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Data on predation are important to reduce the Eltonian shortfall― the lack of knowledge on biotic interactions (Hortal et al., 2015) ―, but in nature, such data are recorded only occasionally (Menegucci et al., 2020). Anurans are an important part of the food web, as the prey of many vertebrate and invertebrate species (Toledo et al., 2007; Hocking & Babbitt, 2014). Brazil is the country with the greatest anuran diversity (Segalla et al., 2021; Frost, 2022), but the knowledge of biotic interactions of Brazilian anurans is deficient, even for common species like Thoropa miliaris (Spix, 1824), an endemic species to rocky environments in the Brazilian Atlantic Forest (Giaretta & Facure, 2004; Feio et al., 2006). In this work, we report opportunistic records of predation on T. miliaris by a snake, spiders, and a bird. We also compile the literature data on predators recorded for this species.
On 18 August 2014, at 20:04, CHON found a dead male snake Chironius laevicollis (Wied, 1824) (Colubridae) of 2.10 m snoutvent length at the Tombo D’água waterfall (Fig. 1A) (district of Mocotó do Imbé, municipality of Campo dos Goytacazes, state of Rio de Janeiro, Brazil; 21.81367° S, 41.75552° W, WGS84, 282 m a.s.l.). Dissection of the snake’s abdomen revealed a partially digested T. miliaris (Fig. 1B). Predator and prey were not collected due to the degree of decomposition, but we were able to identify both species based on their overall morphology and color pattern (Dixon et al., 1993; Feio et al., 2006).
Photos by PSA.
Figure 1 A) Specimen of Chironius laevicollis (Colubridae) found dead in Campos dos Goytacazes, Rio de Janeiro, Brazil. B) Thoropa miliaris (Cycloramphidae) removed from the stomach of C. laevicollis. Photos by CHON. C) Thoropa miliaris being preyed upon by a Ctenus sp. (Ctenidae) spider in Campos dos Goytacazes, Rio de Janeiro, Brazil. D) Thoropa miliaris being preyed on by a Ctenus cf. medius (Ctenidae) in Campos dos Goytacazes, Rio de Janeiro, Brazil. Photos by CHON. E) and F) Furnarius rufus (Furnariidae) preying on T. miliaris in Juiz de Fora, Minas Gerais, Brazil.
Fotos de PSA.
Figura 1 A) Individuo de Chironius laevicollis (Colubridae) encontrado muerto en el município de Campos dos Goytacazes, estado de Rio de Janeiro, Brasil. B) Individuo de Thoropa miliaris (Cycloramphidae) encontrado en el estómago de C. laevicollis, Campos dos Goytacazes, Rio de Janeiro, Brasil. Fotos de CHON. C) Individuo de T. miliaris siendo presa de una araña del género Ctenus sp. (Ctenidae) en Campos dos Goytacazes, Rio de Janeiro, Brasil. D) Individuo de T. miliaris siendo presa de una araña del género Ctenus cf. medius (Ctenidae) en Campos dos Goytacazes, Rio de Janeiro, Brasil. Fotos de CHON. E) y F) Individuo de Furnarius rufus (Furnariidae) predando un individuo de T. miliaris en el município de Juiz de Fora, estado de Minas Gerais, Brasil.
At this same locality, CHON recorded two additional predation events on T. miliaris by spiders of the family Ctenidae: Ctenus sp. and Ctenus cf. medius Keyserling, 1891, identified by the spider taxonomist Leonardo Carvalho, Universidade Federal do Piauí, Brazil. The first record was on 19 February 2020, at 18:35 (21.82724° S, 41.74726° W; WGS84; 174 m a.s.l.; Fig. 1C), and the second on 16 June 2021, at 19:46 (21.81449° S, 41.75748° W; Fig. 1D). The T. miliaris individuals were collected and deposited in the Coleção Herpetológica do Norte Fluminense (CHNF 0897 and CHNF 0975, respectively).
On 21 February 2020, at 12:10, PSPA recorded a T. miliaris being preyed by a juvenile Rufous hornero, Furnarius rufus (Gmelin, 1788) (Furnariidae) in an urban environment near the hospital of the Universidade Federal de Juiz de Fora, municipality of Juiz de Fora, state of Minas Gerais, Brazil (21.78553° S, 43.36787° W, WGS84, 878 m a.s.l.; Fig. 1E). The T. miliaris was initially observed beside a paved road with little traffic, when the bird appeared and repeatedly pecked the frog on its dorsum, venter, and head. The frog attempted to escape several times, but the bird held it with its beak. The bird immobilized the frog and swallowed it alive (Fig. 1F). The bird was subsequently observed for approximately 40 minutes from a distance of 30 cm, but no regurgitation was recorded (see record video at https://doi. org/10.5281/zenodo.6954386). Prey identity was confirmed by Diego J. Santana (Universidade Federal do Mato Grosso do Sul, Brazil).
We reviewed literature records of predators of T. miliaris in Google Scholar on 28 April 2022, searching for the expression “predation OR predator OR prey AND ‘Thoropa miliaris’” in English, Spanish (depredación OR presa OR depredador), and Portuguese (predação OR presa OR predador), and found 267 results. Of these, only eight showed T. miliaris as the prey. We also searched issues of Herpetological Review from 1967-2022, finding four additional records. In addition, we searched the authors' pdf libraries. All reports are shown in Table 1.
Table 1 List of predators of Thoropa miliaris (Anura: Cycloramphidae) based on the authors’ data and literature review.
Tabla 1 Lista de depredadores de Thoropa miliaris (Anura: Cycloramphidae) basada en los datos propios de los autores y en una revisión de la literatura.
| Predator identification | Life stage of prey | Environment | Source |
|---|---|---|---|
| Arachnida | |||
| Cteniza sp. Latreille, 1829 | Post-metamorphic | Forest | Pertel et al., 2010 |
| Ctenus cf. medius Keyserling, 1891 | Post-metamorphic | Forest | This study |
| Ctenus sp. | Post-metamorphic | Forest | This study |
| Trechalea sp. | Tadpole | Forest | Diniz et al., 2020 |
| Anura | |||
| Cycloramphus boraceiensis (Heyer, 1983) | Tadpole | Forest | Hartmann et al., 2003 |
| Thoropa miliaris (Spix, 1824) (Tadpole) | Egg | Forest | Giaretta & Facure, 2004 |
| Aves | |||
| Furnarius rufus (Gmelin, 1788) | Post-metamorphic | Urban | This study |
| Insecta | |||
| Tropisternus sp. (Larvae) | Tadpole | Forest | Siqueira et al., 2006 |
| Squamata | |||
| Bothrops jararaca (Wied, 1824) | Post-metamorphic | Forest | Sazima, 1992 |
| Chironius bicarinatus (Wied, 1820) | Post-metamorphic | Forest | Roberto & Souza, 2020 |
| Chironius flavolineatus (Jan, 1863) | Post-metamorphic | Not informed | Pinto et al., 2008; Roberto & Souza, 2020 |
| Chironius fuscus (Linnaeus, 1758) | Post-metamorphic | Forest | Marques & Sazima, 2004; Hartmann, 2005; Roberto & Souza, 2020 |
| Chironius laevicollis (Wied, 1824) | Post-metamorphic | Forest | This study |
| Erythrolamprus miliaris (Linnaeus, 1758) | Post-metamorphic | Forest | Albolea, 1998; Marques & Sazima, 2004; Mônico et al., 2016; Burg, 2020 |
| Erythrolamprus poecilogyrus (Wied, 1825) | Post-metamorphic | Not informed | Pinto & Fernandes, 2004 |
| Tropidurus torquatus (Wied, 1825) | Unknown - Museum specimen | Urban | Mônico & Mônico, 2022 |
Snakes are among the most important predators of postmetamorphic anurans (Toledo et al., 2007). Most reports of predation on T. miliaris were by Chironius spp., a genus of frogeating species (Marques et al., 2016). Conversely, lizards are the least frequent vertebrate predators of frogs (Toledo et al., 2007). We found a single record of T. miliaris being preyed by a lizard (Mônico & Mônico, 2022): Tropidurus torquatus, a saxicolous species with a generalist diet (Gomides et al., 2013; Guimarães & Sbrek-Araujo, 2018). We also found two records of frogs preying on T. miliaris: i) tadpoles being preyed upon by Cycloramphus boraceiensis (Hartmann et al., 2003), and ii) egg cannibalism by conspecific tadpoles (Giaretta & Facure, 2004). Tadpoles were also preyed upon by larvae of the beetle Tropisternus sp., the only record of an insect preying on T. miliaris, despite Coleoptera being one of the most recorded invertebrate groups of anuran predators (Toledo, 2005). Arachnida is another frequently recorded invertebrate group of anuran predators (Toledo, 2005), although we found only two predation events, by a Cteniza sp. and Trechalea sp. (Pertel et al., 2010; Diniz et al., 2020).
Our records improve the information about the predation of post-metamorphic specimens of T. miliaris by the spider genus Ctenus, whose species often actively forage for anurans in leaf litter (Salvestrini & Gasnier, 2001; Menin et al., 2005). We also report the first avian predator of T. miliaris, the Rufous hornero, Furnarius rufus. Birds are common predators of postmetamorphic anurans (Toledo et al., 2007), but the absence of records for T. miliaris highlights the knowledge gaps on the biotic interactions of this relatively common, conspicuous, and abundant species.
