If you spend enough time around Guyana’s lowland wetlands, blackwater ponds off the Essequibo, flooded savannas in the Rupununi, or quiet backwaters near the lower Demerara, you can run into one of South America’s strangest amphibians: the paradoxical frog, Pseudis paradoxa.
The paradoxical frog, Pseudis paradoxa. (Image credit: Minden Pictures/Alamy)
It’s sometimes called the “shrinking frog” because its tadpoles can reach 25–27 cm long, but the adult frog is only 6–7.5 cm. It is the only frog in our region that starts big and finishes small.
And yes, we do have it in Guyana; regional and Guiana Shield maps list the species, and local observers have posted it from interior and coastal wetlands.
WHY IS IT “PARADOXICAL”?
Most amphibians grow bigger as they develop. The paradoxical frog does the opposite. Its tadpole is the record-holder: up to 27 cm long, free-swimming, and herbivorous.
Then, during metamorphosis, the tail is resorbed and the stored energy is used to build a much smaller adult frog. Biologists think this is an adaptation to big, warm, food-rich wetlands —exactly the kind Guyana gets during the rainy season.
In such wetlands, it pays to grow fast as a plant-eating tadpole and then “cash in” that growth to become an adult before the water level drops.
GUYANA HABITATS WHERE IT FITS
According to AmphibiaWeb and regional checklists, Pseudis paradoxa prefers permanent or long-lasting freshwater habitats: ponds, lakes, slow rivers, flooded grassland, lagoons beside large rivers, and even weedy artificial ponds.
In Guyana, that means coastal and near-coastal ponds that retain water for most of the year, backwaters on the Essequibo and Demerara, and the Rupununi wetland complexes during the long rainy season.
It will also use rice fields or aquaculture ponds if the water is not too polluted.
WHAT THE ADULT LOOKS AND SOUNDS LIKE
Adults are green to olive-brown on top, often with darker mottling or stripes, and whitish underneath. The eyes are yellowish with a brown bar. Toes are well webbed because this is a very aquatic frog.
Field guides from Trinidad and the Guianas describe the call as a grunt or pig-like oink. You are more likely to hear it around dusk than to see it, because it often stays partly submerged.
DIET: PLANT FIRST, PREDATOR LATER
The paradoxical frog is a good example of an amphibian diet shift. The huge tadpoles eat algae, periphyton and other plant material, exactly what grows in sunlit, shallow Guyanese ponds.
As adults, they switch to insects and other small aquatic or semi-aquatic invertebrates, and sometimes small vertebrates. That puts them in the middle of the wetland food web: tadpoles help keep algae in check, and adults help control insects.
WHY SCIENTISTS LOVE IT
There are two main reasons this frog appears in research papers. First, its life history is almost unique: most growth occurs in the larval stage, making it ideal for studying metamorphosis and energy use.
Second, its skin produces antimicrobial peptides, including pseudin-2. Lab studies showed that synthetic pseudin-2 can stimulate insulin release in pancreatic cells, making it a promising target for future diabetes research. So this is not just a weird tadpole, it’s also a frog with medical potential.
CONSERVATION
Globally, the paradoxical frog is listed as Least Concern because it is widespread and still common. In Guyana, we should still watch for three pressures: drainage and infilling of wetlands near towns; agrochemical use in rice and cane fields, which exposes herbivorous tadpoles; and the introduction of predatory fish into small ponds.
Keeping a network of permanent, relatively clean freshwater bodies in coastal and Rupununi landscapes will keep this species secure — and will benefit birds and fish at the same time.
References
- https://amphibiaweb.org/species/5225
- https://www.thebhs.org/publications/the-herpetological-journal/volume-19-number-1-january-2009/537-02-the-paradoxical-frog-i-pseudis-paradoxa-i-larval-habitat-growth-and-metamorphosis
- https://sta.uwi.edu/fst/lifesciences/sites/default/files/lifesciences/documents/ogatt/Pseudis_paradoxa%20-%20Paradoxical%20Frog.pdf
