Description
Ranitomeya variabilis is a small frog; it has a mean snout-vent length of 17.4 mm in adult males and 18.0 mm in females (Brown et al. 2008).

Diagnosis: R. imitator is a Müllerian mimic of R. variabilis. R. variabilis can be differentiated from R. imitator by egg coloration, vocalization, and subtle coloration differences (Schulte et al. 2001; Schulte et al. 2003). Additionally, R. variabilis is a color and pattern variant of R. ventrimaculata (Schulte et al. 2002).

Coloration: Coloration changes on a gradient from the anterior to posterior, going from a yellow-green to a blue-green. This species has a single nose spot with large, ovid dorsal spotting. Limbs are less than half black with small, even spots (Brown et al. 2008).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Colombia, Ecuador, Peru

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (1 records).

This species is known only from one habitat in central Peru, along the eastern slope of the Andes in the upper Rio Huallaga drainage, in San Martin Province (Masche et al. 2010).

R. variabilis is semi-arboreal and lives in secondary to old growth forests and is restricted to the summits of mid-level mountains roughly 900-1200 m above sea level (Brown et al. 2008; Schulte et al. 2002; Icochea 2004). Frogs are found in the understory, canopy, usually above ground on vertical objects, and sometimes in leaf litter (Brown et al. 2008) Despite the frogs’ utilization of pools, R. variabilis is not restricted to areas with certain vegetation or the presence of phytotelmata. (Brown et al. 2009a).

Life History, Abundance, Activity, and Special Behaviors
R. variabilis is a diurnal species. It has potent alkaloid toxins, as indicated by its aposematic coloration (Brown et al. 2008b; Schulte et al. 2002).

Males have short buzz-like calls that are relatively low. When a female is present, a male will call from an elevated perch and increase his call rate as she approaches; he then leads her to the breeding site. The call is repeated when a suitable breeding site is reached. Males only called during courtship. (Brown et al. 2008).

The female lays 2-6 eggs under the surface of the water, in pools that collect in the axils of plants. The male fertilizes them by placing his vent against that of the female (facing opposite directions) while she is laying the eggs, or simply by walking over the already laid eggs. This ritual is performed in pairs or sometimes groups where aggressive male competition has been observed (Brown et al. 2008).

Reproduction occurs during the day and has been seen to peak after rain (Brown et al. 2008). The pools chosen for oviposition, are small to medium sized compared to medium sized pools chosen for tadpole deposition (Brown et al. 2009a).

Average clutch size is 4 to 5 eggs, which hatch into free-living, lentic larvae; the development period lasts 12 to 14 days depending on the temperature (Masche et al. 2010).

Parental care in R. variabilis is restricted to males only and since males cannot provide the tadpoles with trophic eggs, one of the biggest constraints on the tadpoles is food availability. Males return to the pool to transport tadpoles to reduce predation, and competition. The male tears open the embryo sac, using his rear legs. The tadpoles then either wriggle onto his back or are pushed on by the male’s rear legs. Males will carry 1 to 6 tadpoles at a time and place them either in their own individual pool or communally in one pool. However, not all males provide parental care (Brown et al. 2009b).

There are costs associated with tadpole distribution. Small pool size may cause an increase in intraspecific and interspecific competition for food. This poses a tradeoff between safety from predators and nutrient availability, as tadpoles in small pools are more susceptible to starvation (Brown et al. 2009a).

Males may selectively deposit their tadpoles into pools already occupied by unrelated individuals, exhibiting tactical reproductive parasitism (Brown et al. 2009b). Multiple depositions into the same pool will select for tadpoles that compete vigorously and resist cannibalism from conspecifics (Brown et al. 2009a).

Larva
Tadpole/Larval Morphology: The body is depressed. There is a sinistral spiracle on the lower left side of the body and a short medial vent tube on the ventral fin (Masche et al. 2010). It has dorsal, circular nostrils; dorsal eyes that are directed dorsolaterally (Masche et al. 2010). The number of marginal papillae, the presence of jaw sheath serrations, jaw sheath keratinization, and tail color change over the developmental stages (Schulte et al. 2003).

The caudal musculature of the tadpoles is narrow near the posterior tail tip and becomes moderately robust near the anterior. Fins do not extend onto the body of the tadpole and are subequal in height. The caudal fin tip is rounded and there is an anteroventrally directed mouth with an emarginated oral disc. There is a single row of 32 marginal papillae surrounding the oral disk and there are no submarginal papillae. On the marginal papillae of the lips there are two gaps: a small medial gap on the posterior lip and a large medial gap on the anterior lip. Two anterior rows of teeth are not completely keratinized and are equal in length. The upper jaw sheath has slender lateral processes but, like the V-shaped lower jaw sheath, it is moderately robust with serrated edges over its entire length (Masche et al. 2010).

Tadpole Coloration: The tadpoles have grey to dark black-brownish pigmentation (Brown et al. 2008b ; Masche et al. 2010). A single nose spot is present, differentiating the species from R. imitator which has a paired nose spot. In both dorsal and lateral profiles, the snout is rounded (Brown et al. 2008).

Trends and Threats

R. variabilis is threatened by agricultural development, the pet trade to some degree, and habitat fragmenation from the harvesting of wood. The species has not been found in or moved into any protected areas (Icochea 2004).

Possible reasons for amphibian decline

Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Intentional mortality (over-harvesting, pet trade or collecting)

Comments

This species was featured as News of the Week on 13 February 2023:

Poison frogs, with bright colors and potent skin toxins, represent iconic examples of aposematism in rainforests throughout South and Central America. These frogs are also known for intensive parental care– parents carry tadpoles to small pools (phytotelmata) and some species provide trophic eggs as food for their offsprings. Much interest has focused on the question of whether poison frog tadpoles can acquire toxins for protection from predators by consuming eggs from their mothers. Studies have shown two species of Oophaga provide toxins to their tadpoles via obligate trophic egg feeding. In contrast, in Ranitomeya variabilis (and related R. fantastica, R. summersi) do not provide unfertilized eggs to their tadpoles (instead, they subsist on detritus, algae, and insect larvae), although they will sometimes lay fertilized clutches in or above pools that are later cannibalized by tadpoles. Villanueva et al. (2022) investigate this issue in a third species of Oophaga (O. granulifera) and in Ranitomeya imitator and R. variabilis. They found that while O. granulifera receives toxins in its eggs (like other members of this genus), that was not true for either species of Ranitomeya. They infer the degree to which egg feeding is facultative (high in R. variabilis, low in R. imitator, not facultative in Oophaga) is related to the evolution of toxin transfer via egg feeding. This is only a single comparison between the Oophaga and Ranitomeya lineages, so further studies will be necessary for definitive conclusions, but their study provides a fascinating and promising first pass at this question. (Written by Kyle Summers).

This species was featured as News of the Week on 30 September 2024:

Mimetic poison frogs present an evolutionary enigma, where the forces of reproductive isolation and predator selection drive both diversification and speciation. Lorioux-Chevalier et al (2024) focuses on three key species from the Peruvian Amazon: Ranitomeya variabilis, Ranitomeya imitator, and Ranitomeya fantastica. These frogs exhibit strikingly different aposematic signals, but what maintains these differences despite living in close proximity? The authors investigated the prezygotic and postzygotic barriers that prevent interbreeding between distinct ecotypes. Prezygotic mating preferences were generally weak, except in one ecotype of R. imitator, but the real surprise came from R. fantastica, where hybrid males displayed complete sterility, a clear postzygotic barrier. Their study unveils how hidden genetic incompatibilities ignite the astounding diversity of warning signals in these frogs, challenging the conventional wisdom about reproductive isolation. In particular, the sterility of R. fantastica hybrids, align with Haldane’s rule of speciation and emphasize the pivotal role of postzygotic barriers in maintaining species boundaries and driving divergence. By revealing underlying genetic mechanisms, this research sheds new light on how evolution can foster such remarkable phenotypic diversity.(Written by Ugo Lorioux-Chevalier )

References

Brown, J. L., Morales, V., and Summers, K. (2009). ''Home range size and location in relation to reproductive resources in poison (Dendrobatidae): a Monte Carlo approach using GIS data.'' Animal Behaviour, 77, 547-554.

Brown, J. L., Morales, V., and Summers, K. (2009). ''Tactical reproductive parasitism via larval cannibalism in Peruvian poison frogs.'' Biology Letters, 5(2), 148-151.

Brown, J. L., Morales, V., and Summers, K. (2008). ''Divergence in parental care, habitat selection and larval life history between two species of Peruvian poison frogs: an experimental analysis.'' Journal of Evolutionary Biology, 21, 1534-1543.

Brown, J. L., Twomey, E., Morales, V., and Summers, K. (2008). ''Phytotelm size in relation to parental care and mating strategies in two species of Peruvian poison frogs.'' Behaviour, 145, 1139-1165.

Frost, D. (2011). Amphibian Species of the World: an Online Reference. Version 5.5.

Icochea, J., and Jungfer, K.-H. (2004). Ranitomeya variabilis. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. www.iucnredlist.org. Downloaded April 2011.

Masche, S., Zimmermann, H., and Pröhl, H. (2010). ''Description and ecological observations of the tadpole of Ranitomeya variabilis (Anura: Dendrobatidae).'' South American Journal of Herpetology, 5(3), 207-211.

Schulte, R., Summers, K. and Symula, R (2001). ''Molecular phylogenetic evidence for a mimetic radiation in Peruvian poison frogs supports a Müllerian mimicry hypothesis.'' Biological Sciences, 268, 2415-2421.

Schulte, R., Summers, K., and Symula, R. (2003). ''Molecular systematics and phylogeography of Amazonian poison frogs of the genus Dendrobates.'' Molecular Phylogenectics and Evolution, 26, 452-475.

Species Account Citation: AmphibiaWeb 2024 Ranitomeya variabilis: Variable Poison Frog <https://amphibiaweb.org/species/6117> University of California, Berkeley, CA, USA. Accessed Nov 21, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Nov 2024.

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