Skin Glands Accumulate Protective Toxins From Prey

yellow, green and brown frog on the ground

Biological Strategy

Oriental robber frog

AskNature Team

Image: Pierre Fidenci / Wikimedia Commons / CC BY SA - Creative Commons Attribution + ShareAlike

Capture, Absorb, or Filter Chemical Entities

Living systems often require chemical elements and chemical compounds, including complex sugars, proteins, and odor-making compounds, to perform critical activities. These compounds exist in various states–solid, liquid, and gas–and are ubiquitous in soil, water, and air. This requires that living systems not only have ways to capture, absorb, or filter them, but also ways to differentiate among them, selecting those that are valuable or harmful. For example, mangrove trees live with their roots in salty water and sediments. Various mangrove species have different strategies for removing salt from the water they take in so that their tissues can use the fresh water.

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Protect From Animals

Animals–organisms that range from microscopic to larger than a bus–embody a wide variety of harms to living systems, including other animals. They threaten through predation, herbivory, defense, and parasitism, and they compete for resources such as water, nutrients, and space. Any given living organism commonly faces threats from a variety of animals, requiring strategies that effectively defend from each. Trout and other bony fish, for example, escape predators by having scales made of very thin, flake-like pieces of bone covered with slippery mucus. They also have behavioral strategies such as camouflage, fast swimming, and twisting and turning to achieve release from a predator’s grip.

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Amphibians

Class Amphibia (“to live a double life”): Frogs, salamanders, toads

Amphibians live a “double life” by being able to survive both on land and in water. Unlike reptiles with dry, scaly skin, amphibians have smooth skin that needs to be kept moist. Many live in the water through development and start life with gills, and then transition to breathing with lungs. They can get even more oxygen through cutaneous respiration, or breathing through their skin. This class represents the first animal group to be able to efficiently walk on land—aided by the well-defined limbs that gave them a “leg up” on their finned competitors.

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The tiny Cuban frog, Eleutherodactylus orientalis, protects itself from predators by consuming toxin-laden oribatid mites and sequestering the toxins in its skin.

Though many frogs accumulate chemicals in their skin for defense against pathogens and predators, the majority of those species synthesize the substances in their own bodies. In contrast, the tiny Cuban frog species Eleutherodactylus orientalis is among the few frogs that consume toxic alkaloid laden foods and sequester the compounds in the skin. Since the compounds are commandeered from prey, they are sometimes referred to as “cleptotoxins”. These fat-soluble substances are very similiar to those secreted by the better- known poison-dart frogs. The frogs maintain immunity to the toxins due to a hypothesized difference in calcium channels in their muscle cells. An interesting aspect of E. orientalis is that it is potentially capable of selectively consuming species of mites that contain toxic alkaloids previously unknown to science. In fact, several prey species of mites that were once thought to not produce alkaloids were found to be consumed by the frogs for their alkaloid content. Whether the frogs actively seek out these alkaloid-bearing species or do so by random chance is still unknown.