Imitating Poison Frog, Mimic Poison Frog, Rana Venenosa
© 2007 Mark Aartse-Tuyn (1 of 30)
Ranitomeya imitator is a small frog, with adults ranging from 17 to 22 mm (Symula et al. 2001). Dorsal skin is granular (Schulte 1986). The first toe is clearly differentiated (Schulte 1986). Digital discs are expanded as with other dendrobatids, with finger discs being at least twice the width of the finger base (Schulte 1986). Coloration is quite variable depending on the population, as this species mimics both color and pattern of several other sympatric (co-occurring) species of poison frogs (Symula et al. 2001).
Ranitomeya imitator near Tarapoto, Peru, closely resembles the sympatric species Ranitomeya variabilis (Schulte 1986; Symula et al. 2001). Both species have yellow reticulation over a black background on the head, dorsum, flanks, and forearms, resulting in the appearance of large black patches surrounded by yellow (Schulte 1986; Symula et al. 2001). On the venter and legs, both species have blue-green reticulation over a black background, resulting in the appearance of small black patches surrounded by blue-green (Schulte 1986; Symula et al. 2001). They can be distinguished by the patterning of the black spot on the nose; in R. imitator this spot is split in half by gold reticulation, whereas it is solid in R. variabilis (Schulte 1986; Symula et al. 2001). In addition, differences in calls and in egg coloration distinguish the two species (Symula et al. 2001).
In Huallaga Canyon, Peru, Ranitomeya imitator resembles a sympatric population of Ranitomeya fantastica (Symula et al. 2001). Both species in this area have a black ground coloration with yellow stripes, several of which are transverse, running across the body from side to side and extending down the arms and legs and across the midsection (as seen in the photos in Symula et al. 2001). However, R. imitator is smaller and has different ventral coloration and pattern, as well as a different call (Schulte 1986).
Near Yurimaguas, Ranitomeya imitator mimics Ranitomeya ventrimaculata (Symula et al. 2001). These frogs share the coloration pattern of thin longitudinal yellow stripes on a black background, over the head, dorsum, and flanks, while the legs have blue-green reticulation over a black background, resulting in the appearance of small black patches surrounded by blue-green color (as seen in the photos in Symula et al. 2001). Here again Ranitomeya imitator appears to be distinguishable by having a black spot on the tip of the snout bisected by a gold stripe. Male calls also differ between the two species (Symula et al. 2001).
Distribution and Habitat
Life History, Abundance, Activity, and Special Behaviors
Despite the close resemblance of R. imitator to other sympatrically occurring frog species, the call is quite different, and this facilitated the recognition that this frog represented a new species (Schulte 1986). The call of R. imitator has been described as piercing, and can be heard at some distance (Schulte 1986).
Like other dendrobatids, R. imitator is diurnal. It is also arboreal and can be found in vegetation between 0.3 and 6 m above the ground, though it is mainly active between 0.5 and 1.5 m (Schulte 1986). The frog's activity period is bimodal, with a peak early in the morning and again in the afternoon, retreating to the shelter of a plant in between (Schulte 1986). Usually only a single frog occupies a "retreat" plant, and this territory will be actively and vocally defended if another male trespasses (Schulte 1986). In addition to calling, the male will position himself such that his head can be seen from below, over the edge of the leaf, with his pulsing black-flecked yellow throat pouch clearly visible against the green background (Schulte 1986).
Ranitomeya imitator is the only known monogamous amphibian, with monogamy in the wild confirmed by paternity analysis in studies (Brown et al. 2010). Of twelve pairs assessed, all twelve were socially monogamous (interacted only with each other). However, one pair of the twelve showed social monogamy but not genetic monogamy, as the male was found to have sired tadpoles with another female. Mate guarding (of males by females) has been observed for this species in captivity, according to Brown et al. (2010). Both the male and female care for offspring in R. imitator; biparental care in nutrient-poor nurseries appears to have driven the evolution of monogamy, as two other dendrobatid species (Dendrobates auratus and Dendrobates leucomelas) that also show mate guarding by females but have uniparental (male) tending of offspring are not genetically monogamous (Brown et al. 2010; see references therein for D. auratus and D. leucomelas).
Reproduction occurs year-round, with a peak during the rainy season (Schulte 1986). Males call to lure females to a breeding site, running ahead of the female with the female following 1-5 cm behind (Schulte 1986). Eggs are white with clear jelly and laid in dark hiding places in phytotelmata (small water pools within plants; Schulte 1986). Biparental care occurs in this species (Brown et al. 2008a; Brown et al. 2008b; Brown et al. 2010). About 12-14 days post-hatching, tadpoles will be carried singly (or very rarely, in pairs) by the male to a separate brooding site in a different plant (Schulte 1986). The water bodies in which the tadpoles are deposited are very small, just 24 ml in volume, and are nutrient-poor, such that tadpoles cannot survive without being provisioned by the female parent (Brown et al. 2008a, Brown et al. 2008b; Brown et al. 2010). The selection of smaller, nutrient-poor water bodies as nurseries has likely driven the need for biparental care and the evolution of monogamy in this species (Brown et al. 2010). Parental care is given for an extended time, in this case months, as females must provision the tadpoles with trophic (unfertilized) eggs (Brown et al. 2010).
Froglets reach adult size after about six months (Schulte 1986). It is estimated that each pair of adult frogs produces at most two to four offspring a year which reach maturity (Schulte 1986).
This species primarily consumes tiny ants and mites (Schulte 1986; Caldwell and Summers 2003). It is also reported to prey on drosophilid flies, beetle, and springtails (Schulte 1986; Caldwell and Summers 2003).
Like other dendrobatids, R. imitator secretes alkaloids (including a number from the decahydroquinoline class, and possibly from other classes) from cutaneous granular glands in its skin (Spande et al. 1999). Schulte (1986) reports that a strong characteristic smell is emitted from this frog when it is stressed or killed, which he attributes to the skin toxins.
Trends and Threats
Its range overlaps with one protected area, the Parque Nacional Cordillera Azul in Peru. As of 2004, it was deemed stable in population. It is not thought to tolerate habitat modification, and there has been localized habitat loss. It does have a wide range and when it was last assessed by the IUCN/Global Amphibian Assessment in 2004, there appeared to be large areas of suitable habitat remaining. Illegal trade in this species has been noted by IUCN (Icochea et al. 2004).
Relation to Humans
Because both species are toxic in each case, and both benefit from the resemblance, this is an example of Müllerian mimicry.In 2011, the genus Dendrobates was subdivided into seven genera, including the new genus Ranitomeya by Brown et al (2011).
Brown J.L., Twomey E., Amézquita A., De Souza M.B., Caldwell J.P., Lötters S., Von May R., Melo-Sampaio P.R., Mejía-Vargas D., Perez-Peña P., Pepper M., Poelman E.H., Sanchez-Rodriguez M., and Summers K. (2011). ''A taxonomic revision of the Neotropical poison frog genus Ranitomeya (Amphibia: Dendrobatidae).'' Zootaxa, 3083, 1-120.
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., Morales, V., and Summers, K. (2010). ''A key ecological trait drove the evolution of biparental care and monogamy in an amphibian.'' American Naturalist, 175(4), 436-446.
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.
Caldwell, J. P., and Summers, K. D. (2003). ''Imitating poison frog, Dendrobates imitator.'' Grzimek's Animal Life Encyclopedia, Volume 6, Amphibians. 2nd edition. M. Hutchins, W. E. Duellman, and N. Schlager, eds., Gale Group, Farmington Hills, Michigan.
Icochea, J., Angulo, A., and Jungfer, K.-H. 2004. Ranitomeya imitator. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.3. www.iucnredlist.org. Downloaded on 13 September 2010.
Schulte, R. (1986). ''Eine neue Dendrobates-art aus ostperu (Amphibia: Salienta: Dendrobatidae).'' Sauria, 8, 11-20.
Spande, T. F., Jain, P., Garraffo, H. M., Pannell, L. K., Yeh, H. J. C., Daly, J. W., Fukumoto, S., Imamura, K., Tokuyama, T., Torres, J. A., Snelling, R. R., and Jones, T. H. (1999). ''Occurrence and significance of decahydroquinolines from dendrobatid poison frogs and a myrmicine ant: Use of 1H and 13C NMR in their conformational analysis.'' Journal of Natural Products, 62, 5-21.
Symula, R., Schulte, R., and Summers, K. (2001). ''Molecular phylogenetic evidence for a mimetic radiation in Peruvian poison frogs supports a Müllerian mimicry hypothesis.'' Proceedings of the Royal Society of London B, 268, 2405-2421.
Written by Kellie Whittaker and Peera Chantasirivisal (kwhittaker AT berkeley.edu), UC Berkeley
First submitted 2005-11-14
Edited by Kellie Whittaker, Brent Nguyen (2011-11-07)
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