn Reference Fernandes and Kohn2014; Gomes et al. Reference Gomes, Melo, Giese, Furtado and Santos2017; González et al. Reference González, Villegas Ojeda, Caraballo, Ailán Choke, Hamann, Duré, Gómez and González2025; Hamann and González Reference Hamann and González2015; Hamann et al. Reference Hamann, González and Fernández2020a, Reference Hamann, León-Règagnon, Fernández and González2020b; Moravec and Prouza Reference Moravec and Prouza2024; Oliveira et al. Reference Oliveira, Mascarenhas, Batista-Oliveira, Castro Araújo, Ávila and Borges-Nojosa2022; Queiroz et al. Reference Queiroz, Pontes, Neto, Campião and Anjos2020a, Reference Queiroz, López-Hernández, Locke, Pinto and Anjos2020b, Reference Queiroz, Alves, López-Hernández, Anjos and Pinto2021; Santos et al. Reference Santos, Silva, Miguel, Couto, Tavares, Ferreira and Paiva2025). When metacercariae records are considered, this number rises to almost 100 taxa (Campião et al. Reference Campião, Morais, Dias, Aguiar, Toledo, Tavares and Silva2014, Reference Campião, Silva, Dalazen and Tavares2016a; Hamann et al. Reference Hamann, Kehr and González2013, Reference Hamann, Fernández and González2019, Reference Hamann, González and Fernández2020a, Reference Hamann, Fernández and González2023; Lins et al. Reference Lins, Aguiar, Morais, Da Silva, àvila and Silva2017; Queiroz et al. Reference Queiroz, López-Hernández, Locke, Pinto and Anjos2020b). Metacercariae belonging to the families Diplostomidae, Echinostomatidae, Opisthogonimidae, Plagiorchiidae, Proterodiplostomidae, and Strigeidae have been found in both adult and larval anurans, emphasizing the importance of these animals as links within trematode communities by transmitting aquatic larval stages to terrestrial definitive hosts, which may include birds, mammals, reptiles, or even anurans themselves (Hamann et al., Reference Hamann, Gonzalez and Kehr2006; Bolek et al., Reference Bolek, Snyder and Janovy2009; Hamann & González, Reference Hamann and González2009; Hamann et al., Reference Hamann, Kehr and González2013, Reference Hamann, Fernández and González2019, Reference Hamann, González and Fernández2020a, Reference Hamann, Fernández and González2023; Lins et al., Reference Lins, Aguiar, Morais, Da Silva, àvila and Silva2017; Queiroz et al., Reference Queiroz, López-Hernández, Locke, Pinto and Anjos2020b; Santos et al., Reference Santos, Silva, Miguel, Couto, Tavares, Ferreira and Paiva2025).
Considering the geographical extent of this area, it is evident that there is a gap in the knowledge of trematodes occurring in anuran biodiversity hotspots, which need to be studied before both hosts and parasites are lost in the face of the current global decline in biodiversity and climate change (Habibullah et al., Reference Habibullah, Din, Tan and Zahid2022; Jaureguiberry et al., Reference Jaureguiberry, Titeux and Wiemers2022; Pfenning-Butterworth et al., Reference Pfenning-Butterworth, Buckley and Drake2024). Therefore, this study aims to describe the structure of the trematode component community of tadpoles and adult anurans found in a Cerrado fragment in Brazil. In addition, it provides brief morphological descriptions and ecological analyses of each metacercaria and adult stage recovered, thereby contributing to the knowledge of trematode parasite diversity in a poorly sampled region.
Material and methods
Study area and hosts sampling
The study was conducted in a temporary marsh pond within a Cerrado fragment located in the municipality of Selvíria, Mato Grosso do Sul, Brazil (20°23′43.4″S, 51°23′39.8″W). From December 2016 to February 2019, a total of 38 field expeditions were conducted, during which adult anurans and tadpoles were collected. Adult anurans were sampled using the scan searching method (Halliday Reference Halliday and Sutherland2006), not only in the pond but also along its margins and surrounding areas, with one hour of effort during the nocturnal period. With the aid of a rectangular dip net (50 × 75 cm), tadpoles were collected with one hour of effort during the morning period. Tadpoles were placed in plastic bags filled with water, while adults were individually placed in plastic bags, and all specimens were transported to the Ecology of Parasitism Laboratory, UNESP, Ilha Solteira.
In the laboratory, anurans were subjected to macroscopic inspection, and after the euthanasia procedure (CFMV, 2013), their internal organs were removed and transferred to Petri dishes containing physiological saline solution (0.9% NaCl). The organs were then examined under a stereomicroscope to detect the presence of trematodes (acanthocephalans, cestodes, and nematodes were also collected but not included in this study). Additionally, anurans were classified into two major groups—adults and tadpoles—and the developmental stage of each tadpole was determined according to Gosner (Reference Gosner1960) (GS). The taxonomic identification of adult anurans was based on morphological criteria following Provete et al. (Reference Provete, Garey, Silva and Rossa-Feres2011), while tadpoles were identified using the available literature for the species recorded in the study area (Rossa-Feres and Nomura Reference Rossa-Feres and Nomura2006; Schulze et al. Reference Schulze, Jansen and Köhler2015).
Taxonomical identification of Trematodes recovered
Flukes and metacercariae collected were gently compressed between glass slides and fixed in a 2.5% glutaraldehyde solution (pH 7.4 buffer). Specimens were later stained with hematoxylin, serially dehydrated in ethanol solutions, cleared in methyl salicylate, and mounted on permanent slides with Canada balsam (adapted from Amato et al. Reference Amato, Boeger and Amato1991). Some small flukes and metacercariae were euthanised with hot water (65°C) prior to glutaraldehyde fixation and the preparation of permanent slides. in vivo observations of all developmental stages of the digeneans recovered were conducted using temporary slides and vital dyes, methylene blue and neutral red (0.05%).
Morphological, morphometric, and imaging data of both stained and live parasites were obtained using a Leica DM2500 optical microscope equipped with a differential interference contrast (DIC) system and a digital camera. Measurements were taken with an ocular micrometer. Species identification and validation of trematodes were based on the taxonomic references of Travassos et al. (Reference Travassos, Freitas and Kohn1969) and Fernandes and Kohn (Reference Fernandes and Kohn2014).
Ecological analysis
The classic ecological descriptors of parasitism—prevalence of infection (P) and mean intensity of infection followed by standard deviation (MII ± SD; range)—were calculated for all anuran hosts and digenean taxa recovered, following Bush et al. (Reference Bush, Lafferty, Lotz and Shostak1997). Additional ecological analyses included species richness (R), Shannon’s diversity index ( H′ ), and evenness ( J′ ) for each host species, with adults and tadpoles analysed separately, to identify the richest and most diverse infracommunities and to determine the main differences in the trematode communities of adult and larval anurans. The Berger–Parker dominance index ( d ) was applied to determine the dominant trematode species within each infracommunity (adults and tadpoles analysed separately) and for the combined dataset.
Statistical analyses were performed using BioEstat 5.30 (Ayres et al. Reference Ayres, Ayres, Ayres and Santos2007). A cluster analysis using the Bray–Curtis similarity index was conducted to compare host use and abundance among digenean species, separating larval and adult flukes. The cluster analysis was performed in PAST software. For the two host species with larger sample sizes (Boana raniceps and Dendropsophus nanus), differences between adult and tadpole infracommunities were tested. A Chi-square test (χ 2 ) for independence was used to compare differences in prevalence (P%) between adults and tadpoles, while the Mann–Whitney U test ( z ) was used to compare mean intensity of infection (MII ± SD), mean abundance (MA ± SD), and mean trematode species richness (MR ± SD) between both developmental stages of each host species.
Results
The anuran community of adults and tadpoles collected in a temporary pond comprised 569 specimens, with a richness of 17 species distributed across four families (Hylidae, Leptodactylidae, Microhylidae, and Phyllomedusidae). Eleven species were common to adults and tadpoles, and six species were only adults’ anurans. The total prevalence (P) was 61% (352/569), in a separate analysis, 65% (192/296) was for adult anurans, and 58% (160/273) was for tadpoles. Table 1 shows the specific number of each tadpole and anuran species collected, the supplementary table (Table S1) had the specific ecological descriptors of parasitism, prevalence, mean intensity of infection (followed by standard deviation), and abundance of each host and respective trematode species recovered.
Details of anurans species collected in this study with total number of tadpoles and adults of each species
Tadpoles were infected only with metacercarial stages. The highest trematode species richness was recorded in Boana raniceps (6), followed by Dendropsophus nanus (5) and Scinax fuscovarius (5). The most diverse and uniform infracommunity was observed in Pseudis platensis (H′ = 0.87; J′ = 0.63), followed by Dendropsophus nanus (H′ = 0.80; J′ = 0.50), Scinax nasicus. (H′ = 0.40; J′ = 0.28), and Scinax fuscovarius (H′ = 0.39; J′ = 0.24) (Table 2).
Ecological aspects as richness (R), Shannon diversity ( H’ ), uniformity ( J’ ) and dominant species ( d ) of each infracommunity collected in this study. The following tadpoles species: P. cuvieri and P. nattereri were not included in the analysis because no trematode infection was found. The following adult species: D. minutus, S. fuscovarius, S. nasicus, T. typhonius, L. mystaceus, L. mystacinus, P. cuvieri, P. nattereri, Pseudopaludicola sp., D. muelleri and P. azureus were not included in the analysis because they were infected with one or no trematode species
* Brt: B. cf. tetracotyloides; Lpd: L. cf. nephrocystis; Plg: Plagiorchioidea gen. sp. and Stg: Strigeidae gen. sp.
In relation to adult anurans, metacercariae and adult flukes were recovered, the highest trematode species richness was Leptodactylus podicipinus (11), followed by Pseudis platensis (8) and Leptodactylus macrosternum (6), while the most diverse and uniform infracommunity was P. platensis (H′ = 1.41; J′ = 0.68), L. podicipinus (H′ = 1.24; J′ = 0.51), and B. raniceps (H′ = 0.67; J′ = 0.48) (Table 2).
The trematode component community recovered comprised 16 taxa distributed across 10 families: Clinostomidae, Echinostomatidae, Diplodiscidae, Diplostomidae, Gorgoderidae, Haematoloechidae, Macroderoididae, Plagiorchidae, Proterodiplostomidae, and Strigeidae. Of these, six were adult flukes and ten were metacercarial stages (Figures 1–3). A total of 12,397 specimens were analysed, of which 11,479 (92.6%) were metacercariae and 918 (7.4%) were adult flukes. Adult trematodes and two metacercarial species (Bursotrema cf. tetracotyloides and Clinostomum sp.) occurred exclusively in adult anurans, while eight metacercariae were shared between tadpoles and adults.
Metacercariae recovered in tadpoles and adult anurans found in a temporary pond in Cerrado fragment, Brazil. (a) B. cf. tetracotyloides scale bar 100μm; (b) H. lanceolatum scale bar 1mm; (c) L. cf. nephrocystis scale bar 100μm; (d) Tylodelphys sp. scale bar 200μm; (e) Clinostomum sp. scale bar 1mm.
Metacercariae recovered in tadpoles and adult anurans, Cerrado Brazil. (a) Echinostomatidae gen. sp. arrows indicate the collar spine. Scale bar 50μm; (b) Strigeidae gen. sp. scale bar 500μm; (c) Diplostomoidea gen. sp.2 arrow indicate the holdfast organ. Scale bar 200μm; (d) Plagiorchioidea gen. sp. scale bar 100μm; (e) Diplostomoidea gen. sp.1 arrows indicate the pseudo suckers. Scale bar 200μm.
Adult Digenea recovered in adult anurans in Cerrado, Brazil. (a) C. marinholutzi scale bar 500μm; (b) C. cf. incurvatum scale bar 500μm; (c) G. parvicava scale bar 1mm; (d) Gorgoderina sp. scale bar 500μm; (e) Haematoloechus sp. scale bar 200μm; (f) Rauschiella proxima scale bar 1mm.
The metacercaria Lophosicyadiplostomum cf. nephrocystis was the dominant species (d = 0.653) in the entire component community. In a separate analysis, considering only metacercariae or only adults, L. cf. nephrocystis (d = 0.693) was the dominant metacercaria, while Catadiscus marinholutzi (d = 0.700) was the dominant adult fluke. Lophosicyadiplostomum cf. nephrocystis was also the dominant species in tadpoles (d = 0.930), whereas Bursotrema cf. tetracotyloides was dominant in adult anurans (d = 0.480), as shown in Table 3. Analysis of Table 2 further shows that L. cf. nephrocystis was the dominant species in Hylidae hosts, while B. cf. tetracotyloides was dominant in Leptodactylidae hosts.
Details of the Berger-parker ( d ) index that show the dominant trematode species in each community, tadpoles separated from adults and considering the whole community
* indicates the three most dominant.
The cluster analysis of larval trematodes showed a cophenetic correlation coefficient of 0.97 (Figure 4). Metacercariae of Echinostomatidae and Plagiorchioidea were the most similar taxa in terms of host use and abundance (0.45), whereas L. cf. nephrocystis and B. cf. tetracotyloides exhibited the lowest similarity (0.08). For adult trematodes, a cophenetic correlation coefficient of 0.92 was obtained. The most similar taxa were Choledocystus cf. incurvatum and Haematoloechus sp. (0.58), followed by Gorgoderina parvicava and Gorgoderina sp. (0.52), while the lowest similarity was observed for Catadiscus marinholutzi and Rauschiella proxima (0.41) (Figure 4).
Cluster analysis with the Bray-Curtis similarity index related to host use and abundance of adult (a) and larval (b) digeneans.
Of the 27 adult B. raniceps individuals, 15 (55.6%) were infected with trematodes. The component community consisted of four trematode species. The overall mean intensity of infection for all adults was 51.80 ± 49.16 (range: 1–137) flukes per infracommunity, and the mean abundance of trematodes was 27.77 ± 44.60. Mean trematode species richness was 1.03 ± 1.12 per anuran. Multiple-species infections were common, with 0, 1, 2, and 3 trematode species occurring in 12, 6, 5, and 4 anurans, respectively (Table 4). For tadpoles, of the 49 individuals, 38 (77.6%) were infected with trematodes. The component community consisted of six trematode species. The overall mean intensity of infection for all tadpoles was 135.86 ± 253.88 (range: 1–1177) flukes per infracommunity, and the mean abundance of trematodes was 105.28 ± 230.14. Mean trematode species richness was 0.97 ± 0.72 per tadpole. Multiple-species infections were common, with 0, 1, 2, and 3 trematode species occurring in 11, 30, 6, and 2 tadpoles, respectively (Table 4). There were no significant differences in mean intensity of infection, mean abundance, or mean trematode species richness between adult and tadpole B. raniceps. However, a significant difference in prevalence of infection was observed between tadpoles and adults (χ2 = 3.991; p = 0.045).
Statistical comparison between individuals of B. raniceps adults and tadpoles and D. nanus adults and tadpoles. (P%) prevalence, mean intensity of infection (MII±SD), mean abundance (MA±SD)and mean species richness (MR±SD). SD is for standard deviation
* significant differences were found.
Of the 44 adult D. nanus individuals, 33 (75.0%) were infected with trematodes. The component community consisted of three trematode species. The overall mean intensity of infection for all adults was 6.42 ± 5.07 (range: 1–17) flukes per infracommunity, and the mean abundance of trematodes was 4.81 ± 5.20. Mean trematode species richness was 0.95 ± 0.71 per anuran. Multiple-species infections were common, with 0, 1, 2, and 3 trematode species occurring in 11, 25, 7, and 1 anuran, respectively (Table 4). For tadpoles, of the 67 individuals, 59 (88.1%) were infected with trematodes. The component community consisted of five trematode species. The overall mean intensity of infection for all tadpoles was 15.93 ± 23.93 (range: 1–117) flukes per infracommunity, and the mean abundance of trematodes was 14.02 ± 23.03. Mean trematode species richness was 1.29 ± 0.77 per tadpole. Multiple-species infections were common, with 0, 1, 2, and 3 trematode species occurring in 8, 36, 18, and 5 tadpoles, respectively (Table 4). Significant differences were observed in mean intensity of infection, mean abundance, and mean trematode species richness between adult and tadpole D. nanus (Table 4). However, there was no significant difference in prevalence of infection between tadpoles and adults (χ2 = 3.193; p = 0.074). Below is a taxonomic summary of our results.
Platyhelminthes
Digenea Carus, 1863
Family: Clinostomidae Lühe, 1901
Clinostomum sp.
Stage: encysted metacercaria
Host (Adult anurans): L. podicipinus. (P: 0.9%–1/106;1).
Site of infection: Leg musculature
Remarks: The metacercariae recovered have a stout, elongated body with a flattened posterior end, the oral sucker is smaller than the acetabulum, and the acetabular opening has a triangular shape. The general shape of the suckers and the position and shape of the testes, ovary, and cirrus pouch resemble those of Clinostomum species previously recorded as metacercariae in anurans (Aguiar et al., Reference Aguiar, Morais, Silva, Anjos, Foster and Silva2021); however, since the reproductive organs were not fully developed and no eggs were present, precise identification is difficult. The family Clinostomidae comprises cosmopolitan parasites, commonly found in birds, reptiles, and mammals. Their life cycle follows the typical pattern of three hosts and three transmission events, in which fish and amphibians serve as second intermediate hosts (Calhoun et al., Reference Calhoun, Leslie, Riepe, Achatz, Mcdevitt-Galles, Tkach and Johnson2019). Records of amphibians in the life cycles of these parasite taxa are common, with distributions throughout Asia, Africa, Europe, and North America (Calhoun et al., Reference Calhoun, Leslie, Riepe, Achatz, Mcdevitt-Galles, Tkach and Johnson2019; Aguiar et al., Reference Aguiar, Morais, Silva, Anjos, Foster and Silva2021; Sinsch et al., Reference Sinsch, Dehling, Scheid and Balczun2021; Nguyen et al., Reference Nguyen, Woodyard and McAllister2024).
Family Diplodiscidae Skrjabin, 1949
Catadiscus marinholutzi Freitas and Lent, 1939
Stage: young and adult flukes
Hosts (Adult anurans): B. raniceps (P: 18.5%,5/27; MII ± SD: 1.8 ± 1.3;1–4); D. muelleri (P: 16.66%,1/6;1); L. macrosternum (P: 41.6%,5/12; MII ± SD:12.7 ± 20.2;1–43); L. podicipinus, (P: 58.5%,62/106; MII ± SD: 5.0 ± 4.5;1–21); P. platensis (P: 50%,10/20; MII ± SD: 10.1 ± 8.9;1–29), and Pseudopaludicola sp. (P: 35.3%,6/17; MII ± SD: 1.8 ± 1.3;1–4).
Site of infection: Large intestine.
Remarks: Flukes have a pyriform body with a smooth tegument; the oral sucker is terminal with undulated edges surrounding the oral aperture, which is smaller than the acetabulum. The acetabulum is ventral and subterminal, large, with a transverse constriction. Vitellaria consist of large follicles, larger than the eggs, lying between the acetabulum and caecal bifurcation, confluent anteriorly. These morphological features confirm the identification of C. marinholutzi. The family Diplodiscidae comprises flukes that inhabit lower vertebrates (fishes, amphibians, reptiles) and even mollusks (Sey, Reference Sey1983; Hamann, Reference Hamann1992). The genus Catadiscus is distributed throughout South America, parasitizing anurans and reptiles (Fernandes & Kohn, Reference Fernandes and Kohn2014). The life cycle of this genus resembles that of other diplodiscids (Yamaguti, Reference Yamaguti1975; Bolek & Janovy, Reference Bolek and Janovy2008; Bolek et al., Reference Bolek, Detwiler, Stigge, Toledo and Fried2024), in which two transmission events occur: the metacercariae encyst on the substrate or on the skin of metamorphosed frogs, and infection occurs via ingestion of the infective metacercariae. This is the first record of Catadiscus marinholutzi parasitizing D. muelleri.
Superfamily Diplostomoidea Poirier, 1886
Diplostomoidea gen. sp. 1
Stage: Metacercariae unencysted
Hosts (Tadpoles): B. raniceps (GS: 27; P: 2%,1/49;6) and T typhonius (GS: 38; P: 3%,1/31;1).
Site of infection: Tail musculature.
Remarks: The larval stage is probably in an initial phase of development, as no genital organs were identified. The general external morphology prevents precise species-level identification, but the presence of a holdfast organ and lateral pseudosuckers adjacent to the oral sucker, specific features of Diplostomids (Achatz & Tkach, Reference Achatz and Tkach2025), allows identification at the superfamily level. The Diplostomoidea group comprises five families of parasites distributed among reptiles, birds, and mammals (López-Hernández et al., Reference Lopez-Hernáandez, Locke, De Assis, Drago, De Melo, Rabelo and Pinto2019; Pérez-Ponce de León & Hernández-Mena, Reference Pérez-Ponce De León and Hernández-Mena2019; Achatz & Tkach, Reference Achatz and Tkach2025). This record emphasises the crucial role of anurans in the biological cycle of trematodes, acting as a link between aquatic larval forms and the adults of terrestrial vertebrates.
Diplostomoidea gen. sp. 2
Stage: Metacercariae unencysted
Hosts (Tadpoles): Scinax fuscovarius (GS:36; P: 5.5%,1/18; 4).
Site of infection: Body cavity
Remarks: See remarks on Diplostomoidea sp. 1.
Family Diplostomidae Poirier, 1886
Bursotrema cf. tetracotyloides Szidat, 1960
Stage: Metacercariae unencysted
Hosts (Adult anurans): B. raniceps (P: 14.5%,11/27; MII ± SD: 20.0 ± 17.6;4–53); D. nanus (P: 38.63%,17/44; MII ± SD: 3.63 ± 3.70;1–14); D. muelleri (P: 33.33%,2/6;16–56); L. macrosternum (P: 58.33%,7/12; MII ± SD: 130.71 ± 283.09;1–768); Leptodactylus mystacinus (P: 100%,1/1;51), and L. podicipinus (P: 45.28%,48/106; MII ± SD: 24.60 ± 108.03;1–750).
Site of infection: Kidney
Remarks: Although the metacercariae do not show any development of reproductive organs, the general morphology, such as the widely oval body, saccular forebody with an oblique aperture, and oval, elongated holdfast, is identical to that reported by Hamann and González (Reference Hamann and González2009). However, as it is a metacercaria stage, precise identification is difficult. The fluke B. tetracotyloides has been recorded in two marsupial species in Argentina and Peru (Fernandes et al., Reference Fernandes, Justo, Cárdenas and Cohen2015), with no records in Brazil. The life cycle of this parasite reinforces the trophic chain pattern, in which anurans act as links to terrestrial vertebrate hosts. Other studies in Brazil have reported the occurrence of this metacercaria in anurans (Campião et al., Reference Campião, Morais, Dias, Aguiar, Toledo, Tavares and Silva2014; Queiroz et al., Reference Queiroz, Pontes, Neto, Campião and Anjos2020a; Aguiar et al., Reference Aguiar, Morais, Silva, Anjos, Foster and Silva2021), but the adult stage and the complete biological cycle remain unknown. The present study represents the first record of this metacercaria parasitizing B. raniceps, D. nanus, and D. muelleri.
Lophosicyadiplostomum cf. nephrocystis (Lutz, 1928) Dubois, 1937
Stage: Metacercariae unencysted
Hosts (Adult anurans): B. raniceps (P:37.03%,10/27;MII±SD:54.70±53.97;3-137); D. elianeae (P:42.85%,3/7;MII±SD:84.00±99.13;18-198); D. minutus (P:5.55%,1/18;9); D. nanus (P:54.54%,24/44;MII±SD:6.20±5,18;1-17); L. podicipinus (P:22.64%,24/106;MII±SD:6.08±4.88;1-16); P. azureus (P:33.33%,2/6;26-93); P. platensis (P:20.00%,4/20;MII±SD:4.00±2.94;1-8); S. fuscovarius (P:50.00%,3/6;MII±SD:20.66±10.01;11-31) and S. nasicus (P:16.60%,2/12;14-90).
Hosts (Tadpoles) B. raniceps (GS:26-43;P:65.30%,32/49;MII±SD:160.15±269.95;2-1177); D. minutus (GS:26,30,31;P:75.00%,3/4;MII±SD:11.66±4.04;7-14); D. nanus (GS:26-44;P:53.73%,36/67;MII±SD:19.16±27.92;1-117); D. muelleri (GS:44;P:6.45%,4/62;MII±SD:8.00±6.78;1-16); L. podicipinus (GS:28,30;P:10.00%,2/20;1-1); P. platensis (GS:25-26;P:75.00%,6/8;MII±SD:7.00±5.86;1-18); S. fuscovarius (GS:25-43;P:94.00%,17/18;MII±SD:28.88±33.62;1-141); S. nasicus (GS:26,43;P:66.66%,4/6;MII±SD:62.25±52.06;21-138) and T. typhonius (GS:26-43;P:42.10%,8/19;MII±SD:3.88±3.87;1-13).
Site of infection: Kidneys
Remarks: The metacercariae have a bipartite body, with an oval forebody featuring a concave ventral region and a fusiform hindbody. The oral sucker has an equatorial muscular ring surrounding it dorsally and laterally, similar to features reported by Hamann & González (Reference Hamann and González2009). However, as the reproductive organs were not fully developed and no eggs were observed, precise identification is difficult. The genus Lophosicyadiplostomum has been reported in Brazil as intestinal parasites of birds (Fernandes et al., Reference Fernandes, Justo, Cárdenas and Cohen2015). Although the life cycle remains unknown, there are literature records of this metacercaria occurring in anurans (Hamann & González, Reference Hamann and González2009; Lins et al., Reference Lins, Aguiar, Morais, Da Silva, àvila and Silva2017; Queiroz et al., Reference Queiroz, Pontes, Neto, Campião and Anjos2020a; Aguiar et al., Reference Aguiar, Morais, Silva, Anjos, Foster and Silva2021), supporting the idea that the life cycle resembles that of some Diplostomids, in which the definitive host becomes infected by ingesting the second intermediate host, in this case, anurans. This result represents the first record of Lophosicyadiplostomum metacercariae in D. elianeae, D. muelleri, and P. platensis.
Tylodelphys sp.
Stage: Metacercariae unencysted
Hosts: (Tadpoles): B. raniceps (GS:26-39;P:16.32%,8/49;MII±SD:2.37±1.84;1-6) and D. nanus (GS:31,38,41,44;P:7.46%,5/67;MII±SD:3.20±2.28;1-6).
Site of infection: Body cavity.
Remarks: The metacercariae have a linguiform body, slightly concave ventrally, with a rounded anterior end and a small, poorly developed hindbody. The oral sucker is terminal and smaller than the acetabulum. A holdfast organ is present, oval and elongated, located at the end of the forebody. The external morphology allows identification at the genus level, as no development of reproductive organs was observed. In Brazil, two species of Tylodelphys have been recorded parasitizing birds (Fernandes et al., Reference Fernandes, Justo, Cárdenas and Cohen2015). As with previous records of Diplostomid metacercariae in anurans, this finding reinforces the trophic pattern in the life cycle of these parasites. Hamann et al. (Reference Hamann, González and Fernández2020a, Reference Hamann, Fernández and González2023) previously recorded this metacercaria in other Hylidae anurans. Our results represent the first record of this metacercaria parasitizing B. raniceps and D. nanus.
Family Proterodiplostomidae Dubois, 1936
Heterodiplostomum lanceolatum Dubois, 1936
Stage: Metacercariae encysted.
Hosts (Adult anurans): L. podicipinus (P:32.07%,34/106;MII±SD:6.10±6.81;1-25) and P. platensis (P:50.00%,10/20;MII±SD:2.00±1.24;1-5).
Hosts (Tadpoles): P. platensis (GS:26;P:25.00%,2/8;1-10).
Site of infection: hindlimb musculature and abdominal musculature.
Remarks: The body is bi-segmented, with the hindbody connected dorsally to the forebody. The forebody is flattened and spatulate. The oral sucker is subterminal, and the pharynx is globular, larger than the oral sucker. Long intestinal caeca extend laterally into the posterior region of the hindbody, terminating anterior to the copulatory bursa. The acetabulum is oval-shaped, located in the middle region of the forebody, anterior to the holdfast organ. The holdfast organ is prominent, elongate, and located in the posterior portion of the forebody. The hindbody is cylindrical, smaller than the forebody, and contains well-developed sexual organs in most specimens. The excretory pore is terminal, and the genital pore opens dorsally in the hindbody. The genus Heterodiplostomum comprises two known species in South America, both intestinal parasites of snakes (Fernandes & Kohn, Reference Fernandes and Kohn2014). Although this species is poorly known, there are some records of it parasitizing Leptodactylidae anurans in Argentina and Brazil (Hamann et al., Reference Hamann, Kehr and González2013, Reference Queiroz, Pontes, Neto, Campião and Anjos2020a, 2023; Campião et al., Reference Campião, Morais, Dias, Aguiar, Toledo, Tavares and Silva2014; Queiroz et al., Reference Queiroz, López-Hernández, Locke, Pinto and Anjos2020b; Aguiar et al., Reference Aguiar, Morais, Silva, Anjos, Foster and Silva2021).
Family Strigeidae Railliet, 1919
Strigeidae gen. sp.
Stage: Metacercariae encysted
Hosts (Adult anurans): D. nanus (P:2.27%,1/44;1); L. macrosternum (P:16.60%,2/12;5-8); L. podicipinus (P:6.60%,7/106;MII±SD:3.14±2.34;1-8) and P. platensis (P:55.00%,11/20;MII±SD:27.18±28.29;5-95).
Hosts (Tadpoles): B. raniceps (GS:38;P:2.04%,1/49;1); D. minutus (GS:26;P:25.00%,1/4;1); D. nanus (GS:36,37;P:4.47%,3/67;MII±SD:1.66±0.57;1-2); P. platensis (GS:26,44;P:25.00%,2/8;7-94) and S. fuscovarius (GS:36;P:5.55%,1/18;7).
Site of infection: Abdominal cavity, Intestinal mesentery, and tail musculature.
Remarks: Coiled metacercariae were observed within a double-layered cyst wall, with the first layer thin and the second layer thick and resistant. Due to the initial developmental stage of the metacercariae inside the cysts and the absence of reproductive organs, specific identification was not possible, however, they are identical to those reported by Hamann et al. (Reference Hamann, Fernández and González2019). The family Strigeidae comprises intestinal parasites of birds and mammals, with more than 20 species known in Brazil (Fernandes et al., Reference Fernandes, Justo, Cárdenas and Cohen2015). This record further emphasizes the importance of anurans as links transmitting infective larval forms to definitive hosts. Although some previous records exist (Hamann et al., Reference Hamann, Fernández and González2019, Reference Hamann, González and Fernández2020a, Reference Hamann, Fernández and González2023), our results represent the first record of Strigeidae metacercariae in B. raniceps, D. nanus, L. podicipinus, P. platensis, and S. fuscovarius.
Superfamily Echinostomatoidea Loss, 1899
Family Echinostomatidae Poche, 1926
Echinostomatidae gen. sp.
Stage: Metacercariae encysted.
Hosts (Adult anurans): D. elianeae (P:14.28%,1/7;3).
Hosts (Tadpoles): B. raniceps (GS:27,28,31;P:6.12%,3/49;MII±SD:2.34±2.30;1-5); D. nanus (GS:27-43;P:44.67%,30/67;MII±SD:5.33±4.19;1-14); P. platensis (GS:25;P:12.50%,1/8;2); S. fuscovarius (GS:25-38; P:61.11%,11/18;MII±SD:2.90±2.25;1-8); S. nasicus (GS:26;P:33.33%,2/6;2-4) and T. typhonius (GS:38,41,42;P:15.78%,3/19;MII±SD:7.33±3.78;3-10).
Site of infection: Subcutaneous cyst and kidneys.
Remarks: The encysted metacercariae have no specific morphological characteristics or developed reproductive organs that allow precise identification. However, it was possible to observe a metacercaria coiled inside a tiny cyst wall and a collar spine with 35–37 spines. Another morphological trait observed was the presence of numerous small round granules. The family Echinostomatidae comprises parasites of fishes, reptiles, mammals, and birds, with transmission to the definitive host occurring through the trophic chain. Although there are previous records of Echinostomatidae metacercariae using anurans as links for transmission of infective larvae to definitive hosts (Hamann et al., Reference Hamann, González and Fernández2020a; Aguiar et al., Reference Aguiar, Morais, Silva, Anjos, Foster and Silva2021), this is the first record for B. raniceps, D. nanus, P. platensis, and S. fuscovarius.
Superfamily Gorgoderoidea Loss, 1899
Family Gordoderidae Looss, 1899
Gorgoderina parvicava Travassos, 1922
Stage Adult flukes.
Hosts (Adult anurans): L. macrosternum (P:16.66%,2/12;1-3) and L. podicipinus (P:1.88%,2/106;2-3).
Site of infection: Urinary bladder.
Remarks: Fluke with an elongated body and tapered ends. Tegument smooth, without spines. Oral sucker subterminal. Acetabulum cylindrical to ovoid, slightly smaller than the oral sucker. Pharynx absent. Genital pore located posterior to the cecal bifurcation, midway between the oral sucker and acetabulum. Testes mainly intercaecal, anterior testis displaced to the left side, posterior testis postequatorial. Ovary smaller than testes, located between the anterior testis and vitelline follicles. Vitelline follicles consist of two compact follicles with regular contours. The genus Gorgoderina comprises parasites exclusively of amphibians, commonly found in the urinary tract, particularly the urinary bladder. The life cycle involves bivalves of the family Sphaeriidae as first intermediate hosts, various aquatic snails, arthropods, and larval and adult amphibians as second intermediate hosts, and metamorphosed amphibians as definitive hosts. An alternative abbreviated pattern occurs when tadpoles accidentally ingest cercariae, which migrate to the kidneys without forming metacercariae upon metamorphosis and development of the urinary bladder, then the worms move to the bladder and mature into adults (Bolek et al., Reference Bolek, Detwiler, Stigge, Toledo and Fried2024). G. parvicava is widely distributed throughout South America and has been recorded in five families of anurans (Campião et al., Reference Campião, Morais, Dias, Aguiar, Toledo, Tavares and Silva2014; Fernandes & Kohn, Reference Fernandes and Kohn2014; Hamann et al., Reference Hamann, González and Fernández2020a; Aguiar et al., Reference Aguiar, Morais, Silva, Anjos, Foster and Silva2021). Only recently has this taxon been accessed at the genetic level using molecular analyses (Alcantara et al., Reference Alcantara, Úngari, Müller, Ferreira-Silva, Emmerich, O’dwyer and Silva2022), making it the only neotropical Gorgoderid analyzed to date.
Gorgoderina sp.
Stage: Adult fluke.
Hosts (Adult anurans): L. macrosternum (P:25.00%,3/12;MII±SD:3.66±1.15;3-5) and L. podicipinus (P:8.49%,9/106;MII±SD:1.88±1.16;1-4).
Site of infection: Urinary bladder.
Remarks: Fluke with an elongated body and tapered ends. Tegument smooth, without spines. Oral sucker subterminal. Acetabulum cylindrical to ovoid, larger than the oral sucker. Anterior and posterior testes displaced to the left side. Ovary smaller than the testes, located between the anterior testis and vitelline follicles. Vitelline follicles composed of two compact follicles with regular contours. General morphology and morphometrics do not match any previously described species, suggesting this is likely a new Gorgoderina species. For information on the general life cycle, see the remarks on G. parvicava.
Superfamily Plagiorchioidea Luhe, 1901
Plagiorchioidea gen. sp.
Stage: Metacercariae encysted
Hosts (Adult anurans): L. podicipinus (P:8.49%,9/106;MII±SD:3.55±3.35;1-10) and P. platensis (P:30.00%,6/20;MII±SD:1.60±0.89;1-3).
Hosts (Tadpoles): B. raniceps (GS:37,39,40;P:6.12%,3/49;MII±SD:1.66±1.15;1-3); D. minutus (GS:37;P:25.00%,1/4;4) D. nanus (GS:30-42,44;P:17.91%,12/67;MII±SD:5.66±6.95;1-22); D. muelleri (GS:44;P:1.61%,1/62;2); L. podicipinus (GS:28;P:20.00%,4/20;MII±SD:1.50±0.57;1-2); S. fuscovarius (GS:36,37;P:11.10%,2/18;3-3) and S. nasicus (GS:35,43;P:33.33%,2/6;1-4).
Site of infection: Abdominal cavity, liver, kidney, and tail musculature.
Remarks: Metacercariae without developed reproductive organs or morphological traits allowing specific identification. However, the presence of an I-shaped excretory vesicle filled with excretory granules (Smyth & Smyth, Reference Smyth and Smyth1980) enabled identification at the superfamily level. Plagiorchioidea comprises parasites of amphibians, reptiles, and mammals (Campião et al., Reference Campião, Morais, Dias, Aguiar, Toledo, Tavares and Silva2014; Fernandes & Kohn, Reference Fernandes and Kohn2014; Fernandes et al., Reference Fernandes, Justo, Cárdenas and Cohen2015), and our record, together with previous reports (Campião et al., Reference Campião, Morais, Dias, Aguiar, Toledo, Tavares and Silva2014; Hamann et al., Reference Hamann, González and Fernández2020a), reinforces the role of anurans as links through which larval forms can reach definitive hosts. This is the first record for B. raniceps, D. nanus, D. muelleri, L. podicipinus, and S. fuscovarius.
Family Plagiorchiidae Lühe, 1901
Choledocystus cf. incurvatum (Nasir, 1966) Sullivan, 1976
Stage: Adult.
Host (Adult anuran): Pseudis platensis (P:20.00%,4/20; MII±SD:1.80±0.44;1-2).
Site of infection: Small intestine.
Remarks: The morphometrics and morphological characteristics, such as the position of vitelline glands, which are extracaecal and extend from the caeca bifurcation to the final third of the body, as well as the position of the genital pore and reproductive organs, are compatible with this species of Choledocystus, whose records were previously restricted to Argentina and Venezuela in the host Pseudis paradoxa (Fernandes & Kohn, Reference Fernandes and Kohn2014; Hamann et al., Reference Hamann, León-Règagnon, Fernández and González2020b). We were conservative regarding specific identification, as the low number of flukes recovered limits morphometric comparisons. The genus Choledocystus comprises parasites of the liver, biliary ducts, urinary bladder, intestines, and, in some cases, the lungs of anurans throughout South America (Campião et al., Reference Campião, Morais, Dias, Aguiar, Toledo, Tavares and Silva2014; Fernandes & Kohn, Reference Fernandes and Kohn2014; Gomes et al., Reference Gomes, Melo, Giese, Furtado and Santos2017). There are no specific studies on the life cycle of this genus, but it likely follows the pattern of other closely related Plagiorchids, such as flukes of the genus Glypthelmins, in which, in some species, metacercariae form only on the skin of frogs and not tadpoles, with infection occurring when frogs ingest their skin, in other species, cercariae infect only tadpoles and later migrate to the intestine of the frog after metamorphosis (Leigh, Reference Leigh1946; Martin, Reference Martin1969). Our record expands the geographical distribution of this parasite and represents the first record in Brazil and in P. platensis.
Family Haematoloechidae Freitas & Lent, 1939
Haematoloechus sp.
Stage: Young flukes.
Hosts (Adult anurans): Pseudis platensis (P:15.00%,3/20;MII±SD:7.00±8.71;1-17).
Site of infection: Lungs.
Remarks: The specimens recovered were young flukes in an early developmental stage, without mature reproductive organs or eggs, making specific identification impossible. The presence of these young flukes likely indicates a recent infection. The genus Haematoloechus comprises lung parasites of anurans, with 11 species known in South America (Campião et al., Reference Campião, Morais, Dias, Aguiar, Toledo, Tavares and Silva2014; Fernandes & Kohn, Reference Fernandes and Kohn2014; Aguiar et al., Reference Aguiar, Morais, Silva, Anjos, Foster and Silva2021). These parasites mainly use odonate larvae and other aquatic arthropods as second intermediate hosts, with anurans becoming infected through the trophic chain by consuming these infected hosts (Yamaguti, Reference Yamaguti1975; Bolek & Janovy, Reference Bolek and Janovy2007a,Reference Bolek and Janovyb). There are no studies on the life cycle of the species found in South America.
Family Macroderoididae McMullen, 1937
Rauschiella proxima (Freitas, 1941)
Stage: Adult fluke.
Hosts (Adult anurans): B. raniceps; L. macrosternum; L. podicipinus and P. platensis.
Site of infection: Small intestine.
Remarks: Morphological and ecological data related to this species were recently published (Queiroz et al., Reference Queiroz, López-Hernández, Anjos and Pinto2025). The morphological characteristics are consistent with Rauschiella proxima, originally described in Uruguay, with two previous records in Brazil (Travassos et al., Reference Travassos, Freitas and Kohn1969; Fernandes & Kohn, Reference Fernandes and Kohn2014; Portela et al., Reference Portela, Dos Santos and Anjos2020). Flukes of the genus Rauschiella are parasites of anurans and reptiles throughout South and Central America (Fernandes & Kohn, Reference Fernandes and Kohn2014).
Discussion
The trematode community analyzed in our study reports 24 new host records for some parasites and was pioneering in including tadpoles in this analysis, a group poorly studied with respect to its helminth fauna across South America (Araujo & Artigas, Reference Araujo and Artigas1982; Fernandes et al., Reference Fernandes, Sartini, Dias and D’agosto2011; Pinto & Melo Reference Pinto and Melo2012; Gambale et al., Reference Gambale, Batista, Oda, Campos, Takemoto and Bastos2014; Pala et al., Reference Pala, Valladão, Alves, Pilarski and Lux Hoppe2018). Despite the fact that all anuran species analyzed here were previously reported in other studies throughout the country (Campião et al., Reference Campião, Morais, Dias, Aguiar, Toledo, Tavares and Silva2014, Reference Campião, Silva, Dalazen and Tavares2016a, Reference Campião, Ribas, Silva, Dalazen and Tavares2016b; Graça et al., Reference Graça, Oda, Lima, Guerra, Gambale and Takemoto2017; Martins-Sobrinho et al., Reference Martins-Sobrinho, Silva, Santos, Moura and Oliveira2017; Toledo et al., Reference Toledo, Schwartz, Nomura, Aguiar, Velota, Silva and Anjos2018; Queiroz et al., Reference Queiroz, Pontes, Neto, Campião and Anjos2020a,Reference Queiroz, López-Hernández, Locke, Pinto and Anjosb, Reference Queiroz, Alves, López-Hernández, Anjos and Pinto2021; Portela et al., Reference Portela, Dos Santos and Anjos2020; Aguiar et al., Reference Aguiar, Morais, Silva, Anjos, Foster and Silva2021; Alcantara et al., Reference Alcantara, Úngari, Müller, Ferreira-Silva, Emmerich, O’dwyer and Silva2022, Reference Alcantara, Ebert, Ferreira-Silva, Forti, Morais, Pérez-Ponce de Léon and Silva2024), our study reveals the importance of faunal surveys for understanding the patterns of parasite communities, as well as local biodiversity and providing data for further studies.
The ecological analysis of tadpoles infected with digeneans demonstrates that the infracommunities were composed only of metacercariae stages, an expected result considering several described life cycles of trematodes that use tadpoles as second intermediate hosts (Yamaguti, Reference Yamaguti1975; Smyth & Smyth, Reference Smyth and Smyth1980; Bolek et al., Reference Bolek, Detwiler, Stigge, Toledo and Fried2024). The infracommunities of adult anurans were composed of both adult and larval digeneans, with dominance of the metacercariae stage. This distribution pattern reflects the habits of anuran species and highlights their role as second intermediate hosts in digenean life cycles (Aho, Reference Aho, Esch, Bush and Aho1990; Hamann & González, Reference Hamann and González2009; Hamann et al., Reference Hamann, Fernández and González2019, Reference Hamann, González and Fernández2020a, Reference Hamann, Fernández and González2023). Hylid anurans had the most diverse and equitable composition of digeneans compared to other families, which we attribute to the predominantly aquatic-associated behavior of these species (Uetanabaro et al., Reference Uetanabaro, Prado, Rodrigues, Gordo and Campos2008).
Among the 16 recovered trematode taxa, six were anuran-specific parasites: Catadiscus marinholutzi, Choledocystus cf. incurvatum, Haematoloechus sp., Gorgoderina parvicava, Gorgoderina sp., and Rauschiella proxima. Although there are no specific studies on the life cycles of these species, they probably resemble those of other congeneric or related species, as reported in the literature (Yamaguti, Reference Yamaguti1975; Bolek & Janovy, Reference Bolek and Janovy2007a,Reference Bolek and Janovyb, Reference Bolek and Janovy2008; Bolek et al., Reference Bolek, Snyder and Janovy2009, Reference Bolek, Detwiler, Stigge, Toledo and Fried2024; Besprozvannykh et al., Reference Besprozvannykh, Rozhkovan, Ermolenko and Izrailskaya2018). Flukes of the family Diplodiscidae have an abbreviated life cycle in which metacercariae form in the substrate or on the skin of frogs, and infection occurs through ingestion of metacercariae (Bolek & Janovy, Reference Bolek and Janovy2008; Besprozvannykh et al., Reference Besprozvannykh, Rozhkovan, Ermolenko and Izrailskaya2018; Bolek et al., Reference Bolek, Detwiler, Stigge, Toledo and Fried2024). This is probably the reason why C. marinholutzi was the most abundant adult digenean recovered in our study, as also observed in other systems with species of the genus Catadiscus (Hamann et al., Reference Hamann, Kehr and González2013, Reference Hamann, González and Fernández2020a; Campião et al., Reference Campião, Silva, Dalazen and Tavares2016a,Reference Campião, Ribas, Silva, Dalazen and Tavaresb). C. cf. incurvatum and Haematoloechus sp. were recovered only from one host, the Hylidae P. platensis this pattern was reflected in the cluster analysis, which showed both grouped together with a similarity of 0.58.
Metacercariae were the most abundant parasites in this study, with 10 taxa using anurans as intermediate hosts. These parasites may reach maturity in anurans, reptiles, birds, or mammals. Two taxa, L. cf. nephrocystis and B. cf. tetracotyloides, were the most abundant in the community, although they shared low similarity. We observed a certain degree of specialization regarding the trophic relationships involved in transmission to the definitive host: L. cf. nephrocystis was more abundant in hylid anurans, which have aquatic and arboreal habits, whereas B. cf. tetracotyloides was abundant in leptodactylids, which exhibit semiaquatic and terrestrial habits.
The respective correlation is due to L. nephrocystis being a Neotropical species parasitizing birds found in Brazil and Venezuela (Fernandes et al., Reference Fernandes, Justo, Cárdenas and Cohen2015), and Bursotrema tetracotyloides, an intestinal parasite of marsupials in Argentina and Peru, with no adult records in Brazil so far (Fernandes et al., Reference Fernandes, Justo, Cárdenas and Cohen2015). The fact that both species were the most abundant may indicate a high occurrence of definitive hosts in the area or the influence of external factors such as agrochemicals, exotic species, or other disturbances, factors already cited in the literature (Kelly et al., Reference Kelly, Paterson, Townsend, Poulin and Tompkins2009; Hamann et al., Reference Hamann, González and Fernández2020a), which would require further investigation.
The total prevalence of infection was 58% for tadpoles and 65% for adults, a pattern we attribute to the fact that adult anurans include adult trematodes and two additional metacercariae species in the community (Clinostomum sp. and Bursotrema cf. tetracotyloides metacercariae were exclusive to adults). Of the eight metacercariae taxa that infected tadpoles, five also occurred in adults, while only three (Diplostomidae gen. sp. 1, Diplostomidae gen. sp. 2, and Tylodelphys sp.) were restricted to tadpoles. Significant differences were found in the prevalence of infection between B. raniceps adults and tadpoles, with higher prevalence in tadpoles. In D. nanus, significant differences were also observed in mean intensity of infection, mean abundance, and mean trematode species richness, with higher values attributed to tadpoles. Although only two of eleven species were compared, the results reveal an interesting pattern: tadpoles tend to have higher infection rates compared to adults of the same species. If some selective filters act during metamorphosis, such as the death or predation of heavily infected tadpoles, further studies will be necessary to confirm this pattern.
In Brazil, there are few specific studies on trematodes in anurans. However, when comparing our results with other studies on helminths in anurans, we observed a similarity in the reported taxa, particularly with those from Argentina (Hamann & González, Reference Hamann and González2009; Hamann et al., Reference Hamann, Kehr and González2013, Reference Hamann, González and Fernández2020a; Campião et al., Reference Campião, Morais, Dias, Aguiar, Toledo, Tavares and Silva2014, Reference Campião, Silva, Dalazen and Tavares2016a,Reference Campião, Ribas, Silva, Dalazen and Tavaresb; Graça et al., Reference Graça, Oda, Lima, Guerra, Gambale and Takemoto2017; Lins et al., Reference Lins, Aguiar, Morais, Da Silva, àvila and Silva2017; Toledo et al., Reference Toledo, Schwartz, Nomura, Aguiar, Velota, Silva and Anjos2018; Aguiar et al., Reference Aguiar, Morais, Silva, Anjos, Foster and Silva2021). The high similarity with taxa reported in Argentina suggests plasticity in these parasites, which show a wide geographical distribution related to the occurrence of definitive hosts and commonly use anurans as generalist definitive or intermediate hosts. Considering the study area, a fragment of Cerrado surrounded by pasture, the occurrence of ten metacercaria taxa reveals a hidden biodiversity, emphasizing the maintenance of these biological cycles and their hosts in the region, which include birds, mammals, and reptiles.
The component community of trematodes in anurans found in a pond within a Cerrado fragment was composed mostly of metacercariae. Our study emphasizes the importance of anurans as key links in trematode communities, transmitting aquatic larval stages to terrestrial vertebrate definitive hosts. Furthermore, this study reports new host records for certain parasites, some of which are recorded for the first time in Brazil, highlighting the importance of faunistic inventories for a better understanding of parasitism in these hosts, as well as providing a foundation for future research.
Supplementary material
The supplementary material for this article can be found at http://doi.org/10.1017/S0022149X25100928.
Acknowledgements
The author is grateful to all the participants of the manuscript and the National Council for Scientific and Technological Development (CNPq).
Author contribution
MSQ: Formal analysis, data curation, writing, revision. MLRD: Writing, revision. HAP: Writing, revision. LAA.: Formal analysis, data curation, writing, revision.
Financial support
We thank the National Council for Scientific and Technological Development (CNPq) (research scholarship to L.A.A. and H.A.P.).
Competing interests
The authors declare no competing interests.
Ethical standard
All activities were authorized by the Brazilian Institute of the Environment and Renewable Natural Resources (IBAMA) (research permit SISBIO-58746-4). The experimental procedures were carried out in this study following the recommendation of the local committee of ethics in animal experimentation (FEIS/UNESP – protocol CEUA/FEIS – 12/2018).
