The genus Alsodes consists of 19 species, and 2 sister genera, Eupsophus (6 species) and Limnomedusa (1 species), that make up the family Alsodidae (AmphibiaWeb, 2022). The genus Hylorina was included within the same family after GenBank discoveries found DNA similarities to other Eupsophus species, but no taxonomy classifications have been officially changed (Pyron & Wiens, 2011). Alsodes is often distinguished by the males of its species, who have patches of spines on their chests and smaller spines on their first and second digits, both of which are most prominent during mating seasons. As such, these frogs are often referred to as “spiny-chest frogs” with other members of the family commonly called “ground frogs” or “rapid frogs” (AmphibiaWeb, 2022). Despite some tadpoles of the genus displaying various colorings and characteristics, they are all categorized according to their medium body size with rounded tail tips and that they often found in similar freshwater environments. The adults can be classified according to characteristics beyond that of spiny structures on the chest and fingers, such as well-developed hummeral crests and internal morphology (Formas & Cuevas, 2017). Alsodes monticola was the first species of the genus to be described, observed by Charles Darwin and named by Thomas Bell in 1843 in The Zoology of the Voyage of H.M.S Beagle (1832-1836) Volume IV., Reptiles (Lynch, 1968). (AmphibiaWeb, 2022; Formas and Cuevas, 2017; Lynch, 1968; Pyron and Wiens, 2011)

Geographic Range

Species within Alsodes are restricted to small geographical areas throughout central and southern Chile, such as the Chilean Coastal Range and inland Argentina; particularly the shared region between the two countries, known as Patagonia, where they are considered to be the most species-rich frog family of the area (Formas & Cuevas, 2003; Blotto et al., 2013). Alsodes pehuenche and Alsodes gargola are the two species found on both sides of the Andean Mountain Range, in both Chile’s western slopes and Argentina’s eastern slopes (Blotto et al., 2013). The temperate Nothofagus forests of Chile’s coastal mountain ranges are found to house species from both the Eupsophus and Alsodes genera (Cuevas & Formas, 2005). Spiny-chest frogs are found in a variety of provinces, such as Argentina's Mendoza, Chubut, and Rio Negro, and Chile’s Maule, Los Lagos, and Santiago, among others (IUCN, 2022). (Blotto, et al., 2013; Cuevas and Formas, 2005a; Formas and Cuevas, 2003; IUCN, 2022)


Regardless of which side of the Andes the spiny-chest frogs are found on, the habitat is usually terrestrial freshwater and inland wetlands. Altitudes and exact habitats may vary from species to species, such as A. gargola and A. cantillanensis, both of which are also found in shrublands and/or forests (IUCN, 2022). Species found in forested locations may be restricted to meadow areas. They commonly occupy snowmelt streams/ponds with neutral pH’s, alpine lakes or forest streams, and/or under layers of leaf litter and debris near wetlands (IUCN, 2022). The tadpoles reside at the bottom (benthic area) of still bodies of water known as lentic water systems, including wetlands, ponds, and lakes (Fleming, 2019; Formas & Cuevas, 2017). (Fleming, 2019; Formas and Cuevas, 2017; IUCN, 2022)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • coastal

Systematic and Taxonomic History

Alsodes belongs solely to the family Alsodidae, along with Eupsophus and Limnomedusa, but spiny chest frogs boast the greatest number of species of all three genera. Recent research has suggested that Hylorina should be included within the family Alsodidae, while genetic support indicates that Limnomedusa should be considered for removal from the clade (Pyron & Wiens, 2011). The defining characteristic of spines upon their fingers and chests work to identify Alsodes as one collective genus with little debate. For researchers who prescribe to sub-groupings, evidence suggests the family Alsodidae is a subfamily of the larger family Cycloramphidae. Spiny chest frogs and other Eupsophus species were first named in 1843 by Thomas Bell and observed by Darwin on his fifth voyage; however, later research suggests that the A. monticola individuals described may have actually been part of Eupsophus (Lynch, 1968). Lynch (1968) therefore suggests that Alsodes should used as a synonym for Eupsophus based on Bell’s descriptions. (Cuevas and Formas, 2005a; Lynch, 1968; Pyron and Wiens, 2011)

  • Synonyms
  • Synapomorphies
    • Round thorny excrescences on thumb and pectorals
    • Diploid number of 2n=22,26, or 34

Physical Description

Alsodes species are mostly smooth-skinned, small/medium frogs, falling within the length range of 25-70mm and displaying sexual dimorphism in terms of size and the presence of rounded spiny adornments on males' chests and fingers. Both males and females display consistent colors (which are mostly yellow or brown) and reticulated, stripped, or spotted patterns which can feature white or black accents. This is displayed in one of the larger species of the family Alsodidae, A. valdiviensis, which are brown frogs that display a faint yellow triangle on their head and have common size differences between sexes, with males length ranging from 39.5 - 59.8mm in comparison to 39.7 - 63.4 mm females. Most species lack webbing between fingers and only have limited webbing of their hind feet (AmphibiaWeb, 2022). There have been suggestions for two general groups within Alsodes to be distinguished: one having “simple” spiny ornamentation on the fingers due to poor keratinized nuptial pads on the front hands, and the other being “complex” in which species boast stronger and darker thorny protrusions (Blotto et al., 2013). (AmphibiaWeb, 2022; Blotto, et al., 2013)



Alsodes species are known for their males, who produce nuptial rounded spiny thorns on their chests during the reproductive season and have increased presence of finger spines, most commonly on the thumb and forefinger (Cuevas & Formas, 2005b). (Cuevas and Formas, 2005b)

No mating calls have been recorded in this genus. Due to Chile and Patogonia’s neotropical climate, breeding seasons vary slightly depending on the species. A. valdiviensis's breeding season is around November-December, which coincides with their tendency to reproduce in colder streams (AmphibiaWeb, 2022). A. pehuenche females lay eggs in clumps at the beginning of the summer (Corbalan et al, 2014). A. cantillanensis females lay eggs in clutches of roughly 60 and share breeding sites with other amphibians and fish, most notably their sister taxa, A. nodosus. No reproductive isolation mechanisms are currently known for these two species. A. vanzolinii individuals have a reproductive season around January-February, laying yellow-tinted eggs with a 2.33mm diameter, and are often only active at night (AmphibiaWeb, 2022). Overall, more research and observations are needed for Alsodes's reproduction methods. (AmphibiaWeb, 2022; Corbalan, et al., 2014)

Alsodes females carry and lay eggs (AmphibiaWeb, 2022). New research indicates that some species, like A. pehuenche may have larval cycles that can stretch between four or five years (Corbalan et al, 2014). More observations regarding parental care and protective tendencies in this genus are required. (AmphibiaWeb, 2022; Corbalan, et al., 2014)

  • Parental Investment
  • no parental involvement


Alsodes frogs' lifespans in their natural environment is not well documented, and some adult species have yet to be observed more than a handful of times. However, research suggests that several Patagonian species are sensitive to changing water quality and may face issues regarding habitat loss and altercation, which may strongly reduce population size and longevity (Corbalan et al., 2010; AmphibiaWeb, 2022). (AmphibiaWeb, 2022; Corbalan, et al., 2010)


Some spiny chest frog species have yet to have information recorded regarding interactive behaviors amongst other Alsodes species or other amphibian species. Due to the microhabitats they reside in, research suggests most species seem to interact fairly peacefully. This is further demonstrated by the coexistence of species like A. tumultuosus and A. montanus, which have been found to inhabit the same streams with minor spatial segregation seen through their preference for lower stream marginal pools and high stream larger pools, respectively (Diaz & Valencia, 1985). Likewise, peaceful cohabitation between A. cantillanensis and A. nodosus, along with other amphibians in the same water source, have been noted (AmphibiaWeb, 2022). (AmphibiaWeb, 2022; Diaz and Valencia, 1985)

Communication and Perception

There is no available information within the literature regarding communication/perception techniques in this genus. However, the lack of observed mating calls of Alsodes species may indicate communication via methods other than acoustic signaling. Likewise, the protruding spiny thorn on males' chests during breeding season suggests the structure may play a role in mating and communication.

Food Habits

As tadpoles, Alsodes species are phytophagous and detritivorous with their main dietary components being periphytic algae and protozoa (Baffico & Ubeda, 2006). As adults, Alsodes are insectivores like most amphibians. Slight variations occur based on habitats differences, but their most common prey include beetles, springtails, flies, spiders, and isopods, with the frogs' diets focused on the larval stages of beetles, flies and moths (Alveal et al., 2015). (Alveal, et al., 2015; Baffico and Ubeda, 2066)


Most Alsodes species experience long larval periods (about 2 years), which can leave them vulnerable to predation. Recent studies suggest that invasive fish species, specifically rainbow trout (Oncorhynchus mykiss), rapidly increase predation rates of spiny chest frogs and decrease populations of Alsodes in both adult and larval stages (Zarco et al., 2020). (Zarco, et al., 2020)

Ecosystem Roles

Alsodes species fulfill an important ecological role as insectivores. Spiny chest frog populations help balance populations because their diets consist of prominent larval insect species. Many species are considered critically endangered or vulnerable according to both the Chilean government and IUCN Red List, which has further implications for how Patagonian ecosystems will shift in response to a reduction or total loss of spiny chest frog populations (Correa et al., 2018). (Correa, et al., 2018)

Economic Importance for Humans: Positive

Alsodes's insectivorous diets work to regulate insect populations of Patagonia within their microhabitats (Alveal et al., 2015). Available literature lacks information directly linking Alsodidae presence to protection of human agriculture or lumber, but it may be implied. (Alveal, et al., 2015)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Presently, there is no suggestion of any negative economic repercussions of Alsodes species on humans. Their non-poisonous and non-invasive status supports this statement.

Conservation Status

According to the IUCN Red List (2022), the conservation status of five Alsodes species are unknown, and the other 15 species are categorized from vulnerable to critically endangered, with two species (A. nodosus and A. gargola) considered the most stable and therefore of least conservation concern. Populations have been impacted by invasive fish species and changes in climate, both of which increase habitat loss and impact microhabitats and water quality. This reduces lifespan and overall population size (Zarco et al., 2020; Corbalan et al., 2010). (Corbalan, et al., 2010; IUCN, 2022; Zarco, et al., 2020)

  • IUCN Red List [Link]
    Not Evaluated


Alexandra Wettengel (author), Colorado State University, Audrey Bowman (editor), Colorado State University, Sydney Collins (editor), Colorado State University.



living in the southern part of the New World. In other words, Central and South America.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


the nearshore aquatic habitats near a coast, or shoreline.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body


union of egg and spermatozoan


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


mainly lives in water that is not salty.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.


An animal that eats mainly insects or spiders.


marshes are wetland areas often dominated by grasses and reeds.


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.


having the capacity to move from one place to another.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


an animal that mainly eats plankton


specialized for leaping or bounding locomotion; jumps or hops.

seasonal breeding

breeding is confined to a particular season


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.


a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.


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AmphibiaWeb, 2022. "Alsodidae" (On-line). Information on amphibian biology and conservation.. Accessed February 03, 2022 at

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