All organisms develop strategies to survive, reproduce, and adapt to their environment, maintaining their species and influencing ecological balance. However, some organisms adopt more unique adaptations. Today, we’ll talk about one of these strategies, recently discovered in Eiffinger's tree frog (Kurixalus eiffingeri), which inhabits the islands of Ishigaki and Iriomote in Japan.
These animals lay their eggs in small water pools on plants, like tree hollows or bamboo stumps, creating a microecosystem called phytotelma. The larvae, once hatched, feed on trophic eggs—eggs laid specifically as food—and spend their entire larval period in tiny phytotelmata of less than 50 cm² and just 2.5 cm of water depth. So far, nothing unusual. But living in such small spaces presents a big problem for these larvae: waste management.
When animals metabolize proteins, they excrete nitrogen compounds, and there is a close relationship between habitat and nitrogen excretion. Generally, fish and amphibian larvae produce ammonia because they live in water-rich environments, which quickly dilutes the substance, preventing poisoning. Terrestrial amphibians and mammals produce urea (as in our urine) because water is scarce on land for diluting ammonia. Finally, reptiles and birds excrete nitrogen as uric acid, which is insoluble in water and less toxic.
According to this, the larvae should eliminate ammonia. However, living in tiny water pools, if all the tree frog larvae produced ammonia, toxic levels would be reached, causing their death. So they adopt an innovative strategy: not peeing! Or more precisely, holding in the ammonia.
A group of Japanese researchers discovered this extraordinary adaptation by raising adult and larval tree frogs in terrariums with plastic cups that mimicked small water pools. They also raised other frog species for comparison. Every three days, they measured the ammonia levels in the cups and noticed that where there were tree frog larvae, the water remained clean, and the larvae thrived. On the contrary, in systems with larvae of other species, the ammonia accumulation caused the larvae’s death after a week.
In a second experiment, they measured the amount of ammonia in the larvae's intestines. The results showed that the intestines of the tree frog larvae were full of ammonia, while the other species were not. This confirmed that Kurixalus eiffingeri larvae retain ammonia in their bodies during development, keeping their phytotelmata clean.
For these tiny frog larvae, the secret to living in a puddle is not peeing until metamorphosis!
