Mimicry was divided into the subcategories camouflage, homotypy, and nondeceitful homotypy, and these groups were also subcategorized. Dissuasive coloration was divided into behavioral display of colors, polymorphism, and polyphenism. Aposematism was treated apart, but aposematic colorations may be present in other defensive strategies. Finally, we propose functions and forms of evolution for some color systems in post-metamorphic anurans and hope that this review can be the basis for future research, even on other animal groups.
Anuran coloration results from natural selection acting simultaneously on different aspects of natural history, such as protection against solar radiation, thermoregulation, osmoregulation, nitrogen metabolism e. Anurans are remarkable for their color patterns, which may range from a uniform black dorsum, as in Cycloramphus boraceiensis Cycloramphidae , to bright blue, orange, red, yellow, and green in the same individual, as in Agalychnis callidryas Hylidae.
In the context of defensive strategies, these two distinct situations may be related to two different types of primary defenses, which operate regardless of whether or not a predator is in the vicinity [ 7 ].
Both situations: crypsis and aposematism, as generally understood, help anurans to survive in nature. The former may improve chances of avoiding detection, and the latter may signalize that the individual is dangerous in one or several ways, where being toxic is the most common [ 7 ]. Besides these, there are several other defensive strategies involving coloration, such as body rising, mimicry, or flash color e.
The presence of these and other defensive colorations in anurans has been published for several species in a fragmented way, and has never been reviewed. Herein, in order to organize current knowledge and ground future research, we reviewed this subject, added new data, and provided information about the evolution of color usage in anurans, with special reference to Neotropical species.
We reviewed the literature by searching for coloration-related defensive strategies in anurans. Both natural and experimental observations were considered. Additional data were obtained during several field expeditions in Brazil from to , mainly in the Cerrado and Atlantic Forest domains in the southeast.
All amphibian scientific names follow Frost [ 10 ], and the specific nomenclature for coloration categories was adapted from Pasteur [ 11 ]. For the same reason, we will not cover aggressive and reproductive mimicry in this paper.
The use of colors can be divided into three major categories: mimicry, deceptive coloration, and aposematism Table 1. Mimicry is generally considered as per the Batesian mimicry concept, in which a nontoxic or, otherwise, dangerous, e.
However, Batesian mimicry is one of several types of mimicry into which anurans may be included see Table 1. Mimicry as presently defined occurs when a group of organisms, the mimics, has evolved to share common perceived characteristics with another group of organisms, the models, through the selective action of a predator. Collectively, they are known as a mimicry complex. Mimicry was herein divided into three major groups: camouflage, homotypy, and nondeceitful homotypy see what follows.
Camouflage may be defined as the resemblance of an animal with a part of the environment [ 7 ], especially as viewed by the predator at the time and place in which the prey is most vulnerable to predation Endler [ 19 ]. In post-metamorphic anurans, camouflage may be optical, chemical e. In what follows, we will give special reference to optical camouflage, which implies avoidance of detection by possible predators.
The model is undefined, that is, it is the background. As substrates, anurans may use rocks with lichens, tree trunks, leaves, forest litter, as well as mossy and rocky fields, for example. For any such substrates, there are mimic frogs that live there Figure 1. Eucrypsis may be strengthened or weakened by a predator's angle of vision; that is, the anuran may be more cryptic from a lateral view than from a dorsal view Figures 1 f and 1 e , resp.
The more distant predator is from the site occupied by an anuran, the higher may be the crypsis benefits. For instance, it is easy to find a Dendropsophus nanus in its reproductive site when we are close to it. However, from a certain distance, the colors and shape of this hylid get mixed with the general view of the area. The size and colors of D. Furthermore, some predators of anurans, such as pit vipers, may be able to perceive infrared wavebands [ 24 ].
Others, such as rodents, other amphibians, lizards, and mainly birds, have tetrachromatic color vision including ultraviolet cones , and may, therefore, perceive ultraviolet wavelengths e. Therefore, it is possible that infrared reflectance may have evolved for anurans to remain cryptic in the foliage which also has the same infrared reflectance property , even against those predators who are able to detect infrared or ultraviolet spectra e. The model is defined, that is, it is an object.
Many examples may be cited, but to mention some, we may refer to species of genera Proceratophrys and Scythrophrys which resemble fallen leaves Figures 1 i , 1 j , resp. Indeed, their genus name Phasmahyla was coined in allusion to the similarity of their moving style with the walking-sticks of order Phasmatodea [ 27 ]. The illusion created by this behavior is increased with the leaf-like color pattern of this species. As examples, we may cite some Theloderma spp.
This transition may be gradual or abrupt, which could involve different camouflage strategies see [ 28 , 29 ]. Two main functions have been attributed to countershading. In essence, the distribution of light on objects lit from above will cause unequal reflection of light by a solid body of uniform color.
Such shadows could provide predators with visual cues to a prey's shape and projection. Countershading, therefore, reduces the ease with which prey is detected by potential predators by counterbalancing the effects of shadowing. When seen from below, the lighter ventral area blends into the sun or moonlight see [ 29 ]. This second explanation generally occurs with an abrupt transition of colors and seems to be the more adequate for anurans.
Countershading could result from selective pressures other than predation avoidance. Therefore, the occurrence of countershading may result from multiple factors. This system is so widespread among aquatic and terrestrial fauna that several authors have stated that it is perhaps the most universal feature of animal coloration see [ 29 ] and references therein.
Likewise, it is present in several anuran species and might work against terrestrial predators, for example, which may be on the ground when the anuran is perched on a tree branch. In aquatic species, such as the pipids e. Some species may enhance their camouflage by having high-contrast lines on the edges of colored patterns see [ 32 ].
In addition to this, several species present lateral lines that cross the eyes, breaking their rounded shape Figure 1 j. These are the most common forms of disruptive coloration in anurans. Such structures include small, irregular ridges, supraciliary processes e.
Dorsal glands may also enhance crypsis by promoting resemblance with lichens e. It acts differently from camouflage: in homotypy animals can be perceived by the predator.
Homotypy involves the mimetic imitation of another object which can be the same or another species, an object of the environment, or an undefined model , being, therefore, included as mimicry. Thus, a mimic could obtain protection by resembling the unpalatable or less palatable model. For anurans, there are few cases described wherein some palatable frogs may mimic some poison frogs Table 2. Several predators, such as invertebrates in general, are not as well-endowed in terms of sight and memory as are mammals, and, therefore, may not have been the promoters of selective pressures for the evolution and persistence of Batesian mimicry see also [ 11 ].
A Batesian mimic does not necessarily need to be identical to its model. Sometimes, it may exhibit intermediate resemblances to two or more models. In this manner, the mimic may escape from some predators that avoid one model and from others that avoid the other model. This dual mimicry system has been proposed for coral snake mimics [ 39 ] and may be present in anurans.
An intriguing situation is the Batesian mimicry proposed for the Leptodactylus lineatus and Allobates femoralis complex. Upon handling and fixing individuals of L. Haddad, personal observation. However, some tests performed on A. If both species are discovered to be nontoxic, it would be a case of Arithmetic mimicry where both species are palatable; see further explanations below. Therefore, the relationship of this complex remains unresolved and requires further research.
The models can be of the same or opposite sex to the mimics. Albeit never reported that this type of mimicry may be present in aromobatids, bufonids, dendrobatids, mantellids, and myobatrachids, at least. Individuals of the same noxious species of these families cited above acquire the alkaloids contained in their noxious secretions from dietary arthropods e.
Indeed, there are reports that show spatial geographic and temporal seasonal variation in the alkaloid profiles of poison frogs [ 48 ], which may support the Browerian mimicry theory for anurans. Other examples are frogs that rest on leaves and look like bird droppings e. Besides this, the presence of calcars on many species of rainforest tree frogs, and their absence in other anurans, may suggest that they might serve as points of water runoff, mimicking drip tips of leaves [ 49 , page ].
This seems to be the case for the leg interweaving behavior described elsewhere see [ 50 ]. In both cases, the predator is not deceived, that is, the predator can recognize whether the anuran is palatable or unpalatable. These mimicry complexes are formed by species with similar or even exactly the same color pattern. However, it is sometimes hard to distinguish real nondeceitful homotypy from a possible phylogenetic influence; that is, closely related species, such as two species of Dendrobates , may resemble one another due to a simplesiomorphy sharing of an ancestral character and not because of coloration convergence homoplasy.
Google will help you on that. Help them jump. The purpose of bile in a frog is to help digest, or break down fatty foods. Log in. Study now. See Answer. Best Answer. It helps the frog camouflage! Study guides. Q: How does countershading help a frog? Write your answer Related questions.
What is countershading? What animal have countershading? How do whales adapt? What is shark camouflage called? The rest of the body is darker and, when seen from above, blends with the bottom of the body of water in which it lives. Poison dart frogs are well known for their deadly toxins and bright colours, which have made them a classic example of warning coloration.
The Dyeing Dart Frog, for example, is highly toxic and warns its predators with a bright yellow-and-black pattern. Frogs can change their sex even in pristine, pollution free settings.
Past research suggested that male-to-female sex changes happening in frogs in suburban ponds may be caused by increased levels of estrogen released into the water. As far as they know, frogs can only change sex during their tadpole phase.
Multiply your height times number of body lengths frogs could jump. The teeth are used to hold prey in place until the frog can swallow it. Green Hyla cinerea and grey Hyla chrysoscelis tree frogs of the eastern United States are among the best camouflaged frogs in the world, blending in well with leaves and bark, respectively.
A number of tree frogs are also able to change their color to blend in with their surroundings. Almost all mammals in a freshwater biome will prey on frogs if they can catch them.
This includes raccoons, mink, foxes, otters, opossums and humans. They still breathe air, but they typically hold their breath anywhere between 4 and 7 hours!
The frog though, well, almost all frogs and toads are capable of breathing under water. When looking up for potential prey, the light color blends in with the sunlight that is filtering down through the water, and the frog is not noticed by the predator.
Depending on where the frog lives, counter shaded frogs can have a top color that is bright green, faded brown or gray. Bright green-topped frogs live in areas where there is a lot of foliage, such as a rain forest, where birds and other animals that live in the trees will not see them, because they blend in with their surroundings. Frogs that live in murky waters or around areas covered by dead leaves will have a faded brown or grey top color that allows them to hide on the forest floor.
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