Mimic Poison Frog

Ranitomeya imitator is a small frog, with adults ranging from 17 to 22 mm (Symula et al. 2001). Dorsal skin is granular. The first toe is clearly differentiated. 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. 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 . 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. 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).This species is unusual in its mimicry of other species. It mimics not one but three other species of highly toxic poison frogs (Ranitomeya fantastica, Ranitomeya variabilis, and Ranitomeya ventrimaculata). This represents the only known example of mimetic radiation in amphibians, where different populations within a single species mimic several other species in appearance. In each case, a population of R. imitator is sympatric with a population of one of the other dendrobatid species, and looks virtually identical. Despite the similar appearances, in each case the two sympatric species can be distinguished by male calls and by egg coloration. Ranitomeya imitator populations have been confirmed by molecular phylogenetic analysis to be closely related members of a single species (Symula et al. 2001). 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). This species was featured as News of the Week on 18 April 2016:Signaling between parents and offspring is a topic of interest in animal behavior and evolution, mostly in birds and mammals. A common question is whether offspring begging directed at parents represents an “honest signal” of need (hunger), or a signal of quality (with larger, higher quality offspring able to signal more strongly). Yoshioka, Meeks and Summers (2016) tested this question in Ranitomeya imitator, the Mimic Poison Frog, which shows pair-bonding and biparental care. The male and female cooperate to place tadpoles in tiny pools of water (phytotelmata), and then return to feed the tadpoles infertile eggs as it develops. They showed regulating food levels across development, tadpoles receiving less food increased begging levels significantly over the course of development, relative to tadpoles given more food. An experiment manipulating the amount of begging that tadpoles perform (under identical feeding regimes) revealed costs of begging in terms of developmental rate and growth. An experiment on parental feeding revealed that parents preferentially fed tadpoles not receiving supplemental food, relative to siblings whose diet was supplemented with extra food. They conclude that tadpole begging in this species serves as an honest signal of need (Written by Kyle Summers).
This species was featured as News of the Week on 18 March 2019:Monogamy in vertebrate evolution appears multiple times in separate lineages but their underlying genetic underpinnings are only recently explored. Young et al. (2019) compared differential gene expression between the transcriptomes of monogamous and polygamous species in five sets of species pairs across vertebrates (mice, voles, birds, frogs and fish). The frog pair were poison frogs Ranitomeya imitator (monogamous) and Oophaga pumilio (polygamous). Tests for differential gene expression between each pair revealed that congruent sets of genes (orthologous or genes of the same evolutionary genealogy) showed concordant changes in expression between the monogamous and the polygamous lineages. The directions of changes in expression in these gene sets were also concordant, such that genes which decreased in expression in the monogamous lineage of one taxonomic pair were likely to decrease in expression in the other monogamous lineages as well (for all pairwise comparisons). However, the frog species were unique in that some genes displayed the opposite direction of change in expression relative to other monogamous lineages. The poison frogs are the only lineage here in which male parental care is ancestral so monogamy with biparental care in this lineage evolved from male care (rather than female care, as in the other taxa). Overall, their research yielded a novel set of 24 candidate genes likely to be involved in the evolution of monogamy, many of which are involved in neural development, synaptic activity and cognitive function. The study provides evidence for widely conserved sets of shared genes and molecular genetic pathways contributing to the evolution of monogamous mating systems across vast gulfs of evolutionary time and change in the vertebrate lineage (Written by Kyle Summers). This species was featured as News of the Week on 4 May 2020: Neotropical poison frogs provide iconic examples of conspicuous warning coloration, yet we know very little about the biochemical mechanisms that underlie the production of these astonishing colors. Twomey et al. (2020) use a combination of spectral reflectance, chromatography, electron microscopy measurements, and simulations of coloration to identify key components of color variation in a mimetic radiation of the Peruvian mimic poison frog (Ranitomeya imitator) and related model species. They revealed that the mimic frog has a broader "palette" of colors than the models, which accords with their history of evolving to match the color patterns of other species. Surprisingly, however, the major proportion of variation did not appear to be in pigment types. Instead, the key variation occurred in the thickness of guanine platelets in a type of organelle called iridophores. The variation in platelet thickness appears to influence yellows and oranges, contradicting the traditional view that it should affect structural colors like blues and greens and hue (overall spectral reflectance). Their study provides insight into the underlying mechanisms enabling the evolution of both divergence and convergence in aposematic coloration in the Neotropical poison frogs, revealing novel mechanisms that may apply to other taxa as well (Written by Kyle Summers).

These frogs can be found on the eastern foothills of the Andes, from 250 to 1000 m in elevation, in Departamentos San Martin and Huánuco, Peru (Schulte 1986; Caldwell and Summers 2003). They inhabit montane wet forest (Caldwell and Summers 2003; Schulte 1986), and primary lowland tropical moist forest (Icochea et al. 2004) and are usually closely associated with certain secondary forest plant species (Schulte 1986).

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.

Ranitomeya imitator is protected under Appendix II of CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora). Appendix II covers species which are not necessarily threatened with extinction but where controlling trade (import/export) helps avoid overcollecting and thus aids the species' survival. This species has been listed under CITES since 1987. As of 2007, a maximum of 500 "ranched" frogs (where eggs or tadpoles are taken from the wild and reared in captivity) per year may be exported from Peru.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).

Found in the pet trade due to its vivid coloration. The trade in this species is restricted (see Trends and Threats section), and illegal collection has been reported to occur by IUCN.

Ranitomeya imitator (formerly Dendrobates imitator), is a species of poison dart frog found in the north-central region of eastern Peru. Its common names include mimic poison frog and poison arrow frog, and it is one of the best known dart frogs. It was discovered in the late 1980s by Rainer Schulte who later split it up into more subspecies; describing each as a specific color morph, and sometimes having a separate behavioral pattern. The acoustics, morphs, and behavior of the species have been extensively researched.