Frogs are amphibians that navigate both aquatic and terrestrial environments. Their ability to spend extended periods underwater often sparks curiosity. Unlike humans who simply hold their breath, frogs employ physiological processes to absorb oxygen from both water and air, enabling prolonged underwater stays.
The Astonishing Durations
The duration a frog can remain submerged varies considerably, influenced by several factors. Most frog species can stay underwater for approximately 4 to 7 hours before needing to surface. This impressive capacity is a physiological adaptation that allows them to absorb oxygen while submerged. During periods of inactivity or hibernation, some frogs can remain at the bottom of a pond for months, especially in cold temperatures. For instance, the African clawed frog can stay submerged for up to 210 minutes, while northern leopard frogs typically resurface after 15 to 25 minutes.
The Science of Frog Respiration
Frogs utilize diverse respiratory methods to obtain oxygen, particularly when submerged. Their primary method underwater is cutaneous respiration, commonly known as skin breathing. The frog’s skin is thin, permeable, and richly supplied with a network of blood vessels, facilitating the diffusion of respiratory gases between the blood and the surrounding water. Up to 40% of a frog’s oxygen intake can occur through its skin when submerged.
On land or near the surface, frogs also engage in pulmonary respiration, using their lungs, and buccal pumping. Pulmonary respiration involves taking air in through the nostrils and into the lungs. Frogs lack a diaphragm and ribs like humans. Instead, they use buccal pumping, lowering the floor of their mouth to draw air in, then closing their nostrils and raising the mouth floor to force air into their lungs. This rhythmic movement is a primary way amphibians inflate their lungs. The lining of their mouth also serves as a respiratory surface, enabling gas exchange.
Factors Affecting Submergence Time
Several environmental and physiological factors influence how long a frog can remain submerged. Water temperature is a significant determinant; colder water typically allows for longer submergence times. This is because lower temperatures reduce a frog’s metabolic rate, decreasing its oxygen demand. For example, leopard frogs can stay underwater for around 300 minutes at near-freezing temperatures but only about 25 minutes at 20°C. Warmer water holds less dissolved oxygen, making it more challenging for frogs to breathe.
Species-specific adaptations also play a substantial role in underwater endurance. Some frogs are more aquatic by nature, possessing adaptations like thinner skin with an extensive blood supply, which enhances cutaneous gas exchange. Oxygen levels in the water are another critical factor; frogs require sufficient dissolved oxygen to breathe through their skin. If oxygen levels are too low or the water is stagnant, their ability to remain submerged is limited.
A frog’s activity level directly impacts its oxygen consumption and submergence time. An inactive frog uses less oxygen and can remain underwater longer than one that is actively swimming or escaping a predator. For instance, northern leopard frogs can hold their breath for 170 minutes when inactive, but only 85 minutes when moderately active. Frog size also has an effect, with larger frogs potentially showing a greater decline in heart rate during submergence, influencing their underwater duration.