Most animals grow larger as they mature, the paradoxical frog of South America, does the opposite. Its tadpole is one of the largest of any frog species, reaching up to 25 centimeters in length. The adult frog that emerges from metamorphosis is approximately 7 centimeters. The animal shrinks by two thirds during development.
This reversal puzzled naturalists for centuries after the species was first described in 1768. The tadpole is so large relative to the adult that early collectors assumed they were looking at two different species. The explanation lies in the extreme demands of metamorphosis. The tadpole accumulates enormous energy reserves during its aquatic larval phase, and those reserves are consumed during the transformation into the adult body plan. The adult frog is essentially built from the resources stored in the giant tadpole, and what remains after the construction is complete is considerably smaller than what went in.
The paradoxical frog lives in the lakes, ponds, and flooded grasslands of the Orinoco and Amazon basins, spending most of its adult life in water despite being a frog. It is an exceptionally strong swimmer, with fully webbed feet and a streamlined body that allows it to escape predators by diving and remaining submerged. It rarely comes onto land voluntarily.
The skin of skin paradoxical frog has attracted scientific attention for a different reason entirely. It contains peptides with potent insulin-releasing properties, compounds that stimulate the pancreas to produce insulin in a way that has been investigated as a potential basis for new diabetes treatments. A frog that shrinks during development, that spends its adult life underwater, that carries potential pharmaceutical compounds in its skin, has been sitting in South American wetlands largely unnoticed by the general public for millions of years.
The Wetland It Needs
The flooded grasslands and shallow lakes of the Orinoco basin are among the most biodiverse freshwater habitats in South America and among the least protected. Agricultural drainage, cattle ranching, and water diversion have reduced the extent of seasonally flooded habitat across the region, and the paradoxical frog’s dependence on specific wetland conditions makes it sensitive to these changes in ways that more generalist amphibians are not.
The species is not currently listed as threatened, but amphibians as a group are the most endangered vertebrate class on Earth, with chytridiomycosis, habitat loss, and climate-driven changes to rainfall patterns all contributing to declines that have accelerated since the 1980s. The paradoxical frog’s unusual biology makes it worth knowing about. Its habitat makes it worth protecting.