Insuetophrynus acarpicus is a medium sized, robust-bodied frog with a snout-vent length range in adult males of 40.5 – 56.3 mm, young male range of 27.1 – 40.7 mm, newly metamorphosed male range of 19.1 – 28.1 mm, adult female range of 35.2 – 53.0 mm, young female range of 26.8 – 37.9, and newly metamorphosed female range of 20.8 – 26.5mm (Diaz et al. 1983). The head is wider than long with a short rounded snout that extends beyond the jaw. The nostrils are at the tip of the snout. The canthus rostralis is straight and well-developed. The loreal region is slightly depressed. The eye diameter is larger than the distance between the eye and nostril (Barrios 1970). The pupil is horizontal (Silva 2017). The upper eyelid width is greater than the interorbital space. The incomplete tympanic ring is barely visible. The supratympanic ridge extends from the posterior angle of the eye to the arm insertion. A row of glands starts behind the eyes and dorsally extend towards the posterior without crossing the midline and another, less distinct row can be found parallel to and under the first. In the holotype, there is a vocal sac on the right, but not on the left. In general, vocal sacs may be present, singular (to one side) or paired (Barrio 1970). The skin of the dorsum is granular with cornified pectoral plates (Barrio 1970, Rabanal and Nuñez 2012).
The arms are short and thick. The palmar tubercles are distinct with the inner palmar tubercle having cornified horny spines on the inner edge and being larger than the outer palmar tubercle. The fingers are free of webbing and rounded at the tips. Characteristic of the species, the dorsal and lateral surfaces of the first finger in sexually mature adults have keratinized, conical tubercles that have further numerous spines. Similar, small, flat structures can be found on the inner edge of the second. The fingers have slight but evident subarticular tubercles (Barrio 1970).
The legs are slimmer than the arms. When the leg is extended along the body, the tibiotarsal articulation reaches the posterior edge of the eye. The inner metatarsal tubercle is elongated and the outer metatarsal tubercle is small and round. The foot webbing reaches the first phalanx and the subarticular tubercles are well developed. The fifth toe is very well developed (Barrio 1970).
Adult I. acarpicus are easily differentiated from all sympatric species by the cornifications on their first finger and pectoral plate, by their horizontal pupil in their prominent eyes, and by the dark canthus stripe (Silva 2017). Adults also have a firmisternal pectoral girdle (a derived characteristic in which the epicoracoid cartilages are fused both posteriorly and anteriorly) and lack carpal bone ossification (Rabanal and Nuñez, 2012).
In life, the body of adults is grey (Barrios 1970) to greenish brown (Parda et al. 2017) and juveniles have greenish tones (Barrios 1970). There may be small, white granulations. The hind limbs have transverse dark bands (Parda et al. 2017). In alcohol, the dorsum is grey. The body and limbs have white granulations, and the transverse hind limb bands remain. The ventrum is light yellowish grey (Barrio 1970).
Differing degrees of cornification are present depending on the life stage of the individual. Recent metamorphs do not have cornified skin. Despite earlier reports that only adult males have cornification, both adult sexes had cornification on fingers one and two as well as on the inner edge of the inner palmar tubercule and these structures are present year round (Diaz et al. 1983).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Chile
Insuetophrynus acarpicus inhabit cold, clear mountain streams in temperate forests of the coastal range of Chile (Mendez et al. 2005) at an altitudinal range of 50 to 700 m above sea level (Rabanal and Nuñez 2012, Silvia 2017). For over 30 years, the species was only known from the vicinity of Mehuín, Valdivia Province, however new discoveries extended the range 3 km to the north and south to Alerce Costero National Park (Silvia 2017).
During the day, adults are found hiding under semi-submerged rocks in cold, clear mountain streams with sandy and stony bottoms (Barrios 1970) and at night, around rocks on stream banks (Díaz et al. 1983, Rabanal and Nuñez 2012, Silva 1970). Tadpoles are also found under stream stones, but only in slow running streams with muddy bottoms (Rabanal and Nuñez, 2012).
Life History, Abundance, Activity, and Special Behaviors
Insuetophrynus acarpicus is a predominantly aquatic frog (Díaz et al. 1983, Rabanal and Nuñez 2012, Silva 2017) but lack strong swimming ability (Dias et al. 1983). Adults can be found in clear, cold mountain streams with sandy and stony bottoms where they hide under semi-submerged stones (Barrios 1970) during the day and emerge onto the bank at night (Díaz et al. 1983, Rabanal and Nuñez 2012, Silva 1970) where they are presumed to feed along the water’s edge. When disturbed the adults can quickly jump in to the stream to find refuge under rocks (Diaz et al. 1983).
No calls have been recorded in the wild, but captured male frogs make weak vocalizations (Diaz et al. 1983).
Breeding in I. acarpicus occurs in the water (IUCN 2018) and is believed to occur between January and May, as females have been found with mature oocytes during that time (Formas et al. 1980, Diaz et al. 1983). The animal pole of the oocytes is grayish brown and the other pole is creamy white. Females can be found with oocytes and follicles in various stages of development. In 12 adult females, the average number of oocytes and follicles were 67 and 34 and their sizes were 2.33 mm and 1.25 mm respectively (Diaz et al. 1983).
Tadpoles can be found in slow running streams with muddy bottoms under stones (Rabanal and Nuñez, 2012). The smallest tadpoles have been found in May with larvae presence from May to January indicating that reproduction may take 10-12 months (Formas et al. 1980, Diaz et al. 1983). Tadpoles have sucking-morphology mouthparts (Rabanal and Formas 2009) and feed on mud with organic debris (Diaz et al. 1983, Rabanal and Formas 2009). Metamorphs are abundant in January (Diaz et al. 1983) and have a snout-vent length of 20 – 22 mm (Formas et al. 1980).
Vegetation along the stream banks consists of Luzuriaga radicans, Blechnum blechnoides, Hipopterigium sp.,Chusquea quila, Lophosoria quadripinnata, Hymenophyllum plicatum, H. caudiculatum, and various species of liverworts (Diaz et al. 1983) or in forests of Aextoxicum punctatum with an understory of ferns (Blechnum and Hymenophyllum), moss (Hypopterigium arbuscula), and hepatics (Marchantia polymorpha and Plagioschila heterodonta) (Formas et al. 1980). Relative humidity is lowest during the summer in January and highest in May, which is also around the highest rainfall and lowest temperature in July (Diaz et al. 1983).
Insuetophrynus acarpicus can be found in the same habitat as the following amphibian species: Alsodes valdiviensis, A. vittatus, Batrachyla antartandica, B. leptopus, B. taeniata, Eupsophus migueli , E. roseus, E. vertebralis, Pleurodema thaul, Rhinoderma darwinii and Telmatobufo australis (Formas et al. 1980, Silvia 2017). Other animals found in the same habitat include anomuran crabs from the genus Aegla (Formas et al. 1980)
Tadpoles have body lengths at stages 25 - 28 of 12.60 - 20.10 mm and total lengths between 36.10 – 56.10 mm. At stages 29 – 43 the body length ranges from 16.40 - 22.3 mm and total lengths ranging from 54.10 – 61.00 mm. The body is oval in the dorsal and lateral view, slightly vertically compressed at the snout, and twice as long as it is deep. The small, oval nostrils are closer to the eye than the snout, do not protrude, and have a thick cutaneous marginal fringe on the anterolateral side. The internarial distances are a quarter smaller than the interorbital distance. The eyes are small and anterodorsally directed. The eye diameter is half the size of the internarial distance. The pupil is round. The mouth is ventral with an oral disc that is not emarginated, larger than the interorbital distance, and approximately equal to the internarial distance. The disc is surrounded by a single row of marginal papillae with a rostral gap and lateral folds. There is no mental gap or intramarginal papillae. Both jaw sheaths are thin with the lower jaw being U-shaped. Both jaws have small, weak, keratinized serrations with rounded tips. The labial tooth formula is 2(2)/2(1-2) with the upper teeth being well developed and the lower teeth being scarce and small. The skin of the body is smooth with a few curved keratodonts that have blunt dorsal tips. The spiracle is sinstral, positioned posterolaterally at approximately 60° from the main axis of the body and attached at the inner wall all the way to the tip. The spiracle opening is half the size of the eye diameter. The short anal tube is dextral and ventral with an oval opening that is slightly more than half the internarial distance. The posterior edge of the vent connects with the margin of the ventral fin. The tail length is 1.7 times the body length (Formas et al. 1980, Rabanal and Formas 2009) and the tail width is about half the width of the body (Diaz and Valencia 1985). The tail has well developed caudal musculature and ends in a rounded tip. The low dorsal fin does not extend onto the body. The maximum tail height is at the posterior third of the tail (Formas et al. 1980, Rabanal and Formas 2009).
In life, the tadpole dorsum is greenish-brown with irregular mottling. The tail and fin also have irregular, light-brown spots in the form of melanophores and guanophores (Formas et al. 1980, Rabanal and Formas 2009). The lateral line is visible in the dorsal and lateral view on the body and tail. The ventrum is transparent with the viscera visible (Formas et al. 1980). In preservative, the tadpoles are grey and the belly remains transparent (Rabanal and Formas 2009).
From Caudiverbera caudiverbera, and members of Telmatobius, and Alsodes, larval I. acarpicus can be differentiated by the absence of labial papillae, poorly developed mandibles, a tooth formula of 2/2, a spiracle closer to the snout than the vent, a wide tail base that is half the width of the body, and a dorsal fin that does not extend onto the body (Diaz and Valencia 1985). Additionally, in I. acarpicus, the buccal floor arena is rectangular versus “U-shaped” in Alsodes, Limnomedusa, Proceratophrys, and Odontophyrnus, narrowly ovoid-triangular in Macrogenioglotus, and elongated in Hylorina. Lastly, the pars alaris and pars corpora are dorsally and ventrally fused in I. acarpicus but not fused in Alsodes, Eupsophus, Limnomedusa, and Rhinoderma (Rabanal and Formas 2009).
Trends and Threats
Insuetophrynus acarpicus is listed on the IUCN Red list as “Endangered” because of a decreasing population status from habitat destruction due to logging, cattle farming, and afforestation with pine plantations, which is compounded by the species’ limited range. The species is not tolerant of water pollution (Veloso et al. 2010, IUCN 2018). As of 2017, only one population could be found in a protected area, Alerce Costero National Park (Silva 2017), but their habitat is contaminated by people who bathe with soap in the stream (IUCN 2018). Lastly, the genetic diversity of at least three populations is low with the populations appearing to be in decline (Parda et al. 2017). The population at Chanchán in particular should be closely monitored (IUCN 2018). Evaluations are needed to determine the species’ extent in protected areas and their genetic diversity (Silva 2017, Parda et al. 2017).
Possible reasons for amphibian decline
General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Local pesticides, fertilizers, and pollutants
The species authority is: Barrio, A. (1970). “Insuetophrynus acarpicus, un nuevo leptodactilido firmisterno sudamericano.” Physis 30(80): 331-341.
Insuetophrynus acarpicus is a member of the family Rhinodermatidae, and based on Maximum Parsimony, Maximum Likelihood, and Baysian inference of 12S and 16S mitochondrial DNA, is most closely related to members of the genus Rhinoderma (Correa et al. 2006), however, Diaz et al. (1983) suggested that, based on karyotyping, liver hexokinase patterns, morphology, and clutch characteristics, I. acarpicus is related to members of the Alsodes genus.
Insuetophrynus acarpicus is the only species of the genus Insuetophrynus. Genetic analysis of the three original population sites revealed that population divergence occurred during the Pleistocene epoch and led the researchers to suggest that the most ancestral population was the Queule population. The populations at Colegual Alto and Mehuin were closely related to each other, but it is unclear if they were derived from the Queule population. The closer relationship between the Colegual Alto and Mehuin populations could be a result of passive dispersion in streams connecting the populations (Méndez et al 2005). Several other sites have since been found, but relatedness studies has not yet been conducted (Rabanal and Nuñez 2012, Parda et al. 2017, Silva 2017).
Barrio, A. (1970). ''Insuetophrynus acarpicus, un nuevo leptodactilido firmisterno sudamericano.'' Physis, 30(80), 331-341.
Diaz, N. F., Valencia, J., Sallaberry, M. (1985). ''Life history and phylogenetic relationships of Insuetophrynus acarpicus (Anura: Leptodactylidae).'' Copeia, 1985(1), 30-37. [link]
Diaz, N. F., and Valencia, J. (1985). ''Larval morphology and phenetic relationships of the Chilean Alsodes, Telmatobius, Caudiverbera and Insuetophrynus (Anura: Leptodactylidae).'' Copeia, 1985(1), 175-181.
Formas, J. R., Díaz, N. F., Valencia, J. (1980). ''The tadpole of the Chilean frog Insuetophrynus acarpicus.'' Herpetological, 36(4), 316-318. [link]
IUCN SSC Amphibian Specialist Group 2018. ''Insuetophrynus acarpicus.'' The IUCN Red List of Threatened Species 2018: e.T10832A79809262. http://dx.doi.org/10.2305/IUCN.UK.2018-1.RLTS.T10832A79809262.en. Downloaded on 14 May 2019. https://www.iucnredlist.org/species/10832/79809262
Méndez, M. A., Torres-Pérez, F., Correa, C., Soto, E. R., Nuñez, J. J., Veloso, A., Armesto, J. (2006). ''Genetic divergence in the endangered frog Insuetophrynus acarpicus (Anura: Leptodactylidae).'' Herpetological, 16(1), 93-96. [link]
Parada, D.E., Fenolio, D., Olivares, A.P., Nuñez, J.J. (2017). ''Insuetophrynus acarpicus Barrio, 1970 (Anura: Rhinodermatidae): new distribution record at the edge of the Valdivian coastal range, southern Chile.'' Checklist, 13(1), 2034 . [link]
Rabanal, F. E., Formas, J. R. (2009). ''Complementary diagnosis of the genus Insuetophrynus (Anura, Cycloramphidae) based on larval characters.'' Zootaxa, 2116, 59-67. [link]
Rabanal, F. E., Nuñez, J. J. (2012). ''Discovery of a new population of the Critically Endangered frog Insuetophrynus acarpicus Barrio, 1970 (Anura: Cycloramphidae): Latitudinal and altitudinal extension in the Valdivian Coastal Range, Southern Chile.'' Checklist, 8(4), 810-812. [link]
Silva, B.S. (2017). ''New record of Insuetophrynus acarpicus Barrio, 1970 (Anura: Rhinodermatidae) in Chile: implications for its conservation.'' Checklist, 13(1), 2046 . [link]
Veloso, A., Núñez, H., Núñez, J., Formas, R. (2010). ''Insuetophrynus acarpicus.'' The IUCN Red List of Threatened Species 2010: e.T10832A3220550. http://dx.doi.org/10.2305/IUCN.UK.2010-2.RLTS.T10832A3220550.en.
Originally submitted by: Mallory Clouse and Ann T. Chang (first posted 2019-05-30)
Edited by: Ann T. Chang, Michelle S. Koo (2023-01-08)
Species Account Citation: AmphibiaWeb 2023 Insuetophrynus acarpicus: Barrio’s Frog <https://amphibiaweb.org/species/2641> University of California, Berkeley, CA, USA. Accessed Sep 29, 2023.
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Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 29 Sep 2023.
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