A Frog in the Hand
Many people can say they remember catching frogs and toads in their backyards as children - they are widely found throughout the United States, and many of us listen to their cacophonous chorus as the sun slips over the horizon.
Frogs and toads are amphibians. This class also includes newts and salamanders. What they have in common is a metamorphosis that occurs in most amphibs after hatching; the eggs are laid in water, and the babies often are born as larvae with external gills. They then transition into the adult form, with lungs as opposed to gills.
Another trait they have in common is porous skin. Amphibians do not have scales like reptiles do; instead, they have a thin, mucous-coated skin that they can breathe through. The mucus serves to keep the skin moist; without it, the animal can suffocate. Some amphibs can excrete a toxic mucus as a defense mechanism. Other species don’t develop gills or lungs, but rather breathe exclusively through their skin. This is called cutaneous respiration. They can absorb oxygen into the bloodstream straight from the air or water. And in terms of skin texture, the wrinklier the better! More surface area means more opportunity for oxygen absorption.
Why can amphibians breathe through their skin?
Cutaneous respiration is more efficient for amphibians than using their lungs (also called Buccal Pumping). Amphibian lungs are rather primitive in nature, and are slower to diffuse oxygen through the bloodstream. Therefore, many amphibs use a combination of lung and cutaneous respiration, depending on if they’re on land or in the water. Being able to breathe cutaneously is also helpful when the animal needs to escape into the water to get away from a predator. Many can remain underwater for long lengths of time.
Immune responses start only skin deep.
Amphibians rely heavily on their skin as a defense against environmental pathogens. Varga et al expound on this topic in their 2019 article, Frog Skin Innate Immune Defences: Sensing and Surviving Pathogens:
Amphibian skin is a mucosal surface in direct and continuous contact with a microbially diverse and laden aquatic and/or terrestrial environment. As such, frog skin is an important innate immune organ and first line of defense against pathogens in the environment. Critical to the innate immune functions of frog skin are the maintenance of physical, chemical, cellular, and microbiological barriers and the complex network of interactions that occur across all the barriers.
Frog Skin Innate Immune Defences: Sensing and Surviving Pathogens
By J. F. A. Varga, M. P. Bui-Marinos and B. A. Katzenback
When we touch amphibians, we transfer anything on our hands into the amphibian’s body.
Given that they rely heavily on their skin to maintain their health, we need to be as mindful as possible when handling them. Here are some tips for handling amphibians respectfully, to keep you and the animal safe during your interaction.
Don’t wash your hands with soap just before handling. A simple rinse with clean, fresh water should do the trick.
Don’t use hand sanitizer just before handling.
Many people use gloves when handling amphibians. While this is a more sterile option to the simple rinse-and-go method, keep in mind that there is evidence that it can be more harmful than helpful. More research is needed before we disregard using gloves entirely for amphibians, but we are always looking for ways to improve our care and protect the animals as much as possible.
If you do use gloves, rinse them with water from their environment or from your water bottle. Amphibians need their skin to stay moist!
Rinse your hands thoroughly between handling amphibians to reduce the risk of spreading disease between populations.
